Assessment of the INCA Steel-concrete- steel sandwich technology

Assessment of the INCA Steel-concrete-steel sandwich technology- Public Report

Assessment of the INCA Steel-Concrete-SteelSandwich Technology- Public report

CONTACT

[email protected] and [email protected]

Date of issue

December 2010

Final_INCA_public_report_final ETN.doc

Date of first issue: Project No:

30.09.2010 109IN208 Approved by: Organisational unit:

Hans Ramsvik

Project Manager

DNV China

Client: Client ref.:

DNV Research & Innovation Elisabeth Harstad

DET NORSKE VERITAS AS Approval Centre Norway

Materials Technology and

Pressure Equipment

Veritasveien 1

1322 Høvik

Norway

Tel:

Fax:

http://www.dnv.com

NO 945 748 931 MVA

Summary:

In about 2000, DNV came up with the idea to use steel-concrete sandwich as construction material for marine vessels.

The idea was initially developed to address safety issues with bulk carriers. Since then, DNV has been working to explore

the possibilities and potential for the concept together with a large shipyard group and some other industrial partners. A

new project was initiated in 2009 to assess the technical feasibility of using INCA in marine vessels. The project’s focus

was on exploring the commercial potential of the INCA sandwich technology for use within the marine industry.

From the technical assessment it was concluded that the original INCA technology without studs requires further research

before it can be used. However, by using shear studs or pins in accordance with best industry practise for steel concrete

composite structures, the technology can be exploited in the near term. INCA panels are best suited to solutions which are

not weight critical and where other benefits of the technology can be utilised to offer additional advantages.

It was recommended that DNV releases the INCA patents, enabling all interested parties to pursue the technology further.

It was further concluded that, despite the fact that INCA panels do not seem to be competitive for ocean going ships, there

are many other opportunities for use of concrete in marine applications and short sea shipping and river transportation. By

releasing the INCA patent and publicising DNVs work industry is free to exploit these opportunities and DNV can offer

services to assist with future development.

Report No: Subject Group:

2010-1284 E5, E55, H1, H8 Indexing terms Report title: Keywords Service Area

Technology

Qualification Market Sector

Assessment of the INCA steel-concrete-steel

sandwich technology - Public report

Sandwich, Concrete,

Ship design, Adhesion,

Fire Transportation

Work carried out by:

Jan R. Weitzenböck and Thomas Grafton,

see also ch. 2.3

Work verified by:

Dag McGeorge

Date of this revision: Revision No: Number of pages:

30.09.2010 0 148

Unrestricted distribution (internal and external)

Unrestricted distribution within DNV

Limited distribution within DNV after 3 years

No distribution (confidential)

© 2002 Det Norske Veritas AS

All rights reserved. This publication or parts thereof may not be reproduced or transmitted in any form or by any means, including

photocopying or recording, without the prior written consent of Det Norske Veritas AS.

1 EXECUTIVE SUMMARY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

2 INTRODUCTION. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

2.1 History of the INCA project . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

2.2 The current INCA project . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

2.3 Contributors to this report . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

3 PANEL BENCHMARK STUDIES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

3.1 Basic panel design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

3.2 Benchmark – panels with studs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

3.3 Benchmark – panels without studs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

4 GAP ANALYSIS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

5 ASSESSMENT OF INCA TECHNOLOGY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

5.1 Technical assessment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

5.2 Fire Assessment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

5.3 CO2 footprint . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

5.4 Recycling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

6 FEASIBILITY AND OPPORTUNITIES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

6.1 Statement of Feasibility . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

6.2 Statement of Opportunity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

7 MARKET POTENTIAL AND BUSINESS MODELS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

8 CONCLUSIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

9 APPENDIX 1: BENCHMARK STUDY OF INCA PANELS WITH STUDS . . . . . . . . . . . . 23

9.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

9.2 Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

9.3 Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

9.3.1 Relevant codes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

9.3.2 Load and material factors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

9.3.3 Ultimate Limit State . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

9.3.3.1 Bending . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

9.3.3.2 Transverse Shear . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

9.3.3.3 Studs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

9.3.4 Fatigue Limit State . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

9.3.4.1 Concrete . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

9.3.4.2 Steel plates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

9.3.4.3 Studs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

9.3.5 Service Limit State . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

9.4 Evaluation of experimental studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

9.5 Parametric study . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

Report No 2010-1284 - Reference to part of this report which may lead to misinterpretation is not permissible. 3

PUBLIC REPORT

Table of Contents

9.5.1 Methodology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

9.5.1.1 Material properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

9.5.1.2 Load conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

9.5.1.3 Boundary conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

9.5.2 Discussion of results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

9.5.2.1 Effect of pre-stressing panels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44

9.5.2.2 Effect of increasing strength in steel plates . . . . . . . . . . . . . . . . . . . . . . 45

9.6 Deck design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46

9.6.1 RoRo Car deck . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47

9.6.2 FPSO process deck . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51

9.7 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54

9.8 Future work . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56

9.9 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57

10 APPENDIX 2: BENCHMARK STUDY OF INCA PANELS WITHOUT STUDS . . . . . . . 59

10.1 Scope and objectives of study . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59

10.2 Design basis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59

10.2.1 Relevant codes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59

10.2.2 Design approach . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60

10.2.3 Load cases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60

10.2.4 Design equations assuming the core is uncracked and fully effective . . . . . . . . . 61

10.2.5 Design equations for cases when the core is cracked . . . . . . . . . . . . . . . . . . . . . 61

10.2.6 Material properties and allowable stresses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64

10.3 Parametric study . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65

10.3.1 Results: trends . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65

10.3.2 Comparison with parametric study for INCA with studs . . . . . . . . . . . . . . . . . . . 69

10.4 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70

10.5 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70

11 APPENDIX 3: DEFINITION OF SCOPE OF BENCHMARK STUDIES . . . . . . . . . . . . . 73

11.1 Purpose . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73

11.2 Standard ‘Panel’ and Boundary Conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73

11.3 Panels to be Assessed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74

11.4 Preparation of Load Cases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75

11.4.1 Local Loads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75

11.4.2 Axial Loads (due to Global Bending) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75

11.5 Fire Loading . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76

11.6 Fatigue Loading . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76

11.7 Water Resistance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77

11.8 Material Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77

11.8.1 Steel Plating and Stiffeners . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77

11.8.2 Concrete . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77

Assessment of the INCA Steel-Concrete-Steel Sandwich Technology4

DNV RESEARCH & INNOVATION

11.9 Allowable Stresses and Load Factors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77

11.9.1 Steel Ships . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77

11.9.2 Concrete Ships . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78

11.10 Minimum and Maximum Thicknesses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78

11.10.1 Steel Plating . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78

11.10.2 Steel Stiffeners . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78

11.10.3 Core . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78

11.11 Variables for Study . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78

11.12 Optimisation Approach . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78

11.13 Failure Criteria. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79

11.14 Outputs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79

11.15 Other Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79

12 APPENDIX 4: GAP ANALYSIS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81

12.1 Objective and scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81

12.2 Method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82

12.3 Basis for assessment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82

12.4 Novelty assessment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83

12.5 Technology maturity and knowledge gaps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84

12.5.1 Applicability of traditional sandwich theory to INCA panels . . . . . . . . . . . . . . . 84

12.5.2 Assessment in relation to intended use . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85

12.5.3 Robustness and foreseeable abuse . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86

12.5.4 Accidents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86

12.5.4.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86

12.5.4.2 Local contact (grounding, collision) . . . . . . . . . . . . . . . . . . . . . . . . . . 86

12.5.4.3 Crushing (grounding and collision) . . . . . . . . . . . . . . . . . . . . . . . . . . . 87

12.5.4.4 Fire . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87

12.6 Summary of identiied technology gaps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88

12.7 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89

13 APPENDIX 5: MATERIALS TECHNOLOGY & CONCRETE SHIP DESIGN . . . . . . . 91

13.1 Materials properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91

13.2 Fire performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98

13.3 Materials and joining . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103

13.4 History of concrete ships . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112

13.5 INCA project journey . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123

CO2 FOOTPRINT ANALYSIS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 133

RECYCLING SCHEME ANALYSIS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147


PUBLIC REPORT

DET NORSKE VERITAS

Report No: 2010-1284, rev. 1

TECHNICAL REPORT

Page 1 Reference to part of this report which may lead to misinterpretation is not permissible.

Final_INCA_public_report_rev0.doc

1 EXECUTIVE SUMMARY In about 2000, DNV came up with the idea to use steel-concrete sandwich as construction material for marine vessels. The concept was to use a steel sheet – light weight concrete – steel sheet to replace steel plate and secondary stiffener structures. The idea was initially developed to address safety issues with bulk carriers and the abbreviation INCA originates from an INnovative Bulk CArrier design. Since then, DNV has been working to explore the possibilities and potential for the concept together with a large shipyard group and some other industrial partners. A new project was initiated in 2009 to assess the technical feasibility of using INCA in marine vessels. The project’s focus was on exploring the commercial potential of the INCA sandwich technology for use within the marine industry and to identify a way forward for possible industrialisation of the technology. This included also a recommendation on whether to maintain the current patent portfolio.

From the technical assessment it was concluded that the original INCA technology without shear studs requires further research before it can be used. However, by using shear studs or pins, and established industry practise for concrete steel composite design the technology can be exploited in the near term. INCA is best suited to solutions which are not weight critical and where other benefits of the technology can be utilised to offer additional advantages. While this project focused mainly on sandwich panels, it is believed that the full potential can only be realised by designing complete structures, such as floating barges or ships, where the overall arrangement reflects the properties of the INCA concept and not just replaces members in an optimised steel design with INCA members.

t was recommended that DNV releases the INCA patents, enabling all interested parties to pursue

the technology further. Further work for DNV should be based on commercial terms for interested parties and could include assistance with technology qualification, verification and classification.

It was further concluded that, despite the fact that INCA panels do not seem to be competitive for panels in ocean going ships, there are many other opportunities for use of concrete in marine applications and short sea shipping/river transportation. Furthermore it is believed that the full potential can only be realised by designing complete structures, such as floating barges or ships, where the overall arrangement is designed to exploit the properties of the INCA technology.It was also noted that DNV’s technology qualification process is the most efficient approach to qualification of new technology; the more innovative the technology is the more critical it is to manage the qualification according to this process.



DET NORSKE VERITAS

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1 EXECUTIVE SUMMARY In about 2000, DNV came up with the idea to use steel-concrete sandwich as construction material for marine vessels. The concept was to use a steel sheet – light weight concrete – steel sheet to replace steel plate and secondary stiffener structures. The idea was initially developed to address safety issues with bulk carriers and the abbreviation INCA originates from an INnovative Bulk CArrier design. Since then, DNV has been working to explore the possibilities and potential for the concept together with a large shipyard group and some other industrial partners. A new project was initiated in 2009 to assess the technical feasibility of using INCA in marine vessels. The project’s focus was on exploring the commercial potential of the INCA sandwich technology for use within the marine industry and to identify a way forward for possible industrialisation of the technology. This included also a recommendation on whether to maintain the current patent portfolio.

From the technical assessment it was concluded that the original INCA technology without shear studs requires further research before it can be used. However, by using shear studs or pins, and established industry practise for concrete steel composite design the technology can be exploited in the near term. INCA is best suited to solutions which are not weight critical and where other benefits of the technology can be utilised to offer additional advantages. While this project focused mainly on sandwich panels, it is believed that the full potential can only be realised by designing complete structures, such as floating barges or ships, where the overall arrangement reflects the properties of the INCA concept and not just replaces members in an optimised steel design with INCA members.

It was recommended that DNV releases the INCA patents, enabling all interested parties to pursue the technology further. Further work for DNV should be based on commercial terms for interested parties and could include assistance with technology qualification, verification and classification.

It was further concluded that, despite the fact that INCA panels do not seem to be competitive for panels in ocean going ships, there are many other opportunities for use of concrete in marine applications and short sea shipping/river transportation. Furthermore it is believed that the full potential can only be realised by designing complete structures, such as floating barges or ships, where the overall arrangement is designed to exploit the properties of the INCA technology.It was also noted that DNV’s technology qualification process is the most efficient approach to qualification of new technology; the more innovative the technology is the more critical it is to manage the qualification according to this process.


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In the case of the original INCA concept, where the steel could be assembled before casting the concrete and work as the casting mould for the concrete, welding could be done according to standard procedures. This idea has, however, not been developed and focus was placed on assembly of pre-fabricated INCA panels. Since joining methods for load bearing applications have not been developed yet INCA panels should be used in non-critical applications without the need for (load-bearing) joints. Furthermore, the panels should be mainly loaded in bending in order to maximise the benefits from the Sandwich design. During the course of this project two applications were looked at in more detail: an FPSO process decks and RoRo car decks.

2.3 Contributors to this report The two authors Jan R. Weitzenböck and Thomas Grafton wrote the main body of this report (Chapters 1 to 8). Chapter 7 is based on work by Sigrid Eriksen and Eskil Røset. The appendices were written by different members of the INCA project team: • 9 - Appendix 1: Benchmark study of INCA panels with studs: Andreas Lervik, Paola Mayorca

• 10 - Appendix 2: benchmark study of INCA panels without studs: Brian Hayman

• 11 - Appendix 3: Definition of scope of benchmark studies: Thomas Grafton

• 12 - Appendix 4: Gap analysis: Dag McGeorge

• 13 - Appendix 5: Materials technology & concrete ship design: Edward Wang, Thomas Grafton, Jan Weitzenböck

• 14 - Appendix 6 CO2 footprint: Alfhild Aspelin

• 15 - Appendix 7 Recycling: Håkon Hustad

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2 INTRODUCTION This report is a collection of various documents produced in the INCA project. The level of detail varies from PowerPoint presentations to detailed studies. The main purpose of this document is to collate all the background information and conclusions in order to preserve the knowledge and experience from the INCA project for others to utilise later on.

2.1 History of the INCA project In about year 2000, DNV came up with the idea to use steel-concrete sandwich as construction material for marine vessels. The concept was to use a steel sheet – light weight concrete – steel sheet to replace steel plate and secondary stiffener structures. Normal concrete has a density of about 2600 kg/m3 while the light weight concrete in the sandwich structure has a density of less than 1200 kg/m3. The density of steel is about 7800 kg/m3.

The idea was initially developed to address safety issues with bulk carriers and the abbreviation INCA originates from an INnovative Bulk CArrier design. Since then, DNV has been working to explore the possibilities / potential for the concept together with a large shipyard group and some other industrial partners. As result of a restructuring process within the partner company the development process came to a halt and finally the INCA Intellectual Property Rights were taken over by DNV and the patent rights were fully controlled by DNV.

A new project was initiated in 2009 to assess the technical feasibility of using INCA in marine vessels. The project’s focus was on exploring the commercial potential of the sandwich technology for use within the marine industry and to identify a way forward for possible industrialisation of the technology. This included also a recommendation on whether to maintain the current patent portfolio.

2.2 The current INCA project Use of stiffened steel plates is the preferred construction methods for ship and offshore structures. However, there are many different structural solutions for making panels including sandwich designs. Some sandwich solutions are already available commercially, e.g. SPS or I-CORE. Hence INCA needs to offer significant benefits compared with existing solutions in order to justify investment into further development and industrialisation. The initial thoughts were that INCA should be able to offer the following advantages:

• Not heavier than equivalent steel panels

• Simplified construction leading to reduced manufacturing costs

• Multifunctionality leading to reduced outfitting:

o Fire insulation (non-combustible materials)

o Improved sound and vibration damping

o Impact performance



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In the case of the original INCA concept, where the steel could be assembled before casting the concrete and work as the casting mould for the concrete, welding could be done according to standard procedures. This idea has, however, not been developed and focus was placed on assembly of pre-fabricated INCA panels. Since joining methods for load bearing applications have not been developed yet INCA panels should be used in non-critical applications without the need for (load-bearing) joints. Furthermore, the panels should be mainly loaded in bending in order to maximise the benefits from the Sandwich design. During the course of this project two applications were looked at in more detail: an FPSO process decks and RoRo car decks.

2.3 Contributors to this report The two authors Jan R. Weitzenböck and Thomas Grafton wrote the main body of this report (Chapters 1 to 8). Chapter 7 is based on work by Sigrid Eriksen and Eskil Røset. The appendices were written by different members of the INCA project team: • 9 - Appendix 1: Benchmark study of INCA panels with studs: Andreas Lervik, Paola Mayorca

• 10 - Appendix 2: benchmark study of INCA panels without studs: Brian Hayman

• 11 - Appendix 3: Definition of scope of benchmark studies: Thomas Grafton

• 12 - Appendix 4: Gap analysis: Dag McGeorge

• 13 - Appendix 5: Materials technology & concrete ship design: Edward Wang, Thomas Grafton, Jan Weitzenböck

• 14 - Appendix 6 CO2 footprint: Alfhild Aspelin

• 15 - Appendix 7 Recycling: Håkon Hustad


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3 PANEL BENCHMARK STUDIES

3.1 Basic panel design The benchmark studies considered two different configurations of the INCA sandwich panel. The original concept consisted of two steel plates with a concrete core as shown in Figure 1. Load transfer between the steel plates and the concrete core relies entirely on adhesion between the steel interface and the concrete core. Later on this was modified by the introduction of shear studs as adhesion alone was not considered reliable enough. A typical example is shown in Figure 2.

1. Face 1: steel plate. 2. Bondline 1 between face 1 and core:

adhesion of concrete to steel. 3. Core: lightweight concrete. 4. Bondline 2 between core and face 2:

adhesion of concrete to steel. 5. Face 2: steel plate.

3 1

5

2

4

Figure 1 Original INCA sandwich concept – “no studs”

Steel plateShear connector (stud)Concrete core

Figure 2 Typical INCA panel – “with studs”

3.2 Benchmark – panels with studs The evaluation of the INCA sandwich consisting of steel plates and concrete core, i.e. without shear connectors, concluded that in order to ensure an adequate and reliable shear connection between the face sheets and the core it is necessary to use studs. Steel-concrete composites with studs have been successfully used for many years in the construction of buildings and bridges; the latter are subjected to fatigue loading. Therefore, steel-concrete composite with studs can be considered a proven technology. The novelty of the proposed panels is that, in addition to ensuring the shear connection between sandwich elements, the studs are also used to reinforce the core, avoiding shear tension failure and limiting cracking of the concrete core.



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The present benchmark study focused on assessing INCA-panels with studs from the structural point of view and comparing their performance with typical steel solutions. The study looked into the application of panels to ships and offshore facilities, particularly horizontal elements such as decks. Based on the review of existing design standards and recommendations, the basis for design of INCA was proposed. Ultimate and fatigue limit states were covered. Service limit state was only briefly discussed as there are no specific design requirements for control of deflections in ships and offshore facilities. It is assumed that water tightness is provided by the steel skin.

A parametric study was carried out in order to identify typical INCA-panel (with studs) dimensions and spans for various loads and boundary conditions. The results showed that INCA is capable of covering relatively long spans. Because studs were designed to transfer the horizontal shear force between plates and core and to prevent shear tension failure, design was governed by either shear compression or bending capacity.

The challenge that INCA is faced with for most applications in conventional shipping is its self weight. In the parametric study two different concrete cores were considered, light weight concrete (LWC) and high strength concrete (HSC), to investigate if the ten-fold increase in compressive strength could give any benefit in spite of the almost three fold weight increase. It was concluded that for panels, in which the bending capacity limits the maximum feasible length, LWC-core resulted in lighter panels for a given span. It shall be noted that it is possible to increase the capacity, both in bending and shear, of the HSC-panels by pre-stressing the panels or increasing the steel plate strength. However, this option makes HSC-panels competitive only for high imposed loads, which are several times larger than the self-weight.

The parametric study focused on panels with steel plates of identical thicknesses on both sides. Considering plates with different thicknesses will lead to a better utilization of the material, resulting in an optimized panel with respect to both cost and weight.

Two case studies were considered to compare INCA panels with typical steel solutions. The comparison only considered replacing some decks of existing ships with INCA. The main limitation of this approach is that the main structural system is the result of an optimization process meant for a steel structure. Steel structures are good at resisting tensile forces but may buckle under compression forces. The robust INCA-panel is capable to efficiently carry both axial compression and tension. Taking into consideration that INCA behaves differently than steel, it is foreseen that a better utilization of INCA can be achieved if a main structural arrangement, which exploits INCA advantages, is developed instead. These advantages would probably be clearer if the main structural system is made of INCA.

From the case study, advantages and challenges of introducing INCA-panels in marine applications were found as described below.

Advantages:

- Robust panel with better performance under explosion compared to traditional steel structures.


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3.3 Benchmark – panels without studs The results of the parametric study show that for most cases there is a clear advantage in using a design with welded studs to improve the shear strength of an INCA panel. Even if a solution without studs appears to give an approximately equal weight to one with studs, the need to ensure an adequate shear connection between the face sheets and the core makes it adviseable in practice to use studs in all cases. Within the range of properties that can be envisaged and under the above assumptions, the study showed that the technology was inferior to the INCA technology with studs. The conclusion therefore was that the INCA technology without studs should not be pursued further in this study.

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- The INCA panel with shear reinforcement/studs is expected to perform excellently under fire as long as some fire protection/internal reinforcement are provided.

- Reduced need for thermal insulation due to the low heat conductivity of concrete.

- Improved fire insulation which will prevent spreading of the fire from one fire cell to another.

- Fewer details subjected to fatigue damage.

- Welding directly to the steel plates does not damage the steel treatment on the other side of the plate (e.g. the corrosion prevention coating).

- Area of steel that needs fire protection is reduced because stiffeners are avoided. The fire protection will also be easier to apply because of the flat surfaces.

- The panel will be easier to maintain due to the flat surfaces.

- The panel is very robust and have a large potential to absorb energy from impact loading or rough handling.

- With a well-established welding procedure the welding of the studs is very efficient, resulting in reduced time for welding. The amount of welding will also be reduced compared to that needed in traditional steel structures.

- With a well-established production and assembly procedure it is possible to be competitive on costs compared to traditional steel structures.

- Transverse girders can be avoided. Deck height can be decreased giving the possibility of installing extra decks with consequent economical benefits.

Challenges:

- Assembly, connection and production of the panels has to be investigated further.

- For mobile structures, in which weight is critical, it is hard to be competitive with traditional steel structures. This conclusion is based on the case study carried out, which had the limitations mentioned earlier, i.e. only replacement of panels was considered.

- For marine applications where weight is less critical, e.g. slow moving or stationary structures, it must be demonstrated that INCA-panels can be competitive and are reliable.

- Development of structural arrangements that exploits the properties of the INCA technology instead of copying arrangements optimised for traditional steel design.

- Development of technologies for assembly of steel before casting the concrete, using the steel as the casting moulds for the concrete, to overcome difficulties with joining pre-fabricated INCA panels.

-

Although the conclusion of the present benchmark study is that INCA with studs is technically feasible for marine applications, further work is required in order to make this technology ready for commercialization (see also section 9.8).



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3.3 Benchmark – panels without studs The results of the parametric study show that for most cases there is a clear advantage in using a design with welded studs to improve the shear strength of an INCA panel. Even if a solution without studs appears to give an approximately equal weight to one with studs, the need to ensure an adequate shear connection between the face sheets and the core makes it adviseable in practice to use studs in all cases. Within the range of properties that can be envisaged and under the above assumptions, the study showed that the technology was inferior to the INCA technology with studs. The conclusion therefore was that the INCA technology without studs should not be pursued further in this study.


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5 ASSESSMENT OF INCA TECHNOLOGY

5.1 Technical assessment The INCA project team has utilized the experience of many colleagues in DNV, covering concrete technology; sandwich technology; ship and offshore approval; and materials and joining experts to review the previous research and technical reports. The result of this cross-DNV review is summarized in a Statement of Feasibility (section 6).

As a result of this work the project team has further developed the existing concept by utilizing current standards and established steel and concrete design methods to create solutions that could be used in the market today. With the preferred solution the team has studied different applications within the maritime industry searching for areas where the benefits of INCA are used to the full. These areas are in parts of ships and offshore structures, the technology not being mature enough for use in complete, large oceangoing vessels. The team has discussed these promising applications with designers, shipyards and innovators around the globe.

Further studies will be required to prove the proposed applications will display the expected benefits and to take the product to market.

With additional research, there is potential to use INCA solutions for complete maritime constructions, e.g. floating harbours or piers, floating dry docks, or for small inshore ships (the so-called Brown Water Fleet). Whilst these have not been studied in detail in this project, using the experienced gained further exploration of these ideas is considered worthwhile.

The project team has discovered that it is difficult to compete with highly optimized steel structures on weight alone using the INCA technology, and so the team has looked towards solutions which are not so weight critical. In this case standard concrete could be used.

5.2 Fire Assessment INCA panels with unprotected steel face sheets perform differently from stiffened steel plates. As INCA is a sandwich structure, rapid loss in bending stiffness will occur if any of the steel faces loose their material properties due for example to high temperature. This is a ‘sudden collapse’ phenomenon like brittle fracture in steel.

When exposed to fire, steel looses its material properties with increasing heat, the critical temperature being between 500 and 600 degrees Celsius. In a typical fire this is reached within minutes of exposure and therefore steel structures have to be insulated to contain the fire and stop heat

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4 GAP ANALYSIS A gap analysis was carried out in order to assess the results of the work being carried out in the previous INCA project(s) and identify possible gaps addressing specifically the original INCA concept without studs. More details about the assessment can be found in section 12. The following major gaps were identified in this study:

1) The transverse shear capacity of the sandwich panel has not been documented when significant in-plane or bending loads are present at the same time as the shear loading.

2) An expected size effect of the strength of the core has not been investigated. 3) The influence of core cracks on the performance of the sandwich panels in typical service

conditions has not been documented. 4) The long term performance of the bond between the core and the steel faces has not been

documented. 5) Fatigue of welded joints between INCA panels has not been documented. 6) The robustness against local impact loads has not been documented. 7) The crushing resistance of the INCA panel and its effect on collision and grounding risks has

not been documented. 8) The risks associated with the lack of structural integrity of INCA panels in fire have not been

documented. 8a) In case of shear studs enhancing bonding performance, the resulting structural integrity in fire has not been documented.

