KUWAIT OIL COMPANY (K.S.C.)

STANDARDS PUBLICATION

KOC RECOMMENDED PRACTICE

FOR

BLAST RESISTANT DESIGN

OF BUILDINGS

I STANDARDS TEAM I

KUWAIT OIL COMPANY (K.S.C.)

STANDARDS PUBLICATION

KOC RECOMMENDED PRACTICE

FOR

BLAST RESISTANT DESIGN OF BUILDINGS

TABLE OF CONTENTS

FOREWORD

SCOPE

APPLICATION

TERMINOLOGY 3.1 Definitions 3.2 Abbreviations

REFERENCE STANDARDS, CODES AND SPECIFICA' 4.1 Conflicts 4.2 List of Standards and Codes

ENVIRONMENTAL CONDITIONS

HEALTH, SAFETY AND ENVIRONMENT

BASIC CONSIDERATIONS 7.1 General Objectives 7.2 Siting Requirements 7.3 Blast Protection Options 7.4 Blast Waves 7.5 Blast Wave Parameters

DETERMINATION OF DESIGN LOADS 8.1 Overpressures 8.2 Blast Loadings

GENERAL STRUCTURAL SYSTEMS 9.1 Technical Considerations 9.2 Common Systems Used 9.3 Resommended System

STRUCTURAL DESIGN 10.1 Basic Criteria 10.2 Dynamic Response 10.3 Dynamic Design Strength 10.4 Deformation Limits

METHODS OF DYNAMIC ANALYSIS 11.1 General Objectives 11.2 Calculation of Mass and Inertia 11.3 Basic Methods

Page No.

DESIGN PROCEDURES 12.1 General Design Concepts 12.2 Basic Calculation Methods 12.3 Structural Applications

REINFORCED CONCRETE DESIGN 13.1 General 13.2 Design Principles 13.3 Materials t o be Used 13.4 Supplementary Requirements 13.5 Failure Mechanism

STEEL DESIGN 14.1 General 14.2 Design Principles 14.3 Materials to be Used 14.4 Supplementary Requirements 14.5 Failure Mechanism

FOU N DATlON DESIGN

ARCHITECTURAL CONSIDERATIONS 16.1 General Criteria 16.2 External Doors 16.3 Windows 16.4 Uti l i ty Openings 16.5 In~erior Design 16.6 Exterior Design 16.7 Services Connections 16.8 Staffing Levels

EVALU.ATION AND U PRGADING OF EXISTING BUILDINGS 17.1 General Evaluation Strategies 17.2 Upgrade Options

QUALITY ASSU RAN CE

DOCUMENTATION 19.1 General 19.2 Deliverables

APPENDICES Appendix - I: Blast Wave Reflection Coefficient vs.

. .

Angle of Incidence Appendix - 11: General Blast Loading for A Rectangular Building 57 Appendix - Ill: Typical Graphical Solution Chart for

Elasto-Plastic SDOF System 58 Appendix - IV: Nomenclatures Used 5S60

ACKNOWLEDGEMENT 61

FOREWORD

This document "KOC Recommended Practice for Blast Resistant Design of Buildings" (KOC-C-030) is intended to address the basic technical requirements of Control room b~i ld ings / houses and other land based facility buildings subject to potential blast risks, where the consequences of accidental vapour cloud explosions or sudden emissions due to process upsets are already predicted and identified as the probable source; and accordingly the building(s1 are sited at distance(s) to reduce the disastrous blast effects to the minimum.

This Recommended Practice (RP) has been approved by Standards Team in consultation with the Standards Technical Committee for consistent use throughout the corporate engineering and operational functions of Kuwait Oil Company (K.S.C). This RP sets out to achieve the following objectives: a. To recommend the general guidelines of blast resistant requirements for design,

and construction of buildings with a view to provide safe, reliable and economic systems to minimize the detrimental btast effects on personnel and equipment.

b. To provide various design recommendations and suitable technical inputs in order to develop the intended blast resilient systems for new or existing buildings with their inherent dynamic characteristics to endure blast effects.

c. To establish relevant design concepts for forming the basis of a detailed design package and project specifications to be prepared prior to construction tender.

d. To describe minimum design aspects and technical requirements in order to monitor compliance of material, construction and workmanship with a contract.

Feedback as well as any comments or suggestions from the application of this RP derived at any stage of conceptual design, engineering, construction, and maintenance are encouraged and should be directed to:

The Team Leader Standards (Chairman, Standards Technical Committee) Industrial Services Group, KOC P.O. Box - 9758, Ahmadi 61 0 0 8 State of Kuwait

Task Force Responsible for this RP

The preparation of this RP has been entrusted by the Standards Technical Committee (STC) to the Task Force No. (TF-CI08) comprising of the following members:

Mr. S. Kumar Standards Team TF Leader /Author Tel. No. 61407 Mrs. Sana'a Al-Talha Design Team Member Tel. No. 61352 Mr. Mubarak Al-khmed Major Proj. Team Ill Member TeI. No. 61 249 Mr. Rafiq Khan Gen. Projects Member Tel. No. 61 356 Mr. Barun Baruak Safety Team Member Tef. No. 71408 Mr. Meshlej Al-Khaldi Constr. Team Member Tel. No. 61 668

SCOPE

This Recommended Practice (RP) describes the general guidance on the blast resistant design of Control room buildings 1 houses as well as other facility buildings subject to potential blast loading, and provides the minimum technical requirements pertaining to structural and architectural aspects for the blast resilient buildings in KOC Pfants within Kuwait.

However, the facility buildings such as Pump houses, Compressor house, MCCs, Substations and other structures, should be designed to be blast resistant only, when decided by KOC as special cases, on recommendations from th.2 Quantitative Risk Assessment studies.

This RP covers the basic aspects of structural design of any new buildings in reinforced concrete for blast resistance; and necessary upgrading and strengthening of existing buildings exposed to blast loading, in case of any accidental vapour cloud explosions or sudden emissions due to process upsets with a view to minimize its detrimental effects on equipment and personnel.

The content of this RP is intended to be adopted as a design guide to meet the minimum KOC requirements; and should form the basis of a detailed design specification to be prepared prior to construction tender.

APPLICATION

The design, materials and construction of the blast resistant buildings should conform to the minimum requirements of this RP and the reference standards and codes mentioned herein.

Any exceptions or deviations from this RP, along with their merits and justifications, shall be brought to the attention of KOC Controlling Team for their review, consideration and amendment by Standards Team (if required).

Compliance with this RP does not of itself confer immunity from legal or statutory obligations.

TERMINOLOGY

For the purposes of this RP, the following definitions shall apply.

3.1 . I Angle O F Incidence (a)

The angle between the direction of the blast wave movement and a flat surface.

DOC. NO. KOC-C-030 Page 7 of 62

Blast Load

A dynamic load generated by violent transient high-energy waveform out of explosion of flammable material (liquids or gases) at suitable conditions of pressure or temperature.

Blast wave

A transient change in the gas density, pressure, and velocity of the air surrounding an explosion.

Blast Resistant Buildings

Buildings or other structures capable of withstanding the effects of an accidental plant explosion to the minimum damages in their resistance, provided that this does not result in collapse, danger to personnel or render control equipment inoperable.

Conventional Loads

Loads normally considered in structural design such as Dead Loads (DL), Live Loads (LL) and Wind Loads (WL).

Designer

Person 3r persons from Contractor or from any Consulting firm approved by KOC, vvho are undertaking the responsibilities of the actual design and detailed specifications, related to the blast resistant buildings.

Ductility Ratio (p)

A measure of the energy absorbing capacity of a structural element; and computed by dividing the element's maximum deformation I displacement by the vield deformation I displacement at the elastic limit.

Dynamic Increase Factor (DIF)

The ratio of dynamic to static strength which is used to compute the effect of a rapidly applied load to the strength of a structural element.

Impulse

The integrated area under the overpressure time curve.

Incident Side-On Overpressure

Initial peak pressure rise, above ambient (atmospheric pressure), produced by a shock wave or pressure wave as felt by a flat surface oriented parallel to the direction of wave propagation.

Incipient Failure

The level of deformation where collapse can be expected to occur.

Overpressure

Pressure rise above ambient (atmospheric pressure) produced by a shock wave or pressure wave.

Passive Fire Protection

Any fire protection measures such as structural barriers or fixed systems or special coatings/coverings that do not require manual or actuation for them to function to their design intent.

Positive Phase

The portion of the pressure time history where the pressure is above the ambient pressure.

Pressurs Wave

A blast wave that produces a gradual rise in pressure.

Quantitative Risk Assessment (QRA)

A set of methods used in process plants for identifying the potential hazards, assessing the probability of risks involved and consequences of incidents which can cause adverse effects on plant, production, critical equipment and human lives by fire, explosion, damages or deaths; and establishing a road map to eliminate such risks with a view t o avoid any possible recurrence.

Reflected Overpressure

The rise in pressure produced by a shock wave or pressure wave as felt by a flat surface oriented perpendicular to the direction of wave propagation.

