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  • A PARAMETRIC STUDY ON THE EFFECT OF

    SOIL-STRUCTURE INTERACTION ON SEISMIC RESPONSE

    OF MDOF AND EQUIVALENT SDOF SYSTEMS

    by

    BEHNOUD GANJAVI

    B.Sc., M.Sc.

    THIS THESIS IS PRESENTED FOR THE DEGREE OF

    DOCTOR OF PHILOSOPHY

    OF

    THE UNIVERSITY OF WESTERN AUSTRALIA

    Structural and Earthquake Engineering

    School of Civil and Resource Engineering

    June 2012

  • DECLARATION FOR THESIS CONTAINING PUBLISHED WORK

    AND/OR WORK PREPARED FOR PUBLICATION

    The thesis contains published work and/or work prepared for publication, which has

    been co-authored. The biographical of the work and where it appears in the thesis are

    outlined below.

    Ganjavi B., and Hao, H. (2011). A parametric investigation of the influence of soil-structure

    interaction on seismic response of MDOF and equivalent SDOF systems Advances in

    Structural Engineering, under review. (Chapter 3)

    The estimated percentage contribution of the candidate is 80%.

    Ganjavi B., and Hao, H. (2012). Effect of structural characteristics distribution on strength

    demand and ductility reduction factor of MDOF systems considering soil-structure

    interaction Earthquake Engineering and Engineering Vibration; 11(2); 205-220.

    (Chapter 4)

    The estimated percentage contribution of the candidate is 80%.

    Ganjavi B., and Hao, H. (2012). Strength reduction factor for MDOF soil-structure

    systems The Structural Design of Tall and Special Buildings, DOI: 10.1002/tal.1022;

    available online at: http://onlinelibrary.wiley.com/doi/10.1002/tal.1022/abstract. (Chapter 5)

    The estimated percentage contribution of the candidate is 80%.

    Ganjavi B., and Hao, H. (2012). A parametric study on evaluation of ductility demand

    distribution in Multi-Degree-of-Freedom systems considering soil-structure interaction

    effects Engineering Structures, 43; 88-104. (Chapter 6) The estimated percentage contribution of the candidate is 80%.

    Ganjavi B., and Hao, H. (2011). Optimum lateral load pattern for elastic seismic design of

    buildings incorporating soil-structure interaction effects Earthquake Engineering and

    Structural Dynamics, (In Press), DOI: 10.1002/eqe.2252. (Chapter 7)

    The estimated percentage contribution of the candidate is 70%.

    Ganjavi B., and Hao, H., and Bolourchi, S. A. (2012). Optimum seismic-resistant design of shear buildings considering soil-structure interaction effects and inelastic behavior Engineering Structures, to be Submitted. (Chapter 8)

    The estimated percentage contribution of the candidate is 80%.

    Behnoud Ganjavi 06/01/2013

    Print Name Signature Date

    Hong Hao

    Print Name Signature Date

    http://onlinelibrary.wiley.com/doi/10.1002/tal.1022/abstract

  • Abstract The University of Western Australia

    i

    ABSTRACT

    Even though extensive researches have been conducted on Soil-Structure Interaction

    (SSI) since 1960s, there are several aspects of the complex phenomenon of SSI that have

    not been addressed thoroughly. The complex behavior of SSI together with uncertainties

    in soil and structure parameters, and in ground motions result in a significant controversy

    over the effect of SSI on structural response in both elastic and inelastic states. Recent

    studies considered SSI in inelastic response analysis are mainly based on idealized

    structural models of single-degree-of-freedom (SDOF) systems. However, due to

    neglecting the effects of higher modes, the number of building stories and lateral

    strength and stiffness distributions along the height of structures, an SDOF system might

    not be able to realistically capture the SSI effects on the inelastic responses of real

    buildings.

    The primary objective of this research is to advance, through extensive parametric study

    and analytical research, knowledge on the effects of SSI on elastic and inelastic

    responses of Multi-Degree-Of-Freedom (MDOF) systems, and to develop optimization

    techniques for optimum seismic design of elastic and inelastic shear buildings taking into

    consideration the SSI effects.

    Firstly, the study addresses the effect of SSI on elastic and inelastic response of MDOF

    and its equivalent SDOF systems. The adequacy of equivalent SDOF model to estimate

    strength and ductility demand of multi-storey soil-structure systems are intensively

    investigated. It is concluded that using the common E-SDOF systems for estimating the

    strength demands of average and slender MDOF systems when SSI effect is significant

    can lead to very un-conservative results.

