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    Dynamic response of pipe rack steelstructures to explosion loadsMasters Thesis within the Structural Engineering and Building Technology

    programme

    ANTON STADE AARNS, HANNA NILSSON

    Department of Civil and Environmental Engineering

    Division of Structural Engineering

    CHALMERS UNIVERSITY OF TECHNOLOGY

    Gteborg, Sweden 2014Masters Thesis 2014:117

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    MASTERSTHESIS

    Dynamic response of pipe rack steel

    structures to explosion loadsMastersThesis within the Structural Engineering and Building Technology

    programme

    ANTON STADE AARNS, HANNA NILSSON

    SUPERVISOR:

    Reza Haghani Dogaheh

    EXAMINER

    Reza Haghani Dogaheh

    Department of Civil and Environmental Engineering

    Division of Structural Engineering

    CHALMERS UNIVERSITY OF TECHNOLOGY

    Gteborg, Sweden 2014

    Masters Thesis 2014:117

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    Dynamic response of pipe rack steel structures to explosion loads

    Masters Thesis within the Structural Engineering and Building Technology

    programme

    ANTON STADE AARNS, HANNA NILSSON

    Anton Stade Aarns, Hanna Nilsson, 2014

    Department of Civil and Environmental Engineering

    Division of Structural Engineering

    Chalmers University of Technology

    SE-412 96 Gteborg

    Sweden

    Telephone: + 46 (0)31-772 1000

    Cover:Deformed pipe rack steel structure exposed to explosion loading. Modelled in

    Abaqus/CAE with enhanced deflections for illustrative purposes.

    Chalmers Reproservice

    Gteborg, Sweden 2014

    Masters Thesis 2014:117

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    I

    Dynamic response of pipe rack steel structures to explosion loads

    Masters Thesis in the Structural Engineering and Building Technologyprogramme

    ANTON STADE AARNS, HANNA NILSSON

    Department of Civil and Environmental Engineering

    Division of Structural EngineeringChalmers University of Technology

    ABSTRACT

    When performing dynamic explosion analyses on steel pipe racks, a common simplified

    method is to apply the static load multiplied by a fixed dynamic amplification factor

    (DAF). By adapting this amplification, a static analysis is sufficient to account for both

    static and dynamic behaviour in design. Consequently, all structures independent of

    stiffness and mass properties are provided with the same degree of dynamic

    amplification which can produce a high level of conservatism in their design.

    The objective of this thesis is to gain a better understanding of the dynamic behaviour

    of pipe rack steel structures subjected to explosion loading. By achieving this, the aim

    is to provide structural engineers with knowledge leading to a more accurate design in

    future projects.

    To accomplish this, finite element analyses of three pipe racks have been performed

    and their respective DAFs have been calculated. The results show that DAFs vary

    between the structures, which indicate that the dynamic behaviour depends on one or

    several parameters. In addition, the results indicate that the magnitude of the DAF is

    dependent on what the selected inputs to calculate the DAF are. However, as no obvious

    affinity between the parameters of the structures and the dynamic amplification isobserved, a parametric study was required to increase the understanding of how

    different parameters affect the DAF. The results from the parametric study show the

    same variation of the DAF as in the analyses of the first three pipe racks. The results

    even reveal DAFs higher than the DAFs currently used in design procedures. Moreover,

    the results show that the mass distribution has a significant influence on the dynamic

    behaviour. In addition, the results indicate that the DAF currently utilized in design is

    non-conservative. However, the rather large scatter of the results implies that further

    studies are desired.

    Key words: pipe rack, dynamic behaviour, explosion, DAF, FEA,

    pipe mass distribution, base shear, overturning moment

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    II

    Dynamisk respons av fackverksstrukturer i stl p grund av explosionslaster

    Examensarbete inom masterprogrammetKonstruktions- och byggteknik

    ANTON STADE AARNS, HANNA NILSSON

    Institutionen fr Bygg- och miljteknik

    Avdelningen fr KonstruktionsteknikChalmers tekniska hgskola

    SAMMANFATTNING

    Vid dynamisk analys av fackverk i stl tillmpas vanligen en frenklad metod. Den

    innebr att en statisk last multiplicerad med en dynamisk amplifikationsfaktor (DAF),

    dr DAF representerar det dynamiska beteendet hos strukturen. Genom att applicera

    denna frenklade metod antas en statisk analys vara tillrcklig fr att ta hnsyn till bde

    statiskt och dynamiskt beteende. Konsekvensen blir dock att alla strukturer, oberoende

    av styvhet och massa, konstrueras med samma dynamiska amplifikation. Detta leder i

    sin tur till konservativa konstruktioner.