Shockwave

A blast wave that produces a near instantaneous rise in pressure.

DOC. NO. KOC-C-030 REV.l -

3.1.19 Strain Hardening

The observed increase in strength as a material is deformed well into the plastic range.

3.1.20 Ultimate Capacity

The load applied to a structural element as the final plastic hinge, or collapse mechanism, is formed.

Abbreviations

AlSC ASCE FEM HSE KOC MDOF PFP QRA SDOF VCE

American Institute of Steel Construction American Society of Civil Engineers Finite Element Method Health, Safety and Environment Kuwait Oil Company (K.S.C) Multi Degree of Freedom Passive Fire Protection Quantitative Risk Assessment Single Degree of Freedom Vapour Cloud Explosion

REFERENCE STANDARDS. CODES AND SPEClFlCATlONS

Conflicts

In the event of conflicts between this RP and the standards / codes referenced herein, or other contractual requirements, the most stringent requirement shall apply. In case further clarifications are required, the subject shall be brought to the attention of KOC Controlling Team.

List of Standards and Codes

The latest edition of the following standards, codes and specifications shall apply:

Nationa / International Standards

ACI 318Ml Building Code Requirements for Structural Concrete ACI 318RM

ACI SP 66 Details and Detailing of Concrete Reinforcement

AlSC Specification for Structural Steel Buildings - Allowable Stress Design and Plastic Design

AlSC Manual of Steel Construction - Working Stress Design

DOC. NO. KOC-C-030 Page 10 of 62

AlSC Manual of Steel Construction - Load and Resistance Factor Design (Vol. I)

AlSC Manual of Steel Construction (Vol. II) - Connections API RP 752 Management of Hazards Associated with Location of

Process Plant Buildings CMA Manager's Guide

ASCE 7 Minimum Design Loads for Buildings and Other Structures

ASCE Manual 41 Plastic Design in Steel: A Guide and Commentary

ASCE Publication Design of Blast Resistant Buildings in Petrochemical Facilities

ASTM 1136136M Specification for Carbon Structural Steel

ASTM A325

ASTM A490

ASTM A61 5

ASTM A653

ASTM A706

ASTM (31 50

ASTM F1554

AWS D1.l

BS 449 Part 2

Specification for Structural Bolts, Steel, Heat-Treated, 120 / 105 ksi Minimum Tensile Strength

Specification for Heat-Treated Steel Structural Bolts, 150 ksi Minimum Tensile Strength

Specification for Deformed and Plain Billet-Steel Bars for Concrete Reinforcements

Specification for Steel Sheet, Zinc-Coated (Galvanized) or Zinc-Iron Alloy-Coated {Galvannealed) by the Hot-Dip Process

Specification for Low-Alloy Steel Deformed and Plain Bars for Concrete Reinforcement

Specification of Portland Cement

Specification for Anchor Bolts, Steel, 36, 55, and 105 ksi Yield Strength

Structural Welding Society - Steel

Specification for The Use of Structural Steel in Building: Part 2: Metric Units

IS0 Metric Precision Hexagonal Bolts, Screws and Nuts - Specification (Metric Units)

Specification for Sulfate-Resisting Portland Cement

29 CFR 191 0.1 1 9 29 Code of Federal Regulation (CFR) 191 0.1 1 9 Process Safety Management of Highly Hazardous Chemicals

TM-5-1300 Structures to Resist the Effects of Accidental Explosions

UBC (Vd . 1-3) Uniform Building Code Vol. 1 - Administrative Fire and Life Safety, and Field

Inspection Provisions Vol. 2 - Structural Engineering Design Provisions Vol. 3 - Material, Testing and Installation standards

4.2.2 KOC Standards

KOC-C-30 1 KOC Standard for Basic Civil Engineering Design Data

KOC-C-302 KOC Recommended Practice for Engineering Design Basis of Civil and Structural Work

KOC-C-006 KOC Standard for Concrete Work - Materials and Construction

KOC-C-307 KOC Standard for Structural Steel Work - Materials, Fabrication and Erection

BS 5628

BS 5950 Parts 2&8

BS 6399 Part 1

BS 8004

BS 81 1 3 Part 1

BS CP 3 Part 2

Specification for Carbon Steel Bars for the Reinforcement of Concrete

Code of Practice for Use of Masonry

Structural Use of Steel Work in Building: Part 2: Specification for Materials, Fabrication and

Erection: Hot Rolled Sections Part 8: Code of Practice for Fire Resistant Design

Loading for Buildings - Code of Practice for Dead and Imposed Loads

Code of Practice for Foundations

Structural Use of Concrete - Part 1 : Code of Practice for Design and Construction

Specification for Scheduling, Dimensioning, Bending and Cutting of Reinforcements for Concrete

Code of Basic Data for the Design of Buildings - Chapter V: Loading Part 2: Wind Loads

Hot Rolled Products of Non-Alloy Structural Steels - Technical Delivery Conditions

KOC-C-027 KOC Standard for Materials and Workmanship - Fire Proofing of Structural Steel Work

KOC-G-002 KOC Standard for Hazardous Area Classification

KOC-G-007 KOC Standard for Basic Design Data

KOC Fi-e & Safety Regulations (Latest)

ENVIRONMENTAL CONDITIONS

Refer to KOC Standard for "Basic Design Data" (KOC-G-007), which provides the detailed design information regarding the environmental, site and utility supply conditions prevailing throughout the KOC facilities.

HEALTH, SAFETY AND ENVIRONMENT

The engineering design should meet all the applicable Kuwait EPA Regulations and should conform to the KOC Health and Environment (H&E) guidelines with a view to protecting its personnel and surrounding environment.

All relevant safety requirements of KOC Fire & Safety Regulations and KOC Health, Safety and Environment Management System (HSEMS) procedures and manuals as applicable, shall be adhered to by the designer / contractor, while dasigning the blast resistant buildings in KOC areas.

BASIC CONSIDERATIONS

General Objectives

Control room buildings / houses and other functional buildings housing personnel and critical control equipment, 'near hydrocarbon processing plants :;hould be designed with a level of blast resistance, wherever the potential explosions due to sudden process upsets or accidental vapour cloud releases are predicted by blast/explosion impact assessment studies as a part of Quantitative Risk Assessment (QRA) after evaluating the nature, magnitude and consequences of these hazards.

The basic intent for blast resistant design of buildings / facilities is briefly summarized as below:

a. to protect human lives and critical control systems for process and operation with a desired level of safety.

b. to permit an orderly and controlled shutdown after accident, preventing cascading events due to loss of control over critical systems.

c. to organize prompt recovery after accident, minimizing financial losses.

d. to perform other critical services during the incidents.

Siting Requirements

Normally based on the criticality of the functions and expected occupancy of buildings, the following requirements for the blast resistant design should be considered when the control room house or building(s):

a. serves one major unit 1 plant that processes large volumes of volatile and flammable liquids and gases; and/or

b. is located closer to the unit 1 plant than the recommended minimum spscing required.

If a critical building is sited far enough {usually 60 m and above) from a potential blast source, it may not need increased blast resistance.

But if a suitable remote location is unavailable, or proximity of the building to the unit / plant is important for operational reasons, then the choice should be to provide a higher level of blast resistance than a normal building designed for conventional loads.

Generally, buildings designed structurally for conventional loads can be sited in areas where the peak side-on overpressure is less than 1.0 psi (6.9 kPa) or the side-on impuise is less than 30 psi-ms (207 kPa-ms).

When siting buildings the following requirements should be considered so that the resulting blast effects are minimized:

Buildings should be oriented such that the short side faces the most probable explosion source.

Buildings housing personnel not required for actual operation of the unlt should be sited as far away as possible; and the staff level should be kept to the minimum.

Buildings should be sited away from areas of congestion and confinement as these may contribute to the severity of the explosion.

Buildings should not be sited downhill from potential release sources of heavier than air materials.

BuAdings should not be sited in prevailing downwind direction from potential release sources.

Buildings should be made above the surrounding ground level with an elevation so as to avoid any entry of spilled hydrocarbon and pool fire.

-I__- - I DOC. NO. KOC-C-030 Page 14 of 62 Blast Protection Options

7.3.1 Blast protection options will depend on the inherent risk factors from the probable hazards in the adjacent and nearby processing operations; and the appropriate levels of safety to be provided for a given blast load.

7.3.2 Blast resistant design of buildings / facilities that can absorb the blast energy with tolerable consequences should be considered with the options as follows:

a. Conventional building with appropriate modifications as required.

b. New building / structure designed to resist the specified blast load or strengthened fully (if existing).

I c. Reduce building occupancy and functions. d. Consider localized impacts from flying debris.

7.3.3 Further existing buildings which might not be feasible to relocate, should consider the following options to increase their blast capacity as below:

a. Enhance the blast resistance capacity of structures / buildings by

i, adding an external blast resistant reinforced concrete shell.

ii. erecting an external structural barrier (steel or concrete) wall on the most vulnerable sides of the building.

iii. strengthening or replacing critical 'weak link' structural component in the existing building.