    Secondly, the effect of structural property distribution on strength demand and ductility

    (strength) reduction factor of MDOF fixed-base and soil-structure systems has been

    investigated. It has been done through intensive parametric analyses of numerous linear

    and nonlinear MDOF systems and considering five different shear strength and stiffness

    distribution patterns including 3 code-specified patterns as well as uniform and

    concentric patterns subjected to a group of earthquakes recorded on alluvium and soft

    soils. Results indicate that for both fixed-base and flexible-base models, with exception

    of those with very short periods, the averaged total strength demand values of structures

    designed based on uniform story strength and stiffness distribution pattern along the

  • Abstract The University of Western Australia

    ii

    height of the structures are significantly greater than those of the other patterns such as

    code-compliant patterns. This phenomenon is even more pronounced by increasing the

    number of stories. It is concluded that, therefore, using the results of the uniform story

    strength and stiffness distribution pattern which has been the assumption of many

    previous research works would result in a significant overestimation of the strength

    demands, generally from 2 to 4 times, for MDOF systems designed in accordance to the

    code-compliant design patterns. Moreover, through a comprehensive parametric study of

    numerous MDOF and its equivalent SDOF systems subjected to a large number of

    earthquake ground motions effects of SSI on strength reduction factor of MDOF and

    equivalent SDOF systems have been intensively investigated. Based on the numerical

    results of nonlinear dynamic analyses and statistical regression analyses, a new

    simplified equation is proposed to estimate strength reduction factors of MDOF soil-

    structure systems.

    Subsequently, after extensive parametric studies on the effect of SSI on global (total)

    strength and ductility demand of MDOF and the corresponding E-SDOF systems carried

    out in Chapters 3 to 5 as the first part of the thesis, the second part of this research

    focuses on the effect of SSI on local ductility (damage) demand distribution along the

    height of the structures. It is demonstrated that although the structures designed

    according to some of the recently proposed optimum load patterns for fixed-base

    systems may have generally better seismic performance when compared to those

    designed by code-specified load patterns, their seismic performance are far from ideal if

    the SSI effects are considered. Therefore, more adequate load patterns incorporating SSI

    effects for performance-based seismic design needs to be proposed.

    Finally, optimization techniques have been developed for optimum design of elastic and

    inelastic shear buildings taking into consideration the SSI effects. An iterative analysis

    procedure is introduced to estimate the optimum story shear strength distributions for a

    given structure, a given ground motion and soil-structure key parameters, and an

    inelastic target level of interest. Based on numerical analyses and statistical regression

    analyses new simplified equations are proposed for estimation of lateral load patterns of

    elastic and inelastic soil-structure systems. It is shown that the structures designed based

    on the proposed pattern, on average, display remarkably better seismic performance (i.e.,

    less structural weight and more uniform damage distribution over height) than the code-

    compliant and recently proposed patterns by researchers for fixed-base structures.

  • List of Publications The University of Western Australia

    iv

    LIST OF PUBLICATIONS

    REFEREED JOURNAL PAPERS:

    1) Ganjavi B., and Hao, H. (2011). A parametric investigation of the influence of

    soil-structure interaction on seismic response of MDOF and equivalent SDOF

    systems Advances in Structural Engineering, (Under review).

    2) Ganjavi B., and Hao, H. (2012). A parametric Study on Evaluation of Ductility

    Demand Distribution in Multi-Degree-of-Freedom Systems Considering Soil-

    Structure Interaction Effects Engineering Structures, 43; 88-104, October 2012.

    3) Ganjavi B., and Hao, H. (2012). Effect of Structural Characteristics Distribution

    on Strength Demand and Ductility Reduction Factor of MDOF Systems

    Considering Soil-Structure Interaction Earthquake Engineering and

    Engineering Vibration, 11(2); 205-220.

    4) Ganjavi B., and Hao, H. (2012). Strength Reduction Factor for MDOF Soil-

    Structure Systems The Structural design of Tall and Special Buildings,

    (DOI: 10.1002/tal.1022;

    http://onlinelibrary.wiley.com/doi/10.1002/tal.1022/abstract).

    5) Ganjavi B., and Hao, H. (2012). Optimum lateral load pattern for Elastic

    Seismic Design of Buildings Incorporating Soil-Structure Interaction Effects

    Earthquake Engineering and Structural Dynamics, (in Press). DOI:

    10.1002/eqe.2252

    6) Ganjavi B., and Hao, H., and Bolourchi, S.A. (2012). Optimum Seismic-

    Resistant Design of Shear Buildings Considering Soil-Structure Interaction

    Effects and Inelastic Behavior Engineering Structures, (To be Submitted).

    http://onlinelibrary.wiley.com/doi/10.1002/tal.1022/abstract

  • List of Publications The University of Western Australia

    v

    REFEREED CONFERENCE PAPERS:

    1) Ganjavi B., and Hao, H. (2011). Elastic and Inelastic Response of Single- and

    Multi-Degree-of-Freedom Systems Considering Soil Structure Interaction

    Effects Australian Earthquake Engineering Society Conference. Barossa Valley,

    South Australia, 18-20 November.

    2) Ganjavi B., and Hao, H. (2011). Evaluation of the Adequacy of Code Equivalent

    Lateral Load Pattern and Ductility Demand Distribution for Soil-Structure

    Systems Australian Earthquake Engineering Society Conference. Barossa

    Valley, South Australia, 18-20 November.

    3) Ganjavi B., and Hao, H. (2012). Influence of Structural Property Distribution on

    Elastic and Inelastic Strength Demand of Shear Buildings with Soil-Structure

    Interaction, Australasian Structural Engineering Conference. Perth, Western

    Australia.11-13 July. Paper N: 006.