All these gaps, except gap 2, are considered potential showstoppers for general use of the INCA technology without studs in ship structures, but may be less critical for some special applications.



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5 ASSESSMENT OF INCA TECHNOLOGY

5.1 Technical assessment The INCA project team has utilized the experience of many colleagues in DNV, covering concrete technology; sandwich technology; ship and offshore approval; and materials and joining experts to review the previous research and technical reports. The result of this cross-DNV review is summarized in a Statement of Feasibility (section 6).

As a result of this work the project team has further developed the existing concept by utilizing current standards and established steel and concrete design methods to create solutions that could be used in the market today. With the preferred solution the team has studied different applications within the maritime industry searching for areas where the benefits of INCA are used to the full. These areas are in parts of ships and offshore structures, the technology not being mature enough for use in complete, large oceangoing vessels. The team has discussed these promising applications with designers, shipyards and innovators around the globe.

Further studies will be required to prove the proposed applications will display the expected benefits and to take the product to market.

With additional research, there is potential to use INCA solutions for complete maritime constructions, e.g. floating harbours or piers, floating dry docks, or for small inshore ships (the so-called Brown Water Fleet). Whilst these have not been studied in detail in this project, using the experienced gained further exploration of these ideas is considered worthwhile.

The project team has discovered that it is difficult to compete with highly optimized steel structures on weight alone using the INCA technology, and so the team has looked towards solutions which are not so weight critical. In this case standard concrete could be used.

5.2 Fire Assessment INCA panels with unprotected steel face sheets perform differently from stiffened steel plates. As INCA is a sandwich structure, rapid loss in bending stiffness will occur if any of the steel faces loose their material properties due for example to high temperature. This is a ‘sudden collapse’ phenomenon like brittle fracture in steel.

When exposed to fire, steel looses its material properties with increasing heat, the critical temperature being between 500 and 600 degrees Celsius. In a typical fire this is reached within minutes of exposure and therefore steel structures have to be insulated to contain the fire and stop heat


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5.4 Recycling

Table 1 Sale Price of Used Vessels with INCA Construction (illustrative examples where INCA has no commercial value)

Offshore supply 10 % INCA

Passenger 30 % INCA

Bulker 70 % INCA

Price decrease USD -$100,000 -$480,000 -$2,800,000

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transmission between boundaries. For INCA, the concrete core provides superior heat insulation and therefore almost no heat is transferred through the INCA panel.

However, SOLAS requires ‘steel or equivalent materials’ and ‘suitable stiffened’ structures. With some flag states concrete is accepted as an equivalent material. Sandwich panels have been used in SOLAS ships. However, the process to demonstrate equivalence with stiffened steel structures is not clearly defined.

An important intent of SOLAS is to maintain the structural integrity of a ship preventing partial or whole collapse of the structure due to deterioration with heat. Therefore, it seems reasonable that a sandwich structure should be shown to be able to meet the SOLAS fire requirements with at least some loading (bending and shear for operational loads). In the previous INCA research a fire test was performed on a loaded panel without insulation of the steel faces and the panel collapsed due to loss of structural integrity.

Therefore, it is concluded that whilst INCA panels have superior heat insulation properties in comparison with a stiffened steel structure the concept must be improved to meet fire requirements for structural integrity, for example by adding fire insulation to the face plates.

5.3 CO2 footprint The CO2 footprint of the application of SCS sandwich structures and traditional steel structures in ships has been compared by means of a basic high-level assessment of the life-cycle CO2 emissions of each material when incorporated in vessels.

The aim has been to identify the main sources of emissions throughout the lifetime and the order of magnitude of potential changes in emissions by applying INCA technology. The assessment has been conducted by estimating the CO2 emissions at each phase in a simplified life-cycle consisting the following three phases: (I) construction of the ship, (II) life-time ship operations and (III) end-of-life recycling/reuse. In terms of CO2 emissions per ton material produced, the relevant light weight concrete is less CO2 intensive (400 kg CO2/ton) than ship steel (1460 kg CO2/ton). Thus one can expect a certain reduction in CO2 from ship construction, assuming that concrete to a certain degree replaces steel.

However, for shipping in general the all-important CO2 emissions throughout the lifetime origin from the combustion of hydrocarbons for propulsion and power generation during the operation of ships; amount to more than 80-100 times as much CO2 as the production of building materials. No significant potential for reducing the lifetime operational CO2 has been identified for ships applying INCA structures. This is because INCA structures weigh at least as much as an equivalent steel solution.

Steel structures from ships are effectively recycled into second hand steel, which again can be used in many applications with high CO2 saving potential as an alternative to production of new steel. SCS structures are in comparison considered less efficiently recycled. Moreover, second hand concrete,



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even if it is possible to recycle, is not assumed to have a high potential for substituting CO2 intensive new production of materials, such as it is in the case of steel.

In conclusion, no significant change in lifetime CO2 footprint is expected for ships applying INCA technology. The marginal CO2 savings in the construction phase by using concrete may be outweighed by the fact that INCA materials have a lower potential for CO2 saving recycling.

5.4 Recycling The time to recycle an INCA vessel is directly proportionate to the amount of INCA construction incorporated into the vessel design. Separating concrete from steel is labour intensive requiring equipment not readily available in most shipyards.

Compared to recycling any given part of a vessel constructed of only steel it is assumed the same parts of INCA would take twice the amount of time to recycle. Economically the extra time and labour involved to recycle INCA construction will significantly reduce the value of the vessel at the end of its life. If during the design stage of a vessel consideration is given to dismantling opportunities for reuse may arise. By designing INCA panels that have standard sizes, fittings and joining methods, the panels could be dismantled and transported for installation in other applications. If reusing the panels is no longer an option, the raw materials may still be separated and sold.

Assumed Lightship values at the end of life are used in Table 1 with varying amounts of INCA panels utilized in the construction. This table does not represent accurate price reduction. It is only provided as an illustration.

Table 1 Sale Price of Used Vessels with INCA Construction (illustrative examples where INCA has no commercial value)

Offshore supply 10 % INCA

Passenger 30 % INCA

Bulker 70 % INCA

Weight steel (tons) 2250 2800 3000

Weight INCA (tons) 250 1200 7000

Price decrease USD -$100,000 -$480,000 -$2,800,000

Sale Price (400 USD/ton) $900,000 $1,120,000 $1,200,000


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6 FEASIBILITY AND OPPORTUNITIES

6.1 Statement of Feasibility The aim of this assessment was to determine whether the technology is mature enough for use in today’s marine constructions, and to assess the technological benefits of doing so. The main conclusions are:

1. The INCA technology covers a range of patented steel – concrete – steel sandwich solutions reliant on light weight concrete. In the most novel solution the steel plate is adhesively bonded to the concrete. However, the load transfer between steel and concrete using adhesion only is not considered viable due to low bond strength and unproven long-term performance. At best it could be used for small lightly loaded structures.

2. Other INCA solutions show more potential for use in the near term, the most promising is when shear pins (dowels) are used to connect the steel to the concrete and to transfer the loads into the core and increase its strength. Concepts using this solution, utilising existing accepted industrial practices for the design, construction and survey of concrete increase the likelihood of early use with reduced risk.

3. INCA panels can be used to replace plate, stiffeners and some of the girder system in marine structures. INCA panels offer further advantages, for example flat surfaces which are easier to coat and insulate; extremely low heat transmission from one side of the panel to the other; and the ability to modify the concrete mix and to use post or pre-strengthening to improve the strength for a particular application.

4. First applications of INCA should focus on parts of marine structures where structural weight is not the overriding design driver. Further research is needed to develop panel joining and fabrication methods and processes. Therefore, the project team see greatest immediate potential in offshore structures, and candidates for further study have been selected. Applications for structural safety barriers, arctic structures and bulkheads may also be of interest.

5. In summary, the INCA technology requires further research before it can be used. However, by uplifting today’s concrete technology and sandwich structural design theory and experience the technology can be exploited in the near term. INCA is best suited to solutions which are not weight critical and where other benefits of the technology can be utilised to offer additional advantages.

6.2 Statement of Opportunity The principal advantage of using steel-concrete-steel (SCS) sandwich structures is the reduction in the number of traditional structural elements and replacing them with cheaper concrete as part of a simple layered structure. The resulting structure is flat on both sides reducing maintenance costs; for example by reduced coating, inspection and insulation; and offers low heat conductivity and improved resistance to impact and maltreatment.



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For smaller ships and offshore structures a one-shot build could be imagined where thin steel formwork can be easily shaped to make the hull, held apart by connecting studs, and filled with concrete to complete the SCS structure. Techniques exist for such large scale concreting within the building industry. Once larger structural units (or complete ships) are considered it is also possible to leverage even more benefits from the concrete industry, examples include post-tensioning of the structure to improve the performance of the concrete part of the structure, and tuning of the type of concrete used along with associated construction process to suit local material availability, expertise and construction methods.

Through this optimisation of the design and construction method the weight penalty associated with SCS structures when used in place of small parts of a ship or offshore structure may be reduced or possibly eliminated. Hence, the following areas offer the best potential for profitable exploitation of the technology in the near term:

1. Simple stationary floating structures, e.g. a large floating oil storage barge.

2. ‘Brown Water’ ships (e.g. river craft or inshore cargo ships) designed and optimised for complete construction in SCS or traditional re-enforced concrete.

3. Structures for use in cold climates (making best use of the low temperature conduction properties of concrete).

4. Linked to the above, barges for LNG transportation

5. Blast resistant structures and heat boundaries on existing offshore structures, e.g. FPSO Process Decks.

6. ‘Damage tolerant’ structures. E.g. for fendering on offshore platforms or for berthing pontoons subject to impact loads.


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8 CONCLUSIONS From the technical assessment it as concluded that the original INCA technology without studs requires further research before it can be used. However, by using shear studs or pins in accordance with best industry practice for steel concrete composite structures, the technology can be exploited in the near term. INCA panels are best suited to solutions which are not weight critical and where other benefits of the technology can be utilised to offer additional advantages. While this project focused mainly on sandwich panels, it is believed that the full potential can only be realised by designing complete structures, such as floating barges or ships, where the overall arrangement is designed to exploit the properties of the INCA technology. This could include using steel as the casting mould for the concrete thereby overcoming the challenges of joining prefabricated INCA panels.

is recommended that DNV releases the INCA patents, enabling any interested parties to pursue the

technology further. However, DNV should seek to support the industry based upon DNVs well established technology qualification, verification and classification services by exploiting DNVs strength in concrete technology in general and our knowledge of the INCA technology in particular.

It was also concluded that, despite the fact that INCA panels do not seem to be direct competitive for ocean going ships, there are many other opportunities for use of concrete in marine applications, short sea shipping and river transportation. By releasing the INCA patent and publicising DNVs work it is hoped that industry will investigate these areas and DNV can offer services to assist in their successful development.

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7 MARKET POTENTIAL AND BUSINESS MODELS To complement the technical feasibility assessments, a study to evaluate the market potential and to develop business models was carried out. The main conclusions from this study and the recommended way forward can be summed up as follows:

• The original INCA technology, without shear studs or any mechanical interlocking between steel and concrete, should not be pursued further by DNV.

• The modified solution is more promising in the short-term, particularly in parts of stationary offshore units and for volume markets such as river barges.

• However, further development is still required to put this technology into use.

• DNV can have no ownership in the technology itself, and hence no income from it, after commercialisation. It is therefore important that such development does not only result in successful applications of the technology, but also a business opportunity for DNV, e.g. technology qualification, verification and classification services.

• The business opportunities for DNV are uncertain for the areas of application identified, and it is therefore difficult to justify investment into further development of the technology.

Way forward:

• It is recommended that DNV releases the patent, enabling all interested parties to pursue the technology further

• The technical report from the INCA Extraordinary Innovation Project should be made available to enhance any further development efforts

• Further work for DNV should pursue opportunities to assist the industry in bringing INCA technology into use by offering our services such as technology qualification, verification and classification.



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8 CONCLUSIONS From the technical assessment it as concluded that the original INCA technology without studs requires further research before it can be used. However, by using shear studs or pins in accordance with best industry practice for steel concrete composite structures, the technology can be exploited in the near term. INCA panels are best suited to solutions which are not weight critical and where other benefits of the technology can be utilised to offer additional advantages. While this project focused mainly on sandwich panels, it is believed that the full potential can only be realised by designing complete structures, such as floating barges or ships, where the overall arrangement is designed to exploit the properties of the INCA technology. This could include using steel as the casting mould for the concrete thereby overcoming the challenges of joining prefabricated INCA panels.

It is recommended that DNV releases the INCA patents, enabling any interested parties to pursue the technology further. However, DNV should seek to support the industry based upon DNVs well established technology qualification, verification and classification services by exploiting DNVs strength in concrete technology in general and our knowledge of the INCA technology in particular.

It was also concluded that, despite the fact that INCA panels do not seem to be direct competitive for ocean going ships, there are many other opportunities for use of concrete in marine applications, short sea shipping and river transportation. By releasing the INCA patent and publicising DNVs work it is hoped that industry will investigate these areas and DNV can offer services to assist in their successful development.


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9 APPENDIX 1: BENCHMARK STUDY OF INCA PANELS WITH STUDS

9.1 Introduction



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9 APPENDIX 1: BENCHMARK STUDY OF INCA PANELS WITH STUDS

9.1 Introduction The present benchmark study was carried out in order to assess INCA panels with studs from the structural point of view and to compare their performance with typical steel solutions. The study focused on the application of panels to ships and offshore facilities, particularly horizontal elements such as decks. In this study, performance of INCA panels as vertical elements has not been assessed.

Although steel-concrete composites are not common in the ship building and offshore industry, they have been successfully used in the construction of buildings and bridges. A brief review of existing standards for steel-concrete composite design is presented in section 9.2.

Steel – concrete –steel composite structural members are, however, common in offshore structures. Jacket structures are commonly strengthened by either filling the cylindrical members by grout or inserting an internal column and grouting the space between then the inner and outer cylinder member. The strengthening by grout is a very common approach in offshore tubular members. Examples are when the steel structures are damaged and cannot resist original load, when the structure has to carry increased loads due to more topside loads etc. Grout is a concrete material which can easily be pumped and is used to fill enclosed spaces.

Based on the review, design basis for INCA panels are proposed for ultimate and fatigue limit states in section 9.3. Special attention is given to fatigue limit state. Service limit state is briefly discussed as it is understood that ship building standards do not provide acceptance criteria for this.

Using the proposed design basis the results of tests carried out in the INCA panel development program are discussed in section 9.4. Different failure modes and their sequence are identified. Proposed formulation predicts fairly well the behaviour observed in the tests.

A parametric study is then carried out considering different plate thickness, concrete core material, panel thickness, boundary conditions and applied loads. The objective of the study was to find the maximum feasible panel span for each combination of parameters. Conclusions of this study are discussed in section 9.5.

With the experience gained from the parametric study, two panels from existing structures (Ro-Ro ship and FPSO) are designed with the INCA solution and compared with existing steel design in section 9.6. Although INCA panels are heavier than steel panels, they have several advantages which are also discussed.

This benchmark study has been carried out on well defined structural elements, in which elements have to be joined together. A construction approach in which the two layer of steel skin is initially constructed and tied together with the appropriate reinforcement, shear keys, shear reinforcement, longitudinal reinforcement and tendons for later post-tensioning prior to concreting the voids between the inner and outer skin may prove advantageous and economic. This track has, however, not been pursued in this benchmark study.

Finally, the conclusions of the study are summarized and recommended further works are presented in section 9.7.


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Table 3 Material factor for INCA panel design

9.3.3 Ultimate Limit State

9.3.3.1 Bending

Figure 3 Concrete stress-strain relation Figure 4 Steel stress-strain relation

9.3.3.2 Transverse Shear

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9.2 Background Although steel-concrete composites are not common in the ship and offshore industry, they have been successfully used in the construction of buildings and bridges. Eurocode 4 (Ref /1/ and /2/) provides provisions for the design of composite structures and members for buildings and civil engineering works. A composite member is defined as a structural member with components of concrete and structural or cold-formed steel, interconnected by shear connection so as to limit the longitudinal slip between concrete and steel and the separation of one component from the other. British Standards Institution (Ref /3/) and the Norwegian Association for Standardization (Ref /4/) have also published their design recommendations. All these documents are relatively similar and assume bonding between steel and concrete. Ultimate, service and fatigue limit states are covered for onshore structures to different extents in these standards. However, design of steel-concrete-steel sandwich is not specifically covered by them.

The Steel Construction Institute published the “Design Guide for Steel-Concrete-Steel Sandwich Construction – Volume 1: General principles and rules for basic elements” (Ref /5/). This is the only document which was found to address the design of elements similar to INCA panels with studs. It provides rules for the design of sandwich elements considering ultimate and service limit states. It does not cover fatigue limit state.

Ship and offshore facilities were identified as applications for INCA panels. These structures are subjected to fatigue loads and therefore, fatigue limit state is a main design consideration. DNV offshore standards (Ref /7/ and /8/) provide formulation for the assessment of fatigue design life for concrete and steel offshore structures. Therefore, it was decided to use these standards as a basis for design and adopt relevant criteria from the publications mentioned earlier, which are mainly intended for onshore construction.

9.3 Design basis

9.3.1 Relevant codes In this study, following codes have been used for design of INCA panels:

- DNV OS-C502: Offshore Concrete Structures

- DNV OS-C101: Design of Offshore Steel Structures, General (LRFD Method)

- DNV RP-C203: Fatigue Design of Offshore Steel Structures

9.3.2 Load and material factors Load factors used for design are presented in Table 2.

Table 2 Load factors for INCA panel design ULS

Type of load (a) (b)

SLS FLS ALS

Permanent 1.3 1.0 1.0 1.0 1.0

Variable functional 1.3 1.0 1.0 1.0 1.0

Environment 0.7 1.3 1.0 1.0 1.0

Deformation 1.0 1.0 1.0 1.0 1.0



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Material factors are presented in Table 3.

Table 3 Material factor for INCA panel design Material ULS FLS / ALS SLS

Concrete 1.40 1.20 1.0

Unreinforced concrete 1.75 1.50 1.0

Reinforcing steel 1.25 1.10 1.0

Structural steel (plates) 1.15 1.00 1.0

Welds 1.30 1.00 1.0

Studs (similar to reinforcement in concrete) 1.25 1.10 1.0

9.3.3 Ultimate Limit State

9.3.3.1 Bending Bending design is based on the following assumptions:

1. Strain in reinforcement and concrete is assumed directly proportional to the distance from the neutral axis, i.e. depth of sandwich is assumed to be small compared to span.

2. Concrete and steel stress-strain relationships are in accordance to Ref /7/ and shown in Figure 3 and Figure 4. It is assumed that concrete resists no tension.

Figure 3 Concrete stress-strain relation Figure 4 Steel stress-strain relation

3. Plates and concrete core are fully bonded. In order to ensure assumption 3, studs are provided. Design of studs is addressed in section 9.3.3.3.

9.3.3.2 Transverse Shear Transverse shear design is based on the following assumptions:

1. Steel plates do not contribute to transverse shear capacity.

2. Transverse shear capacity with respect to tensile failure is equal to Vcd + Vsd, where the first term is the contribution of the concrete core and the second term is the contribution of shear reinforcement. In the INCA panel, studs with a length equal to concrete core thickness are provided as shear reinforcement. Design of studs, i.e. formulation for Vsd, is addressed in section 9.3.3.3.


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××≤

Eq. 4

× × π ×

×−=σ

Eq. 5

≤+ τσ Eq. 6

×××××≤ πγ

ατ Eq. 7

α ≤

γ × ×

Figure 5 Maximum spacing studs: Shear cracks

× ×

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wtdvw

wc

sAtdcd bfkdb

db

AkfV ××≤×××+×= 66.0)(33.0 γ Eq. 1

where:

ftd : Design concrete tensile strength (MPa)

kA : 100 MPa

As : Cross section area of steel plate on the tension side (mm2)

bw : Width of panel (mm)

d : hc+1.5×th (mm)

hc : Concrete core thickness (mm)

th : Steel plate thickness (mm)

γc : Material factor for concrete

kv : 1.0 if shear reinforcement is provided, otherwise kv = 1.5-d/d1

where: d1=1.0 m and d = [m]. But 1.0 ≤ kv ≤ 1.4

Note that in the formulation presented for Vcd, the effect of normal force in the section is disregarded. This is conservative if the panel is in axial compression, but none-conservative if it is in axial tension. Formulation for these particular cases is presented in Ref /7/.

3. Maximum transverse shear capacity with respect to compression failure is equal to Vccd, where:

zbfzbfV wcdwcdccd ×××≤×××= 45.030.0 Eq. 2

where:

fcd : Concrete design compression strength (MPa)

z : 0.9×d (mm). If the entire cross section is under tensile strain, z is equal to hc+th.

9.3.3.3 Studs Stud design is based on the following assumptions:

1. Studs ensure bonding between steel plates and concrete core even under the condition that steel

plates yield. The corresponding shear stress, τs, is:

225.03

4

Dnn

ftb

LT

pydhw

s ×××××××= −πτ Eq. 3

where:

fyd-p : Steel plate design yield strength (MPa)

nL : Number of studs between the position of maximum moment and the support or the point of contra-flexure

nT : Number of studs in the section

D : Diameter of studs (mm)

2. Studs contribution to the shear capacity of the panel, Vsd, shall not exceed:

Eq. 1

Eq. 2

Eq. 3



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s

zAfV svsdsd ××≤

Eq. 4 where:

fsd : Stud design yield strength (MPa)

Asv : nT × 0.25 × π × D2 (mm2)

s : Distance between studs in the longitudinal direction (mm)

Actual normal stress in the studs is equal to:

z

s

A

VV

sv

cds ×−= )(σ

Eq. 5 where:

V : Applied shear load (N)

3. Combined state of normal and shear stresses in the stud shall satisfy the following criteria:

222 3 sdss f≤+ τσ Eq. 6

4. Concrete around the studs shall not crush. Therefore, shear stress in the studs is limited to:

2

5.02

25.0

)(29.0

D

EfD

v

cmcks ×××

××≤ πγατ Eq. 7

where:

α : 0.2 (hs/D + 1) ≤ 1, where hs is the stud height (mm)

fck : Characteristic cylinder compression strength of concrete (MPa)

Ecm : Secant modulus of concrete (MPa)

γv: Material factor for studs

5. Studs shall not be placed at a distance longer than 0.75 × (hc + 2 × th) so that any potential shear crack in the concrete, whose direction is assumed to be 45o from the longitudinal axis, is crossed by a stud, see Figure 5:

Figure 5 Maximum spacing studs: Shear cracks

6. Studs shall not be placed at a distance longer than 22 × th × (235/fyk-p)0.5 in the compression

side of the panel, in order to avoid plate buckling, where fyk-p is the characteristic yield stress of the plate, see Figure 6:

Eq. 5

Eq. 7

Eq. 6


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−−

= Eq. 11

9.3.4.2 Steel plates

⎟⎟⎠⎞

⎜⎜⎝⎛

⎟⎟⎠⎞

⎜⎜⎝⎛Δ−= σ

Eq. 12

Δσ

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Figure 6 Maximum spacing studs: Local buckling of compression plate

9.3.4 Fatigue Limit State Calculation of design life at varying stress amplitude is based on cumulative linear damage theory. The stresses due to cyclic actions are arranged in stress-blocks (action effect-blocks) each with constant amplitude and a corresponding number of stress cycles, ni. The design criterion is:

∑ ≤

i i

i

N

n333.0

Eq. 8 where:

Ni : Number of cycles with constant amplitude which causes fatigue failure.

The characteristic fatigue strength or resistance (S-N curve) of a structural detail is to be applicable for the material, structural detail, state of stress considered and the surrounding environment. S-N curves for each of the elements in the sandwich are presented.

9.3.4.1 Concrete The design life of concrete subjected to cyclic stresses in bending is calculated from:

cd

cd

f

fN

min

max

10

1

1

12log σσ

−−

= Eq. 9

where:

σmax : Numerically largest compressive stress, calculated as the average value within each stress-block.

σmin : Numerically smallest compressive stress, calculated as the average value within each stress-

block. If σmin is in tension, it shall be taken as zero.

fcd : Concrete design compressive strength.

The design life at tensile failure of concrete subjected to cyclic stresses in shear is calculated from:

cd

cd

V

V

V

V

CNmin

max

110

1

1

log −−

= Eq. 10

Eq. 8

Eq. 9

Eq. 10



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where:

Vmax : Numerically largest acting shear load which is resisted by the concrete, calculated as the average value within each stress-block.

Vmin : Numerically smallest acting shear load which is resisted by the concrete, calculated as the average value within each stress-block.

If the shear force changes sign the calculation shall, if necessary be performed with both the positive and negative values for Vmax and Vmin, respectively in the formulae above. Vcd are calculated according to Eq. 1. The factor C1 shall be taken as:

12.0 for structures in air where the shear force does not change sign

10.0 for structures in air where the shear force changes sign and for structures in water where the shear force does not change sign

If the shear force changes sign, account of this shall be made when calculating the number of stress cycles in the shear reinforcement.

The design life at compression failure of concrete subjected to cyclic stresses in shear is calculated from:

ccd

ccd

V

V

V

V

CNmin

max

110

1

1

log −−

= Eq. 11

For those stress-blocks where the shear force changes sign, Vmin shall be taken equal to 0. Vccd is calculated according to Eq. 2.

