SEISMIC DESIGN, ASSESSMENT AND

RETROFITTING OF CONCRETE BUILDINGS

GEOTECHNICAL, GEOLOGICAL AND EARTHQUAKEENGINEERING

Volume 8

Series Editor

Atilla Ansal, Kandilli Observatory and Earthquake Research Institute,Bogazici University, Istanbul, Turkey

Editorial Advisory Board

Julian Bommer, Imperial College London, U.K.Jonathan D. Bray, University of California, Berkeley, U.S.A.

Kyriazis Pitilakis, Aristotle University of Thessaloniki, GreeceSusumu Yasuda, Tokyo Denki University, Japan

For other titles in this series, go to:http://www.springer.com/series/6011

Seismic Design, Assessmentand Retrofitting of ConcreteBuildingsBased on EN-Eurocode8

by

MICHAEL N. FARDIS

Department of Civil Engineering, University of Patras, Greece

123

Michael N. FardisDepartment of Civil EngineeringUniversity of PatrasP.O. Box 142426504 PatrasGreecefardis@upatras.gr

ISBN 978-1-4020-9841-3 e-ISBN 978-1-4020-9842-0DOI 10.1007/978-1-4020-9842-0Springer Dordrecht Heidelberg London New York

Library of Congress Control Number: 2009926882

c© Springer Science+Business Media B.V. 2009No part of this work may be reproduced, stored in a retrieval system, or transmitted in any form or byany means, electronic, mechanical, photocopying, microfilming, recording or otherwise, without writtenpermission from the Publisher, with the exception of any material supplied specifically for the purposeof being entered and executed on a computer system, for exclusive use by the purchaser of the work.

Printed on acid-free paper

Springer is part of Springer Science+Business Media (www.springer.com)

To Tonia and Nikos

Preface

The goal of the book is to present and explain the state of the art of design orretrofitting concrete buildings for earthquake resistance. To serve this goal, it alsocovers behaviour of concrete members under cyclic loading and seismic response ofconcrete buildings, as well as their modelling. Its main focus is the European DesignStandard EN1998 – Eurocode 8: Design of structures for earthquake resistance, andin particular its Parts 1 and 3, dealing with seismic design of new buildings and withassessment and retrofitting of existing ones, respectively.

The book is addressed to practitioners of seismic design, assessment andretrofitting, to graduate and advanced undergraduate students in structural earth-quake engineering and to researchers with interests in the field of earthquake resis-tant concrete structures. Certain familiarity of the reader with design of structuralconcrete and with structural analysis – including seismic analysis and structuraldynamics – is presumed.

The book has been written in the course of my teaching activity for the MScDegree in Earthquake Engineering and Engineering Seismology (MEEES), grantedjointly by the Universities of Pavia and Patras and the J. Fourier University ofGrenoble in the framework of the Erasmus Mundus programme of the EuropeanCommission. It has drawn from my involvement in the development of Eurocode8 as a European Design Standard, and of its Parts 1 and 3 in particular. It hasalso drawn from my research at the University of Patras during the past 25 yearsand in particular from the joint work with my former doctoral students Dionysis E.Biskinis, Antonis J. Kosmopoulos and Telemachos B. Panagiotakos and my currentcolleague Stathis N. Bousias – as evident from the referencing throughout the book.I would also like to express my gratitude and appreciation to Eduardo C. Carvalhoand Amr S. Elnashai for their very meticulous review and their comments for thebook.

Patras, Greece Michael N. Fardis

vii

From the Reviews of the Book

The book is devoted to the seismic design of new buildings as well as to the assess-ment and retrofit of existing buildings, covering essentially the contents of Parts 1and 3 of Eurocode 8. It must be stressed that its contents which refers to Assessmentand Retrofit is a very important support tool to the application of Part 3 of Eurocode8 which deals with Assessment and Retrofitting of Buildings and which in itself isa quite innovative document.

The book is organised in six chapters dealing sequentially with: the GeneralPrinciples of Seismic Design; the Conceptual Design of Concrete Buildings forEarthquake Resistance; the Behaviour of Concrete Members under Cyclic Loading;the Analysis and Modelling for Seismic Design; the Detailing and Dimensioningand finally the Seismic Assessment and Retrofitting.

Summing up, the book is extremely valuable and represents a much updated stateof the art in seismic design of concrete structures not only in Europe but also in otherparts of the world. It is very carefully written with the clear intent to cover all aspectsof seismic design and not leaving behind any aspect relevant for such. It shall be veryuseful and an authoritative source for the understanding and application of Eurocode8 at several different levels, from the ordinary practitioner to the knowledgeableresearcher passing by the software developer.