I b. Minimizing the hazards associated with windows by i. placing plastic film on the window glasses to reduce flying

fragments.

. .

11 . replacing ordinary glass with tempered glass, polycarbonate sheets or laminated glass which consists of two or more plies of heat treated strengthened glass.

iii. reducing the span width of the open glass with addition of new struts and mullions.

c. Improving conditions o f doors by

i. replacing w i th blast resistant doors.

i i designing statically for inward and outward pressure all the doors, their frames and anchors for external blast resistant walls.

Blast Waves

In the event of a Vapour Cloud Explosion (VCE) followed by fire in a plant, any control room building I house or other facility buildings can be damaged, not by fire itself, but by:

a. overpressure resulting from the ignition and explosion of flammable material that has escaped into the atmosphere, or

b. overpressure or flying components f rom runway reactions.

For blast resistant design, the most significant feature when a VCE occurs is the sudden release of energy t o the atmosphere which results in a pressure transient, or blast wave that rises almost instantaneously over normal pressure t o the overpressure condition; and propagates outward in all directions f rom the source at supersonic or sonic speed in a very short duration (expressed in milliseconds).

This shock wave intensity decays w i th distance and time, and the m a g n i t ~ d e and shape depends on the nature of energy release. The incident side-on overpressure (P,,) attaining t o a peak value then decays rapidly, followed by a period of negative pressure.

I f the shock wave impinges on a rigid surface, such as wall, the wave propagation being obstructed reflects from the wall causing a rapid increase in pressure against the wall, which is much greater than the overpressure. This re'lected overpressure (P,) wi l l be magnified by the reflection co- efficient (C,) and' usually higher by factor o f f rom 2.0 t o 2.5, for the range of peak overpressure used for blast resistant design. Refer t o Fig.1 of Appendix4 for details.

The shock wave wil l also generate drag pressure onto the building, which is due t o air movement associated wi th the shock front moving a t high velocity. This velocity is generally assumed t o be same as the shock front velocity. The drag forces produced by this wind in i ts path should be combined algebraically w i th peak overpressure forces.

The magnitude of the blast overpressure at a building should be a function of the following:

a. Size of the flammable vapour cloud.

b. Material of the cloud.

c. Level of equipment and piping congestion in the vapour cloud.

d. Area of confinement for the vapour cloud.

e. Distance of the building from the Vapour Cloud Explosion.

Blast Wave Parameters

The principal parameters of the blast wave should be specified to define the requirec blast loading for a building's components as below:

a. Peak side-on-positive overpressure Pa0, positive phase duration, t, and the corresponding positive impulse, I,.

b. Peak side-on-negative overpressure (suction), Pc,- negative phase duration, t,- and the associated negative impulse, lo- .

In addition to peak overpressure, duration, and impulse, other blast wave parameters should be considered to determine the blast loads for a structure as follows:

a. Peak Reflected Pressure (Pr)

b. Peak Dynamic (Blast Wind) Pressure (qo)

c. Shock Front Velocity (U)

d. Blast Wave Length (Lw)

These secondary parameters above can usually be determined from the primary blast wave parameters as described in ASCE publication "Design of Blast Resistant Buildings in Petrochemical Facilities" referenced in clause 4.2.1 of this RP.

Page 17 of 62

DETERMINATION OF DESIGN LOADS

The Designer should specify the actual site specific blast loads in consultation with KOC to design control room houses and other facility buirdings as follows:

a. by a simple blanket statement as "All buildings shall be designed for a peak reflected overpressure X psi (kPa), a peak side-on overpressure of Y xi (kPa), and a duration of Z milliseconds"; or

b. by providing overpressures and durations based on the distance between the structure and a potential source, where the distances are given in stepped blocks or a continuous function in order to determine design loads on the appropriate distance.

Overpressures should be determined at the point of the structure closest to the source and then applied to the entire structure. If the structure is large, the average overpressure on the surface or the overpressure at the centroid of the surface may be used.

Normally a building should be designed considering the potential blast wave from the horizontal direction according to QRA, but not from all directions simultaneously.

The crkeria commonly used for design should be at least two (2) blast overpressures for buildings spaced 30 m (1 0 0 f t) from a vapour cloud explosicn (VCE) hazard as follows:

a. High pressure, short duration, triangular shock loading: Side-on overpressure of 1 0 psi (69 kPa) with a duration of 20 milliseconds (ms) .

b. Low pressure, long duration, triangular loading: Side-on overpressure of 3 psi (21 kPa) with a duration of 1 00 milliseconds (ms).

Generally, blast loadsloverpressures are specific to processes and sites; and the greater the spacing from the explosion source, the lesser the overpressure and impulse, but the longer the duration of the blast loading.

Using ASCE recommendations as guidance for structural design, the blast loads to buildings spaced from 3 0 m to 60 m (100 f i to 200 f t) are recommended in the range of I -5 psi to 15 psi (1 0 kPa to 103 kPa) side-on overpressure with positive phase duration varying from 20 ms to 200 ms.

DOC. NO. KOGC-030 Page 18 of 62 REV.1

8.2 Blast Loadinqs

8.2.1 Based on the owner / KOC specified side-on overpressure and duration to design a blast resistant building, the designer shall determine the blast loads from the free field blast overpressure for various structural components of the building such as wall, roof, frame etc. for a closed rectangular box- shaped building as given below. Refer to Figure 2, Appendix - I 1 of this RP for details.

8.2.2 Front VJall Loading

The front walls facing the blast source will experience the reflected overpressure ( PI) much more than the incident side-on overpressure; and the amplification of the reflected blast pressure depends the angle of incidence (a), and on the rise-time (tr) of the side-on overpressure pulse.

For design purposes, the normal shock reflection conditions at a =Or and t, =O should be assumed, unless otherwise stated by the specified design blast scenario.

However, cases shall also be considered where oblique reflection from an angle of about 30 to 60 may be more critical to the overall building as the full reflected overpressure could load two adjacent sides of the building.

8.2.3 Side Walls Loading

a. Side walls will experience less blast loading than the front wall, due to lack of overpressure reflection and to decay of the blast wave with distance from the blast source.

b. Tke peak side-on overpressure should be decreased by a reduction factor (C,) as given in Figure 3 of Appendix II, as it varies with both time and distance when traveling along the building length. Values of Ce will depend on the length of the structural element, L,, in the direction of the traveling blast wave.

c. If the blast wave is traveling perpendicular to the span, then it should be considered on a nominal unit width of the element.

8.2.4 Roof Loading

a. Normally for a building with a flat roof (slope < lo0) , reflection should not be considered, as it does not occur when the blast wave travels horizontally.

DOC. NO. KOC-C-030 Page 19 o f 62 REV.1 -

b. However for roof loading, the side-on overpressure (pJ shall be combined w i th the dynamic wind pressure (qo), the same as the side walls; and the dynamic wind force on the roof acts in the opposite direction to the overpressure (upward).

c. Consideration should also be given t o variation of the blast wave w i th distance and t ime as it travels across a roof element, and the resulting load shall depend on the ratio of blast wave length to the span of the roof element and on i ts orientation relative to the direction of the blast wave.

Rear Wsll Loading

a. Rear wall loading shall be used only t o determine the net overall frame loading.

b. Generally rear wall loading shall be ignored as it is opposite t o the direction of front wall load and reduces the overall lateral blast force.

Frame Loading

a. The building frame system shall also experience the diffraction loading which is the net loading on the front and rear walls considering the t ime phasing.

b. During the travel t ime of blast wave from the front to the back of the building, the structural framing system shall be subjected t o the large lateral unbalanced pressure on the front wall.

Negative Pressure and Rebound Loading

The building components will also experience negative blast load, o p ~ o s i t e in direction to the primary blast load effects due to the suction phase (negative) of the blast wave, together w i th the rebound of the structural components f rom the inertial effects of the ovsrpressure loading.

These negative pressure forces acting on the components are relatively small and should be generally ignored i n the design.

However, these effects should be assessed from the time history dyqamic analysis; and the rebound should be adequately incorporated in the structural detailing for satisfactory performance of members / joints etc.

Buildings over t w o stories in height are, therefore, not recommended as blast resistant structures. Therefore, preference should be given to single storey buildings when designing for any significant overpressure scenarios.

The blast resistant buildings should be profiled as clean and simple as possible in plan and elevation without reentrant corners and offsets, in particukr, to avoid local high concentrations of blast loadings.

The building should also be oriented in such a way that only a smaller area should face the most probable source of an explosion and should withstand the blast induced loads as less as possible. Refer to clause 7.2.4 of this RP for other siting considerations.

GENERAL STRUCTURAL SYSTEMS

Technical Considerations

Any building / structure to be truly blast resistant should attain the basic resilience to blast forces by evaluating their probable magnitude and characteristics as well as by selecting appropriate materials of construction with inherent dynamic properties for adequate and rapid structural response. The stn~ctural systems shall be such designed and detailed that they should achieve in-built ability to absorb blast energy without causing collapse or significant failure(s) as a whole.