9.3.4.2 Steel plates The design life of steel plates is calculated with the following assumptions:

1. Welded studs influence design life.

2. Welding along plates, perpendicular to the element longitudinal direction, are present and influence design life.

3. Plates are free to corrode.

The corresponding S-N curve is thus:

⎟⎟⎠⎞

⎜⎜⎝⎛

⎟⎟⎠⎞

⎜⎜⎝⎛Δ−=

k

reft

tN σlog3921.10log10

Eq. 12 here:

Δσ : Stress range variation in steel

t : Steel plate thickness

tref : Reference thickness equal to 25mm.

k : 0.25

Note that (t/tref) shall not be taken less than 1.0.

Eq. 12

Eq. 11


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Table 4 Properties of material used in the specimens

Figure 8 Typical force deflection relation

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9.3.4.3 Studs Fatigue in the studs will be critical at the welding location. Existing S-N curves for studs need to be assessed taking into account the differences between typical “short” studs and the relatively “long” INCA studs.

9.3.5 Service Limit State Service limit state (SLS) has not been a design limit state in this study. Nevertheless, it is briefly discussed below.

One of the main concerns is the INCA panel water tightness. It is assumed that steel plates ensure the panel water tightness. As a result, cracking of concrete inside the sandwich is not a concern. Furthermore, fatigue design life for concrete is calculated assuming a dry environment.

Design rules for ships do not have specific requirements for deflections. However, it is possible to estimate the panel deflection assuming a cracked concrete section to calculate the section moment of inertia. The height of the concrete compression zone, i.e. uncracked portion, is calculated based on the acting loads.

9.4 Evaluation of experimental studies Ref /10/ presents static and dynamic experiments carried out at Universität der Bundeswehr München. Static tests will be used to assess the design basis presented in section 9.3 and also to interpret test results.

Figure 7 shows static test setup. Five 1200 x 300 x 100mm specimens were prepared. 6mm steel plates were provided on four sides of the specimen. Four-point bending tests were used.

Figure 7 Test setup



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Table 4 summarizes the properties of the materials used in the sandwich panels.

Table 4 Properties of material used in the specimens Characteristic concrete compression cylinder strength 9.0 MPa

Characteristic concrete tensile strength 2.0 MPa

Characteristic concrete modulus of elasticity 5.4 GPa

Steel yield strength 235 MPa

Steel modulus of elasticity 206 GPa

Displacements were measured at the centre of the specimen. A typical force displacement relation is shown in Figure 8. The report concluded that the bond between steel and lightweight concrete was stronger than the shear strength of the specimen.

Figure 8 Typical force deflection relation

Shear strength was assessed using the formulae presented in 9.3.3.2. It was found that shear capacity with respect to tensile failure governed the specimen capacity. Corresponding load was equal to 64kN. On average, shear cracks were observed at 55, 59, and 75kN in the tested specimens. Considering that the formulation for shear capacity with respect to tensile failure is highly dependent on the concrete tensile strength, which is a very scattered property, the load estimation is fairly good.

Under a load equal to 64kN, stress in the plate is equal to 57MPa. This shows that the utilization ratio of the plate is fairly low (57/235 = 24% of yielding stress). This suggests that if shear capacity of concrete core is improved, ideally to ensure that bending failure occurs first, the carried load can be increased four times.

In the test specimen, full bond between the steel outer and inner plates and the concrete core is presumed. Average bond stress was calculated assuming that compatibility of deformations between concrete and steel is ensured only by bond strength between them. For a load equal to 64kN average bond stress is equal to 1.37MPa, a fairly high value for the tested specimen (concrete was cast against sand blasted steel plates.) The reason for this unrealistic value is that in fact additional restrain is provided by the steel plates at both ends of the specimen. Therefore, it is not possible to estimate the actual bond strength of the interface from the experiments carried out.

As suggested earlier, it is possible to increase the panel shear capacity with respect to tensile failure by providing studs. Then, the capacity of the panel will be defined by either shear capacity with respect to


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9.5.1.1 Material properties

Table 5 Material properties for concrete core in parametric study

γ

Table 6 Material properties for steel in parametric study

γ

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compression failure or bending. Based on formulae in sections 9.3.3.1 and 9.3.3.2, it was found that strength will be governed by shear compression failure. The corresponding predicted failure load would be 128kN. Stress in the plate for this case is 95MPa, still 40% of the yield stress.

To ensure that bending is the governing failure mode, concrete strength needs to be increased by a factor of at least 3.2. Considering the relatively low strength of the concrete used in the experimental program, this is feasible if regular concrete is used instead of lightweight. Characteristic cylinder compression strength up to 90MPa is not unusual for high strength concrete. This ten fold increase in strength is achieved at an expense of 2.5 times increase in self weight. Positive and negative aspects of this modification will be assessed in subsequent sections.

9.5 Parametric study

9.5.1 Methodology A parametric study of the INCA-panel was carried out to get an indication of where the INCA-panels could be competitive with typical steel design for marine applications. The full scope of the study is shown in chapter 11 starting on page 63of this report. The objective of this study was to find the maximum feasible length of each panel, for different combinations of parameters, for given loads and boundary conditions. Figure 9 shows a typical INCA-panel where the different parameters are indicated. Note that connectors extend through the panel thickness. Therefore, they serve, in addition to the purposes presented in Section 9.3, as spacers to keep the position of the steel plates during casting.

Steel plateShear connector (stud)Concrete core

Figure 9 Typical INCA-panel

The parameters used in the study were:

Depth concrete core (hc): 150, 200, 250 and 300mm

Thickness steel plates (t): 6, 10, 12 and 15mm

Diameter shear connectors (studs): 6.4, 9.5, 13, 16, 19, 22 and 25mm

The loads and boundary conditions are discussed later in section 9.5.1.2 and 9.5.1.3. The maximum feasible length of the panel was limited by either bending- or shear capacity in ultimate limit states



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(ULS). Since there are no requirements for limiting deflection of the panels in marine applications, the maximum deflection are only calculated as a reference.

9.5.1.1 Material properties The parametric study is performed with two different concrete cores as defined in chapter 11. The material properties of the concrete cores in the parametric study are chosen to represent two extremes. The light weight concrete core (LWC), based on a mixture with light weight aggregate (Liapor), has a very low density and relatively low strengths. The material properties of this light weight aggregate concrete (LWAC) is taken from material tests carried out at Universität der Bundeswehr München, Ref /6/. The high strength concrete (HSC) is chosen as a normal density concrete with higher strength than normally used for traditional offshore concrete structures. The reason for choosing these two extremes was to investigate if the HSC could be more competitive than LWC due to its higher strength, in spite of being 2.5 heavier. The material properties used for the concrete are summarized in Table 5:

Table 5 Material properties for concrete core in parametric study

Density, γ

[kN/m3]

Characteristic cylindrical

compression strength, fck,cyl

[MPa]

Mean tensile strength, fctm

[MPa]

Young’s Modulus, Ecm

[GPa]

Light weight concrete (LWC)

9.8 9 1.1 5.4

High strength concrete (HSC)

25 90 5 44

The material properties of the steel used in the parametric study are dependent on the application of the steel in the INCA-panel. For the parametric study, only plates with steel grade S235 and shear connectors with steel grade C1015 is used, see Table 6. Later on, the effects of increasing the strength of the steel plates and also post-tensioning of the panels are considered. Material properties used in this evaluation are also included in Table 6.

Table 6 Material properties for steel in parametric study

Density, γ

[kN/m3]

Characteristic yield strength, fy

[MPa]

Ultimate strength, fu

[MPa]

Young’s Modulus, Es

[GPa]

Steel plates (S235) 78.5 235 360 206

Steel plates (S355) 78.5 355 510 206

Shear studs (C1015) 78.5 352 450 206

Steel reinforcement (B500C)

78.5 500 575 200

Steel tendons 78.5 16001) 1860 196 1) Characteristic yield strength for steel tendons = fp,0.1


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Figure 12 Summary of INCA-panels used in the present study

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9.5.1.2 Load conditions The parametric study of the INCA-panel was performed with four different load cases, L1, L2, L3 and L4 (see chapter 11 for more details). Each of these load cases consists of a uniformly distributed payload, representing a typical load for a certain application, plus self weight of the panel. See Table 7 for characteristic values and typical applications of these payloads. The characteristic self weight of the panel was calculated from the densities of the materials given in Table 5 and Table 6. These characteristic loads are multiplied with a load factor, according to Table 2, and a dynamic factor of 1.3.

Table 7 Characteristic local payloads for parametric study

Load case

Load Description Static

Load(1) [kN/m2]

Dynamic Factor(2)

Total load [kN/m2]

Rule Reference in DNV Rules for

Ships

L1 Minimum Accommodation

Deck Load 2.5 1.3 3.25

Pt.3 Ch.1 Sec.4 Table C1

L2 Minimum Sea Pressure for

Weather Decks 5.0 1.3 6.5

Pt.3 Ch.1 Sec.8 Table B1

L3 Heavy Equipment/Machinery

Deck Load 16 1.3 20.8

Pt.3 Ch.1 Sec.4 Table C1

L4 Inner Bottom of

Containership Cargo 120 1.3 156

Based on existing designs and Pt.3

Ch.1 Sec.8 Table B1(1) The self weight of the panel shall be added to the static loads

(2) Load factors according to Table 2 shall be taken in addition to the dynamic factor

9.5.1.3 Boundary conditions The panels are considered to span in one direction with boundary conditions applied at two opposite edges. The panels will therefore act as a one-way slab. Two different boundary conditions are considered for the parametric study as shown in Figure 10 and Figure 11.

Figure 10 Simply Support

Figure 11 Fixed Support

9.5.2 Discussion of results In total 256 different combinations of the INCA-panel has been considered in the parametric study, 128 with light weight concrete (LWC) core and 128 with high strength concrete (HSC) core. The chart in Figure 12 shows the possible INCA-panels built up based on the considered parameters.



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Figure 12 Summary of INCA-panels used in the present study

The maximum feasible length, either limited by shear compression or bending capacity, is found for each panel separately. Shear tensile capacity does not limit the maximum feasible span because the number of studs is designed so that shear compression or bending capacity governs the design. Figure 13 to Figure 20 shows the maximum feasible span against total panel self weight for different INCA-panels with 6, 10, 12 and 15 mm steel plates and simply and fixed supported boundary conditions. The legend to the right on the figures indicates what load condition and concrete core the curves represents. Each of the curves contains four points representing various thickness of the concrete core, i.e. 150, 200, 250 and 300 mm. The markers of the data points indicates the type of failure that is limiting the maximum feasible span, e.g. triangle indicates bending failure and square indicates shear compression failure.

The results presented in Figure 13 to Figure 20 show that identical panels with LWC and HSC core can span the same length for very high loads, i.e. L4, if design is governed by bending capacity. This is because bending is mostly carried by the steel plates and the self weight is not significant compared to the external load. However, HSC-core panels are heavier than LWC-panels.

As load decreases, L3 and L2, LWC core panels have larger spans than HSC core panels, if design is governed by bending capacity, because self weight becomes a significant part of the total carried load. For the lightest load case, L1, HSC has no benefit compared to LWC since the selfweight is larger than the external load.

The analysis showed that concrete compressive strength in HSC panels is not fully utilised. Pre- or post-tensioning the panels may contribute to better utilisation of the concrete and therefore section reduction. This option will be discussed further in section 9.5.2.1.

When design is governed by the shear compression capacity the maximum span will be shorter for LWC panels than for HSC panels. This is caused by the relative low compression strength of the LWC compared to the HSC. Shear compression failure will typically govern the maximum span for LWC-core panels under the heaviest load cases, L3 and L4. This is clearly illustrated in Figure 20 where maximum feasible span for LWC panels under load case L3 and L4 are limited by shear compression failure.

INCA

LWC HSC

Simply Supported

Simply Supported

Fixed Fixed

hc = 150, 200, 250 and 300 mm

hc = 150, 200, 250 and 300 mm

ts = 6, 10, 12 and 15 mm

ts = 6, 10, 12 and 15 mm

hc = 150, 200, 250 and 300 mm

ts = 6, 10, 12 and 15 mm

hc = 150, 200, 250 and 300 mm

ts = 6, 10, 12 and 15 mm

Load case = L1, L2, L3 and L4





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0

200

400

600

800

1000

2,5 5,0 7,5 10,0 12,5 15,0 17,5 20,0 22,5

Max span [m]

Sel

f wei

ght p

anel

[kg/

m2] LWC, L1

LWC, L2LWC, L3LWC, L4HSC, L1HSC, L2HSC, L3HSC, L4

Triangle indicates: maximum span is limited by bending. Square indicates: maximum span is limited by shear compression.

Figure 15 Maximum feasible span against total weight for Simply Supported INCA-panels with 12 mm steel plates

0

200

400

600

800

1000

1200

2,5 5,0 7,5 10,0 12,5 15,0 17,5 20,0 22,5 25,0

Max span [m]

Sel

f wei

ght p

anel

[kg/

m2] LWC, L1




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0

200

400

600

800

1000

2,5 5,0 7,5 10,0 12,5 15,0 17,5

Max span [m]

Self

wei

ght p

anel

[kg/

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Figure 19 Maximum feasible span against total weight for Fixed Supported INCA-panels with 12 mm steel plates

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In Figure 21 to Figure 28 is the maximum feasible span against weight of studs presented. The low compression strength of LWC results in a large number of shear connectors to prevent local crushing of the concrete. For LWC panels under load case L4, where the maximum span is between 2.5 and 5 m, the density of studs is very high, see Figure 21 to Figure 28. In this case, the connectors will be mainly resisting the vertical shear. When lighter load cases are considered, where maximum feasible span is larger, the number of shear connectors to prevent local crushing of the concrete is distributed over a longer span, i.e. the density of studs will decrease. For the HSC, local crushing of the concrete is not the governing design condition for the shear connectors. In this case, the number of connectors needed is dependent on the shear capacity of the stud itself, and therefore the number of shear


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Figure 23 Maximum feasible span against weight studs for Simply Supported INCA-panels with 12 mm steel plates

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connectors to transfer the horizontal shear is fewer than for the LWC. However, in order to comply with maximum spacing of studs, as described in 9.3.3.3, the number of studs needs to be increased. As a result, the number of studs for LWC panels is not that larger than the number of studs for HSC panels for the lightest load cases L1 and L2.

The discontinuities in some of the curves presented in Figure 21 to Figure 28 are a result of selected intervals of the stud diameter and to obtain a reasonable spacing between each stud.

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Figure 27 Maximum feasible span against weight studs for Fixed Supported INCA-panels with 12 mm steel plates

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In the parametric study, the thickness of the top and bottom plate is equal. However, considering top and bottom steel plates with different thicknesses may lead to a better utilization of material. The total weight may not change much but costs could be reduced.


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CAPACITY CURVE - SANDWICH WITH LIGHT WEIGHT CONCRETE

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Figure 30 Capacity curve for LWC panel with 200 mm core and 10 mm steel plates

9.5.2.2 Effect of increasing strength in steel plates

Figure 31 Simplified approach to calculate the bending capacity

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9.5.2.1 Effect of pre-stressing panels If bending governs the design, pre-stressing of the panels may contribute to a better utilisation of the concrete by increasing the portion of the panel in compression. The compression strength of HSC is 10 times higher than that of LWC, see Table 5, and the pre-stressing will therefore give a larger benefit for the HSC core panel.

Figure 29 shows the capacity curve for an INCA-panel with 10 mm steel plates on top and bottom and 200 mm HSC core. It is clear from the figure that a 55% increase in bending capacity by pre-stressing is possible for this panel. This increase in bending capacity will lead to a better utilisation of the concrete and therefore it will be possible to cover longer spans with the same section. However, this improvement may not be enough to make HSC panels weight-competitive for low loads, i.e. L1 to L3.

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The capacity curve for the same INCA-panel as in Figure 29, but with LWC core, is shown in Figure 30. From this figure it can be seen that only a little increase in the bending capacity of the section, equal to 9%, is possible. This is due to the low compression strength of the LWC. Therefore, there will be no benefit from pre-stressing because the cost and work will increase significantly.

Pre-stressing force

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CAPACITY CURVE - SANDWICH WITH LIGHT WEIGHT CONCRETE

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Figure 30 Capacity curve for LWC panel with 200 mm core and 10 mm steel plates

9.5.2.2 Effect of increasing strength in steel plates For panels where bending capacity governs the design a strength increase in the steel plates will result in longer feasible spans. For the parametric study the concrete core contribution to the bending capacity is considered. However, since the neutral axis of the cross section is just beneath the upper steel plate the contribution from the concrete is almost insignificant. A simple estimate of the bending capacity can be calculated according to Figure 31, where only the steel plates contribute in the bending capacity. From the equation in Figure 31 it can be seen that the bending capacity will increase proportionally to the strength in the steel plates.

Figure 31 Simplified approach to calculate the bending capacity

Steel grade S235 is used for the steel plates in the parametric study. But in order to show the effect of increasing strength in the steel plates, some additional panels are calculated with steel grade S355. Figure 32 and Figure 33 show the capacity curves for two identical panels with different core material, LWC and HSC, and different steel grades to show the increase in bending capacity. The INCA-panels shown have a core thickness of 200 mm and steel plate thickness, top and bottom, of 10 mm. The predicted moment capacity for pure bending increases with a factor of approx. 1.5, this factor is according to the strength increase 355/235 = 1.5.

Pre-stressing force

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9.6.1 RoRo Car deck

Figure 34 Cross section of the RoRo vessel

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Figure 33 Capacity curve for INCA-panel with HSC core, 200 mm core thickness and steel plate thickness 10 mm

The side effect of increasing strength in the steel plates is that it will also increase the horizontal shear force between the steel plate and the concrete core. As a result, a larger stud area is needed to transfer the horizontal shear force to ensure that the different layers will act as a sandwich panel.

9.6 Deck design The parametric study gave an indication of the INCA-performance for different cross sectional parameters, load - and boundary conditions. Knowledge gain from the parametric study could therefore indicate what span was feasible to cover and the expected self weight of the panels. Based on the knowledge from the parametric study, two typical marine applications were selected to compare original steel design with the INCA-solution and then highlight positive and negative aspects of introducing INCA-panels with LWC core, for marine applications.



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The first comparison is against decks in a RoRo (Roll-on/roll-of) vessel. The RoRo deck case study underlines the challenge that INCA is faced with for most applications in conventional shipping, namely weight.

The second comparison is against a process deck on a FPSO (Floating Production, Storage and Offloading) vessel. Since the FPSO vessel is a stationary unit the total cost will be the critical factor instead of the weight.

The limitation of these comparisons is that the main structural system used for steel and INCA panels is the same. This system is the result of an optimization process meant for a steel structure. However, taking into consideration that INCA behaves differently than steel, it is foreseen that a better utilization of INCA can be achieved if a main structural system, which exploits INCA advantages, is used instead.

9.6.1 RoRo Car deck The RoRo deck comparison is performed with a vessel earlier approved by DNV. Local and global loads on the decks and dimensions of the ship are therefore extracted from the already built vessel.

Cross section of the RoRo vessel is illustrated in Figure 34. The RoRo vessel is built with 14 decks, one navigation bridge deck and one tank bottom. For the comparison data from three different decks, number 3, 8 and 13, as highlighted in red on Figure 34 are collected.

The objective is to replace all existing steel structure, steel plates, stiffeners and transverse girders, with exception of the longitudinal girders.

Static load, self weight and depth of each deck is summarized in Table 8. Each deck characteristics is listed with and without transverse girders. If the INCA panel are capable to carry the load while spanning in the transverse direction transverse girders may also be avoided.

Figure 34 Cross section of the RoRo vessel


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Figure 36 Deck 3 RoRo vessel

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Table 8 Deck properties for RoRo vessel Deck Static load [tons/m2] Self weight [kg/m2] Panel depth [mm]

13 (incl. transverse girders) 0.165 75.3 306

13 (excl. transverse girders) 0.165 58.2 106

8 (incl. transverse girders) 0.5 130.1 730

8 (excl. transverse girders) 0.5 100.2 190

3 (incl. transverse girders) 1.0 162.0 598.5

3 (excl. transverse girders) 1.0 138.9 233.5

The lightest panel considered in the parametric study has a 150 mm LWC core and 6 mm steel plates. This panel weights 241.2 kg/m2 without taking the studs into account. Since the weight is so critical for this application deck 8 and 13 are excluded from further investigation.

Cross section for deck number 3 with steel plate, stiffeners and girders are shown on Figure 35.

Figure 35 Cross section deck 3

Three different options are considered for the comparison against deck 3 in the RoRo vessel. The first option is an 11.4 m simply supported panel between the longitudinal girders, as indicated to the left on Figure 36. The second and third option is to optimize the design by using INCA-panels as a continuous beam over three spans, as indicated to the right on Figure 36. The continuous beam will reduce the bending moment and may therefore allow a lighter panel to carry the load. The second option represents thick steel plates and thin core, and the third option represents thin steel plates and thick core.



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Figure 36 Deck 3 RoRo vessel

Panel design is controlled by ultimate limit state, i.e. bending and shear caused by the local static loads from cargo and self weight. The fatigue design life is checked for dynamic axial forces, acting in the longitudinal direction of the vessel, caused by global hogging/sagging moment. As a reference, the maximum deflection at midspan is calculated in serviceability limit state. The maximum deflection was found to be 75 mm, which is considered acceptable.

Table 9 shows the INCA-panels proposed to replace the existing steel structure in deck 3. Option number 2 and 3, with a continuous panel over three spans, is most advantageous with respect to weight and material costs. Option 2, with thick steel plates and thin core, has the lightest weight and option 3, with thin steel plates and thick core, has the lowest material costs. The material costs in Table 9 are based on a material cost estimate of 300 USD pr ton concrete and 700 USD pr ton steel. The material costs used in the comparison are based on discussion with shipyards in Asia and are only used to give an indication of the cost. The material costs for the existing steel structure, plates, stiffeners and transverse girders, is 113.4 USD/m2.


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Figure 37 Process deck on FPSO vessel

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Table 9 INCA-panels for deck 3 Boundary conditions Simply supported Continuous Continuous

Depth concrete core [mm] 200 150 235

Thickness steel plates [mm] 10 (S235) 10 (S235) 6 (S235)

Studs 83Ф13 pr m2 110Ф16 pr m2 66Ф16 pr m2

Weight concrete [kg/m2] 194 144 227

Weight steel incl. studs [kg/m2]

173 182 118

Total weight panel [kg/m2] 367 326 345

Material cost concrete [USD/m2]

58.2 43.2 68.1

Material cost steel incl. studs [USD/m2]

121.1 127.4 82.6

Total material cost [USD/m2] 179.3 170.6 150.7

Maximum deflection [mm] 63 75 52

Although INCA-panel is heavier than the steel panel, for the given load, INCA-panels can span between longitudinal girders and then transverse girders are not needed. This has the benefit of reducing deck depth.

Some initial conclusions regarding advantages and challenges for replacing the existing steel structure with a continuous INCA-panel are shown below:

Advantages:

- Total depth of deck is decreased from 598.5 till 170 mm. This 72% reduction in deck height gives a potential to install an extra deck, with economical interests, if the same reduction applies for several decks.

- Area of steel that need fire protection is reduced because stiffeners are avoided. The fire protection will also be easier to apply because of the flat surfaces.



- With a well-established welding procedure the welding of the studs will be very efficient, i.e. reduced time for welding. The amount of welding will also be reduced compared to the existing steel structure.

Challenges:

- Total weight of the panel is increased by 101%, from 162 till 326 kg/m2.

- Estimated material costs are increased by 33%, from 113.4 till 150.7 USD/m2.

- Assembly, connection and production of the panels have to be investigated further.



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9.6.2 FPSO process deck Loads and dimensions for the comparison are extracted from an existing process deck on a FPSO vessel, see Figure 37.

Figure 37 Process deck on FPSO vessel

The objective is to replace all existing steel structure, steel plates and stiffeners, except longitudinal and transverse girders with INCA-panels.

The static loads on the process deck are caused by operational loads and self weight from structural elements, equipment, piping, valves etc. Large point loads, from the operating separators, make the process deck heavy loaded at some areas. The comparison is performed for a 2.5 m wide INCA-panel at the heaviest loaded area, as indicated in Figure 38. The dimensions of the process deck are 18.4 m times 27.7 m.

Picture only for illustration


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Table 10 INCA-panels for process deck

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Figure 38 INCA-solution for process deck

The static model for the process deck is indicated in Figure 39, spanning in the shortest direction as shown in Figure 38.

Figure 39 Static model of process deck on FPSO

Because of the heavy loads and large span for the process deck, a higher steel grade (S355) is chosen for the steel plates. The concrete core has to be larger than the cores evaluated in the parametric study. Two different panels are chosen to replace the existing steel structure, one with thin steel plates and thicker core and the second with thick steel plates and smaller core as shown in Table 10. The design of the proposed panels is controlled by bending- and shear capacity in ultimate limit state. As a reference the maximum deflection is calculated.



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The material costs in Table 10 are based on a material cost estimate of 300 USD pr ton concrete and 700 USD pr ton steel. The steel weight of the existing steel structure is 359 kg/m2 that give an estimated material cost of 251.3 USD/m2.

Table 10 INCA-panels for process deck INCA-panel 1 INCA-panel 2

Depth concrete core [mm] 360 460

Thickness steel plates [mm] 10 (S355) 8 (S355)

Studs 37Ф25 pr m2 30Ф25 pr m2

Weight concrete [kg/m2] 346 444

Weight steel incl. studs [kg/m2] 207 178

Total weight panel [kg/m2] 553 622

Material cost concrete [USD/m2] 103.8 133.2

Material cost steel incl. studs [USD/m2] 144.9 124.6

Total material cost [USD/m2] 248.7 257.8

Maximum deflection [mm] 89 67

Some initial conclusions regarding advantages and challenges for replacing the existing steel structure with INCA-panel 1 are shown below:

Advantages:

- Better performance under explosion.

- Improved fire insulation.

- Simpler solution with increased flexibility for the location of the equipment.

- Although estimated material costs are almost the same, further optimization may lead to reduction of material costs.