The book reflects the very solid knowledge of the author in earthquake engineer-ing and his leading role in the recent developments of Eurocode 8, as well as theextreme care that was devoted to its planning and writing. No doubt, it shall becomea reference in the field.

Eduardo C. CarvalhoChairman of CEN/TC250/SC8Lisbon, Portugal

ix

x From the Reviews of the Book

The book starts with a Preamble that highlights a most important aspect of design,which is its interaction with construction, and emphasises the safety aspect of awell-designed structure that is difficult to build. The introductory notes set the scenefor the subsequent detailed treatment of issues of seismic design of RC structures, afeature that is lacking in most design-oriented books in the earthquake engineeringfield. This leads naturally to Chapter 1, where the general principles of seismicdesign of RC structures are presented in a rational framework, which demonstratesthe author’s experience in conceptual and practical seismic design alike. Issues ofsingle and multiple performance levels and their relationship with seismic hazardlevels are succinctly explained. Covering both US and European practice, withemphasis on the latter, the author explains capacity design and the criteria used toestablish a hierarchical dissipative and non-dissipative sequence of events. Capacitydesign is also applied in this chapter to typical systems, as well as to the flexure-shear problem.

Chapter 2 addresses conceptual design, guiding the reader through the steps pos-tulated by the author for the selection of layout and preliminary sizing. The criticalrole of conceptual design in facilitating final and detailed design and reducing thenumber of iterations required is emphasised. A detailed treatment of regularity isgiven and examples are provided to demonstrate the adverse effects of irregularityon performance. Redundancy, continuity and mass minimisation are other featuresdiscussed in this chapter, with examples and practical guidance. The chapter con-cludes with examples of poorly conceived buildings that have been damaged inrecent European earthquakes.

A most detailed and exhaustive treatment of the behaviour of RC members andconnections is given in Chapter 3, with a wealth of behaviour-oriented expressionsfor deformation and strength. Examples from the literature are quoted and put intocontext to provide the reader with a comprehensive set of models for deformationand strength of members subjected to multi-axial stresses. This chapter is ratherunique amongst recent seismic design books and on its own is worth reading care-fully.

Another exhaustive treatment of modelling for design and assessment is givenin Chapter 4, which also includes aspects of input motion. Elastic and inelasticanalyses are addressed in detail, and examples and guidance on their applicabil-ity or otherwise are provided. Exceptionally insightful comments and guidance aregiven with regard to the intricate issue of modeling infill walls in frames. Threedetailed examples are given in the closing part of the chapter where the guidancegiven throughout the chapter is applied to a test bed 3D frame structure, thus givingcredence to the guidance.

Detailing and dimensioning requirement of Eurocode 8 are addressed in Chapter5. Two worked examples that will prove invaluable to readers and potential usersof the Eurocode are also given. The worked examples not only address the casesdealt with, but give clues as to how to apply Eurocode 8, as seen by the researcherwho guided its final stages of development and implementation, to a wider range ofdesign situations.

From the Reviews of the Book xi

The last main chapter in the book, Chapter 6, deals with retrofitting of RC struc-tures using Eurocode 8, with very considerable amounts of backup material fromthe research literature. The rules described in the chapter are then applied to twocase studies, which are continuation of the “analysis” case studies, thus providing athread through the various chapters. This thread will be valuable to readers becauseit establishes a clear link between design and analysis for assessment of the design,as well as retrofitting.

Amr S. Elnashai, FREngBill and Elaine Hall Endowed ProfessorDirector of the Mid-America Earthquake CenterDirector of NEES@Illinois Earthquake Simulation FacilityDirector of the Council on Global Engineering InitiativesUniversity of Illinois, Urbana, Illinois, USA

Preamble

The main activity of today’s civil engineers is the production of structures. Thisactivity has two phases:

– design, and– construction – also termed “execution”, as “construction” is also used for civil

engineering works in general.

In the construction phase the civil engineer does not necessarily have the centralrole. In design, by contrast, his/her role is not just prime but almost exclusive.

With design being the 1st phase of the production process, many areas of thebroader field of Earthquake Engineering ultimately serve design. For instance:

– a prime goal of Engineering Seismology and Geotechnical Earthquake Engineer-ing is to determine the ground motion for the seismic design;

– a major role of Structural Dynamics – within the context of Earthquake Engi-neering – is the calculation of the response of the structure to a given seis-mic motion, either to verify that performance is satisfactory, or to provide thebasis for the dimensioning of structural elements so that performance is indeedsatisfactory.