Further, any impact of fire impingement shall also be determined by QRA on the ability of structural system to resist blast loads; accordingly the most effective means of protection system (coating /cladding) against fire shall be applied as required.

Construction materials in blast protective structures shall be chosen for those having good properties of ductility and material strength as the most important features to withstand the blast loads and ensure safety against catastrcphic failures. Besides, structure component parts shall have adequate deformation capacity to form the yield mechanism,

Brittle materials such as un-reinforced concrete, brick, and un-reinforced masonry shall not be used for blast resistant structures.

Reinforced concrete is normally found the most suitable and economical material for robust construction; and shall be used for blast resistant buildings, specially in areas where they are close to a potential blast source and where they are likely to be subjected to relatively high overpressure and thermal effects in the event of an explosion.

Normally, the cost of blast resistance increases with the building height for given building volume and a taller building / structure attracts much more blast loads and overturning effects than a low profile building.

9.2 Common Svstems Used

9.2.1 Buildings of normal construction with conventional loads may provide some level of blast resistance; but are generally vulnerable to even low-level blast effects due to presence of certain features such as large windows, un- reinforced masonry walls and weak structural connections causing improper performance.

9.2.2 Normal construction includes, except reinforced concrete, other common systems used in industries for load transfer such as pre-engineered steel framing with metal cladding, and steel framing with masonry or precast concrete walls.

These types of structures could withstand (without collapse) blast loadings on the order of 1.0 psi (6.8 kPa) side-on overpressure; but architectural items sclch as doors, windows and glasses etc. shall be designed adequately so as to prevent severe damages and become flying fragments.

9.2.3 However, the types of construction referred above in clause 9.2.2 could be used with necessary strengthening and upgrading measures, where appropriate for increasing levels of blast forces and decreasing spacing from potential hazards as described below.

9.2.4 Enhanced Pre-engineered Metal Building

This type of building should be comprised of steel frames with cold-formed steel panels supported on cold-formed steel girts and purlins. The steel frame shall be designed to resist all vertical and lateral loads, incorporating necessary design improvements to enhance blast resistance that can be achieved by:

a. Specifying closer spacing of steel frames.

b. Using symmetric sections (back to back C-shapes) for purlins and gitrts and reducing their spacing.

c. lncreasing size of anchor bolts and strengthening wall panel connections at the foundation and at the roof.

d. lncreasing the number of cladding fasteners and using oversized washers to reduce tear-out of siding material.

e. Fixed base of columns.

f. lncreasing the degree of static indeterminacy in the structure to improve the dynamic response and blast resistance.

With enhancements, these buildings can attain structurally blast resistance ranging from 1 to 3 psi (6.9 to 21 kPa) side-on overpressure.

I , .- DOC. NO. KOC-C-030 Page 22 of 62 - -

9.2.5 Reinforced Masonry Clad Building

a. Reinforced masonry clad buildings similar to conventional buildings should normally be constructed to resist conventional loading by means of structural steel or concrete frame that is used to support vertical loads and resist lateral forces.

b. Reinforced masonry is used for the exterior walls and shall be designed tc span either vertically or horizontally. The walls that run parallel to a directional blast force can also be designed as shear walls to transmit lateral forces to the foundation.

c. The reinforced masonry wall shall be attached to the building frame to connect all components together and provide resistance to rebound forces.

This type of building can be economically designed to withstand blast loadings on the order of 3 psi (21 kPa) side-on overpressure; but adequate design protection shall be taken for architectural items against severe damages.

9.2.6 Metal Clad Building

a. Generally, metal clad building should be designed conventionally using hot-rolled structural shapes for frames, girts and purlins. Metal siding or insulated sandwich panels, with thicker gauge metal and more ccnnectors, shall be used for exterior walls.

b. The steel frame should behave like pre-engineered metal buildings resisting all vertical and lateral loads; and the connections should be enhanced to develop the full plastic strength (ultimate moment and / or shear capacities) of the structural members.

This type of building can be economically designed to withstand structurally blast loading on the order of 3 psi (21 kPa) side-on overpressure; but adequate design protection shall be taken for architectural items against severe damages.

9.2.7 Precast Concrete Wall

a. Tkis type of construction should use precast concrete walls on steel or concrete frames that resist all vertical loads; and precast shear walls resist lateral loads.

b. Ductile connections for precast panels shall be provided by embedding steel connection devices attached to the building frame by bolting or welding.

Page 23 of 62 REV.l

c. The roof is usually a concrete slab on metal deck which should be attached to steel framing by studs or puddle welds. The roof needs to be designed to cater for negative pressure impacts.

This tyse of building can be economically designed to withstand structurally blast loadings on the order of 7 to 10 psi (48 to 69 kPa) side-on overpressure; but architectural items shall be selected with adequate design protection against severe damages. Refer to clause 1 6.0 of this RP for details.

Cast-in--Place Concrete Wall

a. Cast-in-place concrete construction should be used to resist relatively high blast overpressures where precast concrete is not economical or practical.

b. Hcrizontal loads are resisted by shear walls whereas the structure depends on the structural steel or concrete frame to support vertical loads. Thickness of the concrete walls, and size and placement of the reinforcing steel shall be chosen suitably and designed to provide necessary resistance to any anticipated design blast loads.

c. Concrete sections should be under-reinforced, thereby ensuring ductile yield occurs.

This tyge of concrete building can normally be required for higher blast loading and for side-on overpressure greater than 7 psi (48 kPa); but adequate design protection shall be taken for architectural items against severe damages. Refer to clause 7 6.0 of this RP.

Recommended Svstem

Notwithstanding the structural systems described above, the new blast resistant buildings shall generally be of reinforced concrete construction, and clad with reinforced concrete walls and roof supported on reinforced concrete frames. Each structural element should have energy absorption capacity up to the point of collapse more than the values recommended in this RP that required resisting the design blast loading, which shall be at least 3 psi (21 kPa) as minimum if not specified otherwise.

Unless specified otherwise, blast resistant building o f new construction should be l imited to rectangular box shaped single storey building in reinforced concrete for better performance.

For upgrading and strengthening existing buildings, the other ductile materials should be used on a case by case basis, depending on the materials of construction and effective blast load(s) from the potential source.

Page 24 of 62 REV.1

STRUCTURAL DESIGN

Basic Criteria

The basic design of a blast resilient building should be to achieve rapid structural response under transient dynamic loading, while ductile materials shall attain a strength increase that can significantly enhance the structural resistance. Structural elements should be allowed to undergo permissible plastic (permanent) deformation to absorb the explosion energy.

The intent of the design should be to accept moderate structural damage to the building without collapse while still maintaining protection for personnel and control equipment. Some distortion of the building structural elements and external doors may occur at blast loading even less than the specified design load.

For design purposes, it should be assumed that the explosion occurs as a surface burst and no reflected loads shall be imposed on the roof.

It shall be assumed that the blast load should be unidirectional with respect to building orientation and front face of the structure should be designed for the full reflected overpressure. The location of blast source should be assume3 perpendicular to the center of the building wall. Refer to clause 8.2 and Figures 2 & 3, Appendix - II of this RP for blast loading details on walls.

Moreovx the buildings may suffer impacts from high velocity debris of flying objects, in addition to the overpressure condition from the blast.

Dynamic Response

Blast loaded structures would experience a very rapid application of the load under transient condition and a corresponding rapid rise in member stresses; and then normally return to ambient conditions in a very short period of time in milliseconds (ms).

The member should be stressed in the plastic region to absorb the blast by balancing the kinetic energy of the explosion against the total strain energy of the nember, which shall be a function of dynamic material properties, section properties and the amount of plastic deformation allowed. The adequacy shauld be based on the maximum deformation l imits rather than stress limits.

The dynamic response of the structure (law, medium & high) should be determined by using the simplified bilinear resistance-deflection curve in which stress increases linearly with strain to yield and a constant value after yield, thus including strain hardening effects and then decreases linearly with strain in the elasto-plastic range of the rebound.

DOC. NO. KOC-C-030 1 Page 25 of 62 !I REV.l 10.2.4 Low response limit shall be selected if a high degree of protection to

personnel and equipment are desired to be provided.

10.2.5 This dynamic response should be modeled accurately to incorporate into the SDOF analysis by selecting a design stress equal to the average stress occurring in the actual response. The stress shall be obtained by estimating the maximum response range and using the ASCE recommendations given in Tables IA to IC as follows:

Table IA: Response Criteria for Reinforced Concrete

Element Type

Beams

Slabs

Beams-Columns

Shear Walls, Diaphracrms

C-

Controlling Stress Ductil ity Support Rotation 0, (Note 21 I Ratio I Low I Medium 1 High - Concrete only - Concrete + Stirrups

Notes: (11 - Shear controls when shear resistance is less than 120% of flexural resistance. ("$ - Stirrups are required for support rotations greater than 2 degrees. (5) - Ductil ity Ratio =0.05 (p - $1 < 10.