- For the existing steel structure, welding directly on one side of the plate damage the steel treatment on the other side of the plate. For the INCA-panel, welding directly on the top side of the upper plate will only damage the bond between the concrete and the plate. However, this bond is not taken into account since studs are provided to transfer the shear stress between the layers. The steel treatment on the bottom surface of the lower plate is not affected by this welding.





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- With a well-established welding procedure the welding of the studs will be very efficient, i.e. reduced time for welding. The amount of welding will also be reduced compared to the conventional steel structure.

- With a well-established production and assembly procedure it is possible to be competitive on costs.

Challenges:

- Total weight of the panel is increased by 54%, from 359 till 553 kg/m2.


9.7 Conclusions The evaluation of the INCA sandwich consisting of steel plates and concrete core, i.e. without shear connectors, concluded that in order to ensure an adequate and reliable shear connection between the face sheets and the core it is necessary to use studs. Steel-concrete composites with studs have been successfully used for many years in the construction of buildings and bridges; the latter are subjected to fatigue loading. Therefore, steel-concrete composite with studs can be considered a proven technology. The novelty of the proposed panels is that, in addition to ensuring the shear connection between sandwich elements, the studs are also used to reinforce the core, avoiding shear tension failure and limiting cracking of the concrete core.

The present benchmark study focused on assessing INCA-panels with studs from the structural point of view and comparing their performance with typical steel solutions. The study looked into the application of panels to ships and offshore facilities, particularly horizontal elements such as decks. Based on the review of existing design standards and recommendations, the basis for design of INCA was proposed. Ultimate and fatigue limit states were covered. Service limit state was only briefly discussed as there are no specific design requirements for control of deflections in ships and offshore facilities. It is assumed that water tightness is provided by the steel skin.

A parametric study was carried out in order to identify typical INCA-panel (with studs) dimensions and spans for various loads and boundary conditions. The results showed that INCA is capable to cover relatively long spans. Because studs were designed to transfer the horizontal shear force between plates and core and to prevent shear tension failure, design was governed by either shear compression or bending capacity.

The challenge that INCA is faced with for most applications in conventional shipping is its self weight. In the parametric study two different concrete cores were considered, light weight concrete (LWC) and high strength concrete (HSC), to investigate if the ten-fold increase in compressive strength could give any benefit in spite of the almost three times weight increase. It was concluded that for panels, in which the bending capacity limits the maximum feasible length, LWC-core resulted in lighter panels for a given span. It shall be noted that it is possible to increase the capacity, both in bending and shear, of the HSC-panels by pre-stressing the panels or increasing the steel plate strength. However, this option makes HSC-panels competitive only for high imposed loads, which are several times larger than the self-weight.

The parametric study focused on panels with steel plates of identical thicknesses on both sides. Considering plates with different thicknesses will lead to a better utilization of the material, resulting in an optimized panel with respect to both cost and weight.



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Two case studies were considered to compare INCA panels with typical steel solutions. The comparison only considered replacing some decks of existing ships with INCA. The main limitation of this approach is that the main structural system is the result of an optimization process meant for a steel structure. Steel structures are good at resisting tensile forces but may buckle under compression forces. The robust INCA-panel is capable to efficiently carry both axial compression and tension. Taking into consideration that INCA behaves differently than steel, it is foreseen that a better utilization of INCA can be achieved if a main structural system, which exploits INCA advantages, is used instead. These advantages would probably be clearer if the main structural system is made of INCA.

From the case study, advantages and challenges of introducing INCA-panels in marine applications were found as described below.

Advantages:

- Robust panel with better performance under explosion compared to traditional steel structures.

- The INCA panel with shear reinforcement/studs is expected to perform excellently under fire as long as some fire protection/internal reinforcement are provided. This INCA panel behaves different from the INCA panel tested in the study, which relied on bond between steel and concrete for composite action (load carrying capacity). The INCA panel with shear connectors does not rely on this bond for composite action; hence no sudden collapse of the structural member under fire load will occur due to bond failure.

- Improved fire insulation which will prevent spreading of the fire from one fire cell to another.

- Fewer details subjected to fatigue damage.

- Welding directly to the steel plates does not damage the steel treatment on the other side of the plate.




- With a well-established welding procedure the welding of the studs is very efficient, resulting in reduced time for welding. The amount of welding will also be reduced compared to that needed in traditional steel structures.

- With a well-established production and assembly procedure it is possible to be competitive on costs compared to traditional steel structures.

- Transverse girders can be avoided. Deck height can be decreased giving the possibility of installing extra decks with consequent economical benefits.

Challenges:


- For mobile structures, in which weight is critical, it is hard to be competitive with traditional steel structures. This conclusion is based on the case study carried out, which had the limitations mentioned earlier, i.e. only replacement of panels was considered.


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9.9 REFERENCES

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- For marine applications where weight is less critical, INCA-panels can be competitive.

9.8 Future work Although the conclusion of the present benchmark study is that INCA with studs is technically feasible for marine applications, there are further works that are required in order to make this technology ready for commercialization. These are summarized below:

- Testing program:

o Confirmation of design assumptions and procedures: Although accepted design procedures have been used, INCA is not the typical composite structure covered by the standards.

o Performance under impact loading: Similar structural systems have reportedly being tested under impact loading and have shown excellent performance. It is expected that INCA will also have the same robustness for this loading case.

o Performance under fire loads: As it is currently proposed, fire protection cover is necessary to protect the steel from fire. However, other options, such as providing longitudinal reinforcement embedded in the concrete to carry the loads when the steel plate no longer has tensile strength should be explored. With internal steel reinforcing bars in the concrete no fire protection cover may be required as the temperature of the longitudinal steel will be protected by the concrete.

- Mock-up test: To confirm methods to connect panels or to reassess the construction procedure. Particularly, the feasibility of one time cast, in which the steel skin of the whole structure is prepared first and then the concrete is poured inside, needs to be assessed.

- Detailed design of the connections between panels and vertical walls to ensure water tightness.

- Further evaluation shall be made regarding construction of the main load (hogging and sagging longitudinal and transverse moment) carrying hull using INCA approach. The jointing of the INCA panel may be considered as a disadvantage for such application, but technically the ship hull can be assembled using thin steel plates in two layers with a space between. The plates are pre-mounted with the necessary shear studs, ducts for post tensioning reinforcement are installed together with other reinforcement found necessary by design. The two steel layers are connected together to form a robust steel formwork. This formwork can be easily shaped to any form due to thinner steel plates compared to traditional steel ships. The formworks can also be prefabricated and mounted together in the shipyard. This steel formwork is later filled with concrete of the quality required based on actual design calculations. There exist techniques for performing such concreting in the building industry. The method will depend on the size of the separation between the two steel layers. A successful concreting will require venting out of air present inside the formwork. This venting shall be based on design evaluations and experience. Whether the full height can be concreted in one step or has to be divided in several steps will depend on the strength of the formwork, in this case the thickness of the plates and the strength of the bolts connecting the steel layers together. The great advantage of using the INCA sandwich structure in the main structure is it superior buckling performance, its strength robustness and its resistance for failure under impact loading like grounding. Using the INCA sandwich structure in the hull will also reduce the leakage potential and also reduce the condensation of water on the inner side of the hull. The inner side will become dry due to the good insulation properties of the INCA sandwich structure. It shall be noted that the current



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benchmark study has not compared the weight and cost for such an application. Such comparative design work shall be carried out as part of further work along these lines. For outside wave pressure, the weight of the structural element will have a positive effect and not negative as assumed in the benchmark study. The benchmark study only considered replacement of an internal deck with an INCA sandwich element. Design of the sandwich hull as outlined above can be carried out using the design approach outlined in the Appendix, provided the appropriate global and local loads are determined.

9.9 REFERENCES /1/ Eurocode 4 – Design of composite steel and concrete structures – Part 1: General rules and

rules for buildings, 2004

/2/ Eurocode 4 – Design of composite steel and concrete structures – Part 2: General rules and rules for bridges, 2005

/3/ Steel, concrete and composite bridges – Part 5: code of practice for design of composite bridges, British Standards Institution, 1979

/4/ NS 3476 – 3 Prosjektering av samvirke-konstruksjoner i stål og betong, beregning og dimensjonering, Norges Standardiseringsforbund, 1988

/5/ Design guide for steel-concrete-steel sandwich construction, Volume 1: General principles and rules for basic elements, Steel construction Institute, 1994

/6/ Testing of LWAC as Core Material for Sandwich Constructions, Final Report, Universität Der Bundeswehr München, October 2004.

/7/ DNV-OS-C502 Offshore concrete structures, April 2007

/8/ DNV-OS-C101 Design of offshore steel structures, General (LRFD Method), October 2008.

/9/ DNV-OS-RP203 Fatigue design of offshore steel structures, April 2008.

/10/ Test Report, Static Sandwich Testing, Dynamic Sandwich Testing, Universität Der Bundeswehr München, November 2006.


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10 APPENDIX 2: BENCHMARK STUDY OF INCA PANELS WITHOUT STUDS

10.1 Scope and objectives of study

• • • • •

10.2 Design basis

10.2.1 Relevant codes

• • • •



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10 APPENDIX 2: BENCHMARK STUDY OF INCA PANELS WITHOUT STUDS

10.1 Scope and objectives of study The purpose of the study of INCA panels without studs was to provide a comparison with the results of the parametric study on panels with studs reported in chapter 9. It must be emphasised that use of the INCA sandwich concept without studs is not recommended in view of the uncertainty regarding the effectiveness of the bond between the concrete and the steel face sheets when not provided with studs. In fact the DNV Offshore Standard for Concrete Structures /1/ effectively forbids the use of such configurations in which a combination of steel and concrete has to rely on a bond between concrete and a smooth steel surface. The study represents an idealised, limiting case in which a perfect bond is in some way achieved as long as the shear stress at the interface doesn not exceed the shear strength of the concrete core.

Attention is confined to the following:

• Rectangular panels supported on two edges only, with spans up to 18 m between the supported edges.

• Alternative simply supported and rotationally constrained boundary conditions at the two supported edges.

• Lightweight concrete core with thickness from 100 mm to 300 mm

• Steel plates of steel with 235 MPa yield strength in thicknesses from 3 mm to 15 mm; only cases with face sheets of equal thickness are considered.

• Uniform, static, lateral pressure loading over the entire upper surface of the panel.

The possible use of an alternative, high-strength steel with yield strength of 355 MPa is considered in addition.

Note that the results presented are independent of the width of the panels (i.e. the distance between the unsupported edges).

10.2 Design basis

10.2.1 Relevant codes There are no existing design codes that apply directly to sandwich structures with steel faces and lightweight concrete cores, without the use of studs attached to the faces. However, design codes have been referred to as follows:

• DNV-OS-C502 Offshore Concrete Structures /1/

• DNV-OS-C501 Composite Components /2/

• Eurocode 1992-1-1:2004 Eurocode 2: Design of concrete structures Part 1-1: General rules and rules for buildings /3/

• DNV Rules for Classification of Ships /4/


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10.2.4 Design equations assuming the core is uncracked and fully effective

ρρ +=ρ ρ

++=

( ) ( ) ( )ννν −+−+−=ν ν

( )( )νσ −+=

( )νσ −=

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The Eurocode /3/ has sections on lightweight concrete and on design of unreinforced concrete. It also specifies a procedure for deriving the shear strength of unreinforced concrete from the measured tensile splitting strength. This standard (together with measured shear strength and tensile splitting strength given in INCA project reports) has been used as the basis for determining the allowable shear strength for the sandwich core.

For the steel faces an allowable stress of 160f1 has been adopted as specified in the benchmark study specification /5/, where f1 = 1.0 for steel with yield strength 235 MPa and 1.39 for steel with 355 MPa yield strength. This is consistent with allowable stress levels in the DNV Rules for Classification of Ships /4/.

10.2.2 Design approach The design is based initially on conventional sandwich plate theory, assuming isotropic materials in the core and in the face sheets.

Conventional sandwich plate theory makes the following assumptions:

• Fully linear-elastic material behaviour, including that of the core (i.e. no cracking)

• Perfect bonds between the face sheets and the core

• First order shear deformation theory formulation, i.e. plane sections initially normal to the plate surface remain plane, but do not necessarily remain normal to the plate surface.

It is common in analysis of sandwich structures to make two further assumptions:

• That the face sheets are much thinner than the core, so that the contribution to the elastic bending stiffness D of the sandwich from the separate bending stiffnesses of the face sheets about their own mid-planes can be neglected.

• That the core material is much more compliant (less stiff) than the face sheet material, so that the contribution from the core to the elastic bending stiffness D of the sandwich can be neglected.

If both of the above conditions are satisfied simultaneously, the distribution of through-thickness shear stress over the cross section can be considered constant, and equal to the shear force T per unit length divided by d, where d is the distance between the mid-planes of the face sheets.

For the INCA panels investigated, the first of these assumptions (thin face sheets) was found to be well satisfied in all cases, but the latter assumption (compliant core) was not satisfied by any of the panels. Thus the full expressions for the bending stiffness and for the variation of shear stress over the thickness were applied.

It has been found that, for the lightweight concrete considered here, tensile cracking of the concrete core due to tensile bending stresses may be expected at bending moments below those that induce yielding of the steel face sheets. In view of this a refined procedure has also been used in which the region of the core experiencing tensile bending stresses is assumed to crack, with a resulting shift of the neutral axis.

10.2.3 Load cases The load cases considered are as defined in the benchmark specification /5/:

• LC1: 2.5 kN/m2

• LC2: 5.0 kN/m2



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• LC2a: 16 kN/m2

• LC3: 50 kN/m2

• LC4: 120 kN/m2

LC1, LC2, LC3 and LC4 may be compared with the study performed for INCA with studs (Appendix 1).

The actual loading considered is the combination of the above with the self-weight of the sandwich panel. A dynamic amplification factor of 1.3 is applied to each of these loads.

10.2.4 Design equations assuming the core is uncracked and fully effective The mass per unit area m of a sandwich panel is given by

ccff ttm ρρ += 2

where tf and tc are the thicknesses of the face sheets (here assumed equal) and core, and ρf and ρc are the densities of the face sheets and core, respectively.

The bending stiffness of a sandwich beam having equal face sheets is given by

1226

323ccffff tEdtEtE

D ++=

where Ef and Ec are the Young’s moduli of the face sheets and core, respectively, and d = tc + tf is the distance between the mid-surfaces of the face sheets. For a sandwich plate this is modified to

( ) ( ) ( )2

3

2

2

2

3

1121216 c

cc

f

ff

f

ff tEdtEtED ννν −+−+−=

where νf and νc are the Poisson’s ratios of the face sheets and core, respectively.

The first term represents the bending stiffnesses of the face sheets about their own mid-planes. This can be neglected if the thin-face approximation is valid. The third term represents the contibution from the core, and can be neglected if the core is very compliant. In the case of the INCA panels, the thin-face condition is satisfied but not that for compliant core. In fact the full expression has been used in the present study.

The maximum tensile or compressive stress in the face sheet caused by a bending moment per unit length M in the sandwich panel is given by ( )( )2max

1

2

f

cfff

D

ttEM

νσ −+=

The maximum tensile or compressive stress in the core caused by the same bending moment is given by

( )2max1

2

c

ccc

D

tEM

νσ −=

As the tensile strength of concrete is always smaller than the compressive strength, a concrete core will always fail in tension before compression.


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TECHNICAL REPORT10.2.5 Design equations for cases when the core is cracked

( )( ) ( ) =−−−+ νν

( ) ( ) ( ) ( )[ ] ( )ννν −++−++−+−=

( )( )νσ −−+=

( )( )νσ −+=

( )νσ −=

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The maximum transverse shear stress in the core caused by a shear force per unit length T in the sandwich panel is located at the mid-plane and is given by

( ) ( )⎥⎥⎦⎤⎢⎢⎣⎡

−+−=2

2

2max1812 c

cc

f

ff tEdtE

D

T

νντ

The maximum bending moment per unit width Mmax and shear force per unit width Smax in a panel supported at two opposite edges and carrying a uniform pressure load p are given by

8

2

max

pLM = for a simply supported beam and

12

2

max

pLM = for a beam with clamped ends.

2max

pLT = for either simply supported or clamped conditions.

From the above equations it is possible to obtain the maximum allowable span of beam so as not to exceed an allowable face sheet stress σall or core shear stress τall: ( )( )2

1 2allmax

bendingcff

f

ttEp

Dk

p

kML +

−== νσwhere k = 8 for simply supported edges and 12 for clamped.

( ) ( )1

2

2

2

allmaxshear

1812

22−

⎥⎥⎦⎤

⎢⎢⎣⎡

−+−==c

cc

f

ff tEdtE

p

D

p

TL νν

τ

The maximum allowable span will then be the lower of the two values given by these conditions.

For small spans the core shear stress condition governs, while for larger spans the face sheet stress governs. The transition between the two occurs when the two expressions for maximum span are equal: ( )( ) ( ) ( )

1

2

2

2

allshear

2all

bending1812

2

2

1−

⎥⎥⎦⎤

⎢⎢⎣⎡

−+−== +−=

c

cc

f

ff

cff

f tEdtE

p

DL

ttEp

DkL νν

τνσ

For a given configuration the condition is best explored by solving the above for p and then calculating the corresponding length L.

Bending of a sandwich plate induces also stresses in the direction perpendicular to the stresses described above. Thus it could be argued that, instead of just considering the bending stress σ in the direction parallel to the beam’s axis one should allow for the fact that, in a plate there will be a perpendicular stress induced by the prevention of strains in the perpendicular direction. Then it is relevant to consider the von Mises equivalent stress which in such a case is given by

21 ffe ννσσ +−=

However, in the DNV Ship Rules /4/ the allowable stresses for plating under lateral pressure loading are specified as allowable bending stresses and are considered to allow for this effect, so this has not been considered in the present evaluation. The effect, if included, would be to increase the allowable span slightly for a given layup and loading.



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10.2.5 Design equations for cases when the core is cracked If the core consists of a material that is weak in tension, the tensile bending stresses may cause cracking of the core at a lower value of applied bending moment than yielding of the faces. If this happens the part of the core that experiences tensile strains will undergo extensive cracking and contribute little to the bending stiffness. This will cause a shift of the neutral axis towards the compressive face of the panel. By assuming that the core material on the tensile side of the neutral axis makes no contribution to the bending stiffness, and equating the net axial force across the remaining section to zero, an equation for the position of the neutral axis is found: ( )( ) ( ) 02

1

12

2

22 =−−

−+ c

fc

cff th

E

Eth ν

ν

where h is the distance of the neutral axis from the face-core interface on the compressive side of the sandwich cross-section. This quadratic equation is readily solved for h.

The removal of the part of the core in tension and associated shift of the neutral axis results in a modified flexural stiffness Dcracked :

( ) ( ) ( ) ( )[ ] ( )2

322

22

3

cracked13

2221216 c

cfcf

f

ff

f

ff hEthtth

tEtED ννν −++−++−+−=

The maximum tensile stress in the face sheet is then given by ( )( )2cracked

max,tensile1 f

cfff

D

httEM

νσ −−+=

The maximum compressive stress in the opposite face sheet is given by ( )( )2cracked

maxe,compressiv1 f

fff

D

htEM

νσ −+=

The magnitude of this is smaller than the maximum tensile stress.

The maximum compressive stress in the core is given by

( )2cracked

maxe,compressiv1 c

cc

D

hEM

νσ −=

When the core is cracked, calculation of the shear stress distribution is not straight forward since the theory normally used assumes that plane sections remain plane, so that the tensile face sheet remains effective, requiring a continued shear connection to the remainder of the section. This implies that, although the part of the core on the tensile side of the neutral axis is ineffective as far as bending stresses are concerned, it still effectively carries shear stresses. While it is possible to derive expressions for the shear stress distribution under these circumstances, they give the anomalous result (at least for the cases analysed here) that the maximum core shear stress in the cracked panel is smaller than that in a similar uncracked panel under the same loading. It is concluded that checking for shear failure of the core is meaningful only for the case where it is not already cracked due to tensile bending stresses.


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10.3.1 Results: trends

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10.2.6 Material properties and allowable stresses In accordance with the benchmark study specification, the allowable stress in the steel is limited to 160 MPa for normal steel. This is consistent with the requirements in the DNV Rules /4/ for many locations where there are not simultaneous stresses from global bending of the hull girder. For high strength steel with 355 MPa yield stress the Rules give correspondingly an allowable bending stress of 160 x 1.39 = 222 MPa. These values are used for the face sheets in the present study. The allowable shear stress in the concrete is set at 0.301 MPa. This was derived on the basis of Eurocode EN 1992-1-1 as follows: The test report /6/ lists six test values for the tensile splitting strength:

1.11, 1.05, 1.31, 1.14, 1.15 and 1.25 MPa.

The mean is 1.168 MPa and the standard deviation 0.095 MPa. The characteristic value if defined as the 2.5 percentile value of the distribution is then

fct,sp2.5% = 1.168 – 4.3 x 0.095 = 0.760 MPa

Here the 4.3 factor is taken from DNV-OS-C501 /2/ Section 4 Table B2. However, the concrete standards Eurocode 1992-1-1 /3/ and DNV-OS-C502 /1/ both define the characteristic value as the 5 percentile value, which is given by

fct,sp5% = 1.168 – 3.71 x 0.095 = 0.816 MPa

Here the 3.71 factor is taken from the DNV Standard for Wind Turbine Blades, DNV-OS-J102 /7/, which also uses the 5 percentile value.

According to EN 1992-1-1 §3.1.2 the axial tensile strength should be taken as fctk = 0.9 fct,sp = 0.734 MPa.

For unreinforced concrete, EN 1992-1-1 §12.3.1 states that the tensile design strength shall be taken as fctd = fctk x αct/γc , where αct = 0.8, γc = 1.5. Thus fctd = 0.391 MPa. This is used here as the maximum allowable value for bending stresses in the concrete.

In the absence of axial force, EN 1992-1-1 §12.6.2 requires that the shear stress τcp ≤ fcvd = fctd. This apparently acknowledges that the principal tensile stress for a state of pure shear stress is equal to the applied shear stress, so that for a brittle material the shear strength is equal to the tensile strength.

The standard requires that the shear stress τc be calculated on the basis of the compressive cross-sectional area, with a factor k = 1.5 applied, presumably to allow for non-uniformity of the stress over this part of the section. However, we assume here that the entire core section is uncracked, and allow for the actual non-uniformly distributed shear stress for the given sandwich cross-section, so it is more appropriate to take k = 1.

To convert the requirement to an allowable stress format fctd has to be reduced by the load factor γL. For steel the LRFD standards use a material factor 1.15, and we are using an overall safety factor 1. 5 = 1.3 x 1.15. Thus we set γL = 1.3 and the allowable shear stress becomes

fctd / γL = 0.301 MPa.

This figure is actually 41% of the characteristic axial tensile strength of 0.734 MPa (and thus the corresponding shear strength). This is consistent with the DNV HSLC Rules /8/, which specify an allowable core shear stress for sandwich structures that is 40% of the ultimate shear strength.



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Use of DNV-OS-C502 results in a similar shear strength to the above. The normalised tensile strength for a lightweight concrete (by extrapolation of Section 6 Table C1) is to be taken as about 1/15 times the characteristic cube strength. The test report /6/ gives values of cube compressive strength from three tests: 11, 11 and 10 MPa. From these the 5 percentile characteristic value is 8.52 MPa. The normalised tensile strength is then about 0.57 MPa. Dividing this by the required material strength partial factor 1.5 and load factor 1.3 gives an allowable tensile shear stress of 0.29 MPa.

An alternative approach for the concrete shear strength is to use directly the results of tests on INCA beams in four-point bending. In DNV Report No. 2006-1058 /9/, values of maximum shear stress at failure are given for three test beams. Attention is here focused on occurrence of the first crack, which defines the point at which tensile shear failure of the concrete is initiated so that there ceases to be a full connection between the face sheets. (A shear crack of this type will always propagate along the face-core interface.) For the first crack the values 1.02, 1.08 and 0.96 MPa are given. The values for second and third cracks are not used here because they do not represent independent tests and, following the development of the first crack, some stress redistribution will have occurred. From these three results the mean is 1.02 and the standard deviation 0.06 MPa. The 2.5 percentile value is thus 0.762 MPa and the 5 percentile value is 0.797 MPa. These are quite close to the corresponding percentile values for the splitting strength as derived previously. However, according to EN 1992-1-1, the characteristic axial tensile strength is obtained by multiplying the splitting tensile strength by 0.9, giving 0.734 MPa for the 5 percentile value; this is 9% lower than the value from the beam tests.

Note that the beam tests were performed with steel plates closing the beam ends. These plates are likely to have altered the distribution of the shear stresses in the core, so the derived values of shear strength cannot be fully relied on. Thus the values derived from the splitting strength are used in the current study.


10.3.1 Results: trends The results of the parametric study are shown graphically in Figures 1 to 8. Figure 1 shows the case of a sandwich beam with 3 mm thick faces of 235 MPa yield strength steel. Here the sandwich panel’s mass per unit area is plotted against the maximum allowable span for the case of simple supports, for each of the five load cases. Core thicknesses of 100, 150, 200, 250 and 300 mm are included. The broken (dashed) curve shows the boundary between cases for which shear failure in the core governs the design and those for which yielding in the face sheets governs; cases in the region to the left of this curve (shorter spans) are governed by core shear and those to the right (longer spans) by face sheet yielding. The condition for face sheet failure is here calculated allowing for cracking in the core due to tensile bending stresses. The condition for core shear failure is based on analysis that does not allow for cracking, for the reason given in Section 10.2.5. Figure 2 shows the corresponding curves for the case of rotationally restrained (clamped) supported edges.

It is seen that, for simply supported edges, core shear failure governs for all load cases other than LC1 and LC1a. For clamped edges core shear failure governs also for the lighter (thinner) layups with LC1a. In Figures 3 and 4 the corresponding results are superimposed (blue curves) for cases with faces of higher strength steel having 355 MPa yield strength. These illustrate the obvious point that it is only of benefit to use the higher strength steel when the strength is governed by the face sheet strength rather than the core shear strength.