There is strong interaction between design and construction of a structure. Designcan be considered to govern production of a structure, as construction imple-ments design drawings and specifications. However, design is influenced by, ordepends on, construction as well. A structure is designed to be ultimately built;so the way it will be constructed should be a determining factor for its design.So, when designing the structure the engineer should have a clear and preciseidea of how his/her design will be implemented with the human resources, equip-ment and materials available for that particular project. A design that seems excel-lent on paper but cannot be easily implemented with the available means andresources may in reality be poor or even unsafe, because bad implementationmeans poor quality. This point is very important for earthquake resistant concretestructures, as:

xiii

xiv Preamble

– Seismic performance depends heavily on the detailing of the reinforcement;– In seismic regions a building’s safety problem may remain hidden for long and

show up only through its catastrophic consequences in the event of a strongearthquake. By contrast, in structures controlled by non-seismic actions, safetyproblems due to poor construction quality may become evident early on (e.g.upon striking off the formwork and falsework, or after all permanent loads areapplied), before delivering the facility to the users.

The engineer should keep in mind that the earthquake will “see” the structure as itis built. The intentions of the designer, the assumptions made, the analysis methodsused and the care exercised in its design, matter only to the extent they are indeedreflected in the as-built structure.

The seismic design process of a new concrete structure comprises four distinctphases:

(1) Conceptual design: the selection of the type and layout of the lateral-load-resisting system and of preliminary member sizes.

(2) Analysis: the calculation of the effects of the design actions, including the seis-mic one, in terms of internal forces and deformations in structural members.

(3) Detailed design: the verification of the adequacy of member dimensions and thedimensioning of the reinforcement on the basis of calculated action effects.

(4) Preparation of the end product of the design to be applied in the field: materialspecifications, construction drawings with detailing of the reinforcement, andany other information that may be necessary or helpful for the implementationof the design.

The design of the seismic retrofitting of an existing structure has the same fourphases, but referring specifically to the retrofitting. In this case, however, we havetwo preliminary phases:

(–2) Collection of information on the history, geometry, reinforcement, materials,etc., of the as-built structure, as input for the subsequent phases.

(–1) Analysis and verification of the as-built structure, to confirm that retrofitting isindeed necessary and identify the deficiencies to be remedied.

The outcome of the design is just that of phase (4) and is often considered asthe “design”. The outcomes of phases (2) and (3) (and of (–2) and (–1) for exist-ing structures) are just documentation of the “design”. Stage (1) is the designer’spersonal business and is not documented anywhere.

Be it for a new building or for retrofitting an existing one, conceptual design isof utmost importance for the economy and the seismic performance of the structure.The choices and decisions made there are entirely based on the experience, judg-ment and ingenuity of the designer, even on his/her personal design philosophy andpreferences. To some people design is just the conceptual design; all other phasesbeing considered as “code checking”.

Preamble xv

During all design phases the engineer should use not just the scientific/technicaltools at his/her disposal, but also judgment and experience, to produce a designthat – to the best of his or her knowledge – cost-effectively fulfils the performancerequirements. Experience is very important for the successful design of earthquake-resistant buildings. It provides ideas from previous, possibly similar, projects andhelps avoiding poor choices, pitfalls or even design errors. Experience is also valu-able to understand the “idiosyncrasy” of an existing building which is assessed forpossible retrofitting.

The technology for earthquake resistance evolved essentially after 1970. Sincethen, scientific knowledge and technology in earthquake engineering and seismicdesign codes alike have seen a very rapid, and still ongoing, development. As aresult, structures designed and constructed according to present generation codesenjoy a much higher safety level against earthquakes than older ones. The higherlevel of seismic safety comes at a higher cost (albeit less than proportional to theadded safety). Moreover, the ultimate criterion for the success or not of currentseismic codes and technology will be the performance of structures built with themin the event of an earthquake. Note that, owing to the short history of exposureof concrete construction to earthquakes (shorter than the time intervals betweenstrong earthquakes, even in highly seismic regions) and the continuous evolutionof seismic design codes during that history, we still lack sufficient feedback fromthe actual performance of concrete buildings. Finally, the short-term future willsee further advances, as our knowledge and technology for earthquake resistanceis in a state of continuous development. So, although we presently believe that ourcurrent know-how is satisfactory and produces safe structures, most likely in themedium-term seismic design will be quite different. Developments are expectedmainly towards further rationalisation of seismic design, to achieve the same or bet-ter performance at lower cost. Empirical and prescriptive approaches will certainlygive way to procedures based on more solid and rational grounds. The main vehiclefor the transfer of such progress to engineering practice will be codes and stan-dards for earthquake resistant design, notably those of the countries or regions mostadvanced in earthquake engineering (in alphabetical order, of the EU, Japan and theUS). Practitioners of seismic design should follow the developments in codes and beprepared for changes to come. For those active in seismic assessment and retrofittingof existing buildings as well, certain knowledge of past codes and practice will helpthem identify and remedy their problems and deficiencies.