Table 16: Response Criteria for Structural Steel

4 - Element t y p e Response Range Low 1 Medium

Note (1) : Side-sway l imits for Frames: Low = H150, Medium = H135, High = HI25

Table IC: Res~onse Criteria for Reinforced Masonrv

Notes:

The following descriptions shall apply to the response ranges mentioned above in Tables IA t o IC:

Low Response: Localized building / component damage. 8uilding can be used; however repairs are required to restore integrity of structural envelope. Totat cost of repairs i s moderate.

Medium Response: Widespread building I component damage. Building can not be used until repaired. Total cost of repairs is significant.

High Response: Building / component has lost structural integrity and may collapse due t o local weather conditions (wind / rain). Total cost of repairs approach replacement cost o f building.

10.3 Dvnamic Desiqn Strength

10.3.1 A strength increase factor (SF) for the static properties of materials shall be accounted as the average strength used for various materials are normally greater than the specified minimum values and shall be applied as specified in Table II of this RP.

Table II: Strenqth Increase Factors (SIF]

11 Concrete (Note 1) I 1.0 - I

Structural Steel (fM S 50 ksl ) Reinforcing Steel (f, 2 60 ksi 1 Cold-Formed Steel

Note

1.1 1.1

1.21 -

(1): --he results of compression tests are urualty well above the specified cmcrete wefigtha and nay be used in lieu of the above fastor. Some conservatism may be warranted because soncrete strengths have more influence on shear design than bending capacity.

The material dynamic design strength shall be determined by multiplying the increased static strength by the dynamic increase factor (DIF) in order to account for strain hardening effects under rapidly applied loads. DlFs are a function of material type as well as strain rate and shall depend on the type of stress (flexuretdirect shear) as specified in Tables ll lA to 1118 of this RP.

Table MA: Dvnamic lncrease Factors (DIF) for Concrete, Reinforcinq Bars and Masonry

DOC. NO. KOC-C-030

Table IIIB: Dvnamic Increase Factors (DIF) for Structural Steel, Cold Formed Steel, and Aluminum

Page 27 of 62

A446 Stainless Steel Type 304 Aluminum 6061 -T6 -

10.3.3 The dynamic design strengths shall be derived from the maximum design stresses of materials as specified in Tables IVA to IVB of this RP in accordance with ASCE recommendations, after multiplying with appropriate SIF and DIF of the material from Tables II & III of this RP.

Table IVA: Dvnamic Desiqn Stress for Reinforced Concrete -

Type of Stress Type of Maximum Support Dynamic Design Stress Reinforcement Rotation ( Fds)

Bending Tension and 0 < 8 ~ 2 h, Compression 2 ~ 8 1 5 F, + 1/4 (Fh - FJ

5 < 6 5 1 2 !h (F*, -+ FJ

Diagona Tension Stirrups Fdt

Direct Shear Diagonal Bars 0 < 8 1 2 Fat, 2 < 8 < 5 F,, + '/4 (F.,,, - Fd,) 5 < 8 ~ 1 2 1/2 (Fdr + Flu)

Compression Column All F, i

Table IVB: Dynamic Desisn Stress for Structural Steel

Maximum Ductility Ratio All p s 10

At low response ranges, the maximum design stress shall be equal to the dynamic yield stress and at higher response ranges, the design stress shall be increased to account for strain hardening. But with greater deformation the stress level and thus resistance becomes unpredictable by the design stress.

Deformation Limits

Approp-iate deformation limits should be used to ensure that the adequate response to blast loads can be provided in design; and these limits shall be based on the type of structure or component, construction materials used, locatior of the structure and desired protection level as given in Tables IA to IC of this RP.

The primary method of evaluating adequate response of the blast loaded structures shall be to limit maximum ductility ratio (p) for structural steel members and support hinge rotation (8) for concrete members by allowing them without failures t o exceed yield stresses beyond elastic zones for economy. Frame systems shall not exceed the side-sway limits t o minimize the chance of progressive collapse and to reduce ?-A effects on columns.

Structu-at collapse shall not be permitted and suspended equipment shall be adequately anchored within the structure.

Maximum acceptable values for ductility and support rotation shall be in compliance with Tables IA to IC of this RP as per ASCE recommendations.

DOC. NO. KO cb

REV.l

METHODS OF DYNAMIC ANALYSIS

General Obiectives

The ovarall objective of a dynamic blast analysis should be to assess the capability of a structure to resist the defined blast load by predicting with a fair degree of accuracy the dynamic response of the structure.

A resistance function or applied force versus displacement relationship should be developed based on assumed failure mechanisms, the member configuration, and estimated section capacities. The analysis should specifically provide:

a. Maximum relative deflections of each structural element.

b. Relative rotation angles at plastic hinge locations.

c. Dynamic reactions transmitted to the supporting elements.

d. Deflections and reactions due to rebound and negative pressure.

The method(s) of dynamic analysis should normally be applied based on the probable blast load and its pressure time relationship to the simplified structural models with a number of approximations that may affect the accuracy of the results.

However, the analysis methods shall not be too complex and / or time consuming depending on the structural configuration; and shall provide the necessary balance between the sufficient accuracy and calculation simplicity to predict its behaviour.

Calculation o f Mass and Inertia

The mass of the structure shall be calculated by including its self weight and the weight of permanently attached equipment divided by gravity. Normally 50% of the supported beam's mass shall be considered to be lumped at the mid-span of each supporting girder when beam is more rigid than the girder, such as in concrete construction and 20% for structural steel members.

Live loads which would be blown away by a blast wave or which would not increase the inertia of a supporting member shall not be included in the mass calculation for dynamic analysis.

Fioor live load representing personnel and furnishings shall not be included in the analysis. However, floor live load shall include heavy racks and equipment like in Auxiliary room.

The moment of inertia shall be calculated for gross and cracked sections of concrele as per ACI 31 8 and of steel members as per AISC. For deflection calculation purposes, the average of the inertia(s) for the gross and cracked concrete sections shall be used in the analysis.

Basic Methods

The basic analytical model used in most blast design applications should be generally single degree of freedom (SDOF) system. However in some cases, multi-degree of freedom (MDOF) system should be applied, if the situation is warrawced.

For enclosed buildings, the blast loads shall be applied to the exterior walls and rocf, and shall be transmitted through various structural members to the foundation; and the blast energy should be absorbed through elastic and plastic deformation of the structure. The portion of blast energy not absorbed by the structure should be transmitted into the ground, establishing a continuous load path to ensure a safe design.

The s t rx tu re should be separated into its major components for simplifying the dynamic analysis and should be analyzed as uncoupled member by member approach, thus neglecting dynamic interaction effects.

Normally coupling should be negligible if the natural frequencies of connec~ed elements differ by a factor of two (2) or more. Otherwise, frequencies of interconnected members need to be tuned by changing their stiffness or weight to achieve this separation of frequencies.

If neglecting dynamic interaction effects of the connected members can not be justified, multi-degree of freedom (MDOF) system should be used to consider these effects inherently.

Damping of materials should normally be ignored in blast resistant design as the structure reaches its maximum response in short time and it has little effect on peak displacements.

In blast analysis, the resistance should usually be specified as a nonlinear function to simulate elastic, perfectly plastic behaviour of the structure; and when the ultimate resistance (RJ has been reached upon forming the collapse mechanism in the member, the dynamic equilibrium equation becomes then as below:

Ma + I? = F, where R = Lesser of Ky or R, and Ky = Resistance = Stiffness x displacement Ma = Inertia Force = Mass x acceleration F, = Applied force as a function of time

The ratio of a member's natural frequency to the natural frequency of the support system is in the range of 0.5 to 2.0, such that an uncoupled analysis may yield significant inaccuracies.

Time varying support reactions or member forces are desired to evaluate the structure or its foundation in great detail in an effort to minimize costs of structural back fit modifications.

Overall structural behaviour is to be evaluated with regard to structural stebility (frame buckling), gross displacements and P-A effects.

The structure has unusual features such as unsymmetrical or non- uniform mass and stiffness characteristics.

11.3.7 Several methods of solutions for the above equation are available in simple graphical non-dimensional charts, closed form solutions (i.e. equations) or empirical formulas for SDOF systems in technical publications for triangular and rectangular load pulses, to determine the maximum ductility demand and the time of maximum response in both elastic and elastic-plastic stages. See Figure 4, Appendix - Ill of this RP for reference.

11.3.8 However for more appropriate and wide applications, numerical time integration method or as generally known as t ime history method should be recommended for use due to availability of several tested computer programs solving the equation of motion.

A small time increment equal to l / l O t h of either the load duration or the natural vibration period of the structure shall be used initially in the analysis to evaluate response; and may be further reduced if required to generate adequate time deflection curve.

11.3.9 When :he structural configuration is not simple or significant dynamic interaction between interconnected members can not be avoided; a compreclensive dynamic analysis of the entire superstructure should be conducted by involving the use of many degrees of freedom with coupled analysis approach for the structural system.