    4) Ganjavi B., and Hao, H. (2012). New lateral Force Distribution for Elastic

    Seismic Design of Shear Buildings Incorporating SSI Effects, Australasian

    Structural Engineering Conference. Perth, Western Australia.11-13 July. Paper

    N: 030.

    5) Ganjavi B., and Hao, H. (2012). An Optimization Technique for Uniform

    Damage Distribution in Inelastic Shear Building Incorporation Soil-Structure

    Interaction Effects,15 World Conference on Earthquake Engineering. Lisbon,

    Portugal, 24-28 September.

    6) Ganjavi B., and Hao, H. (2012). Ductility Reduction Factor for Multi-Degree-

    of-Freedom Systems with Soil-Structure Interaction, 15 World Conference on

    Earthquake Engineering. Lisbon, Portugal, 24-28 September.

  • Table of contents The University of Western Australia

    vi

    TABLE OF CONTENTS

    ABSTRACT....i

    LIST OF PUBLICATIONS...iv

    LIST OF CONTENTS...vi

    LIST OF FIGURES..xii

    LIST OF TABLESxviii

    ACKNOWLEDGEMENTS.xix

    CHAPTER 1 INTRODUCTION...1

    1.1 Background and Motivation...1

    1.2 Research Goals...7

    1.3 Outlines..7

    1.4 References..9

    CHAPTER 2 MODELING AND ANALYSIS PROCEDURES...14

    2.1 Introduction...14

    2.2 Soil-Foundation- Structure Model15

    2.2.1 Soil-Foundation Model.15

    2.2.2 Superstructure Models .18

    2. 3 Key Parameters ...19

    2.4 Methodology and Procedures for Analysis...21

    2.5 OPTSSI Computer Program..21

    2.5.1 Soil and Structural Modelling and Assumption21

    2.5.2 Structural Damping Modelling.24

    2.5.3 Earthquake Ground Motion Parameters24

    2.5.3 Story Shear Strength and Stiffness Distribution Pattern..25

    2.6 Computational Features of OPTSSI.25

    2.7 Evaluation of MDOF Soil-Structure Systems Designed Based on Fixed-Base

    Assumptions...27

    2.7 Database for Parametric Analysis28

    2.9 References31

  • Table of contents The University of Western Australia

    vii

    CHAPTER 3 EFFECT OF SOIL-STRUCTURE INTERACTION ON

    ELASTIC AND INELASTIC RESPONSE OF MDOF AND EQUIVALENT SDOF

    SYSTEMS ...33

    3.1 Introduction...33

    3.2 Methodology and Procedures for Analysis...35

    3.2. 1. General Procedure...36

    3.2. 2 Proposed Iterative Procedure...36

    3.2.3 Step-by-Step Procedure for Parametric Study..38

    3.3 Effect of SSI on Strength Demands of MDOF and E-SDOF Systems.39

    3.3.1 Strength Demands for E-SDOF Systems Corresponding to Different

    Number of Stories .39

    3.3.2 Strength Demands for MDOF and E-SDOF Soil-Structure Systems...41

    3.3.2 Adequacy of E-SDOF systems in estimating strength demands for MDOF

    fixed-base and soil-structure systems46

    3.4 Effect of SSI on Ductility Demand of MDOF and E-SDOF Systems..49

    3.5. CONCLUSION53

    3.6 References.55

    CHAPTER 4 Effect of Structural Characteristics Distribution on Strength

    Demand and Ductility Reduction Factor of MDOF Systems Considering Soil-

    Structure Interaction..58

    4.1 Introduction...58

    4.2 Selected Story Strength and Stiffness Distribution Patterns 59

    4.3 Analysis Procedure ..61

    4.4 Effect of Structural Characteristics Distribution on Strength Demand of MDOF

    Systems...62

    4.5 Comparison between Strength Demands of Fixed-Base and Flexible-base

    MDOF Systems ..66

    4.6 Validation of the Numerical Results 68

    4.7 Effect of Structural Characteristics Distribution on Ductility Reduction Factor

    of MDOF Systems .68

    4.7.1 Effect of Structural Characteristics Distribution..69

    4.7.2 Effect of Soil Flexibility...71

    4. 8. Summary and Conclusions74

    4.9 References76

  • Table of contents The University of Western Australia

    viii

    CHAPTER 5 Strength Reduction Factor for Multi-Degree-Of-Freedom Systems

    Considering Soil-Structure Interaction Effects...........................................................78

    5.1 Introduction..78

    5.2 Selected Earthquake Ground Motions..81

    5. 3 Procedure for Analysis82

    5. 4. Effect of SSI on Strength Reduction Factor of E-SDOF Systems.82

    5.4.1 Strength Reduction Factors of E-SDOF Systems for Structures with

    Different Number of Stories .82

    5.4. 2 Effect of Ductility Ratio...84

    5.4.3 Effect of Dimensionless Frequency..84

    5.4.4 Effect of Aspect Ratio ..85

    5.4.5 Using R of E-SDOF Fixed-base Systems for Soil-Structure

    Systems.86

    5. 5. Effect of SSI on Strength Reduction Factor of MDOF Systems88

    5...

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