Chapter 2 of the book is devoted to conceptual design of new building struc-tures for earthquake resistance. Chapter 1 provides an overview of the performancerequirements for new building structures, of the philosophy of current seismicdesign codes for new earthquake-resistant buildings and of the main instrumentsfor its implementation. Chapter 3 covers the behaviour under cyclic loading of theconstituent materials and of concrete members of the type common in buildings, aswell as the quantification of this behaviour. That chapter provides the backgroundfor Chapters 5 and 6. Chapter 4 is devoted to analysis and modelling issues, withemphasis on the analysis approaches commonly used within the context of codifiedseismic design or assessment (phase (2) of the design process). Chapter 5 deals with

xvi Preamble

dimensioning and detailing of new building structures for earthquake resistance andgives the background of some of the rules in Eurocode 8 on the basis of the materialof Chapters 1 and 3. Chapter 6, on assessment and upgrading of the seismic perfor-mance of existing buildings, builds on Chapters 3 and 4, as well as on the generalperformance requirements set out in Chapter 1.

To a certain extent the book develops with reference to the European Stan-dards for seismic design, assessment and retrofitting of buildings, Parts 1 and 3of Eurocode 8. Some parts of Chapter 1 and 4 include references to Eurocode 8, butalso to US seismic design standards. Chapters 5 and 6 are linked with Eurocode 8 –Chapter 5 very closely, but Chapter 6 less so.

In December 2004, Part 1 of Eurocode 8 (CEN 2004a) was published by theEuropean Committee for Standardisation to become the first in history EuropeanStandard for seismic design of new buildings, complementary to the other EN-Eurocodes. It was followed in June 2005 by Part 3 of Eurocode 8 (CEN 2005a), forseismic assessment and retrofitting of existing buildings. The 31 member countriesin CEN have since then published these European Standards as their own NationalStandards, together with their National Annexes. These Annexes state the nationalchoices for the so-called “Nationally Determined Parameters”, devised to providethe flexibility required for the application of Eurocode 8 in a whole continent withdiverse engineering traditions and seismicity. Until March 2010 national designstandards will be used in parallel with Eurocode 8, but by March 2010 nationaldesign standards that conflict in any aspect with any EN-Eurocode should be with-drawn.

In the USA seismic design of buildings follows a building design code thatcovers also non-structural aspects (architectural, mechanical, electrical, buildingequipment, etc.). Seismic design provisions for new buildings were traditionallydeveloped either by the Building Seismic Safety Council (BSSC) and published as“NEHRP Recommended Provisions for the Development of Seismic Regulationsfor Buildings and Other Structures” (BSSC 2003), or by the Structural EngineersAssociation of California (SEAOC) and published as “SEAOC Recommended Lat-eral Force Requirements” (SEAOC 1999). With some time-lag the NEHRP provi-sions have traditionally been reflected in (but not fully adopted by) the “NationalBuilding Code”, the “Standard Building Code” and more recently the “Interna-tional Building Code” (ICC 2006). The SEAOC requirements have been in generalreflected in the “Uniform Building Code”, the last version of which was issuedin 1997 (ICBO 1997). Local Authorities (States, counties, cities) formally adoptone of the three model codes after adaptation to local traditions/conditions. Recentyears have seen a convergence of the seismic design provisions in the NEHRPand SEAOC documents, extending also to the main material codes referred to,or used as source documents by them, such as the ACI 318 code (ACI 2008),prepared by the American Concrete Institute. Moreover, in 1997 the “Interna-tional Code Council” was formed and issued in 2000 the “International BuildingCode”. Since then, the updated code (ICC 2006) is gradually adopted throughoutthe US.