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Max span for SS INCA panel (3 mm steel plates)Full theory, with core cracking

0

50

100

150

200

250

300

350

400

2.5 5.0 7.5 10.0 12.5 15.0 17.5

Max span (m)

Self-

wei

ght (

kg/m

2 )

LC1 - MSLC1a - MS

LC2 - MS

LC3 - MS

LC4 - MS

LC1 - HSSLC1a - HSS

LC2 - HSS

Limit MS

Limit HSS

Max span for CL INCA panel (3 mm steel plates)Full theory, with core cracking

0

50

100

150

200

250

300

350

400

0.0 2.5 5.0 7.5 10.0 12.5 15.0 17.5

Max span (m)

Self-

wei

ght (

kg/m

2 )

LC1 - MS

LC1a - MS

LC2 - MS

LC3 - MS

LC4 - MS

LC1 - HSSLC1a - HSS

LC2 - HSS

Limit MSLimit HSS

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Figures 5 and 6 show the results for panels with 6 mm thick face sheets, simply supported and clamped. These show that core shear failure is now governing for even more cases than with 3 mm faces; for clamped edges it is governing for all cases within the range studied. Figures 7 and 8 show the results for 10 mm thick faces. Now all cases studied are governed by core shear failure. This applies also for all cases with faces thicker than 10 mm. Furthermore it is seen that, because core shear failure is now governing, there is no benefit in increasing the face thickness; all this does is to increase the weight.

Figure 1 Maximum spans for simply supported INCA beams with 3 mm steel faces (235 MPa yield strength) and lightweight concrete cores of 100 to 300 mm thickness

Figure 2 Maximum spans for clamped INCA beams with 3 mm steel faces (235 MPa yield strength) and lightweight concrete cores of 100 to 300 mm thickness


0

50

100

150

200

250

300

350

400

0.0 2.5 5.0 7.5 10.0 12.5 15.0 17.5

Max span (m)

Sel

f-wei

ght (

kg/m

2 )

LC1 - MS

LC1a - MS

LC2 - MS

LC3 - MS

LC4 - MS

Limit MS


0

50

100

150

200

250

300

350

400

0.0 2.5 5.0 7.5 10.0 12.5 15.0 17.5

Max span (m)

Self-

wei

ght (

kg/m

2 ) LC1 - MS

LC1a - MS

LC2 - MS

LC3 - MS

LC4 - MS

Limit MS



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Figure 3 Maximum spans for simply supported INCA beams with 3 mm steel faces (red: 235 MPa yield strength, blue: 355 MPa yield strength) and lightweight concrete cores of 100 to 300 mm thickness

Figure 4 Maximum spans for clamped INCA beams with 3 mm steel faces (red: 235 MPa yield strength, blue: 355 MPa yield strength) and lightweight concrete cores of 100 to 300 mm thickness


0

50

100

150

200

250

300

350

400

2.5 5.0 7.5 10.0 12.5 15.0 17.5

Max span (m)

Self-

wei

ght (

kg/m

2 )

LC1 - MSLC1a - MS

LC2 - MS

LC3 - MS

LC4 - MS

LC1 - HSSLC1a - HSS

LC2 - HSS

Limit MS

Limit HSS


0

50

100

150

200

250

300

350

400

0.0 2.5 5.0 7.5 10.0 12.5 15.0 17.5

Max span (m)

Self-

wei

ght (

kg/m

2 )

LC1 - MS

LC1a - MS

LC2 - MS

LC3 - MS

LC4 - MS

LC1 - HSS

LC1a - HSS

LC2 - HSS

Limit MSLimit HSS


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10.3.2 Comparison with parametric study for INCA with studs


0

50

100

150

200

250

300

350

400

450

500

0.0 2.5 5.0 7.5 10.0 12.5 15.0 17.5

Max span (m)

Self-

wei

ght (

kg/m

2 )

LC1 - MS

LC1a - MS

LC2 - MS

LC3 - MS

LC4 - MS

Limit MS


0

50

100

150

200

250

300

350

400

450

500

0.0 2.5 5.0 7.5 10.0 12.5 15.0 17.5

Max span (m)

Self-

wei

ght (

kg/m

2 ) LC1 - MS

LC1a - MS

LC2 - MS

LC3 - MS

LC4 - MS

Limit MS

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0

50

100

150

200

250

300

350

400

0.0 2.5 5.0 7.5 10.0 12.5 15.0 17.5

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Sel

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ght (

kg/m

2 )

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LC2 - MS

LC3 - MS

LC4 - MS

Limit MS


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2 ) LC1 - MS

LC1a - MS

LC2 - MS

LC3 - MS

LC4 - MS

Limit MS



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10.3.2 Comparison with parametric study for INCA with studs For a given lay-up (combination of core and face sheet thicknesses) the weight of a panel without studs is slightly lower than for the corresponding case with studs (Appendix 1). This is simply due to the weight of the studs themselves.


0

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LC2 - MS

LC3 - MS

LC4 - MS

Limit MS


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LC1a - MS

LC2 - MS

LC3 - MS

LC4 - MS

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For cases when the solution without studs is governed by face sheet failure the maximum allowable span, for a given layup and given boundary conditions, is almost identical for design with and without studs. (See for example simply supported panels with 6 mm face sheets under LC1.) However, without studs most cases within the range studied are governed by core shear failure so that the face sheets are not well utilised. Thus it is an advantage to use studs so as to improve the shear strength and make more optimal use of the face sheets. Consequently, in this regime, for a given span a solution with studs is lighter than one without studs.

It should also be pointed out that, even if a solution without studs appears to give an approximately equal weight to one with studs, the need to ensure an adequate shear connection between the face sheets and the core makes it adviseable in practice to use studs in all cases.

10.4 Conclusion The results of the parametric study show that for most cases there is a clear advantage in using a design with welded studs to improve the shear strength of an INCA panel. Even if a solution without studs appears to give an approximately equal weight to one with studs, the need to ensure an adequate shear connection between the face sheets and the core makes it adviseable in practice to use studs in all cases.

10.5 References /1/ Offshore Standard DNV-OS-C502 Offshore Concrete Structures. Det Norske Veritas, 2007.

/2/ Offshore Standard DNV-OS-C501 Composite Components. Det Norske Veritas, 2003.

/3/ EN 1992-1-1:2004 Eurocode 2: Design of concrete structures, Part 1-1: General rules and rules for buildings

/4/ DNV Rules for Classification of Ships Part 3 Chapter 1 Hull Structural Design – Ships with Length 100 metres and above. Det Norske Veritas, January 2008

/5/ INCA – Panel Benchmark Study: Scope of Work, Revision 6, 12 February 2010.

/6/ Testing of LWAC as Core Material for Sandwich Constructions Final Report. Universität

der Bundeswehr München Report, October 2004.

/7/ Offshore Standard DNV-OS-J102 Design and Manufacture of Wind Turbine Blades, Offshore and Onshore Wind Turbines. Det Norske Veritas, 2006.

/8/ DNV Rules for Classification of High Speed Light Craft and Naval Surface Craft, Part 3 Chapter 4, Hull Structural Design, Fibre Composite and Sandwich Constructions. Det Norske Veritas, January 2003, with revisions to July 2009.

/9/ Steel – Concrete Sandwich Concept, Concept Description, Acceptance Criteria and Calculation Procedure. Det Norske Veritas Report No. 2006-1058, Rev. 2, 2006.




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11 APPENDIX 3: DEFINITION OF SCOPE OF BENCHMARK STUDIES

11.1 Purpose

• o o • • • o o o o

11.2 Standard ‘Panel’ and Boundary Conditions



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11 APPENDIX 3: DEFINITION OF SCOPE OF BENCHMARK STUDIES Revision 6 - Prepared by: Thomas Grafton (GRAFT) 12 February 2010

11.1 Purpose To compare an INCA concrete-steel sandwich panel with stiffened steel plate and concrete structural solutions representative of typical applications in the offshore industry. The study should assess: • Performance for a given load

o Panel thickness to carry load o Panel Weight • Effective of increases in panel span on the above • Effect of changes in boundary conditions (and core density?) • Other performance characteristics o Fire o Sound insulation o Vibration o Impact

11.2 Standard ‘Panel’ and Boundary Conditions The panel is assumed to be representative of a ship structural element; either between transverse and longitudinal girders; or between girders, bulkheads and the ships side.

The panel with have length L and breadth B and have four nodes in each corner (N1 to N4). The following boundary conditions and loads should be considered:

L

B

N1

N2 N3

N4 y

x

z


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TECHNICAL REPORT11.4 Preparation of Load Cases

11.4.1 Local Loads

Load Description Static Load (KN/m2) (*)

Dynamic Factor

Total Load

(KN/m2)

Rule Reference in DNV Rules for Ships

11.4.2 Axial Loads (due to Global Bending)

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Boundary Conditions(*) Panel Nodes Edges

Load Type

I (Simple Support on short edge)

To restrict global movement of the

panel

Fixed displacement x,y and z on the short edge (B)

Local Pressure

II (Fixed in y-rotation on short edge)


panel

Fixed displacement x,y and z and fixed in rotation about the y axis on short edge (B)

Local Pressure

III (Axial Tension/compression on y-axis)


panel

Fixed in z-displacement and fixed in rotation about the y

axis on short edge (B). Fixed in rotation about the x-

axis on the long edge (**)

Axial (from Global Bending)

IV (Axial Tension/compression on y-axis)


panel

Fixed in z-displacement and fixed in rotation about the y

axis on short edge (B). Fixed in rotation about the x-

axis on the long edge (**)

Axial (from Global Bending) and Local Pressure

(*) Extra boundary conditions may be considered later after discussion of first results

(**) This assumes that when subjected to global bending (axial load) that the panel is supported at the

edges by a girder system. If no girder system is needed then the fixation on the long edge (L) is not

necessary.

11.3 Panels to be Assessed To be completed by PAMAJ (and/or others to be advised)

1. Sandwich considering light weight concrete and full composite action with steel (including stud design)

2. Sandwich considering high strength concrete (not light weight) and full composite action with steel (including stud design)

3. Sandwich considering prestressed concrete and full composite action with steel (including stud design)

4. Prestressed concrete and minimum reinforcement steel (steel plates may be used but mainly as formwork)

To be completed once suitable design rules have been researched. Lead person GRAFT

5. Traditional Concrete Ships using ‘Post War 1950’s’ technology To be completed by GRAFT (and/or others to be advised)

6. Stiffened steel panel 7. iCore Panel (Meyer Werft Light weight deck concept) 8. Intelligent Engineering’s SPS system (Polymer core sandwiched between two steel plates) 9. INCA “As-is” – based on the existing work



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11.4 Preparation of Load Cases The concrete analyses are being prepared assuming a uniform beam (two-dimensional). For stiffened steel structure, iCore and SPS a three dimensional plate analysis may be needed. To limit the number of load cases to study when three-dimensional analysis is needed example pieces of ship structure will be selected from DNV approved ships. These examples will be compared to the database of concrete results for strength and weight. Through this approach loads and panel sizes will be down-selected to focus on the areas where steel-concrete-steel sandwich panels (with or without studs or other re-enforcement) are most competitive on weight (or size if this gives a less complicated structure to build). The examples of structural elements will be chosen to give local and global loads within the ranges given in the two tables that follow.

11.4.1 Local Loads

Load Description Static Load (KN/m2) (*)

Dynamic Factor

Total Load

(KN/m2)

Rule Reference in DNV Rules for Ships

Minimum Accommodation deck load

2.5 1.3 3.25 Pt.3 Ch.1 Sec.4 Table C1

Minimum Sea Pressure for Weather Decks

5.0 1.3 6.5 Pt.3 Ch.1 Sec.8 Table B1

Heavy Equipment/Machinery Deck Load

16 1.3 20.8 Pt.3 Ch.1 Sec.4 Table C1

Cargo Deck (RoRo/Offshore Ship)

50 1.3 65 Based on existing designs and Pt.3 Ch.1 Sec.8 Table B1

Inner Bottom of Containership Cargo Hold

120 1.3 156 Based on existing designs and Pt.3 Ch.1 Sec.8 Table B1

(*) The self weight of the panel should be added to the static loads.

11.4.2 Axial Loads (due to Global Bending) Global bending of a ship will give axial loads acting along the y-axis. For ships, local pressure loads may also act on the structure and the allowable stresses for the local loads are reduced to take account of the utilisation of the structure for global loading. The tensile and compressive loads should be selected from the following (as close as practical):


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TECHNICAL REPORT11.7 Water Resistance

11.8 Material Properties

11.8.1 Steel Plating and Stiffeners

σσσ

11.8.2 Concrete

Property Dimension

11.9 Allowable Stresses and Load Factors

11.9.1 Steel Ships

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Load Description(**) Load (N/mm2) (*) Total Load (kN) NPS Ship ID NumberCar Carrier Upper Deck (no. 13)

85.7/-61.5 Calculate force based on panel length (L)

D27949

Car Carrier Deck Near Neutral Axis (no. 8)


D27949

Car Carrier Deck Near Bottom (no.3)


D27949

Bulk Carrier Inner Bottom

TBC TBC TBC

Others, to be confirmed

(*) Positive values are tension, negative are compression

(**) Further details in Excel spreadsheets (available from GRAFT/RENAUD)

11.5 Fire Loading Of the 8 panels to be assessed there are no fire resistance requirements for panel numbers 1, 2, 6, 7 and 8. Fire resistance of these panels is to be provided by additional insulation material (e.g. Rock Wool). Option 4 should be designed to withstand a standard fire test for a time of 60 minutes. The normal offshore codes should be used for temperature requirements and heat up curves based on a hydrocarbon fire. The fire resistance of options 3 and 5 should be assessed in a qualitative way to determine, in approximate terms, the likely fire resistance time based on standard offshore hydrocarbon fire tests (as mentioned above).

11.6 Fatigue Loading Important for shear pin design

Load Description (*) Mean Stress (N/mm2)

Stress Range (N/mm2)

Number of Cycles

NPS Ship ID Number

Car Carrier Upper Deck (no. 13)

-1.83 34 69303915 D27949

Car Carrier Deck Near Neutral Axis (no. 8)

-0.62 12 69303915 D27949

Car Carrier Deck Near Bottom (no.3)

0.63 12 69303915 D27949

Bulk Carrier Inner Bottom

TBC TBC TBC TBC

Others, to be confirmed

(*) Further details in Excel spreadsheets (available from GRAFT/RENAUD)



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11.7 Water Resistance The beams should be designed to be watertight throughout the design life of the structure.

11.8 Material Properties

11.8.1 Steel Plating and Stiffeners Modulus of Elasticity, E = 2.06 x 105 N/mm2 Yield Strength (Normal Steel), σy = 235 N/mm2 Yield Strength (High Tensile Steel), σy = 355 N/mm2

Shear yield strength, 3

yσ N/mm2

11.8.2 Concrete Lightweight Concrete:

Property Dimension Cube Strength

dcubecf 7,,1 MPa 10

Cube Strength dcubecf 28,,1 MPa 11

Cylinder Strength dcylindercf 28,,1 MPa 9

De-moulding Density Kg/m3 975

Splitting Tensile Strength dcylindercf 28,,1 MPa 1.1

Flexural Tensile Strength dflcf 7,,1 MPa 1.8

Modulus of Elasticity MPa 5400

Water Absorption % by mass 13

Reference: DNV Concrete Floater, 19/02/2008 (Proposal Document). Other values were used in the history of the INCA project – details available on request. “Normal” Concrete: As used for traditional offshore concrete structures

11.9 Allowable Stresses and Load Factors

11.9.1 Steel Ships The approach in the DNV Rules for Ships is to put a ‘factor of safety’ on the stress to give an allowable stress for a given load. For local loads:

The allowable bending stress is 160f1 N/mm2 The allowable stress for shear is 90f1 N/mm2


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TECHNICAL REPORT11.13 Failure Criteria

11.14 Outputs

• • • • • • •

• • • • 11.15 Other Information

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For global loads:

The allowable stress varies depending on utilisation in bending. A reasonable value to use is 120f1 N/mm2

The material factor f1 is: • 1.0 for normal steel (NV-NS) • 1.39 for High Tensile Steel (NV-36) Buckling of steel face plates and of the complete concrete-steel beam should also be considered.

11.9.2 Concrete Ships As appropriate from the offshore design standards – we can discuss this further as necessary. We can provide the material properties for the lightweight concrete used in previous studies if needed.

11.10 Minimum and Maximum Thicknesses

11.10.1 Steel Plating For stiffened steel panels the minimum thicknesses shall be 6 mm (based on DNV Rules for Ships Pt.3 Ch.1 Sec.8). For steel plate forming the skin of a sandwich panel carrying significant loads (bending, tensile or compression) a minimum thickness of 3mm should be used for each face. For steel plate forming the skin of a sandwich panel not carrying significant loads a minimum thickness of 2 mm should be used for each face. Less may be allowed if it can be demonstrated that plate wrinkling or debonding will not occur.

11.10.2 Steel Stiffeners There is no restriction on the web height of the stiffeners or girders. However, note that traditional steel panel structures are not usually deeper than 600 mm.

11.10.3 Core There is no restriction on the thickness of the core.

11.11 Variables for Study L – to be varied in steps between 2.5 and 18 metres. B – 2.5 metres. This was considered the limit for easy transportation. Core density??

11.12 Optimisation Approach The panels should be designed to withstand the applied loads and be the lowest weight practical. For concrete solutions the target weight should be the weight of the equivalent stiffened steel panel, or lighter.



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11.13 Failure Criteria The current INCA research has used a factor of safety on first crack in the core. This was developed using the DNV Recommended Practice for Composite Components (DNV-OS-C501). This can be used (if considered appropriate) or other suitable concrete design standards. (The Steel should be designed up to the allowable stresses given above.)

11.14 Outputs For combination of panel type, boundary condition, load and length the following should be calculated: • Bending Stresses • Shear Stresses • If beam fails, cause of failure (e.g. shear through core) • Panel Weight • Panel thickness (of total panel and sandwich parts where relevant) • Maximum Deflection of the panel • Others, if considered important for the beam type In addition to the above the following should be studied in a qualitative way (accurate values not needed, just information for comparison purposes): • Fire resistance in a loaded condition • Sound insulation properties • Vibration damping properties • Impact resistance

11.15 Other Information For this study it is assumed that panels will not be joined together. This decision can be discussed further once initial results are available. For missing information please contact GRAFT and this document will be updated! Please check you


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12 APPENDIX 4: GAP ANALYSIS

Summary:

12.1 Objective and scope



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12 APPENDIX 4: GAP ANALYSIS

MEMO: Gap analysis of the INCA sandwich technology (Rev.1) To: Hans Ramsvik, Thomas Grafton, Jan Weitzenböck From: Dag McGeorge Date: 2010-03-25 Summary: This memo is issued in response to a specific request by “The Extraordinary Innovation Project on Steel-Concrete Sandwich Technology” and aims at identifying gaps in the documentation of the original INCA technology without steel studs protruding into the core. A simplified technology assessment method (Section 12.2) based on the key elements of the INCA technology (Section 12.3) identified novel aspects that need to be considered in qualification of the INCA technology (Section 12.4). This resulted in the identification of eight (8) knowledge gaps (Sections 12.5 and 12.6) of which seven are considered potential showstoppers for general application of the INCA technology in ship structures. These gaps need to be closed before the INCA technology can be applied.

12.1 Objective and scope The objective of this assessment is to identify potential gaps in the qualification documentation for the original INCA technology without steel studs protruding into the core. The new documentation produced as part of the ongoing extraordinary innovation project was not considered (see endnote 1). As time did not permit a full review of all documents produced by the INCA project, it is acknowledged that some information may have been missed and that some gaps may be closed by the project team as a follow-up of this memo. Focus is placed on the point of view of an INCA panel as a sandwich panel. Less emphasis is placed on the point of view of an INCA panels as reinforced concrete or a steel concrete composite structure. It is recommended that experts on concrete structures are consulted to review the technology from the second point of view. The scope is confined to assessment of the technology and not the potential business of exploiting the technology. Nevertheless, it is recommended that the project team evaluates whether there exists a viable business model for the INCA concept as INCA structures seem to be more costly and heavy than traditional welded steel structures /1/ and that advantages would only be achievable where other potential benefits of the INCA concept are attractive or if the costs can be reduced significantly.


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12.4 Novelty assessment

•

•

•

• • •

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12.2 Method This assessment was performed in two steps. 1. The first step was an independent hazard identification exercise and novelty assessment performed

by the author based on general knowledge and experience with sandwich structures in the marine environment. The basis for this assessment is described in Section 12.3 and the novel aspects are summarised in Section 12.4.

2. In a second step, a structured document review was performed to check if the identified hazards

have been addressed. Identified hazards for which appropriate documentation was not found were identified as gaps. Section 12.5 summarises the main hazards and associated knowledge gaps.

Time and availability imposed on this study did not permit to use the formal technology qualification process recommended by DNV /2//3/.

12.3 Basis for assessment The INCA technology considered was the original INCA concept being a structural sandwich consisting of 5 technology elements:

6. Face 1: steel plate. 7. Bondline 1 between face 1 and core:

adhesion of concrete to steel. 8. Core: lightweight concrete. 9. Bondline 2 between core and face 2:

adhesion of concrete to steel. 10. Face 2: steel plate.

3 1

5

2

4

This constitutes a sandwich panel where the faces primarily carry in-plane loads and bending and the core primarily carries transverse shear loads. Sandwich panels are particularly effective in carrying transverse loading and providing flexural stiffness. This is described in any textbook on sandwich structures, e.g. /4//5/. As a base case, the bondline consists of the concrete that adheres onto the steel. To promote adhesion, the steel has received appropriate surface treatment such as degreasing and grit blasting. As a variant, also the case with mechanical connectors such as shear studs (hooks, dowels) as bondline enhancers is considered briefly1. Structures assembled from INCA panels in addition have to contain other elements: joints, supports, load introduction devices, cut-outs etc. These are not assessed in detail but are nevertheless important in practical applications.

1 This assessment was performed before the work on the INCA concept with shear studs had been performed. These footnotes have been added afterwards for completeness.



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Sandwich theory is covered by existing standards, e.g. DNV-OS-C501 Composite components /6/. This standard appears to have been used as the basis for qualification of the INCA concept /9/. Two of the elements of the INCA panels, the two bonds, are a made in the fabrication process and their performance is a result of how that process is carried out. Therefore an assessment of the INCA concept must be closely linked to a clearly specified manufacturing process including the quality system in operation to control manufacturing and any inspection and checks to confirm quality.

12.4 Novelty assessment Concrete steel composite structures (Norwegian: samvirkekonstruksjoner) are well established and covered by standards such as EN 1994 /7/. EN 1994 expressly excludes the possibility to permit the structural integrity to rely on adhesion between the steel and concrete. • One of the key novel aspects of the original INCA concept is that it is relying on such

adhesion. The documentation for the INCA technology is based on established sandwich theory assuming that the sandwich effect can be relied on. Sandwich theory is well established for sandwiches with rigid faces and cores of greater ductility than the faces. • The novelty of the INCA concept in this respect originates from the use of a brittle core

material. The use of concrete as a structural material is well established. Load-bearing concrete structures are reinforced such that the concrete that is loaded in tension is permitted to crack and let the reinforcement take over tensile and shear loads. Carrying the shear load is assisted by the concrete by ensuring that the reinforcement keeps the cracks narrow enough that there is mechanical interlocking across the crack surfaces. • The novelty of the INCA concept in this respect originates from the use of concrete as a critical

load-bearing component without any reinforcement. Note: The INCA sandwich concept relies on the adhesion between the concrete core and the steel faces. This may be considered a weakest link system: the sandwich functions only if all 5 elements function at the same time; if one element fails, the sandwich fails. This contrasts with the redundancy of traditional reinforced concrete where the concrete can crack and the forces are then redistributed to the reinforcement bars. Qualification of the INCA technology would have to address these novel aspects carefully in relation to the intended use of the technology over the service life and foreseeable accident scenarios: • Reliability of adhesion between concrete and steel • Reliability of the sandwich concept with the brittle concrete core • Reliability of the concrete that forms the core without reinforcement The variant of the INCA concept with shear studs (hooks, dowels) as bondline enhancers requires documentation of the performance of the shear studs. In the case that these studs penetrate the core entirely (from one face through the core to the opposite face), then the studs also provide


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Gap 12

Gap 2

12.5.2 Assessment in relation to intended use

Gap 3

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reinforcement for the core. If the shear studs are designed according to an existing design code, proof of compliance with the code would provide sufficient documentation of performance. This variant of the INCA technology would be proven (known) technology according to /2/ and could be designed according to the applicable standard, e.g. EN1994 /7/. For ship structures there are no applicable standard for such structures, but with due consideration of the particulars of ships, the design principles of established standards could be applied. This would involve consideration of the most important accident types for ships as discussed in Section 12.5.4.