11.3.10 Finite element analysis method (FEM) should be recommended as an advanced analysis method, when one or more of the following conditions exist:

12.0 DESIGN PROCEDURES

12.1 General Desiqn Conce~ts

1 2.1.1 While designing blast resistant buildings or structures, the key concepts should include in the systems such important features as high energy absorption, safety factors, limit states, load combinations, resistance functions, structural performance considerations and redundancy as described below to achieve the most satisfactory results without any catastrophic failures.

12.1 -2 Energy Absorption

a. The overall structure and its members shall achieve both strength and ductility having high energy absorption capacity, which should be derived from the area under the load vs. displacement diagram or resistance function of members.

b. The high energy absorption capacity shall be attained through the use of appropriate materials of ductility and suitable construction details.

c. These details must accommodate relatively large deflections and rotations in order to provide redundancy in the load path.

12.1.3 Safety Factors

a. Safety factors in terms of strength requirements such as load- resistance factors or allowable stresses used for conventional static loads are not applicable in blast resistant design.

b. They shall be measured by strain energy demand vs. strain energy absorption capacity which is quantified by the allowable deformation.

c. Margins of safety against structural failure shall be attained by the use of allowable deformation criteria as described in clause 10.0 of this RP using ASCE recommendations.

1 12.1.4 Limit State Design a. Limit state design methods shall be used in blast resistant design.

b. Ths Strength Design Method shall be applied as per ACI 318 or BS 81 I 0 for structural concrete and masonry materials.

c. Thz Load and 8esistance Factor Design (LRFD) Method shall be used for structural and cold-formed steel.

a. Resistance functions shall be established from the force vs. deflection relationships for the overall structure or each member to determine the dynamic response of the equivalent SDOF systems.

b. These relationships (force vs. deflection) are generally nonlinear due to material properties or geometry; but should be assumed to be linear with few approximations to simplify the analysis and design process ignoring some nonlinear effects.

d. Special provisions for detailing and design requirements as applied to high seismic conditions shall be considered for blast resistant design in order to assure ductility and strength and to protect against non-ductile failure modes, such as buckling or premature crushing of materials.

12.1.5 Loading Combinations

a. Blast Loading

i. The required dynamic resistance to blast loads in the basic limit state loading combination with other loads for all material types shall be as follows:

U = Required total structural resistance DL = Dead Load LL = Live Load (refer to clause 11.2) BL = Blast Load

ii. Blast load should not be considered in combination with wind load WL) .

iii.The required rebound resistance such as for roofs, should normally be considered in combination with dead loads only.

b. Normal Loading

i. Normal conventional loadings such as DL, LL and WL acting on the structure and its members shall be considered in accordance with KOC-C-001 "KOC Standard for Basic Civil Engineering Design Data" and other applicable standards / codes such as ASCE 7 or BS 6399 Part 1 or UBC as referenced in clause 4.2.1 of this RP.

. .

11. The basic limit state loading combinations with normal conventional loads shall be calculated with the appropriate load factors as per ACI 318 or BS 81 10 for structural concrete and AlSC (LRFD) for structural steelwork.

12.1.6 Resistance Functions

DOC. NO. KOC-C-030 Page 34 of 62 -

12.1.7 Structural Performance Considerations

The structural performance requirements for blast resistant design shalt include limits imposed on member deflections, story drift and damage tolerance levels as described in clause 10.2 of this RP.

12.2 Basic Calculation Methods

12.2.1 The members of a blast loaded structural system shall be analyzed member by member for the above criteria as described in clause 12.1 of this RP in order to determine their adequacy and critical response as outlined below:

1 2.2.2 Load Determination

a. D ~ l e to blast load on the primary members such as external walls and roof slabs etc. the incident and reflected overpressures shall be computed in accordance with clause 8.2 of this RP by using the formulas given in ASCE Publication "Design of Blast Resistant Buildings in Petrochemical Facilities".

b. Loads on supporting or interior members shall be determined either by the tributary area method or from a computed dynamic reaction from the numerical time history analysis.

1 2.2.3 Membef Properties

a. Generaily, the member properties shall be obtained from the test results from the Supplier (concrete) or from the Manufacturers (steel).

b. The required dynamic properties shall usually include unit weight, modulus of elasticity, elastic yield strength and allowable deformations as well as post yield strength or membrane resistance.

12.2.4 Mathematical Models

a. Suitable mathematical models shall be developed for individual members, usually idealizing them as simple one way beams or two way plates as mostly applied in the analysis of SDOF systems. The common practice is to use as one way members for simplicity.

b. Boundary conditions should be assessed on the type of connections to be used for member supports to ensure that support details must provide sufficient strength, ductility and stability to enable the member to develop full collapse mechanism.

c. When assessing boundary conditions, the support capability to resist reaction forces for both the loading and rebound phases of the response must be considered.

12.2.5 Trial Selection

a. The dynamic analysis should be carried out by selecting sizes of members on trial basis to determine the nonlinear response properties in order to check its adequacy by iterative process.

b. The process shall be continued until the close results are derived for economy and satisfactory performance levels of the trial members.

12.2.6 Dynamic Analysis

The dynamic analysis itself shall then be performed by one of a number of different methods as outlined in clause 11.3 of this RP to compute member deformations and reactions.

12.2.7 Deformation Criteria Check

a. Thz analysis results should indicate peak element deformations in terms of ductiIity ratios, support rotations, deflections, or as deflection - span ratios; and shall be compared to the allowable values as given in ~dause 10.2 of this RP.

b. In case the allowable values are not met, the analysis shall be repeated with some changes to trial member sizes or to structural configurations to arrive at close values.

1 2.2.8 Connec-:ion Sizing

Connections shall be sized and adequately detailed to transfer the computed reaction forces and to assure that plastic hinges can be meintained in the assumed locations.

Fot. reinforced concrete design, splices and development lengths of reinforcing bars shall be provided for the full yield capacities of reinforcements.

For structural steel design, connections shall be designed for a greater capacity than that of its supported member.

Geqerally the frame type structures should be modeled using MDOF approach with simultaneous application of lateral and vertical blast loads on the frame, resulting combined axial and bending load combinations in the individual frame.

De~ending on the symmetry of the structural resistance, mass and the loading, a two dimensional plane frame model can be used for analysis.

Material model should be incorporated with proper consideration for non-linear properties and piastic behaviour in the analysis which should provide displacements and plastic hinge rotations for comparison against acceptance criteria given in Tables IA to IC of this RP.

12.3 Structu ~ a l Ap~l ica t ions

Any building or structure subject to blast should behave structurally like seismic condition with an instantaneous response to the dynamic loads so that the transient loads will be transferred to the foundations; and normally the follcwing structural models shall be applied for dynamic analysis:

a. Shear Wall / Diaphragm Type Structures; or

b. Frame Type Structures

12.3.1 Shear Wall / Diaphragm Type Structures

a. This analysis usually envisages that the front wall facing the blast will be designed for lateral blast loads, and will span vertically as a flexural member between the roof and the foundation.

b. The roof system will act as a horizontal diaphragm spanning between the side walls of the building and shall be designed accordingly.

c. Side walls will then be designed as shear walls which carry the lateral loads as well as the overturning effects t o the foundations.

d. Alternatively lateral loads could be resisted by a compact building by cantilever beam action instead of the shear wall / diaphragm action depending on the proportions of the building; and the appropriate behaviour shall be decided by the designer.

1 2.3.2 Frame Type Structures

REINFORCED CONCRETE DESIGN - - . - - - . .

General

For blast resistant buildings, reinforced concrete shall be used mostly for new construction with cast-in-situ or pre-cast walls as exterior faces directly exposed to blast effects.

Roof and side walls shall also be made of reinforced concrete for resistance against projectile penetration and fire hazards. These structural elements should be designed for adequate ductile response to absorb blast energy and should also utilize the inherent in-plane strength of concrete to resist lateral Mast forces.

Rectangular box shaped buildings shall be generally chosen as per clauses 7.2.4 & 9.3.2 of this RP; and shall be designed for the blast pressures given as below. Refer to clause 8.2 for blast loadings and Figures 2&3, Appendix-Il of this RP for details.

a. Vertical Exterior Walls: Front wall facing the blast load, for the peak reflected pressure and side walls for the appropriate incident side-on overpressures.

b. Roofs: Flat roof slabs and beams for the incident side- on overpressure.

c , Structural Frames: The main structural frames for the blast pressure on any wall as per the above loading criteria (a) together with roof loading (b).

Due to very high design loads under blast condition, interior columns should normally be provided when roof spans exceed 9.1 5 m (approx. 30 ft).

Depth of the structural elements like beams should be chosen in such a way that the overall building height will be minimized to reduce blast effects; and blast exposure trough requirements of HVAC ducts wherever required, shall be incorporated in false ceiling of the building. Height of the parapet roof wall shall also be kept to minimum to reduce blast exposure.

Founda-tions shall be always constructed of reinforced concrete. Spread footing!; with a grade beam system or raft foundations shail be used to minimize relative displacements between individual footings.