Contents

1 General Principles for the Design of Concrete Buildings forEarthquake Resistance . . . . . . . . . . . . . . . . . . . . . . . . . 11.1 Seismic Performance Requirements for Concrete Buildings . . . 1

1.1.1 The Current Situation: Emphasis on Life Safety . . . . . 11.1.2 Performance-Based Requirements . . . . . . . . . . . . 21.1.3 Performance-Based Seismic Design, Assessment

or Retrofitting According to Eurocode 8 . . . . . . . . . 51.1.4 Performance-Based Design Aspects of Current

US Codes . . . . . . . . . . . . . . . . . . . . . . . . . 81.2 Force-Based Seismic Design . . . . . . . . . . . . . . . . . . . 9

1.2.1 Force-Based Design for Energy-Dissipation and Ductility 91.2.2 Force-Based Dimensioning of Ductile

“Dissipative Zones” and of Other Regions of Members . 111.3 Control of Inelastic Seismic Response Through Capacity Design 15

1.3.1 The Rationale of Capacity Design . . . . . . . . . . . . 151.3.2 The Importance of a Stiff and Strong Vertical

Spine in a Building . . . . . . . . . . . . . . . . . . . . 161.3.3 Overview of Capacity-Design-Based Seismic

Design Procedure . . . . . . . . . . . . . . . . . . . . . 191.3.4 Capacity Design of Columns in Flexure . . . . . . . . . 201.3.5 Design of Ductile Walls in Flexure . . . . . . . . . . . . 241.3.6 Capacity Design of Members Against

Pre-emptive Shear Failure . . . . . . . . . . . . . . . . 261.4 The Options of Strength or Ductility

in Earthquake-Resistant Design . . . . . . . . . . . . . . . . . . 361.4.1 Ductility as an Alternative to Strength . . . . . . . . . . 361.4.2 The Trade-Off Between Strength and

Ductility – Ductility Classification in SeismicDesign Codes . . . . . . . . . . . . . . . . . . . . . . . 38

1.4.3 Behaviour Factor q of Concrete BuildingsDesigned for Energy Dissipation . . . . . . . . . . . . . 41

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xviii Contents

2 Conceptual Design of Concrete Buildings for Earthquake Resistance 472.1 Principles and Rules for the Conceptual Design

of Building Structures . . . . . . . . . . . . . . . . . . . . . . . 472.1.1 The Importance of Conceptual Design

for Earthquake Resistance . . . . . . . . . . . . . . . . 472.1.2 Fundamental Attributes of a Good Structural Layout . . 502.1.3 Clear Lateral-Load-Resisting System . . . . . . . . . . 502.1.4 Simplicity and Uniformity in the Geometry

of the Lateral-Load-Resisting System . . . . . . . . . . 522.1.5 Symmetry and Regularity in Plan . . . . . . . . . . . . 522.1.6 Torsional Stiffness About a Vertical Axis . . . . . . . . 582.1.7 Geometry, Mass and Lateral Stiffness Regular

in Elevation . . . . . . . . . . . . . . . . . . . . . . . . 602.1.8 Lateral Resistance Characterised by Regularity

in Elevation . . . . . . . . . . . . . . . . . . . . . . . . 632.1.9 Redundancy of the Lateral Load Resisting System . . . 642.1.10 Continuity of the Force Path, Without Local

Concentrations of Stresses and Deformation Demands . 672.1.11 Effective Horizontal Connection of Vertical

Elements by Floor Diaphragms at All Floor Levels . . . 682.1.12 Minimal Total Mass . . . . . . . . . . . . . . . . . . . 712.1.13 Absence of Adverse Effects of Elements

Not Considered As Part of the Lateral-LoadResisting System and of Masonry Infills in Particular . . 72

2.2 Frame, Wall or Dual Systems for Concrete Buildings . . . . . . . 832.2.1 Seismic Behaviour and Conceptual Design of

Frame Systems . . . . . . . . . . . . . . . . . . . . . . 832.2.2 Seismic Behaviour and Conceptual Design of

Wall Systems . . . . . . . . . . . . . . . . . . . . . . . 942.2.3 Dual Systems of Frames and Walls . . . . . . . . . . . 1032.2.4 The Special Case of Flat-Slab Frames . . . . . . . . . . 105

2.3 Conceptual Design of Shallow (Spread) FoundationSystems for Earthquake-Resistance . . . . . . . . . . . . . . . . 1082.3.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . 1082.3.2 Foundation of the Entire Building at the Same Level . . 1102.3.3 The Options for Shallow Foundation Systems . . . . . . 1122.3.4 Capacity Design of the Foundation . . . . . . . . . . . . 1152.3.5 A Look into the Future for the Seismic Design

of Foundations . . . . . . . . . . . . . . . . . . . . . . 1182.4 Examples of Seismic Performance of Buildings with

Poor Structural Layout . . . . . . . . . . . . . . . . . . . . . . . 1192.4.1 Introductory Remarks . . . . . . . . . . . . . . . . . . 1192.4.2 Collapse of Wing of Apartment Building in the