12.5 Technology maturity and knowledge gaps

12.5.1 Applicability of traditional sandwich theory to INCA panels In traditional sandwich theory, the functions of the sandwich panel are to provide load-bearing capacity and to limit deformation in response to loading. Sandwich theory as presented in codes /6//8/ and textbooks /4//5/ is quoted as the design basis for the INCA concept /9/. This theory assumes a number limit states. They appear to have been accounted for in the INCA documentation. Only the ones that are of particular relevance in relation to the novel aspects of the INCA concept are addressed here. It is interpreted from the INCA documentation /9/ that first shear cracking of the core is the limit state considered in design (that will be considered failure). This is in general agreement with traditional sandwich theory. In traditional sandwich theory, the rupture of the faces and the fracture of the core are assessed separately. Core fracture is assumed to occur if the out-of-plane shear stress in the core exceeds some specified critical shear stress for the core material. This approach has a long and successful track record e.g. in high speed craft. The track record mainly relates to sandwich panels consisting of laminated composite faces and polymeric foam core material. The core material is ductile and permits deformation far in excess of that of the laminates that the core is enclosed within. Only shear deformation can develop in the core without a corresponding development of deformation of the faces. In this case one can therefore safely assume that the in-plane deformations, which are limited by the rigid faces, do not significantly affect the capacity of the core to carry transverse shear loading. The use of balsa wood as sandwich core material received particular attention at one stage because there was a concern that the in-plane strains as limited by the faces (up to 1 – 2% typically) could conceivably affect shear capacity of the rather brittle balsa wood core. A dedicated study was performed where a key element was to test sandwich beams and panels with different spans and face thicknesses resulting in different levels of bending and hence axial strains in the faces (and the core adjacent to the faces) when the shear fracture stress was reached in the core. It was confirmed that the traditional sandwich theory assuming a shear fracture stress for the core that is independent of in-plane deformations can be used with confidence for balsa-cored composite sandwiches /10/. In the INCA project, it appears that no systematic assessment has been made of the effect of bending or in-plane deformations in the panels on the shear capacity of the brittle concrete core. In fact the beams tested were indeed short such that the utilisation of the steel faces when the core fractured was insignificant. This favourable condition may not prevail in practice where often bending and shear have their maxima at the same position. In some of the reported tests, however, cracks formed at mid-



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span (where shear loading is absent) suggesting that the core is vulnerable to in-plane strains (see e.g. Figs 8-11 in /11/). As an example, for the dimensions and loads reported in /12/, the stress in the steel faces at the measured fracture load is about 60 MPa corresponding to 20 – 25% of the yield stress or 0.03% strain. On this basis, it seems appropriate for mild steel face sheets to suggest testing beams with 4 – 5 times the tested span to allow the face sheets to almost reach the yield stress before core fracture (even longer beams for higher strength steels). Without such results, there is no documentation to support using the test results for cases that differ from the tested conditions that appear to be particularly favourable (Gap 12). Another concern with brittle materials is the size effect that implies that the fracture stress is a function of the size of the stressed volume. This effect was also covered by the above-mentioned balsa wood study /10/ where it was concluded that the core thickness had a strong influence on shear stress at fracture, indeed the shear stress at fracture in typical sandwiches in shipbuilding (high speed craft) was found to be about 50% of what one would estimate from typical samples used for material characterisation. In the INCA project it appears that only a single size of beams has been tested providing no information on whether there is such a size effect also in INCA panels. In view of the brittleness of the concrete, such an effect should be expected. However it is noted that the specimens used have a core thickness that may be typical of the intended use in many cases such that the results may be representative for cases where the core thickness does not exceed 90 mm (Gap 22).

12.5.2 Assessment in relation to intended use For shear loading, the INCA panels are designed against first core fracture. But it is possible that the brittle core could crack for some other reason, e.g. due to shrinkage of the concrete, localised loads or impacts, local imposed deformations etc. The INCA documentation does not appear to provide evidence that such cracks can be ruled out as a possibility. It would then be necessary to assume such cracks may be present and consider the effect of such cracks on the performance of the INCA panels in normal service conditions (including extreme weather conditions). The beam tests performed in the INCA project were continued beyond first cracking showing what is denoted as ductile behaviour where the beam resisted considerable shear load after first cracking of the core. This suggests some tolerance against cracks. But the short beams tested with the applied loading rather close to the supports would tend to squeeze the core between the rigid faces and limit the crack widths. Furthermore, the in-plane strains developing in the short beams are indeed small (see Section 12.5.1). This particularly favourable condition can not be expected to always occur in real structures. Furthermore, in consideration of tolerance to cracks it would be necessary consider the range of loading histories to be expected in practice, including sequences of varying stress directions, load reversals, etc. This does not appear to have been covered in the qualification documents (Gap 32). In bonding technology, a major concern is related to the long term performance of the bond. It appears that the INCA design basis is exclusively based on short term test results without consideration of any degradation that may occur with time. No documentation has been found that provides evidence that the short term bond strength can be expected to be maintained for the entire life of a ship. No documentation has been found concerning the effect of a potential leakage from the outside of the

2 In the variant of INCA with shear studs that fully penetrate the core, the studs reinforce the cure such that cracks in the core are not critical. This gap is therefore not relevant for that variant.


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TECHNICAL REPORT12.5.4.3 Crushing (grounding and collision)

Gap 76

12.5.4.4 Fire

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panel into the core and its interface to the steel face, e.g. in the event of a weld defect or fatigue crack (Gap 43). Fatigue of welded joints is a general problem in shipbuilding and is expected to be that also for welded joints between INCA panels. No documentation has been found that provides evidence of the fatigue performance of welded joints between INCA panels (Gap 54).

12.5.3 Robustness and foreseeable abuse Besides resisting the loads considered in design, any structure needs to be robust in the sense that it is not sensitive to loads that may occur but are not considered explicitly in design. Such loads can be impacts due to handling of panels in transport and assembly, impacts from dropped objects or objects floating in the sea, abrasive loads etc. Such robustness does not seem to have been addressed for the INCA panels (Gap 65).

12.5.4 Accidents

12.5.4.1 General In general, structural safety needs to be assessed in relation to accidental situations. This is preferably done in a risk-based approach where a cost benefit assessment relates the costs of risk reduction measures to their effectiveness in reducing risks. For ship structures, accident scenarios are covered by prescriptive regulations in the SOLAS convention /13/. Conceptually, these regulations may be regarded as means of managing risk proven by service experience to be sufficient and reasonably cost effective. With this approach, it makes sense to consider accident scenarios in a risk management perspective also for ship structures. It should be noted that the specific regulations in the SOLAS convention are closely related to traditional shipbuilding practice with welded steel construction. Deviating from that, one would need to consider the extent to which the alternative arrangement would perform differently from a traditional steel arrangement. This is very clearly stated for fire safety where a dedicated part of SOLAS concerns equivalence of alternative arrangements (Ch II-2 Reg.17 of /13/). But there are also other equivalence clauses such as e.g. the general one in Ch 1 Reg. 5 of /13/. Therefore, in the assessment of applications of the INCA concept to ships, it is recommendable to consider whether the same level of safety is achieved as with a traditional welded steel design.

12.5.4.2 Local contact (grounding, collision) In severe contact loading, the core would crack and the transverse stiffness would drop. This would permit large local deformations while at the same time the inner steel face will be protected from contact with the penetrating object by (what remains of) the core. It is likely that this would reduce the extent of damage and reduce the risk of penetration compared to a traditional steel design. Unfortunately, it is a challenge to capitalise on this potential advantage of the INCA concept because SOLAS /13/ prescribes fixed cases of damage independently of the form of construction.

3 The variant of INCA with shear studs does not rely on bonding. This gap is therefore not relevant for that variant. 4 The studded INCA version will simplify the fatigue problem because the studs can control the core thickness during assembly such that it becomes feasible to grout large sections. That would allow the critical joints to be welded before grouting thereby avoiding the problem. 5 The studded INCA version is to be expected to be considerably more robust than traditional steel structures.



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12.5.4.3 Crushing (grounding and collision) In a scenario where the effects of the contact are not only a transverse loading on panels but also in-plane loading such as would occur in the striking ship in a collision, also the in-plane crushing performance of the INCA panels is important. Considering the brittle nature of the core and the complex dynamic responses to be expected in such scenarios, there would be a concern that the faces would probably delaminate from the core. Then the buckling resistance of what remains of the panels, without any stiffeners and the like, would drop to only a small fraction of the intact resistance. One would expect that the panels could collapse without much resistance leading to an increase in the extent of damage compared to typical welded steel structures. No documentation has been found that provides information about the INCA panels in this respect (Gap 76).

12.5.4.4 Fire INCA panels, with a reasonably thick concrete core, would inherently provide insulation capacity that is useful in the event of a fire. This has been tested and the insulation capacity was reported to be better than expected and easily exceeding the insulation standard of traditional A60 panels. In view of the fact that insulation levels corresponding to A60 is only required in some critical divisions, it is clear that a ship constructed from INCA panels could raise the level of containment of fires considerably as compared to that implied by the SOLAS regulations. This would represent an advantage, particularly in the early phases of fires onboard, and hence reduce the risk that fires would escalate in comparison with traditional designs. So-called boundary cooling, where divisions containing the fire are cooled from the unexposed side, is a key element in fire damage control in ships and is effective in preventing fire spread. Such boundary cooling would have no effect in an INCA ship due to the insulating core that would hinder cooling of the hot steel from outside the fire zone. But for as long as the steel on the unexposed side remains cool, this could be regarded an advantage because resources need not be spent on boundary cooling and could instead be used to fight the fire or assist crew or passengers. These advantages, of primary benefit early on in a fire, come along with a disadvantage that appears a bit later in typical fire scenarios: The steel face that is exposed to the fire and is mounted on an insulating backing (the concrete core) would be heated very quickly. In practice, the temperature of the steel in the exposed face would follow the temperature in the fire zone. Furthermore, the concrete at the bondline would be exposed to the same temperature. According to observations in fire tests performed on INCA panels, the first critical failure would be debonding of the exposed steel face from the concrete core. When this occurs, the sandwich loses most of its stiffness and strength. In a statically determinate structure, collapse should be expected at this point. In a redundant ship structure, loads may be redistributed. But in comparison with traditional welded steel structures, it seems clear that an INCA panel would be much more vulnerable to a given fire scenario. Note also that the loss of structural integrity is permanent and would not recover when cooled due to the permanent debonding. This contrasts with a traditional steel structure where much of the structural integrity is recovered if the structure is cooled before it collapses. On this basis, it becomes evident that a fire risk assessment is

6 For INCA with studs, the crushing resistance is not known to be documented, but it should be expected to be by far better than that of a traditional steel structure: the studs maintain integrity such that energy absorption can occur by yielding of the steel, crushing of the concrete and friction. This is potentially a large advantage of INCA with studs over traditional welded construction.


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12.7 References /1/ NN. INCA Final Report, Advanced feasibility Study of Steel-Concrete-Strucure in merchant

shipbuilding. Aker Ostsee, Wismar, 2004. /2/ DNV-RP-A203 Qualification procedures for new technology. /3/ DNV-OSS-401 Technology qualification management. /4/ Zenkert D. An Introduction to Sandwich Construction, EMAS, 1995. /5/ Allen HG. Analysis and design of structural sandwich panels. Pergamon Press, 1969. /6/ DNV-OS-C501 Composite Components. /7/ EN 1994:2004. Eurocode 4: Design of composite steel and concrete structures. /8/ DNV Rules for Classification of High Speed, Light Craft and Naval Surface Craft, 2009. /9/ Bakken K. Steel-concrete sandwich concept. Concept description, acceptance criteria and

calculation procedure. DNV Report 2006-1058 Rev. 2. /10/ McGeorge, D. and Hayman, B. Shear Strength of Balsa-Cored Sandwich Panels. 4th Int. Conf.

on Sandwich Construction, 1998. /11/ Mangerig I. Test Report - Preliminary Draft, Static Sandwich Testing, Dynamic Sandwich

Testing, Universität München, 2006 /12/ Echtermeyer AT and Bakken K. Steel-concrete sandwich concept. Static and dynamic sandwich

testing. DNV Report 2004-1315 Rev.0. /13/ IMO. International Convention for the Safety of Life at Sea (SOLAS), 1974 (as amended).

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needed to show that the INCA technology can be used safely in ship structures. Such an assessment should consider the structural integrity of the ship in realistic fire scenarios (i.e. not limited in duration to the 60 minutes reference duration used in standard fire tests). No documentation of such risk assessment has been found (Gap 8). The variant of the INCA technology with shear studs could provide improvement over the original concept if the shear studs are so closely spaced that it would prevent buckling of the steel plate between the studs after debonding. Nevertheless, as soon as the exposed face reaches a critical temperature of 5-600 °C say, the material softens to the extent that the panel loses structural integrity. Mitigating measures would be to insulate the panel to delay reaching the critical temperature at the exposed face or incorporating in-plane tensile reinforcement embedded inside the core. No documentation has been identified that shows how improved fire performance can be achieved with shear studs (Gap 8a).

12.6 Summary of identified technology gaps The following major gaps were identified:

1) The transverse shear capacity of the sandwich panel has not been documented when significant in-plane or bending loads are present at the same time as the shear loading.

2) An expected size effect of the strength of the core has not been investigated. 3) The influence of core cracks on the performance of the sandwich panels in typical service

conditions has not been documented. 4) The long term performance of the bond between the core and the steel faces has not been

documented. 5) Fatigue of welded joints between INCA panels has not been documented. 6) The robustness against local impact loads has not been documented. 7) The crushing resistance of the INCA panel and its effect on collision and grounding risks has

not been documented. 8) The risks associated with the lack of structural integrity of INCA panels in fire have not been

documented. 8a) In case of shear studs enhancing bonding performance, the resulting structural integrity in fire has not been documented.

All these gaps, except gap 2, are considered potential showstoppers for general use of the INCA technology without studs in ship structures, but may be less critical for some special applications. As time did not permit a full review of all documents produced by the INCA project, it is acknowledged that some information may have been missed and that some of the identified gaps may be closed by the project team as follow-up of this memo.



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12.7 References /1/ NN. INCA Final Report, Advanced feasibility Study of Steel-Concrete-Strucure in merchant

shipbuilding. Aker Ostsee, Wismar, 2004. /2/ DNV-RP-A203 Qualification procedures for new technology. /3/ DNV-OSS-401 Technology qualification management. /4/ Zenkert D. An Introduction to Sandwich Construction, EMAS, 1995. /5/ Allen HG. Analysis and design of structural sandwich panels. Pergamon Press, 1969. /6/ DNV-OS-C501 Composite Components. /7/ EN 1994:2004. Eurocode 4: Design of composite steel and concrete structures. /8/ DNV Rules for Classification of High Speed, Light Craft and Naval Surface Craft, 2009. /9/ Bakken K. Steel-concrete sandwich concept. Concept description, acceptance criteria and

calculation procedure. DNV Report 2006-1058 Rev. 2. /10/ McGeorge, D. and Hayman, B. Shear Strength of Balsa-Cored Sandwich Panels. 4th Int. Conf.

on Sandwich Construction, 1998. /11/ Mangerig I. Test Report - Preliminary Draft, Static Sandwich Testing, Dynamic Sandwich

Testing, Universität München, 2006 /12/ Echtermeyer AT and Bakken K. Steel-concrete sandwich concept. Static and dynamic sandwich

testing. DNV Report 2004-1315 Rev.0. /13/ IMO. International Convention for the Safety of Life at Sea (SOLAS), 1974 (as amended).


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13 APPENDIX 5: MATERIALS TECHNOLOGY & CONCRETE SHIP DESIGN

13.1 Materials properties This summary was prepared by Eskil Røset using reports from the previous INCA project.The

readability may be reduced and interested parties can contact DNV in order to investigate the

detailed results.



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13 APPENDIX 5: MATERIALS TECHNOLOGY & CONCRETE SHIP DESIGN

13.1 Materials properties This summary was prepared by Eskil Røset using reports from the previous INCA project.The

readability may be reduced and interested parties can contact DNV in order to investigate the

detailed results.


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© Det Norske Veritas AS. All rights reserved.

Fire performance of INCA panels

12 March 2010

4



12 March 2010

5

When exposed to fire steel looses its material properties with increasing heat, the critical temperature being between 500 and 600 degrees Celsius.

In a typical fire this is reached within a few minutes of exposure and therefore steel structures have to be insulated to contain the fire and stop heat transmission between boundaries.

For INCA, the concrete core provides superior heat insulation and therefore almost no heat is transferred through the INCA panel.

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13.2 Fire performance

WEITZ12 March 2010




12 March 2010

2

Outline

INCA panels with unprotected steel face sheets perform differently from stiffened steel plates.

As INCA is a sandwich structure, rapid loss in bending stiffness will occur if any of the steel faces loose their material properties due for example to high temperature.

This is a ‘sudden collapse’ phenomenon like brittle fracture in steel.

Assessment Of The INCA Steel-Concrete-Steel Sandwich Technology98


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12 March 2010

4

Fire Load Test with Uniform Load – “during”



12 March 2010

5

INCA fire test

When exposed to fire steel looses its material properties with increasing heat, the critical temperature being between 500 and 600 degrees Celsius.

In a typical fire this is reached within a few minutes of exposure and therefore steel structures have to be insulated to contain the fire and stop heat transmission between boundaries.

For INCA, the concrete core provides superior heat insulation and therefore almost no heat is transferred through the INCA panel.


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Fire performance

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12 March 2010

8

Concrete and steel loose their strength at high temperatures

Critical temperature for steel is about 500oC

Concrete can cool and insulate (20-30 times reduced heat conductivity)

Fire safety approach:outer layer of concrete insulates core with steel reinforcementseffective cross-section of concrete member in a fire is much smaller (t concrete = 40-50 mm)



12 March 2010

9

An important intent of SOLAS is to maintain the structural integrity of a ship preventing partial or whole collapse of the structure due to deterioration with heat.

Therefore, it seems reasonable that a sandwich structure should be shown to be able to meet the SOLAS fire requirements with at least some loading (bending and shear for operational loads).

In the previous INCA research a fire test was performed on a loaded panel without insulation of the steel faces and the panel collapsed due to loss of structural integrity.

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12 March 2010

6

Temperature curve for fire test

500oC after 5min



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7

Fire performance – strength of steel at high temperatures

http://www.ssina.com/composition/temperature.html



Fire performance

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12 March 2010

8

Fire protection of concrete in civil engineering

Concrete and steel loose their strength at high temperatures

Critical temperature for steel is about 500oC

Concrete can cool and insulate (20-30 times reduced heat conductivity)

Fire safety approach:- outer layer of concrete insulates core with steel reinforcementseffective cross-section of concrete member in a fire is much smaller (t concrete = 40-50 mm)



12 March 2010

9

INCA and SOLAS

An important intent of SOLAS is to maintain the structural integrity of a ship preventing partial or whole collapse of the structure due to deterioration with heat.

Therefore, it seems reasonable that a sandwich structure should be shown to be able to meet the SOLAS fire requirements with at least some loading (bending and shear for operational loads).

In the previous INCA research a fire test was performed on a loaded panel without insulation of the steel faces and the panel collapsed due to loss of structural integrity.


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Fire performance

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IMO SOLAS Fire Regulations

CHAPTER II-2 - PART A GENERAL Regulation 3 Definitions

2 "A" class divisions" are those divisions formed by bulkheads and decks which comply with the following criteria:.1 they are constructed of steel or other equivalent material;.2 they are suitably stiffened; => test loaded panels! (load Is not defined by regulation).3 they are insulated with approved non-combustible materials such that the average

temperature of the unexposed side will not rise more than 140ºC above the original temperature, nor will the temperature, at any one point, including any joint, rise more than 180ºC above the original temperature, within the time listed below:class "A-60" 60 min class "A-30" 30 min class "A-15" 15 min class "A-0" 0 min

.4 they are constructed as to be capable of preventing the passage of smoke and flame to the end of the one-hour standard fire test; and

.5 the Administration has required a test of a prototype bulkhead or deck in accordance with the Fire Test Procedures Code to ensure that it meets the above requirements for integrity and temperature rise.



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11

Conclusions

Therefore, it is concluded that whilst INCA panels have superior heat insulation properties in comparison with a stiffened steel structure the concept must be improved to meet fire requirements for structural integrity, for example by adding fire insulation to the face plates.

Stiffened steel deck with H-120 insulation



Materials and joiningTECHNICAL REPORT13.3 Materials and joining

Jan W eitzenböck3rd Marc h 2010

© Det Norske Veritas A S. A ll rights reserved.

INCA - m aterials and fabrication technology3r d March 2010

2

Fabrication & cost

Joining

Outfitting

Attaching items by welding to surface of INCA panel

Simplified corrosion protection

Ice resistance

Noise and vibration

Impact

Alternative steel-concrete solutions


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13.3 Materials and joining

Jan W eitzenböck3rd Marc h 2010

INCA - materials and fabrication technology



2

Outline

Fabrication & cost

Joining

Outfitting



Ice resistance

Noise and vibration

Impact

Alternative steel-concrete solutions

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5



6

Panel to panel joint

Panel to structure joint:

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3

Fabrication cost – bigger panels are more efficient

Increasing panel size and optimizing to avoid wastage gives considerable cost saving

No need to use levelling compound

Assumed n o need to apply fire insulation



4

Advantage of using sandwich construction



Materials and joining

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5

Joining INCA panels



6

Joining INCA panels cont.

Panel to panel joint

Panel to structure joint:


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10

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7

Joining – shipyard trials



8

Joining – qualification testing

The joint test programme needs to be defined based on where and how are they going to be used

Do joints transfer:- in-plane loads and/or- bending moments?

How are panels loaded?- In plane ?- Out of plane?- Global loads or only local loads?

Boundary conditions?- How are panels connected?- How are decks connected to girders?




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9

Outfitting



10

Outfitting - water jet cutting


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14

Use fillet weld

Out of plane loading should be l ess than 50% of allowable stress

If not need to specify higher purity steel (not likely)

Need to have qualified welding procedure

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11

Outfitting - drilling



12

Outfitting - cutting




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13

Outfitting - grinding



14


Use fillet weld

Out of plane loading should be l ess than 50% of allowable stress

If not need to specify higher purity steel (not likely)

Need to have qualified welding procedure


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17

There are two sources for noise:Low frequency vibrationNoise radiation within the structure

Will the INCA panel make ship structures quieter?

VibrationTo reduce vibration it is an advantages to increase the mass of the panel INCA panels tend to be heavier than an equivalent steel solutionImprovement is expected

Noise radiation:To reduce radiation one needs to have a flexible panelsINCA panels are very stiffMore noise radiation is expected!

Net-effect of using INCA panels for noise and vibration damping is expected to be neutral



18

Experience has shown that concrete usually does very well

However, this is a complex issues that needs testing at a realistic scale (e.g. whole panel) to confirm these assumptions

S. Iwata & Y. Hattori, 1994

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15


INCA panels have smooth surfaces that simplify the coating process

PVC applies has been shown to extend the lifetime of coated steel structures

Increases re-coating intervals by many years

Films are easier to clean and washed away

Marfilm project



16

Ice resistance – one example

From http://www.pr ecastdesign.c om/

Concrete Island Drilling System (CIDS)Glomar Beaufort 1 (now called the Orlan)




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17

Noise and vibration

There are two sources for noise:- Low frequency vibration- Noise radiation within the structure

Will the INCA panel make ship structures quieter?

Vibration- To reduce vibration it is an advantages to increase the mass of the panel - INCA panels tend to be heavier than an equivalent steel solution- Improvement is expected

Noise radiation:- To reduce radiation one needs to have a flexible panels- INCA panels are very stiff- More noise radiation is expected!

Net-effect of using INCA panels for noise and vibration damping is expected to be neutral



18

Impact

Experience has shown that concrete usually does very well

However, this is a complex issues that needs testing at a realistic scale (e.g. whole panel) to confirm these assumptions

S. Iwata & Y. Hattori, 1994


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13.4 History of concrete ships

THOMAS G RAFTON AND JA N W E ITZENBÖCK22 Febr uary 2010

The history of concrete shipbuilding

Innovation - Technology Qualification - Operation - Extinction


T he history of concrete shipbuilding22 F ebruar y 20 10

2

Aim of Presentation

To describe the history of concrete ships and explore why there are not more of them operating

Truth Truth or or Myth?Myth?

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3

Our story starts in the 1917



4

Based on the book by:

N.K. Fougner, “Seagoing and Concrete Ships”, Oxford Technical Publications, 1922.

A Norwegian Pioneer who shaped the early DNV involvement in concrete ships

Fougner went to America to help buil d a concrete emergency f leet for W orld War 1

Fougner’s experimental c oncrete ship –Namsenfjord (1917)



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3

Part 1 – The Beginning of concrete ships

Our story starts in the 1917



4

Outline

Based on the book by:

N.K. Fougner, “Seagoing and Concrete Ships”, Oxford Technical Publications, 1922.

A Norwegian Pioneer who shaped the early DNV involvement in concrete ships

Fougner went to America to help buil d a concrete emergency f leet for W orld War 1

Fougner’s experimental c oncrete ship –Namsenfjord (1917)


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5

DNV Involved in Concrete Ships from the Beginning

- DNV published "Preliminary Regulations for the Classification in Det norske Veritas of Reinforced Concrete Vessels" in 1917. The regulations remained in force until the 1950’s.

- Our managing director from 1909 to 1939 was not very positive to concrete vessels, and all drawings etc had to be sent directly to him for approval - or more likely or more likely –– rejectionrejection!

- Today we publish an offshore- standard for - Offshore Concrete St ructures

- No rules for ships anymore!



6

The first Seagoing Concrete Ships – Stier & Askelad

1917 - 1918

Designed to have 20% more strength than an equivalent steel ship (government requirement for permit)

Annual survey until proven in-service

600 ton and 1000 ton deadweight

Thick hulls so no need for double bottom

Both ships traded successfully- Technically and comm ercia lly

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7

Sister ships but MS Concrete was built to and maintained in DNV class…

Deadweight of MS Concrete 6 3.5 tons less (as a result of DNV requiring he avier structure)Increased cost of 9.5% per ton de adweight for class

Class approach was to reverse engineer steel rules and make concrete equivalent

Conservative

Allowable bending moment in waves was half that of an equivalent steel ship

Tw ice as strong!Increase first cost of 15% compared to Askelad (not classed)



8




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7

MS Askelad and MS Concrete (55 metres, ˜ 1000 tons deadweight)

Sister ships but MS Concrete was built to and maintained in DNV class…- Deadweight of MS Concrete 6 3.5 tons less

(as a result of DNV requiring he avier structure)

- Increased cost of 9.5% per ton de adweight for class

Class approach was to reverse engineer steel rules and make concrete equivalent- Conservative

Allowable bending moment in waves was half that of an equivalent steel ship- Tw ice as strong!- Increase first cost of 15% compared to

Askelad (not classed)



8

Floating Docks


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9

Damages

Aground for two Aground for two weeks on rising weeks on rising and falling tide and falling tide --almost no damage!almost no damage!