Design Principles

The structural concrete shall be designed with higher concrete strengths as per ACI 31 8 or BS 81 10 to attain sufficient member strength and ductility requirements as specified in clauses 10.2 & 10.3 of this RP.

The resistance of concrete elements shall be computed by using the dynamic material strengths as given in clause 10.3 of this RP.

Strength reduction factors shall not be applied (i.e.cll= 1 .O) to load cases involving blast.

Thickness of reinforced concrete blast walls shall be established as per design blast load combinations specified in clause 12.1.5 of this RP, but shall nor. be less than 250 mm. Roof slab shall be minimum 150 mm thick.

Blast walls shall be taken to the minimum depth of 1500 mm below NGL or up t o the top of foundations whichever are shallower, maintaining the wall thickness and reinforcements same as in the wall above ground level.

All concrete surfaces shall be doubly reinforced to take care of rebound and negative forces.

Maximum spacing of bars in wall as well as in roof slab shalt not exceed 150 mrri c/c; and minimum diameter should be used 12 mm for flexure.

Higher strength concrete may be used to reduce field labour costs by eliminat ng shear reinforcements, if possible. Refer to KOC-C-006 for other details of design and construction.

Materials to be Used

Normally stronger concrete grade should be preferably used for new construction of blast resistant structures; but shall not be less than the minimurn concrete compressive strength of Grade 3 0 (27.6 MPa or 4000 psi) in accordance with KOC-C-006 "KOC Standard for Concrete Work - Materials and Construction".

Reinforcing bars of Grade 6 0 (No.1 1 and smaller) with a specified yield strength 60,000 psi conforming to ASTM A615 or Grade 460 with a specified characteristic strength of 460 ~ / m m ' conforming to BS 4449 shall be used to derive sufficient ductility for dynamic loading.

Bars with higher yield strength shall not be used as they may have less ductility for flexural resistance and shop bending.

1 3.4.5 Serviceability Requirements

These criteria intended to reduce cracking at service load levels shall not be applied to load combinations with blast, as some tolerable cracking as well as perrnanent deformations resulting from the plastic range response are acceptable for blast load. The ductility limits shall be used for the consistent performance requirements of the buildings under blast as per cause 10.2 of this RP.

13.3.4 Welding of reinforcement shall be generally discouraged for blast design applications; however i t may be required for anchorage. ASTM A706 bars may be used in these cases.

13.4 Supplernentarv Requirements

In addition to the above requirements, the following items shall be considered for blast resistant design.

13.4.1 Minimum Reinforcement

The mi-rimum reinforcing provisions shall be applicable as per ACI 318 or BS 81 1 0 and reinforcement in excess of the cracking moment should be provided to prevent a premature ductile failure. The dynamic material strength should be used as per clause 10.3 of this RP in computing minimum reinforcement.

13.4.2 Maximum Reinforcement

Maximum reinforcement provisions shall be applicable as per ACI 31 8 or BS 81 ' 0 to prevent crushing of concrete prior to yielding of steel; and should be used for compression reinforcement to offset maximum tension reinforcement requirements. Each face shall be equally reinforced to resist rebound stresses for blast resistant concrete members.

13.4.3 Substitution of Reinforcements by Higher Grades

The reinforcements shall not be allowed to be substituted by higher grades as it can alter a ductile response to become non-ductile. Stronger reinforcing will increase the moment capacity of the concrete section, thereby increasing the dynamic reaction to the supporting member, while not affecting the concrete shear capacity.

13.4.4 Development Lengths

Development lengths should not be reduced for excessive reinforcement. The full actual length of reinforcements should be used in computing section capacities, as plastic hinges will cause over-designed reinforcements to yield.

13.4.6 Lacing

The lacing shall be provided to tie together longitudinal bars, as a special type o f shear reinforcing in a continuous zigzag shape, where large deformations are to be tolerated. Otherwise, standard tie bars or stirrups should be used t o restrain longitudinal reinforcing bars to achieve adequate plastic rotation capacity.

1 3.4.7 Combined Forces

Some concrete elements subjected to simultaneous loadings from both planes, should be designed to resist the combined forces from out-of-plane bendinc loads in combination with in-plane shear loads. Side walls shall resist side overpressures acting in its plane, with reactions from the roof diaphragm acting in the plane of side wall. This situation shall be dealt with the ways as follows:

a. Separate sets of reinforcements should be determined for bending and shear to be resisted; and shall be provided accordingly at the exterior faces for bending while a layer of center reinforcements for in-plane shear only.

b. otherwise, the interaction equation shall be applied to check the acceptable behaviour of the concrete elements as follows:

[A~,IA,I,~ +IAJA,I~~ 1 1 where,

A, = Computed deformation (ductility ratio or support rotation) A, = Allowable deformation (ductility ratio or support rotation) i = in-plane deformations o = out-of-plane deformations

13.4.8 Joints

While designing, contraction I expansion joints shall be avoided in the blast resistant structure as far as possible; and construction joints shall be planned to be minimum. In case of shear walls, additional care shall be taken to form keys or epoxy resin bonding agents may be used in horizontal joints. In case of precast elevation, panels shall be designed with an overlap.

DOC. NO. KOC-C-030 11 Pase41 of 62 11 REV.l

Failure Mechanism

The reiqforced concrete building shall be designed and detailed in such a way that the concrete elements under blast loading should undergo preferably flexure failure mechanism rather than direct shear and diagonal tension failures to achieve an extended plastic response.

Other common failure mechanism in a blast loaded structure should be suitably avoided by proper design and detailing of the elements, which shall include failures such as reinforcing development, overlapping of pre-cast connec-:ions, anchor bolt embedment and door connections.

STEEL DESIGN

General

Structural steel should normally be applied in blast resistant design, where specified, for beams and columns for the support of vertical loads, braced and rigid frames for the support of vertical and horizontal loads, and specialized elements such as doors, frames, decking, and protection of duct openin~s.

Steel being a factory produced material, has the distinct advantage of having well controlled and predictable strength and post-yield properties; and unlike concrete, has tensile as well as compressive strength.

However, the most disadvantage of structural steel in blast design should be the possibility of premature local or general buckling due to its inherent slenderness ratio.

The st r~ctura l steel for blast resistant design shall be as per the AISC Load and Resistance Factor Design Specification (AISC LRFD) or BS 5950 to attain sufficient member strength and ductility requirements as specified in clause 10.2 & 10.3 of this RP.

The rezistance of structural steel elements shall be computed by using the dynamic material strengths as given in clause 10.3 of this RP, plastic analysis and detailing provisions similar to seismic conditions.

Strength reduction factors shall not be applied (i.e. a= 1.0) to load cases involving blast.

Slenderness of structural steel members shall be particularly considered to the ductility in blast design so that the effects of overall and local instabillties upon the ultimate capacity shall be avoided due to general thinness of members.

Proper to the higher

width-thickness provisions shall be applied in design so that not only extent a full plastic capacity can be achieved, but to the extent that ductility ratios can also be safely reached.

For this purpose, refer to Table 8-1 from the AlSC Seismic Provisions of Structusal Steel Buildings for the width-thickness ratios.

Materials to be Used

Low and medium carbon structural steels, such as ASTM A36 / A50 or BS equal, having sufficient ductility shall normally be used in blast design. High strength materials should be discouraged in most applications to prevent problerrrs with decreased ductility.

Generally for strengthening of existing structures to higher blast resistance, structural steel (rolled shapes) and plates used shall be in accordance with ASTM A36 or 8 s EN 10025 Grade 275JR or equivalent and shall comply with K3C-C-007 "KOC Standard for Structural Steel Work - Materials, Fabricarion and Erection".

Structural bolts shall be mechanically galvanized and of high strength conforming to either ASTM A325 / A490 or BS 3692 Grade 8.8.

Welding shall be carried out in compliance with all requirements specified in AWS D l .l.

Supplementary Requirements

In addit:ion to AlSC LRFD and above requirements, the following shall be considered for blast resistant design:

Substitution of Steel by Higher Grades

Substitution of steel by higher grades shall not be allowed, as they possess less effective resistance-deflection curves, may alter the relationship between flexural and shear capacity, and tend to increase the dynamic reaction on the supporting members to resist.

Cold-Formed Steel

AlSl shall be used with several adjustments; and the special provisions within these specifications pertaining t o seismic design shall also be adopted for blast resistant design.

14.4.3 Diaphragms

Generally it shall be assumed that to resist blast pressure loads, the walls are supported at opposite sides for one way slab design or su~ported at four sides for two way slab design. The roofs or floors sh-x~ld, therefore, be designed adequately as diaphragms to resist the in-plane loads and transmit them to the resisting shear walls.

In addition to the above in-plane loads, the roof diaphragms shall be designed for normal positive overpressures and to a less severe extent, normal negative pressures.

Roof diaphragms should also be designed to resist lateral wall reactions as in-plane loads as well as blast overpressures as out-of- pkne loads through the interaction formula in clause 13.4.7(b) of this RP.