Athens 1999 Earthquake . . . . . . . . . . . . . . . . . 119

Contents xix

2.4.3 Collapse of Four-Storey Hotel Building in theAegio (GR) 1995 Earthquake . . . . . . . . . . . . . . 123

2.4.4 Collapse of Six-Storey Apartment Buildingin the Aegio (GR) 1995 Earthquake . . . . . . . . . . . 124

3 Concrete Members Under Cyclic Loading . . . . . . . . . . . . . . . 1293.1 The Materials and Their Interaction . . . . . . . . . . . . . . . . 129

3.1.1 Reinforcing Steel . . . . . . . . . . . . . . . . . . . . . 1293.1.2 The Concrete . . . . . . . . . . . . . . . . . . . . . . . 1413.1.3 Interaction Between Reinforcing Bars and Concrete . . . 1643.1.4 Concluding Remarks on the Behaviour

of Concrete Materials and Their InteractionUnder Cyclic Loading . . . . . . . . . . . . . . . . . . 174

3.2 Concrete Members . . . . . . . . . . . . . . . . . . . . . . . . . 1753.2.1 The Mechanisms of Force Transfer in Concrete

Members: Flexure, Shear and Bond . . . . . . . . . . . 1753.2.2 Flexural Behaviour at the Cross-Sectional Level . . . . . 1773.2.3 Flexural Behaviour at the Member Level . . . . . . . . 2143.2.4 Behaviour of Members Under Cyclic Shear . . . . . . . 2513.2.5 Cyclic Behaviour of Squat Members, Controlled

by Flexure-Shear Interaction . . . . . . . . . . . . . . . 2723.3 Joints in Frames . . . . . . . . . . . . . . . . . . . . . . . . . . 281

3.3.1 Force Transfer Mechanisms in Concrete Joints:Bond and Shear . . . . . . . . . . . . . . . . . . . . . . 281

3.3.2 The Bond Mechanism of Force Transfer in Joints . . . . 2833.3.3 Force Transfer Within Joints Through the Shear

Mechanism . . . . . . . . . . . . . . . . . . . . . . . . 287

4 Analysis and Modelling for Seismic Design or Assessmentof Concrete Buildings . . . . . . . . . . . . . . . . . . . . . . . . . . 2994.1 Scope of Analysis in Codified Seismic Design or Assessment . . 299

4.1.1 Analysis for the Purposes of Seismic Design . . . . . . 2994.1.2 Analysis for Seismic Assessment and Retrofitting . . . . 302

4.2 The Seismic Action for the Analysis . . . . . . . . . . . . . . . 3044.2.1 Elastic Spectra . . . . . . . . . . . . . . . . . . . . . . 3044.2.2 Design Spectrum for Forced-Based Design

with Linear Analysis . . . . . . . . . . . . . . . . . . . 3104.3 Linear Static Analysis . . . . . . . . . . . . . . . . . . . . . . . 311

4.3.1 Fundamentals and Conditions of Applicability . . . . . 3114.3.2 Fundamental Period and Base Shear . . . . . . . . . . . 3134.3.3 Pattern of Lateral Forces . . . . . . . . . . . . . . . . . 315

4.4 Modal Response Spectrum Analysis . . . . . . . . . . . . . . . 3164.4.1 Modal Analysis and Its Results . . . . . . . . . . . . . 316

xx Contents

4.4.2 Minimum Number of Modes . . . . . . . . . . . . . . . 3194.4.3 Combination of Modal Results . . . . . . . . . . . . . . 320

4.5 Linear Analysis for the Vertical Seismic Action Component . . . 3214.5.1 When is the Vertical Component Important

and Should Be Taken Into Account? . . . . . . . . . . . 3214.5.2 Special Linear Static Analysis Approach

for the Vertical Component . . . . . . . . . . . . . . . . 3224.6 Nonlinear Analysis . . . . . . . . . . . . . . . . . . . . . . . . . 324

4.6.1 Nonlinear Static (“Pushover”) Analysis . . . . . . . . . 3244.6.2 Nonlinear Dynamic (Response- or Time-History)

Analysis . . . . . . . . . . . . . . . . . . . . . . . . . 3304.6.3 Concluding Remarks on the Nonlinear Analysis Methods 336

4.7 Combination of the Maximum Effects of the IndividualSeismic Action Components . . . . . . . . . . . . . . . . . . . . 3374.7.1 The Two Options: The SRSS and the Linear

Approximation . . . . . . . . . . . . . . . . . . . . . . 3374.7.2 Combination of the Effects of the Seismic

Action Components in Dimensioningfor Vectorial Action Effects . . . . . . . . . . . . . . . 339