Abandoned Abandoned –– did not break up did not break up after many months!after many months!

After three collisions!After three collisions!



10

American Built Ships

Fast design and build time due to war conditions- Up to 5 000 ton de adweight- Build time of 6 weeks after pouring of first con crete!

Standard Designs Intended to be mass produced

Trans-Atlantic c rossings with cargo

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Concrete ships are cheaper to buildThe hull of a steel ship is 35% more expensive in first cost than that of a concrete ship of the same type and deadweight capacity

Concrete ships cheaper to runClass requirement for annual renewal survey for ‘experimental ship’ a big part of this costapproximately 20% running costs of a steel ship

No higher fuel cost than steel ships of the same deadweight capacityConcrete ship bigger to support added structural weightFor a speed range 8-12 knots

More robust structuresA thick hull is a survivable hull

Great opportunity to reduce weight with lightweight concrete and more advanced re-enforcement methods



12




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11

Fougner’s Conclusions (1917 – 1922)

Concrete ships are cheaper to build- The hull of a steel ship is 35% more expensive in first cost than that of a concrete ship of the

same type and deadweight capacity

Concrete ships cheaper to run- Class requirement for annual renewal survey for ‘experimental ship’ a big part of this costapproximately 20% running costs of a steel ship

No higher fuel cost than steel ships of the same deadweight capacity- Concrete ship bigger to support added structural weight- For a speed range 8-12 knots

More robust structures- A thick hull is a survivable hull

Great opportunity to reduce weight with lightweight concrete and more advanced re-enforcement methods



12

Part 2 – The 1930’s to the 1970’s


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13

Outline

Based on the paper by:

1) Rowland Morgan, “History and Experience with Concrete Ships”, Conference on Concrete Ships and Floating Structures, Berkley 1975



14

Barge built in Italy 1905 by Gabellini – 150 tons 1

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16




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Barge built in Germany in 1940s – pre-tensioned concrete 1



16

Typical cross section of wartime ship (WW1 or WW2) 1


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Weight of concrete ships – predicted and actual 1



18

Cost of reinforced concrete ships 1

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Ferrocement is part of concrete familyUses hig h perfo rmance, low perm eability motar

A very finely divided steel mesh is needed

Surface area of steel greatly increased compared to re-enforced concrete

Increases bond fo rcesdeterm ine s allowable crack size in ferro cem ent

Allowable stress levels raised significantly in comparison with re-enforced concrete

BUTBUT has lim ited flexural strength (much much less than ‘equivalent’ mild steel)ANDAND uses hull curvature producin g co mpre ssive membrane effects to utilise th e co ncreteSOSO t he advantage g reatly red uces w ith increased size as flat panels between girders are required. (e xtremely fine mesh not practical)

NOT FOR SHIPS!NOT FOR SHIPS!



20

Bad luck and a Conservative IndustryBad luck and a Conservative Industry…………??

Generally considered/built when their has been a shortage of steel or a s hortage of shipbuilding capacity

After wartime, the requirement for shipping reduced with many spare ships‘Novel’ concrete ships were less likely to find new ownersConcrete ship builders and designers moved on to other projects (Roads, Runways,….)

Next wave of interest during 1960’s and 1970’s during the oil exploration boomMany designs consideredNo experienced buildersDesigns still considered ‘novel’ (even though first classed ships in 1918!)Oil crash of early 1980’s ended interestBig ships were generally heavier…..needed to be more advantages than just weight (cheep build? faster build? insulation properties? survivability?)




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Ferrocement for Boats but not Ships

Ferrocement is part of concrete family- Uses hig h perfo rmance, low perm eability motar

A very finely divided steel mesh is needed

Surface area of steel greatly increased compared to re-enforced concrete- Increases bond fo rcesdeterm ine s allowable crack size in ferro cem ent

Allowable stress levels raised significantly in comparison with re-enforced concrete-- BUTBUT has lim ited flexural strength (much much

less than ‘equivalent’ mild steel)-- ANDAND uses hull curvature producin g co mpre ssive

membrane effects to utilise th e co ncrete-- SOSO t he advantage g reatly red uces w ith

increased size as flat panels between girders are required. (e xtremely fine mesh not practical)

NOT FOR SHIPS!NOT FOR SHIPS!



20

Why are there no concrete ships?

Bad luck and a Conservative IndustryBad luck and a Conservative Industry…………??

Generally considered/built when their has been a shortage of steel or a s hortage of shipbuilding capacity

After wartime, the requirement for shipping reduced with many spare ships- ‘Novel’ concrete ships were less likely to find new owners- Concrete ship builders and designers moved on to other projects (Roads, Runways,….)

Next wave of interest during 1960’s and 1970’s during the oil exploration boom- Many designs considered- No experienced builders- Designs still considered ‘novel’ (even though first classed ships in 1918!)- Oil crash of early 1980’s ended interest- Big ships were generally heavier…..needed to be more advantages than just weight (cheep

build? faster build? insulation properties? survivability?)


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21

Some conclusions

Type of concrete and aggregates chosen to achieve water tightness

Will probably always be heavier than equivalent steel structure – in particular for large ships

Can be quicker and cheaper to bu ild than steel ships

Vessels seem to be qui te robust

Large ships need prestressing to be competitive

Reinforced concrete only suitable for smaller vessels

Concrete ships have been build and traded successfully!

Can be built without large shipbuilding infrastructure

Proven technology



22

DNV – Update

The DNV Offshore Standard will be updated based on the INCA project to include Steel-concrete-steel sandwich structures- DNV-OS-C502

What about standards for ships? Our last standard for concrete ships fell out of use in the 1970’s

Some Thoughts:- This presentation shows that historically it has been difficult to bring new technologies to the

shipbuilding market –– the same is true todaythe same is true today!

TECHNICAL REPORT13.5 INCA project journey

INCA Project Team11 March 2010

From INCA Bulk to INCA Deck and some diversions in-between


INCA Project Journey11 M arch 2010

2

Innovation and research INCA project W ay fo rward?

Technical review

Applications assessments

Opportunities

Past Present Near future




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13.5 INCA project journey

INCA Project Team11 March 2010

INCA Project Journey

From INCA Bulk to INCA Deck and some diversions in-between



2

An innovation journey about to be concluded


Technical review


Opportunities



PUBLIC REPORT

TECHNICAL REPORT





3

The INCA IPR and novelty

NorwayUK

USASpain

ChinaItaly

J apanFin land

Hong KongGermany

S outh KoreaFrance

Other patent countries (pending):

The EuropeanP atent (EP) covers:

The patent claims ensure: -…coverage of all floating marine structures

-…flexibility in use of core material (less than 1200 kg/m3)

-…flexibility in connection solutions, including usage of shear studs

Replace stiffened steel panels (panel, stiffeners and even girders) with a sandwich consisting of a light-weight concrete core between two steel plates

The basic idea of the INCA solution:



4

Technical review


Opportunities

The journey begins…….

(1)

(2)

TECHNICAL REPORT



5

Strenghts

Opportunities Threats

Weaknesses

StrenghtsSmooth sur faces and no sharp edges

Reduced co ating area

Improved impact perfor mance

Improved insu lation pr operties

Sandwich properties can be tai lo r made

Reduced number o f c orrosion and fatigue prone d etai ls



6

Primary structure ofbulk carriers & container ships

Tanks (integrated solutions) for chemical & gas carriers

FPSOs

App

licat

ion

area

Ship typeHigh Complexity Sta ndardisedPrim ary stru cture

Secondary stru cture



INCA project journey

TECHNICAL REPORT





5

Strenghts


Weaknesses







INCA technology strengths - 2010



6

The shift in focus from 2002 to 2010



FPSOs

App

licat

ion

area

Ship typeHigh Complexity Sta ndardisedPrim ary stru cture



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TECHNICAL REPORT





7

The first phases of the INCA project (2002-2004)

Bulk carriers

Local structure o r overlays

Barges etc

Container ships

Crude oil and

product tankers

Chem ical carriers

Accom modati on

Deck(s)

RoRo / RoPax

G as carriers

Bulkheads

(Double) bot tom

Side shel l panels

FSO / FPSO

Offshore support

Plat form s, rigs

Low-end shipsHighly standardised

production INCA used for primary

structureConservative market

segments

Very high entrance barriers for the technology

High Comp lexity Standardised

Primary structure

Secondary structure



8

Other applications - input from the industry (2005-2006)

Bulk carriers

Loca l structure or overl ays

Barges etc

Container ships

Crude oil and

product tankers

Chemical carriers

Accom modat ion

Deck(s)

RoRo / RoPax

G as carriers

Bulkheads

(Double) bot tom

Side shel l panels

FSO / FPSO

Offshore support

Plat form s, rigs

Moving towards the high-end segments

The focus is still on using INCA for pr imary elements of the structure

Relatively conservative shipping segments

High entrance barriers for the technology

Prim ary stru ctu re

Seconda ry stru ctu re

High Comp lexity Standardised

TECHNICAL REPORT



9

Cu rrentCu rrent

Previou sPreviou s



FPSOs

Local structure of FPSOs ,offshore support vessels, others

Decks on RoRo an d Passenger

Low- tech bargesand r iver vessels

App

licat

ion

area

Ship typeHigh co mplexity Standardised

Prim ary stru cture




10

Heavy loaded deck structures

Offshore applications

Other applications?

Simpler units




TECHNICAL REPORT





9

Shifting focus from large standard ships to simpler solutions

Cu rrentCu rrent

Previou sP reviou s



FPSOs

Local structure of FPSOs ,offshore support vessels, others

Decks on RoRo an d Passenger

Low- tech bargesand r iver vessels

App

licat

ion

area

Ship typeHigh co mplexity Standardised

Prim ary stru cture




10



Other applications?

Simpler units

Possible applications (2010)


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11

Strenghts


Weaknesses







WeaknessesHeavier than optimis ed s teel construc tions

Bond between steel and concrete (studs can be used in the interim)

Structural in tegri ty du ring f ire

Hotwork cou ld cause delamination

Light w eight concrete ha s low mec hanical strength

Technology strengths and weaknesses (2010)



12


Strenghts Weaknesses

OpportunitiesOffshor e in dustry ha s knowledge of, and acceptanc e for, concre te as construction m ateria l

Y ards a re lo oking t o di ffe rentiate du e to tigh t m ark et s ituation

Increased A rctic a ctivity may induce new m ark ets

E merging mark ets, e. g . r iver trans portation, have la rge potential

ThreatsCompeting w ith wel l-developed p roduc tion technologies

S hipp ing a nd s hipbuilding are tradi tional ly v ery c onserv ative mar kets

Increased e nvi ronmenta l focus potential ly bringing al ong add itiona l requ irements for new technology ( Recycl ing etc.)

Technology opportunities and threats (2010)

TECHNICAL REPORT



13

Technical review


Opportunities



14

1. Use many of INCAs benefits

2. W eld ing to panels a fter fitting to structu re p ossible

3. L ow thermal conductivity

4. Bo ttom plate not d amaged b y welding t o t op pla te (no re-paintin g)



1. Reduced panel thickness

2. Simpler structure a nd more robust

3. Faster bu ild time for large p anels

4. Flat su rfaces – less coating an d fire insulation




TECHNICAL REPORT





13

Technical review


Opportunities



14

Opportunity assessments of the applications

1. Use many of INCAs benefits

2. W eld ing to panels a fter fitting to structu re p ossible

3. L ow thermal conductivity

4. Bo ttom plate not d amaged b y welding t o t op pla te (no re-paintin g)



1. Reduced panel thickness

2. Simpler structure a nd more robust

3. Faster bu ild time for large p anels

4. Flat su rfaces – less coating an d fire insulation


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17


Technical review


Opportunities






TECHNICAL REPORT



15


• Fast and simple co nstructio n = low cost

• Concrete ships and bo ats h ave a lo ng history ( ju st n ot recently!)

• La rge un-tappe d market, robust long life structu res

• Can build locally u sing semi-skilled labour and local mater ials (less impo rted steel)

Simpler units



16



TECHNICAL REPORT





17

An innovation journey about to be concluded


Technical review


Opportunities



PUBLIC REPORT




Extraordinary Research Project INCA- CO

2 Footprint Analysis

CONTACT

Magnus Christiansen and Håkon Hustad (mailadress)

Date of issue

December 2010

1 INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .135

2 METHODOLOGY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .135

3 LIFE CYCLE GHG EMISSIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 136

3.1 CO2 from ship construction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .136

3.1.1 CO2 from the production of steel and concrete . . . . . . . . . . . . . . . . . . . . . . .136

3.1.2 Material consumption and comparison of construction phase CO2 . . . . . . .138

3.2 CO2 from ship operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .139

3.2.1 Conventional ships . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .139

3.2.2 Ships applying INCA technology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .140

3.3 CO2 in a recycling perspective . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .141

4 CONCLUSION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .141

DET NORSKE VERITAS

TECHNICAL REPORT

Head Office: Veritasveien 1, 1322 Høvik, Norway

DET NORSKE VERITAS AS DNV Maritime, Region Nordic Countries, the Baltic and Germany

Advisory Services Norway

Veritasveien 1 1322 Høvik Norway Tel: +47 67 57 99 00 Fax: +47 67 57 99 11 http://www.dnv.com Org. No: NO 945 748 931 MVA

Date of first issue: Project No.:2010-01-19 109IN208 Approved by: Or ganisational unit:Ari Marjamaa Head of Department

Maritime Solutions

Client: Client ref.:DNV

Summary: The CO2 footprint of the application of steel/light weight concrete sandwich structures and traditional steel structures in ships has been compared by means of a basic high-level assessment of the life-cycle CO2 emissions of each material when incorporated in vessels. The aim has been to identify the main sources of emissions throughout the lifetime and the order of magnitude of potential changes in emissions by applying INCA technology. The assessment has been conducted by estimating the CO2 emissions at each phase in a simplified life-cycle consisting the following three phases: (I) construction of the ship, (II) life-time ship operations and (III) end-of-life recycling/reuse. In terms of CO2 emissions per ton material produced, the relevant light weight concrete is less CO2 intensive (400 kg CO2/ton) than ship steel (1460 kg CO2/ton). Thus one can expect a certain reduction in CO2 from ship construction, assuming that concrete to a certain degree replaces steel. However, for shipping in general the all-important CO2 emissions throughout the lifetime origin from the combustion of hydrocarbons for propulsion and power generation during the operation of ships; in order of magnitude 80-100 times as much CO2 as the production of building materials. No significant potential for reducing the lifetime operational CO2 has been identified for ships applying INCA structures. Steel structures from ships are effectively recycled into second hand steel, which again can be used in many applications with high CO2 saving potential as an alternative to production of new steel. Steel/concrete sandwich structures are in comparison considered less efficiently recycled. Moreover, second hand concrete, even if feasibly recycled, is not assumed to have a high potential for substituting CO2 intensive new production of materials, such as is the case with steel. In conclusion, no significant change in lifetime CO2 footprint is expected for ships applying INCA technology. Marginal CO2 savings in the construction phase by using concrete may be lost due to materials having a lower potential for CO2 saving recycling.

Report No.: Subject Group: 2010 - 0097 Indexing termsReport title: Key words Service Area

Environmental excellence Market Sector

CO2 footprint analysis Steel concrete sandwich INCA CO2 emissions

Transportation Work carried out by: Magnus Christiansen and Håkon Hustad

Work verified by: Alvar Mjelde

Date of this revision: Rev. No.: Number of pages:2010-01-19 00 10

No distribution without permission from the client or responsible organisational unit (however, free distribution for internal use within DNV after 3 years)

No distribution without permission from the client or responsible organisational unit.

Strictly confidential Unr estricted distribution

© 2002 Det Norske Veritas AS All rights reserved. This publication or parts thereof may not be reproduced or transmitted in any form or by any means, including photocopying or recording, without the prior written consent of Det Norske Veritas AS.

1 INTRODUCTION

2 METHODOLOGY

• •

•

Extraordinary Innovation Project INCA – CO2 Footprint analysis134


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1 INTRODUCTION In this study the CO2 footprint of the application of INCA steel/concrete sandwich structures and traditional steel structures has been compared by means of a basic high-level assessment of the life-cycle CO2 emissions of each material when incorporated in vessels. The aim has been to identify the main sources of emissions throughout the lifetime of a ship and the order of magnitude of potential changes in emissions by applying INCA technology.

The assessment has been conducted by estimating the CO2 emissions at each phase in a simplified life-cycle consisting the following three phases: (I) construction of the ship, (II) life-time ship operations and (III) end-of-life recycling/reuse.

2 METHODOLOGY The study constitutes a high level GHG (greenhouse gases) footprint analysis, thus exact emission figures for different scenarios will not been presented. Only emissions of CO2 have been considered, even if shipping also results in other GHG emissions (such as methane). However, in a ship construction, - operation and - decommissioning perspective, CO2 has been considered the predominant and sufficient parameter for a high level comparative study.

For the study of the construction phase CO2, material production (steel versus concrete) has been considered the main relevant emission source for comparison between conventional ships and ships applying INCA technology, including • the relevant emission processes associated with steel and concrete production

(literature study), • the relevant factors for CO2 emissions per ton material produced for the relevant ship steel and light weight concrete (literature study and communication with the industry), and • the assumed likely material consumption and associated estimated CO2 emissions from ship building applying INCA technology, compared with the alternative use of conventional structures. Steel weights of the example ships have been roughly assumed based on registered lightweight tons in DNV databases, approximately estimated steel weights based on DNV in-house knowledge.

Production of other materials, material transportation and the building process itself will also result in emissions, however considered much less and marginal in terms of differences between INCA based concepts and conventional ship building. Such emissions are thus not included in the analysis.

For the study of the operation phase CO2, the combustion of hydrocarbons for propulsion and power generation has been considered the main emission source. Future alternative energy sources and carriers (for example Hydrogen) potentially radically changing the point source emissions from shipping has not been accounted for; first because the prediction of the effects of such developments are highly unsure; secondly because it is expected that such developments will effect ships applying INCA technology not very differently compared to conventional ships.


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The expected life time operational CO2 emissions from selected example ship types have been calculated for an assumed 30 years of operation, based on typical reported and estimated yearly fuel consumption figures as indicated by DNV in-house experience and EASNOS environmental modelling tool (ref. /1/), taking into account installed effect and specific consumption rates combined with theoretically assumed average engine loads and number of operational hours throughout a year. A superficial evaluation of the potential for changed energy efficiency of ships applying INCA technology is summarized based on input from the other work packages of the INCA project regarding attributes such as ship weight, hull shape, machinery configuration and other features with effect on energy efficiency. However a detailed and independent study of the energy efficiency aspects of each and every aspect of the operation of ships applying INCA technology has not been part of the scope of this CO2 footprint analysis.

For end-of-life related CO2-considearations, the main issue of interest is whether the materials used in ship building can be re-used and recycled in a way that replaces CO2-intensive new production of materials. This section briefly consider to which degree the use of INCA structures due to recycling/reuse issues can be expected to increase or decrease the CO2 footprint of ships applying the INCA concept. No figures for CO2 emissions will be estimated for the recycling part.

An overall comparison of the contribution of emissions from different life phases of a ship is presented in a conclusive section, and different scenarios for changed emission performance by using INCA technology are shown.

3 LIFE CYCLE GHG EMISSIONS

3.1 CO2 from ship construction 3.1.1 CO2 from the production of steel and concrete Steel Production from virgin materials The raw material for steel production is liquid iron, which is produced by heating iron ore in a blast furnace in the presence of a reducing agent (coke or coal). The liquid iron is further processed in an oxygen furnace, in which the carbon content is reduced to about 1 %, yielding steel. Steel production is energy intensive and result in significant emissions of CO2. Typically, the emissions of CO2 when producing steel from virgin iron ore lie in the range 1 460 (ref. /2/) to 1 700 (ref /3/) kg CO2 per ton steel. Depending on the steel production process employed, the emissions from the production of liquid iron from iron ore constitute about 70 – 80 % of the total emissions (ref. /2/). The majority of these emissions are process emissions (reduction of C to CO2), whereas the remaining are direct- and indirect emissions from the consumption of energy.

Production from scrap metal

World average production mix

Emission factor applied in this study

1460 kg CO2 per ton steel Concrete Production of cement

• •

Production of lightweight concrete



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Production from scrap metal Currently about 80 – 90 % of scrap steel is recycled, and in 2006 recycled scrap steel amounted to 37 % of world total steel production in that year (ref. /3/). Steel production from scrap requires significantly less energy than production from virgin materials. The emission of CO2 when steel is produced from scrap metal is only about 8 kg CO2 per ton steel (ref. /2/). World average production mix Currently, the world production of steel is based on a mix of production from virgin materials and recycling of scrap steel. Furthermore, different production technologies are employed for both production pathways. The Intergovernmental panel on Climate Change (IPCC) has developed a world average emission factor for emission of CO2 from steel production based on the world steel production raw material mix and mix of different production technologies. On average, IPPC reckons that world steel production CO2 emissions is 1 060 kg CO2 per ton steel (ref. /2/).

Emission factor applied in this study For the purpose of this study it is assumed that ship steel is produced from virgin materials only. The IPPC emission factor for steel production from virgin materials in basic oxygen furnaces is applied, corresponding to 1460 kg CO2 per ton steel (ref. /2).

Concrete Production of cement Cement is produced by calcination of limestone (CaCO3) to produce lime (CaO), a thermal process in which CO2 is released as a by-product. The resulting product is normally referred to as clinker. Commercial cement is produced by grinding clinker and adding gypsum and/or other mineral components such as fly ash or granulated slag.

The main sources of CO2 emissions in the production of clinker are:

• Direct emissions from the calcination process • Direct- or indirect emissions from the energy consumed in the calcination process

In 2006, the world average gross emission of CO2 in the production of clinker was 866 kg CO2 per ton clinker (Ref x). Based on an average clinker content of 78%, the world average gross emissions for cement was 679 kg CO2 per ton cement (ref. /4/). Production of lightweight concrete Concrete in general is produced by mixing cement with suitable aggregates, for example sand or gravel, and chemical additives. The amount of cement in concrete typically varies between 5 and


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20 % depending on the desired quality (ref. /5/), however also higher cement content is common when required.

The CO2 emissions associated with the aggregates are minimal, and typically the CO2 emissions from production of the cement accounts for about 90 % of the total emissions from the production of concrete (ref /6/).

Thus the CO2 emission factor is closely related to the cement content. An example of a given average factor is about 100 kg CO2 per ton, as suggested by The Concrete Industry Sustainable Construction Forum (CISCF) (ref. /7/). However different purpose concretes may differ significantly from this due to specific requirement to the mixes.

The emission factor applied in this study Based on industry specific information (ref. /8/) for the specific light weight concrete of relevance for the INCA structures, an average emission factor of 400 kg CO2 per ton concrete is applied in this study.

3.1.2 Material consumption and comparison of construction phase CO2 Some of the currently relevant application concepts considered by the INCA-project indicates a concrete percentage of about 10-30 % of the ship weight, assuming that the total weight of the ship will be approximately the same compared to a conventional similar ship. Table 1 shows the comparison of construction CO2 between some example ships with assumed material amounts and different degrees of concrete use, given the CO2 factors explained above in Section 3.1.

It is underlined that the exemplified material figures and concrete percentages are chosen for illustrative purposes only, they don’t necessarily represent actual features of studied INCA concepts. Thus, included is also a scenario where concrete is the dominating construction material onboard.

Table 1 CO2 emissions from material production for ships with assumed different extent of concrete use as a result of applying INCA technology

Offshore supply,

Conventional

Offshore supply, INCA

10 % concrete

Passenger, Conventional

Passenger, INCA

30 % concrete

Bulker, Conventional

Bulker, INCA 60 %

concrete

- -

- -

CO2 Total 3650 3385 5 840 4568 1 4600 7180 INCA CO2 reduction (%)

- -7 % - -22 % - -51 %

3.2 CO2 from ship operation 3.2.1 Conventional ships



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Table 1 CO2 emissions from material production for ships with assumed different extent of concrete use as a result of applying INCA technology Offshore

supply, Conventional

Offshore supply, INCA

10 % concrete

Passenger, Conventional

Passenger, INCA

30 % concrete

Bulker, Conventional

Bulker, INCA 60 %

concrete Weight steel (tons)

2500 2250 4000 2800 10000 3000

Weight concrete (tons)

- 250 - 1200 - 7000

kg CO2 / ton steel

1460 1460 1460 1460 1460 1460

kg CO2 / ton concrete

- 400 - 400 - 400

CO2 Total 3650 3385 5 840 4568 1 4600 7180 INCA CO2 reduction (%)

- -7 % - -22 % - -51 %

As seen from the table, a reduction in construction CO2 can be expected if a part of the steel mass of a ship is replaced with concrete – corresponding to the lower CO2 emissions from the concrete production.

3.2 CO2 from ship operation 3.2.1 Conventional ships For shipping in general the all-important CO2 emissions in a life cycle perspective origins from the combustion of hydrocarbons for propulsion and power generation. The total emitted CO2 is a direct function of fuel consumption and will obviously vary depended upon vessel type, machinery capacity, operational characteristics and life span. The estimated typical life time CO2 for some example ship types relevant for the application of the INCA technology are shown in Figure 1.


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360000

480000

830000

0

100000

200000

300000

400000

500000

600000

700000

800000

900000

Offshore supply (5000 GT) Passenger /RoPax (11000GT)

Panamax (65000 DWT)

Lifetime CO2 (tons)

Figur 1. Comparison of operational CO2 (propulsion and power generation) for selected example ship types. The emissions exemplified in Figure 1 may typically be representative for ships with installed machinery effect in the 5000 - 15000 kW, exact figures of course depending on the operational features of the shipping segment in question. However other ship types and size categories may have installed effect in an order of magnitude five to ten times higher than this, corresponding to substantially higher emissions.

