Structural Design Calculation Sample

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UPD-BC-G4-CS-DR-6003DESIGN OF JACKET STRAND JACK SUPPORT

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Document type: System/Subsystem :Discipline : Error! Unknown

document property name.

Revision : D1Rev. Date :

Contractor Job No : 365 Contract No : 4600006595 Page 1 of 17

HESS (INDONESIA-PANGKAH) LTD

UJUNG PANGKAH DEVELOPMENT

OFFSHORE PHASE II

(WHP-B EPCC)

Strandjack Bracket Design For Jacket and Topside

D1 22-July-09 Issued For Approval DBES HKM MARK

A 18-May-09 Issued for Review DBES HKM MARK

By Check App By DateRev. Date Description Contractor Approval Company Approval

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TABLE OF CONTENTS

CHAPTER PAGE

1.0 INTRODUCTION 4

2.0 SCOPE OF WORK 4

3.0 DESIGN SPECIFICATION 4

4.0 DESIGN APPROACH 5

5.0 DESIGN OF STRAND JACK SUPPORT 6

6.0 MANUAL DESIGN VERIFICATION 11

APPENDICES

APPENDIX – A STRAND JACK SPECIFICATION

APPENDIX – B WEIGHT CONTROL SUMMARY & ESTIMATION OF REQUIRED PULL

FORCE

APPENDIX – C STRAND JACK SUPPORT DRAWINGS

APPENDIX – D FEM INPUT & OUTPUT FILES

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1.0 INTRODUCTION

This document presents the analysis and structural design of strand jack support for loading out

WHP-B Jacket Structure at Bakrie Fabrication Yard. The WHP-B Jacket Structure will be skidded out

from its fabrication position onto the transportation barge using hydraulic strand jack system. These

strand jacks will be mounted on the existing skid frame temporary support structures that support the

entire weight of the WHP-B Jacket Structure.

For typical strand jack specification and details, refer to Appendix – A.

2.0 SCOPE OF WORK

Design checks are limited to global and local strength of the strand jack support and its attachments

where the strand jack supports are to be mounted and maximum pull forces are supported.

Detailed skid frame, tie back system and jacket member structural integrity strength checks are

beyond the scope of this report.

3.0 DESIGN SPECIFICATION

(1) API RP 2A 21st Edition – Recommended Practice fo Planning, Designing and Constructing

Fixed Offshore Platforms (WSD) by American Petroleum Institute

(2) AISC Manual of Steel Construction (Allowable Stress Design) – by American Institute of Steel

Construction

Generally, increases in basic allowable stresses ARE NOT allowed for load out condition.

The following basic and combined allowable stressed criteria are adopted (Fy is material yield

strength):

Axial Tension, Fat = 0.60Fy

Axial Compression, Fac = Max 0.60Fy

Bending Stress, Fby = 0.66Fy

Shear Stress, Fv = 0.40Fy

Von Mises Stress, Fvm = 0.80Fy for combined axial, bending and shear stresses

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4.0 DESIGN APPROACH

(a) Strand Jack Support Arrangement

The Strand Jack Support System are to be arranged in such the manner that the induced forces due to

skidding operation will be adequately transferred to the existing temporary support structures and skid

frame system.

(b) Design Loadings / Assumptions

The following design loadings are considered:

Weight Control Report No: UPD-BC-W2-WC-RP-0002, Rev 3

Factored Weight = 403.7MT

Assumed vertical static load on support can = 73MT per leg

Assumed coefficient of friction = 20% during initial skidding stage,

Nos of Strand jack, N = 2 Nos

Estimated pull force per jack = 43.4MT / jack

(Refer to Appendix – B for Weight Control Summary & Estimation of Required Pull

Capacity)

(c) Analysis and Design Methodology

Analysis and design are performed using SAP2000 Finite Element Software (FEM) and verified by

manual calculation.

(d) Materials

All plate materials shall be of ASTM 36 (Min. Yield Strength = 248MPa) or equivalent, unless

specified otherwise. All welding shall comply with AWS1.1 and shall be of full penetration welds,

unless specified otherwise.

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5.0 DESIGN OF STRAND JACK SUPPORT

5.1 GENERAL ARRANGEMENT

The Strand Jack Support System are to be arranged in such the manner that the induced forces due to

skidding operation will be adequately transferred to the existing temporary support structures and skid

frame system. It shall be ensured that the all the strands are clash-free with jacket or other temporary

structures. For detail strand jack support drawings, refer to Appendix – C.

SAP2000 Ver.10 software is used for structural modelling and analysis of the strand jack support

system. The temporary support can and strand jack supports are modelled as finite element (shell

element) with appropriate restraint conditions (fixed-supported).

The following presents the isometric view of the simplified structural model of strand jack support

system:

Temporary Support Can Dia1181x32thk

Strand Jack Support (Typ)

Exist'g Bottom FLG/Ring PL25

Top FLG/Ring Plate PL25

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5.2 ELEMENT PROPERTIES

The following table summarizes the element and material properties assumed in the analysis:

Material

S/N Description Yield Strength

[mm] [Mpa]

1 Strand Jack Support Shell PL25 25 248

2 Support Can Dia1181mm Shell PL32 32 248

3 Exist'g Bottom Flange Plate Shell PL25 25 248

4 Additional Top Flange/Stiff Plate Shell PL25 25 248

Shell GrpShell Thk

Element Type

5.3 LOAD COMBINATION

The following table summarizes all the basic load cases, associated load factors and combined load

condition:

Load

Case 1000 -

Jacket Weight = 73MT* per leg STA1 1.00

Stand Jack Pull Force = 44MT per leg PUL2 1.00

Note *Assumed max static vertical load on each leg for design purpose only.

Combined Load ConditionBasic Load Case

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5.4 ANALYSIS RESULT

The following presents the Finite Element Model Analysis results – Max Von Mises Stresses

(Combined Axial, bending, and shear stresses) of the proposed strand jack design:

(a) Von Mises Stress – Overall

(b) Von Mises Stress – Support Can (32mm thk Pipe Wall)

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(c) Von Mises Stress – Strand Jack Support Bottom Flange / Skid Frame Top Flange Plate

(d) Von Mises Stress – Strand Jack Support Top Flange Plate (with additional flange plate)

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Findings

Generally, the overall stress level (Von Mises Stress) is less than 105MPa.

High stress zones (i.e. 186MPa) are limited to areas such as the strand jack bearing surface, mainly

attributed to modelling technique using point load at strand jack supporting joint locations.

Stress levels on Temporary Support Can are also less than 90MPa (at interface between strand jack

support and support can).

For detailed FEM Input & Output Files, refer to Appendix – D.

Summary

Conservatively, max Von Mises Stress is found to be 186.7MPa, which is within the allowable stress

(0.80Fy = 0.80 x 248 = 198MPa) as specified in Section 3.0.

Therefore, the strand jack design appears to be structurally fit.

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6.0 MANUAL DESIGN VERIFICATION

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APPENDIX – A

STRAND JACK SPECIFICATION

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APPENDIX – B

WEIGHT CONTROL SUMMARYAND

ESTIMATION OF REQUIRED PULL FORCE

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APPENDIX – C

STRAND JACK SUPPORT DRAWINGS

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APPENDIX – D

FEM INPUT & OUTPUT FILE

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Structural Design Calculation Sample