4.8 Analysis for Accidental Torsional Effects . . . . . . . . . . . . . 3464.8.1 Accidental Eccentricity . . . . . . . . . . . . . . . . . . 3464.8.2 Estimation of the Effects of Accidental

Eccentricity Through Linear Static Analysis . . . . . . . 3484.8.3 Combination of Accidental Eccentricity Effects

Due to the Two Horizontal Components of theSeismic Action for Linear Analysis . . . . . . . . . . . 349

4.8.4 Simplified Estimation of Accidental EccentricityEffects in Eurocode 8 for Planwise SymmetricLateral Stiffness and Mass . . . . . . . . . . . . . . . . 350

4.8.5 Accidental Eccentricity in Nonlinear Analysis . . . . . . 3514.9 Modeling of Buildings for Linear Analysis . . . . . . . . . . . . 352

4.9.1 The Level of Discretisation . . . . . . . . . . . . . . . . 3524.9.2 Effective Elastic Stiffness of Concrete Members . . . . 3534.9.3 Modelling of Beams and Columns . . . . . . . . . . . . 3544.9.4 Special Modelling Aspects for Walls . . . . . . . . . . . 3574.9.5 Modelling of Floor Diaphragms . . . . . . . . . . . . . 3594.9.6 A Special Case in Modelling: Concrete Staircases . . . . 3624.9.7 2nd-Order (P-Δ) Effects . . . . . . . . . . . . . . . . . 3634.9.8 Modelling of Masonry Infills . . . . . . . . . . . . . . . 3654.9.9 Modelling of Foundation Elements

and of Soil Compliance . . . . . . . . . . . . . . . . . . 3694.10 Modelling of Buildings for Nonlinear Analysis . . . . . . . . . . 379

4.10.1 Nonlinear Models for Concrete Members . . . . . . . . 3794.10.2 Nonlinear Modelling of Masonry Infills . . . . . . . . . 4044.10.3 Modelling of Foundation Uplift . . . . . . . . . . . . . 410

Contents xxi

4.10.4 Special Provisions of Eurocode 8 for Nonlinear Analysis 4124.10.5 Example Applications of Nonlinear Analysis in

3D and Comparison with Measured Dynamic Response 4134.11 Calculation of Displacement and Deformation Demands . . . . . 426

4.11.1 Estimation of Inelastic Displacements andDeformations Through Linear Analysis . . . . . . . . . 426

4.11.2 Evaluation of the Capability of Linear Analysisto Predict Inelastic Deformation Demands . . . . . . . . 429

4.12 “Primary” V “Secondary Members” for Earthquake Resistance . 4324.12.1 Definition and Role of “Primary”

and “Secondary Members” . . . . . . . . . . . . . . . . 4324.12.2 Constraints on the Designation of Members as

“Secondary” . . . . . . . . . . . . . . . . . . . . . . . 4334.12.3 Special Design Requirements for “Secondary

Members” in New Buildings . . . . . . . . . . . . . . . 4344.12.4 Guidance on the Use of the Facility

of “Secondary Members” . . . . . . . . . . . . . . . . . 4354.12.5 Modelling of “Secondary Members” in the Analysis . . 437

5 Detailing and Dimensioning of New Buildings in Eurocode 8 . . . . 4415.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . 441

5.1.1 “Critical Regions” in Ductile Elements . . . . . . . . . 4415.1.2 Geometry, Detailing and Special Dimensioning

Rules in Eurocode 8: An Overview . . . . . . . . . . . 4425.2 Curvature Ductility Requirements According to Eurocode 8 . . . 4515.3 Detailing Rules for Local Ductility of Concrete Members . . . . 454

5.3.1 Minimum Longitudinal ReinforcementThroughout a Beam . . . . . . . . . . . . . . . . . . . . 454

5.3.2 Maximum Longitudinal Reinforcement Ratioin “Critical Regions” of Beams . . . . . . . . . . . . . . 455

5.3.3 Confining Reinforcement in “Critical Regions”of Primary Columns and Ductile Walls . . . . . . . . . 456

5.3.4 Boundary Elements at Section Edges in “CriticalRegions” of Ductile Walls . . . . . . . . . . . . . . . . 462

5.4 Detailing and Dimensioning of Beam-Column Joints . . . . . . . 4635.4.1 Maximum Diameter of Longitudinal Beam Bars

Crossing or Anchored at Beam-Column Joints . . . . . 4635.4.2 Verification of Beam-Column Joints in Shear . . . . . . 466