3.2.2 Ships applying INCA technology Optimization of ship design and machinery configuration for the purpose of improving energy efficiency is currently high on the agenda of international shipping. However, summarizing the results and assumptions from the other work packages of the INCA project, no significant changes in areas such as ship weight, hull shape, cargo carrying capacity and machinery configuration that significantly changes the energy efficiency have been identified for the concepts currently considered most relevant by the INCA project. Thus the figures given in section 3.2.1 would in general be applicable also for a ship applying INCA technology.

3.3 CO2 in a recycling perspective

4 CONCLUSION

Lifetime CO2 for a supply ship, 10% concrete

Ship operation CO2

Material production CO2

INCA reduction onprouction CO2

Figure 2.



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3.3 CO2 in a recycling perspective Steel structures from ships are effectively recycled into second hand steel, which again can be used in a range of applications with high CO2 saving potential as an alternative to production of new steel. Steel/concrete sandwich structures are in comparison considered less efficiently recycled. Assuming a vessel where INCA structures are the predominant building material, the recycling may take twice the amount of time as vessels constructed of only steel; however it will be possible with the right equipment, at the right price (ref. /9/).

Although recycling of concrete entails numerous positive environmental impacts, there is no appreciable impact on reducing the carbon footprint of concrete (ref. /5/). The reason for this is that the cement content in concrete cannot be viably separated and reused or recycled into new cement, from which the majority (> 90%) of the total CO2 emissions from concrete production arises. Thus second hand concrete, even if feasibly recycled, is not assumed to substitute CO2 intensive new production of materials, such as is the case with steel.

Re-use of INCA modules “as is” may contribute positively for the CO2 footprint. However, the real potential for such reuse is not known.

4 CONCLUSION A comparison between life time operationally generated CO2 and construction generated CO2 for some example ships built with concrete in varying degrees are shown in Figure 2 to 4. The potential for reduction in construction generated CO2 emissions by applying concrete as part of the INCA technology is shown.

Lifetime CO2 for a supply ship, 10% concrete

Ship operation CO2



Figure 2. Lifetime CO2 emissions from operation and construction of a supply ship, and reduction potential by replacing 10 % of the steel mass with lightweight concrete.


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Lifetime CO2 for a passenger ship, 30 % concrete

Ship operation CO2



Figure 3. Lifetime CO2 emissions from operation and construction of a passenger vessel, and reduction potential by replacing 30 % of the steel mass with lightweight concrete.

Lifetime CO2 for a bulk ship, 60 % concrete

Ship operation CO2



Figure 4. Lifetime CO2 emissions from operation and construction of a Panamax bulk ship, and reduction potential by replacing 60 % of the steel mass with lightweight concrete.

In terms of CO2 emissions per ton material produced, production of the specific light weight concrete is less CO2 intensive (400 kg CO2/ton) than production of ship steel (1460 kg CO2/ton). Thus one can expect a certain reduction in ship construction related CO2, assuming that concrete to a certain degree replaces steel. As seen from the above Figures 2 and 3, the reduction potential is moderate to low when considering relevant applications of steel/concrete sandwich structures



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as currently studied by the INCA project, i.e. assuming concrete constituting 10-30 % of the ship weight. The CO2 saving potential in the construction phase is higher when considering more large scale use of concrete, see Figure 4.

However, under all circumstances the estimated potential changes in construction CO2 by applying INCA technology are marginal in comparison with the CO2 from the combustion of hydrocarbons for propulsion and power generation during the operation of ships; in order of magnitude 80-90 times as much CO2 as the production of building materials. No significant potential for reducing this lifetime operational CO2 has been identified for ships applying INCA structures.

Steel structures from ships are effectively recycled into second hand steel, which again can be used in a range of applications with high CO2 saving potential as an alternative to production of new steel. Steel/concrete sandwich structures are in comparison considered less efficiently recycled. Moreover, second hand concrete, even if feasibly recycled, is not assumed to have a high potential for substituting CO2 intensive new production of materials, such as is the case with steel. Re-use of INCA modules “as is” may contribute positively for the CO2 footprint. However, the real potential for such reuse is not known.

In conclusion, no significant change in lifetime CO2 footprint is expected for ships applying INCA technology compared to conventional ships. Potential marginal CO2 savings in the construction phase by using concrete may be lost due to materials having a lower potential for recycling in a way that substitutes new and CO2 intensive material production.


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References

/1/

DNV Report No. 2002-1645. Environmental Accounting System for Norwegian Shipping –EASNoS, Phase 1. Documentation of Principles, Methodology & Structure

/2/

Intergovernmental Panel on Climate Change (2006): Guidelines for National Greenhouse Gas Inventories – Metal Industry Emissions. http://www.ipcc-nggip.iges.or.jp/public/2006gl/index.html

/3/

World Steel Association (2008): 2008 sustainability report of the world steel industry. http://www.worldsteel.org

/4/ World Business Council for Sustainable Development (2009): Cement Industry Energy and CO2 Performance “Getting the Numbers Right”. http://www.wbcsdcement.org/

/5/ World Business Council for Sustainable Development (2009): Recycling Concrete. http://www.wbcsdcement.org/

/6/ Nordic Innovation center (2005): The CO2 Balance of Concrete in a Life Cycle Perspective. http://www.nordicinnovation.net/prosjekt.cfm?Id=1-4415-226

/7/ The Concrete Center (2009): Sustainable concrete website. http://www.sustainableconcrete.org.uk

/8/ E-mail correspondence with Mr. Geir Norden, R&D Manager, Exclay. Saint-Gobain Weber. Dated 18.01.2010.

/9/ DNV Report 2010 – 0050. Extraordinary Innovation Projects INCA. Recycling Scheme Analysis

- o0o -




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Extraordinary Research Project INCA- Recycling Scheme Analysis

CONTACT

Alfhild Aspelin (mailadress)

Date of issue

December 2010

1 INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 149

2 METHODOLOGY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 149

3 DESIGNING FOR DECONSTRUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 149

3.1 Size Matters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 150

3.2 Standardization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 150

4 REUSE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 150

4.1 Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 151

5 RECYCLING STEEL VERSUS INCA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 151

5.1 Value of INCA Vessels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 152

6 DISMANTLING END OF LIFE INCA STRUCTURES . . . . . . . . . . . . . . . . . . . . . . . 153

6.1 Recycled Concrete . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 153

6.2 Hazardous Material Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 154

7 CONCLUSION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 154

8 REFERENCES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 154

Appendix A Joining Panels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 155

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1 INTRODUCTION INCA technology used either partially or wholly in the construction of a vessel will proportionately decrease the value of the vessel. Separating steel from concrete before recycling is more challenging and time consuming than simply recycling steel. If reuse potential is taken into consideration during the design phase, recycling INCA structures could become more economically viable. Design considerations that allow for easier installation and dismantling of INCA structures will simplify both the building stage and the recycling process. Designing INCA technology as panels with features such as standardized sizes and joining methods would maximize reuse potential.

2 METHODOLOGY The starting point of the recycling scheme analysis began by researching standard practice in the industry for separating steel from concrete. Internal experts and external industry professionals were contacted, not limited to the maritime industry but also the offshore industry and land based building industry where concrete is a more common building material. The findings are based on best practice with comparative concrete and steel structures as recycling INCA structures has never been done before.

By taking into consideration the known methods used to recycle ships today, comparisons were made to the methods that would need to be used to dismantle INCA ships. Today, there are many unknown variables with regard to what the final INCA panels will look like, what joining methods will be used, and what the exact lightweight concrete mixture be composed of. Regardless, it’s not anticipated that these variables will change the content of this report significantly.

3 DESIGNING FOR DECONSTRUCTION Deconstruction is a word synonymous with words like reuse and recycling, both of which contribute to a sustainable environment. However, designing for deconstruction from a practical standpoint is often a difficult concept to grasp since designing a vessel that can be taken apart goes against shipbuilding principles. Nevertheless, if we consider deconstruction at the design phase, it could provide economic potential and environmental incentives.

Because separating steel from concrete is time consuming and labour intensive, before demolishing INCA structures when they reach the end of their life, reuse potential should be explored. In order to reuse INCA sandwich structures, special considerations must be given to dimensions, applications and how to most effectively install, dismantle and reassemble these structures. An interchangeable panel concept would be best solution for maximizing reuse potential. The closest examples that exist today in the market of modular or panel type construction are in use by the building industry. Panels are prefabricated and fitted together through standardized interfaces in a variety of applications from homes and office buildings to parking garages. Size and standardization should be taken into consideration during the design stage in order to maximize the reuse potential of prefabricated INCA panels.



Extraordinary Innovation Project INCA – Recycling Scheme Analysis148


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1 INTRODUCTION INCA technology used either partially or wholly in the construction of a vessel will proportionately decrease the value of the vessel. Separating steel from concrete before recycling is more challenging and time consuming than simply recycling steel. If reuse potential is taken into consideration during the design phase, recycling INCA structures could become more economically viable. Design considerations that allow for easier installation and dismantling of INCA structures will simplify both the building stage and the recycling process. Designing INCA technology as panels with features such as standardized sizes and joining methods would maximize reuse potential.

2 METHODOLOGY The starting point of the recycling scheme analysis began by researching standard practice in the industry for separating steel from concrete. Internal experts and external industry professionals were contacted, not limited to the maritime industry but also the offshore industry and land based building industry where concrete is a more common building material. The findings are based on best practice with comparative concrete and steel structures as recycling INCA structures has never been done before.

By taking into consideration the known methods used to recycle ships today, comparisons were made to the methods that would need to be used to dismantle INCA ships. Today, there are many unknown variables with regard to what the final INCA panels will look like, what joining methods will be used, and what the exact lightweight concrete mixture be composed of. Regardless, it’s not anticipated that these variables will change the content of this report significantly.

3 DESIGNING FOR DECONSTRUCTION Deconstruction is a word synonymous with words like reuse and recycling, both of which contribute to a sustainable environment. However, designing for deconstruction from a practical standpoint is often a difficult concept to grasp since designing a vessel that can be taken apart goes against shipbuilding principles. Nevertheless, if we consider deconstruction at the design phase, it could provide economic potential and environmental incentives.

Because separating steel from concrete is time consuming and labour intensive, before demolishing INCA structures when they reach the end of their life, reuse potential should be explored. In order to reuse INCA sandwich structures, special considerations must be given to dimensions, applications and how to most effectively install, dismantle and reassemble these structures. An interchangeable panel concept would be best solution for maximizing reuse potential. The closest examples that exist today in the market of modular or panel type construction are in use by the building industry. Panels are prefabricated and fitted together through standardized interfaces in a variety of applications from homes and office buildings to parking garages. Size and standardization should be taken into consideration during the design stage in order to maximize the reuse potential of prefabricated INCA panels.


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3.1 Size Matters Weight and size limitations will determine the applications of the INCA panels. If the panels can be designed in such a way that allows for transport via road or train they could also provide realistic building materials for alternative uses other than for only marine applications. Not only do size and weight restrictions vary considerably from state to state, but also country to country. Semi trailer truck size limitations in the United States differ from state to state but on average limits are set as 2.6 meters wide, 4.1 meters in height, and 36.3 metric tons with a length of 16.7 meters. In the UK, the overall length of semi trailers can reach 22.75 meters for concrete and steel transport. In Denmark, the Netherlands and Norway the length can reach up to 25.25 m with a weight of 60 tons /2/. In some Asian countries, truck limitations are much smaller than Europe and the United States. Many roads are congested, some are too small and others are under development. Design considerations should therefore take into account the preferred method of transport and its size limitations of the various countries in order to enhance reuse potential.

3.2 Standardization Very often new construction projects, both on land and at sea, are one off designs. Each project has new challenges and different client expectations. This is the reason each deconstruction/demolition job presents new challenges. Standardization is important to make the deconstruction process more efficient and also to maximize the reuse potential. Standardization of the fittings and of size of the finished panels is important to simplify installation and dismantling. Including features such as pad eyes embedded in the panel face for easy lifts and joints that can allow for easy connection and disconnection make recycling more feasible and more cost effective. By having modular standardized panels time and money could be saved on the installation and again when recycling.

Appendix A contains pictures taken from a test carried out on how to join INCA panels. A new concept might look something like diagram 7-2 in Appendix A. This new concept would allow for two completed panels to be joined by only welding, eliminating the need to fill with concrete, thereby saving time. Although this concept is just an idea, and has not been proven or tested, a solution like this could dramatically reduce installation time and allow for reuse of the panels afterwards.

4 REUSE Reusing the INCA panels is the most economically viable and environmentally sound method of recycling end of life concrete and steel structures. Prefabricated panels that could be easily installed and later dismantled maximize potential for reuse.

Reuse of concrete buildings, for example, is becoming more common since it’s more likely that a modern concrete building will come to the end of its life because no further use can be found for it rather than the concrete having failed due to age. If buildings need to be demolished, then it provides a potentially rich source of recycled aggregate for a range of applications. Recycled aggregate was estimated to account for almost a fifth of the UK’s aggregate supply in 2001 and is estimated to have grown each year since. /1/

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Unlike the building industry, the reuse potential in new marine construction is limited, as new systems and equipment installed should in general be new. Furthermore, the more complex the ship shape the less likely it is the INCA panels will be standardized, making reuse for the major part of the ship structure improbable.

If however, a suitable application is found for reuse of INCA panels onboard new construction, there is an opening in the DNV Rules for Classification of Ships for using second hand systems and equipment under special consideration. “If second hand equipment complies with applicable rules for the newbuilding, it may upon special consideration be installed on newbuildings, provided the owner has given a written acceptance.” /8/ The actual requirements for reuse to be possible and how the INCA panel integrity can be verified is a technical issue that would need to be resolved. It is unknown how well these INCA panels will hold up under various stresses and wear and tear they will experience while in operation.

Potential for reusing the INCA panels across business areas from maritime to land based building applications is also a possibility. This would pose many challenges however, as different building and structural codes will require very different designs thus not much potential for standardization.

4.1 Applications We have outlined that reuse potential in marine applications is possible but not straightforward in new construction, and we believe that reuse of INCA panels in the building industry is unlikely as building codes and structural requirements differ significantly. What we should take into consideration are alternative applications outside the maritime and building industries that take advantage of the panel properties. Since the strength rating of the panels are likely to be reduced as their integrity will be difficult to verify after their life in operation, other applications that are not ship or building specific have the most reuse potential. Marine applications

The best reuse potential for marine applications might be as local strengthening or overlays as deck support when temporarily transporting heavy loads, typically for offshore supply vessels. Another may be the actual deck structure in the accommodation areas if the panels’ integrity can be verified.

Alternative applications Considering other applications that are not ship specific, creative reuse of the panels could be as sea walls, fixed piers, levees, artificial reefs, flood defence systems and refrigeration boxes.

5 RECYCLING STEEL VERSUS INCA The majority of vessels today reach the end of their life on the beaches of the Indian subcontinent with yards such as Alang Beach in India and Chittagong in Bangladesh whom recycle the most tonnage each year. The main equipment used to break apart vessels includes cutting torches and winches. Operations are carried out on tidal flats with limited access for heavy machinery therefore making deconstruction of an INCA vessel challenging. Since





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Unlike the building industry, the reuse potential in new marine construction is limited, as new systems and equipment installed should in general be new. Furthermore, the more complex the ship shape the less likely it is the INCA panels will be standardized, making reuse for the major part of the ship structure improbable.

If however, a suitable application is found for reuse of INCA panels onboard new construction, there is an opening in the DNV Rules for Classification of Ships for using second hand systems and equipment under special consideration. “If second hand equipment complies with applicable rules for the newbuilding, it may upon special consideration be installed on newbuildings, provided the owner has given a written acceptance.” /8/ The actual requirements for reuse to be possible and how the INCA panel integrity can be verified is a technical issue that would need to be resolved. It is unknown how well these INCA panels will hold up under various stresses and wear and tear they will experience while in operation.

Potential for reusing the INCA panels across business areas from maritime to land based building applications is also a possibility. This would pose many challenges however, as different building and structural codes will require very different designs thus not much potential for standardization.

4.1 Applications We have outlined that reuse potential in marine applications is possible but not straightforward in new construction, and we believe that reuse of INCA panels in the building industry is unlikely as building codes and structural requirements differ significantly. What we should take into consideration are alternative applications outside the maritime and building industries that take advantage of the panel properties. Since the strength rating of the panels are likely to be reduced as their integrity will be difficult to verify after their life in operation, other applications that are not ship or building specific have the most reuse potential. • Marine applications

The best reuse potential for marine applications might be as local strengthening or overlays as deck support when temporarily transporting heavy loads, typically for offshore supply vessels. Another may be the actual deck structure in the accommodation areas if the panels’ integrity can be verified.

• Alternative applications Considering other applications that are not ship specific, creative reuse of the panels could be as sea walls, fixed piers, levees, artificial reefs, flood defence systems and refrigeration boxes.

5 RECYCLING STEEL VERSUS INCA The majority of vessels today reach the end of their life on the beaches of the Indian subcontinent with yards such as Alang Beach in India and Chittagong in Bangladesh whom recycle the most tonnage each year. The main equipment used to break apart vessels includes cutting torches and winches. Operations are carried out on tidal flats with limited access for heavy machinery therefore making deconstruction of an INCA vessel challenging. Since


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roughly 80% of the steel supply in Bangladesh comes from the recycling of scrap steel, recycling INCA vessels will not be nearly as attractive as more traditional steel vessels.

Crushing machines and large industrial equipment would need to be purchased in order to have the ability to recycle the INCA vessels. Hydraulic cutting machines and other fancy tools are not likely available in the majority of yards where ships are recycled today. Not to mention operating some types of large industrial equipment requires upgrading of power generation systems which can support such industrial equipment.

The majority of vessels recycled in 2009 were dry cargo, container, LPG’s, Car Carriers and a few tankers. /6/ The below diagram shows the number of days to recycle an INCA vessel as compared to a conventional steel vessel both for yards that employ the beaching method and yards that carry out pre-cleaning before dismantling alongside a dock. It is estimated that INCA vessels will take 50% more time to recycle regardless of which recycling method is employed. /5/

020406080

100120140160180

Beaching Method Pre-cleaning Alongside

Average Number of Days to Recycle a Vessel 100% Steel vs. 100% INCA

SteelINCA

/6/ /7/

5.1 Value of INCA Vessels Owners should be prepared to get less money for INCA vessels when selling to a cash buyer or recycling yard. We anticipate the value of the vessel will decrease exponentially proportionate to the amount of INCA construction in the vessel design. If reuse of INCA panels proves feasible and is economical, these could be sold. The cost however of reselling the INCA panels is not likely to be significant enough to make much of a profit. If separating the steel from the concrete for resale is the alternative, it is labour intensive and equipment for effectively breaking down INCA panels is limited. Below is an example with varying amounts of INCA used in the construction for three types of vessels. This table illustrates the decrease of value proportionate to the amount of INCA used in the vessel construction. For this illustration we make the assumption that INCA construction has zero value when recycled.

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Sale Price Vessels with INCA Construction Offshore supply

10 % INCA

Passenger 30 % INCA

Bulker 70 % INCA



Price decrease USD - Weight INCA (tons)

-$100,000 -$480,000 -$2,800,000

Sale Price (400 USD/ton)

$800,000 $1,120,000 $1,200,000

Assumed Lightship values are used in this table with varying amounts of INCA utilized in the construction. This table does not represent accurate price reduction. This table is only provided as an illustration given INCA with a value of zero.

6 DISMANTLING END OF LIFE INCA STRUCTURES Traditional methods for recycling an end of life vessel include cutting the vessel into manageable pieces and then smelting the steel into steel plates or rebar. Steel gets the most money per ton, from $150/LT during the slowest periods in history 2004-2008 up to $800/LT or more during record highs, /6/ it’s a more valuable resource than concrete which may only yield $13 per ton. . Demolition equipment for steel concrete structures ranges from hand-held tools to large plants. Concrete can be crushed, reinforcing steel removed, cleaned, graded and recycled for reuse in construction. The most basic methods of recycling concrete and steel structures are by using heavy machinery, i.e. wrecking ball attached to a crane or industrial size cutters. By distorting the steel sheets on both sides of the sandwich, the concrete will crack and separate from the steel. More advanced methods can also be employed such as hydrodemolition and hydraulic bursting. The best method to break apart a concrete and steel structure depends on the size and configuration of the structure which will vary depending on the demolition job.

If the panels could be easily separated from each other, the deconstruction process could be simplified. If standardized panels are to be demolished, the method for separating the materials would allow for improved efficiency. However if recycling facilities do not have the ability to process the INCA panels, they will need to be transported off site to a facility that can. Transporting panel’s offsite may be the only option for facilities that do not have the ability to break apart the materials; this could create logistical challenges.

6.1 Recycled Concrete Although not as profitable as recycled steel, recycled concrete is an increasingly popular material used in a variety of applications. By using a crushing machine that can be located on site, concrete can be crushed into various sizes. The most common application of concrete is as sub-base gravel for road construction. Other uses of recycled concrete include levies, breakwater, gravel for new construction projects, rip-rap for erosion control, landscaping stone, Wire gabions





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Sale Price Vessels with INCA Construction Offshore supply

10 % INCA

Passenger 30 % INCA

Bulker 70 % INCA



Price decrease USD - Weight INCA (tons)

-$100,000 -$480,000 -$2,800,000

Sale Price (400 USD/ton)

$800,000 $1,120,000 $1,200,000

Assumed Lightship values are used in this table with varying amounts of INCA utilized in the construction. This table does not represent accurate price reduction. This table is only provided as an illustration given INCA with a value of zero.

6 DISMANTLING END OF LIFE INCA STRUCTURES Traditional methods for recycling an end of life vessel include cutting the vessel into manageable pieces and then smelting the steel into steel plates or rebar. Steel gets the most money per ton, from $150/LT during the slowest periods in history 2004-2008 up to $800/LT or more during record highs, /6/ it’s a more valuable resource than concrete which may only yield $13 per ton. . Demolition equipment for steel concrete structures ranges from hand-held tools to large plants. Concrete can be crushed, reinforcing steel removed, cleaned, graded and recycled for reuse in construction. The most basic methods of recycling concrete and steel structures are by using heavy machinery, i.e. wrecking ball attached to a crane or industrial size cutters. By distorting the steel sheets on both sides of the sandwich, the concrete will crack and separate from the steel. More advanced methods can also be employed such as hydrodemolition and hydraulic bursting. The best method to break apart a concrete and steel structure depends on the size and configuration of the structure which will vary depending on the demolition job.

If the panels could be easily separated from each other, the deconstruction process could be simplified. If standardized panels are to be demolished, the method for separating the materials would allow for improved efficiency. However if recycling facilities do not have the ability to process the INCA panels, they will need to be transported off site to a facility that can. Transporting panel’s offsite may be the only option for facilities that do not have the ability to break apart the materials; this could create logistical challenges.

6.1 Recycled Concrete Although not as profitable as recycled steel, recycled concrete is an increasingly popular material used in a variety of applications. By using a crushing machine that can be located on site, concrete can be crushed into various sizes. The most common application of concrete is as sub-base gravel for road construction. Other uses of recycled concrete include levies, breakwater, gravel for new construction projects, rip-rap for erosion control, landscaping stone, Wire gabions


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(cages filled with crushed concrete for retaining walls) and if free of contaminants, crushed recycled concrete can also be used as the dry aggregate for brand new concrete.

6.2 Hazardous Material Testing Testing for hazardous materials in the INCA structure will be required before reuse or final disposal. This requirement will be automatically fulfilled if a vessel already has an Inventory of Hazardous Materials as per IMO’s newly adopted Ship Recycling Convention (SR/CONF/45). Concrete in itself is not considered a hazardous material, but without knowing the exact composition of the lightweight concrete for the INCA application, assumptions can’t be made. Other materials may also end up as part of the final INCA sandwich such as an adhesive epoxy material to bond the steel sheets to the concrete. In addition, various coatings may be applied during operational periods which could contain heavy metals such as TBT or PCB thereby necessitating material testing before recycling.

7 CONCLUSION Recycling an INCA vessel could take twice the amount of time to recycle as vessels constructed of only steel and significantly reduce the sale value. It is therefore advantageous to find reuse applications before recycling. Designing INCA technology into panels with standardized sizes, fittings and joining methods will allow for easier dismantling and ease of transport for installation in other reuse applications. Standardization will however limit these reuse applications to areas where standard modules can be used. If reusing the panels is no longer an option, the raw materials can be broken down and sold. Taking into account reuse applications at the design stage may be the key to INCA’s success.

8 REFERENCES

/1/

Sustainable Concrete

http://www.sustainableconcrete.org.uk/main.asp?page=127

/2/

Wikipedia

http://en.wikipedia.org/wiki/Semi-trailer_truck

/3/ The Concrete Society email correspondence 13.01.2010

/4/ INCA Final Report Phase III Aker Yards

/5/ Fosen Gjenvinning AS

/6/ GMS Anil Sharma “The collapse of scrap steel prices: an analysis of an uncertain climate” Lloyd’s List Events Ship Recycling Conference London 18 Feb 2009

/7/ Mærsk Ship Management Tom Peter Blankenstjin “Ensuring capacity at global ship recycling yards conforming to environmental and safety standards” Lloyd’s List Events Ship Recycling Conference London 18 Feb 2009

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Test welding and casting of joints 8-1 /5/

New idea (not proven or tested) for a standardized way of joining panels allowing for reuse and easy welding or cutting 8-2

Weld seam

Pad eye

Void Space for cabling

Standard End Fitting





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/8/ DNV Rules for Classification of Ships, January 2010, Pt.1 Ch.1 Sec.2 A 700 Installation of systems and equipment

- o0o -

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Test welding and casting of joints 8-1 /5/

New idea (not proven or tested) for a standardized way of joining panels allowing for reuse and easy welding or cutting 8-2

Weld seam

Pad eye

Void Space for cabling

Standard End Fitting

Appendix A

Joining Panels


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Documents

Assessment of the INCA Steel-concrete- steel sandwich technology