Normally, separate structural bracing members should be provided to transfer lateral wall reactions.

14.4.4 Connection Design

The connection design shall be such that it will not control the capacity of the member to maximize the plastic response and preferably, a moment connection should be used to force a plastic hinge away from the connection and into the member.

Connection strength shall be determined through AlSC LRFD design methods and ductility requirements shall be implemented through the use of appropriate connection details.

Both welded and bolted type connections shall be used in rigid and semi-rigid construction, as there is no particular advantage of using one type over the other with regard to joint performance under blast lozding conditions.

Sharp corners and weld details prone to undercutting should be avoided.

Cladding

Cold-formed light gauge sheet metal panels should be used only for lo-,^ blast pressure due to premature buckling of the relatively thin wsbs.

Materials conforming to ASTM A653 should be used for cold formed sections with yield strengths ranging from 3 3 ksi (228 MPa) to 65 ksi (1450 MPa); and should also be checked for the blast load case in accordance with the AlSl LRFD Cold-Formed Steel Design Manual.

Sd:rength reduction factors shall not be applied (i.e.cIj= 1 .O) to load cases involving blast.

The resistance of cold-formed steel panel should be computed by using dynamic increase factors (DIF) given in clause 10.3 of this RP.

P r~pe r care shall be taken in selecting the suitable section for the anticipated load, as the deflection increase with the increase of load intensity causes steel panels to act as a membrane in tension.

Ccrld-formed steel panels shall be checked for thin webs against web crippling and should provide larger bearing are to preclude this problem.

Lcw response range values as specified in Table IB of this RP shall be used when tension membrane action is not present; otherwise high range values can be used when tension membrane action is permitted and steel panel end connections are properly designed.

Failure Mechanism

The structural steel building shall be designed and detailed to ensure that the pririary load bearing elements under a given blast loading shall undergo maximum deformation within the recommended ductility limits for steel members to preclude any gross member collapse due to failure of the member itself or its connections.

Local and gross member instabilities shall be prevented by providing adequate bracing and stiffeners.

Generally the structural connections shall be developed for full strength of the member to ensure its integrity and to withstand fire exposure without appreciable loss of strength if recommended by QRA.

c. Sliding: 1.0 for lateral loads resisted by frictional soil resistance, and 1.5 for lateral loads (in excess of friction) resisted by passive

resistance

In case the foundation designed by equivalent static method has found to be too massive or of impractical sizes, dynamic analysis method should be adopted for more economical and rational design that can take into account the inertia of the foundation mass in resisting all the loads and appropriate soil stiffness as springs in two directions (x, y & 8).

FOU N GATION DESIGN

The foundation of a blast resistant building 1 structure shall be designed generally more rigid than the building with conventional loads in order to minimize any excessive relative displacements between columns and walls to maintain structural integrity.

Normally structural columns of the building on spread footings shall be tied together by using grade beams for uniform behaviour of the footings. Combined mat foundations or raft foundations shall be used for rigidity, where soil conditions are poor either having low bearing capacity or chances of settlements are quite high due to excessive blast forces.

Allowat~le static soil bearing and passive pressures should be obtained from the in-situ field and laboratory test reports of the location or Site.

As blast is a rare event, the bearing pressure under blast load combination as per :lause 12.1.5 of this RP, should be considered in design not less than twice (2) the allowable static bearing pressure.

Usually foundations shall be designed by equivalent static method after summing up the peak reactions from the super-structure dynamic analysis with other conventional static loads from the load bearing cohmns.

The downward force from the overpressure on the roof shall atso be applied simultar~eously with the horizontal force from the peak reflected pressure on the front wall.

However, the compensating effects of blast forces acting on the rear wall should be neglected.

The fol'owing design criteria with factors of safety should be used in equivalent static design for foundations as below:

a. Vertical loads on soil: 1.2

b. Overturning: 1.2

DOC. NO. KOC-C030 1 Page 46 of 62 However, i f the maximum movements are found to be excessive, the foundation should be enlarged to increase the contact with the soil or deepened to increase the passive soil resistance.

ARCHITECTURAL CONSIDERATIONS

General Criteria

Besides any blast loaded building or structure being adequately designed for the specified structural performance, the safety aspects related to the architectural requirements shall also be deeply looked into in order to minimize the chances of human injury and damages to equipment by the falling debris and flying fragments.

Further buildings may be elevated above the surrounding ground to minimize any chance of spilled oil entry and subsequently being engulfed by pool fire. Refer to clause 7.2.4 for other siting considerations.

The designer should ask the supplier I manufacturer to furnish the tested records or performance results of the prime architectural elements for review and records; and if required to demonstrate that these items can sustain the blast without damage or fail in such a way that they do not increase the risk to personnel or equipment within or outside the building.

Some c f the main architectural elements, generally to be used in a building shall comply with the following blast resistant requirements as described below.

External Doors

External doors in a blast resistant building shall be kept to a minimum consistent with escape requirements; and normally should be provided on the rear or side walls where the overpressures are less than that on the front wall. Doors in the external walls shall be no less weaker than the requirements for the design areas walls, floors, roofs and other structural cornpor ents.

Blast resistant doors should be categorized to distinguish varying levels of blast prsssures they can sustain with the following definitions as below:

a. Low-range Door

A door designed to withstand an equivalent static pressure that will be less than 3 psi (21 kPa).

b. Mid-range Door

A door designed to withstand an equivalent static pressure that will be less than 3 psi to 25 psi (21 kPa to 172 kPa).

DOC. NO. KOC-C-030 Page 47 of 62 REV.l -

c. High-range Door

A door designed to withstand an equivalent static pressure that will exceed 25 psi (172 kPa).

For elastic behaviour, it shall be assumed that an applied static force shall be half that of the applied dynamic force of infinitely long duration.

Doors shail open outward and butt on all four edges, against the steel frames fixed into the concrete. Doors should preferably be flush with the outside of the building.

Doors, atches, and hinge mechanisms should be designed to be tight and should remain operable after being subjected to the blast loads.

Doors shall be made of steel plates on both faces, internally reinforced, and generally having the appearance of conventional flush metal doors.

The doors shall be so designed that easy operation under normal conditions can be done with proper selection of closing and locking mechanisms. Power assistance may be needed to employ for the opening and closing of blast resistant doors.

The door frames should be rigidly anchored into the surrounding walls by several methods such as casting in place in new concrete, bolted in with concrete expansion anchors, welding the frame to an existing steel embed or structure, or bolted to an existing structure, as designed or specified by the door manufacturer in conformity with the given blast load.

Guidelines for Blast Resistant Door Design

a. Based on the desired end-use, the guidelines for acceptance of the bfast resistant doors should be recommended as foliows:

i. Category I

'The door must remain operable after the loading event and does not exceed pre-established design criteria for stress, deflection and the permanent deformation limits. It should have a ductility ratio of 1.0 lor less within elastic range and edge rotation no more than 1.2 degrees.

'This category should be recommended when the door is a primary 13xit point or personnel may be entrapped or when i t may have to resist repeated blast loads.

ii. Category II

The door must remain operable after the loading event but significant permanent deformation to the door is permitted. It should have a ductility ratio in the range of 2 to 3 and edge rotation no more than 2.0 degrees.

This category should be recommended when personnel entrapment IS a concern.

b. The designer shall coordinate with blast resistant door manufacturer at an early stage of design with the specific design information, performance and testing requirements for acceptance of the specific p~rpose-built door with all its accessories.

c. Tbe blast resistant doors shall have also approved fire labels such as 3 hour "A" or 2 hour "B" on low-range and mid-range doors respectively, certifying that the construction of the doors have been fir3 tested by Underwriters Laboratories (UL) or equal.

Windows

Windows in blast resistant buildings should be avoided; or kept to the minimum except for specific purposes required for operations. Windows if provided shall be protected by the use of blast resistant glass that should also be heat and noise proof as well.

Windows including the frames and glass should be designed to withstand the same blast loads as on the walls. The window frames shall be properly anchored in the walls.

The window frames shall be flush with external wall and recessed with the back side on supporting concrete wall. Glass shall be recessed on profiled window frame and fixed from the outside to withstand better blast exposure.

Windows should be equipped with mechanism that enables persons to open them from inside out in case of fire breakout in the building.

Fire rating of the windows shall be same as of the doors.

Windows parapet height shall be studied carefully in respect of the users like sitting operator in Control Room overlooking the facilities.

Higher strength type glass and glazing materials such as tempered glass, polycarbonate, and laminated glass with plastic interlayer should be considered acceptable depending on the design overpressures. These materials may be used either by themselves or as components in a composite construction.

16.3.8 Wire g l s s (annealed glass) shall be avoided in blast resistant buildings, as it has relatively low strength compared to tempered glass and tends to fracture into dagger shaped razor sharp fragments.

16.3.9 Windows may be configured with two reinforced glass sheets with void space of either negative or positive air pressure.

16.3.1 0 Glass shall be of