    Mlet med den hr avhandlingen r att skapa bttre frstelse gllande det dynamiska

    beteendet hos fackverk i stl som utstts fr explosionslaster. Frhoppningen r att bist

    konstruktrer med kunskap som kan leda till mer verklighetsnra konstruktioner i

    framtida liknande projekt. Fr att uppn detta har frst tre fackverksstrukturer

    analyserats. Resultaten visar att DAF varierar mellan strukturerna vilket tyder p att det

    dynamiska beteendet beror av en eller flera faktorer. I tillgg visar resultaten att

    omfattningen av DAF beror av vilket vrde den r baserad p. Likvl observeras ingen

    tendens mellan faktorerna som vrderats. En parameterstudie var drfr ndvndig fr

    att utvrdera hur olika faktorer pverkar DAF. Resultaten frn den parametriska studien

    visar samma variationer av DAF som i den frsta studien. Ett av resultaten avsljarven DAF hgre n idag generellt tillmpade DAF. I tillgg influerar tyngdpunktens

    lge signifikant det dynamiska beteendet.

    En slutsats kan dras att tyngdpunktens lge r en vsentlig faktor att ta hnsyn till vid

    konstruktion av fackverk i stl som utstts fr explosionslaster. I tillgg indikerar

    resultaten att den nuvarande tillmpade DAF r icke-konservativa. En stor spridning av

    resultaten finns dock och vidare studier r drfr nskvrda.

    Nyckelord: fackverk, dynamiskt beteende, explosion, DAF, FEA, massdistribution,

    basskjuvning, lyftmoment

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    III

    Contents

    ABSTRACT I

    SAMMANFATTNING II

    CONTENTS III

    PREFACE VI

    NOTATIONS VII

    LIST OF ABBREVIATIONS VIII

    1

    INTRODUCTION 1

    1.1

    Background 1

    1.2

    Objective 3

    1.3

    Limitations 3

    1.4

    Questions at issue 3

    2

    THEORY 4

    2.1

    Static and dynamic applications 4

    2.1.1 SDOF- and MDOF-systems 4

    2.1.2

    Static and dynamic loads 5

    2.1.3

    Analysing structures 5

    2.2

    Introduction to explosion loading 6

    2.2.1

    Definition of an explosion 6

    2.2.2

    Blast waves 7

    2.3

    Interaction between blast and structure 8

    2.3.1 Side-on pressure and reflected pressure 8

    2.3.2

    Drag load 9

    2.4

    Utilized computer software 12

    3

    DESIGN PRACTISE IN NYX 13

    3.1

    Load specification 13

    3.2

    The design process 13

    3.3

    Method of calculation 14

    3.3.1

    Simplified method 14

    4 STRUCTURES TO ANALYSE 15

    4.1 Pipe racks 15

    4.2 Choice of structures in NYX 15

    4.3 Input to analysis 16

    4.4

    Simplifications in modelling 16

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    IV

    4.5

    Sought outputs from analysis 19

    5

    FEA IN ABAQUS/CAE 20

    5.1

    Geometry model and boundary conditions 20

    5.2

    Choice of elements and meshing 21

    5.3

    Material models and properties 22

    5.4

    Loads and load sequences 22

    5.4.1

    Initial step 22

    5.4.2

    Self-weight step 22

    5.4.3

    Blast load step 23

    6

    RESULTS 24

    6.1

    Output from FEA 24

    6.1.1

    Maximum DAFs 256.1.2

    Parameters 26

    6.2

    Verification of FEA 26

    7

    DISCUSSION OF RESULTS 27

    7.1

    NYX structures 27

    7.1.1 DAFs based on BS 27

    7.1.2

    DAFs based on OT 27

    7.1.3 Difference between BS and OT 28

    7.2

    Parametric study 287.2.1

    Choice of parameters and matrix 29

    7.2.2

    Results 31

    7.2.3 Discussion of parametric study 43

    7.3 MDOF-systems represented by the Biggs-curve 45

    8

    CONCLUSIONS 46

    9

    FURTHER WORK 47

    10

    SUMMARY 50

    11

    REFERENCES 52

    APPENDIX ABLAST LOAD CALCULATIONS I

    APPENDIX BPOINT BLAST LOADS VI

    APPENDIX CA STUDY OF TEFFECTS VI

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    V

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    VI

    Preface

    In this study, the dynamic behaviour of pipe rack steel structures due to explosion loads

    has been studied. The study has been carried out from January to May 2014. The

    masters thesis has been written for the Department of Civil and Environmental

    Engineering at Chalmers University of Technology (Chalmers) in collaboration withthe Structural Department at Aker Solutions (AKSO) in Oslo as part of the Nyhamna

    Expansion Project (NYX).

    Supervisor for the masters thesis project has been Reza Haghani Saeed (Assistant

    Profe