5.5 Special Dimensioning Rules for Shear . . . . . . . . . . . . . . 4695.5.1 Dimensioning of Shear Reinforcement in

“Critical Regions” of Beams or Columns . . . . . . . . 4695.5.2 Inclined Reinforcement Against Sliding Shear

in “Critical Regions” of DC H Beams . . . . . . . . . . 4705.5.3 Shear Verification of Ductile Walls of DC H . . . . . . . 471

xxii Contents

5.6 Systems of “Large Lightly Reinforced Walls” in Eurocode 8 . . . 4725.6.1 Definitions . . . . . . . . . . . . . . . . . . . . . . . . 4725.6.2 Dimensioning of “Large Lightly Reinforced

Walls” for the ULS in Bending and Axial Force . . . . . 4745.6.3 Dimensioning of “Large Lightly Reinforced

Walls” for the ULS in Shear . . . . . . . . . . . . . . . 4755.6.4 Detailing of the Reinforcement in “Large Lightly

Reinforced Walls” . . . . . . . . . . . . . . . . . . . . 4785.7 Implementation of Detailed Design of a Building Structure . . . 480

5.7.1 The Sequence of Operations in Detailed Designfor Ductility . . . . . . . . . . . . . . . . . . . . . . . . 480

5.7.2 Detailed Design of Beam and Joints . . . . . . . . . . . 4815.7.3 Detailed Design of Columns . . . . . . . . . . . . . . . 4895.7.4 Detailed Design of Ductile Walls . . . . . . . . . . . . 502

5.8 Application Examples . . . . . . . . . . . . . . . . . . . . . . . 5075.8.1 3-Storey Frame Building on Spread Footings . . . . . . 5075.8.2 7-Storey Wall Building with Box Foundation

and Flat Slab Frames Taken as Secondary Elements . . . 553

6 Seismic Assessment and Retrofitting of Existing Concrete Buildings 5956.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5956.2 Seismic Vulnerability of Existing Concrete Buildings . . . . . . 598

6.2.1 System and Layout Aspects and Deficiencies . . . . . . 5986.2.2 Common Deficiencies and Failure Modes

of Concrete Members . . . . . . . . . . . . . . . . . . . 5996.3 The Predicament of Force-Based Seismic Assessment

and Retrofitting . . . . . . . . . . . . . . . . . . . . . . . . . . 6006.4 Seismic Performance Requirements and Criteria for

Existing or Retrofitted Buildings . . . . . . . . . . . . . . . . . 6016.5 Performance- and Displacement-Based Seismic

Assessment and Retrofitting in Eurocode 8 . . . . . . . . . . . . 6026.5.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . 6026.5.2 Performance Requirements . . . . . . . . . . . . . . . . 6036.5.3 Information on the As-Built Geometry, Materials

and Reinforcement . . . . . . . . . . . . . . . . . . . . 6046.5.4 Seismic Analysis and Models . . . . . . . . . . . . . . 6086.5.5 Estimation of Force Demands by Capacity

Design In Lieu of Linear Analysis . . . . . . . . . . . . 6126.5.6 Verification Criteria for Existing, Retrofitted,

or New Members . . . . . . . . . . . . . . . . . . . . . 6186.5.7 Masonry Infills in Assessment and Retrofitting . . . . . 6246.5.8 Force-Based Assessment and Retrofitting (the

“q-factor Approach”) . . . . . . . . . . . . . . . . . . . 6256.6 Liability Questions in Seismic Assessment and Retrofitting . . . 627

Contents xxiii

6.7 Retrofitting Strategies . . . . . . . . . . . . . . . . . . . . . . . 6286.7.1 General Guidelines . . . . . . . . . . . . . . . . . . . . 6286.7.2 Reduction of Seismic Action Effects

Through Retrofitting . . . . . . . . . . . . . . . . . . . 6306.7.3 Upgrading of Member Capacities . . . . . . . . . . . . 6326.7.4 Completeness of the Load-Path . . . . . . . . . . . . . 633

6.8 Retrofitting Techniques for Concrete Members . . . . . . . . . . 6346.8.1 Repair of Damaged Members . . . . . . . . . . . . . . 6346.8.2 Concrete Jacketing . . . . . . . . . . . . . . . . . . . . 6376.8.3 Jackets of Externally Bonded Fibre Reinforced

Polymers (FRP) . . . . . . . . . . . . . . . . . . . . . . 6496.8.4 Steel Jacketing . . . . . . . . . . . . . . . . . . . . . . 661

6.9 Stiffening and Strengthening of the Structure as a Whole . . . . . 6676.9.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . 6676.9.2 Addition of New Concrete Walls . . . . . . . . . . . . . 6676.9.3 Addition of a New Bracing System in Steel . . . . . . . 676

6.10 Application Case Studies . . . . . . . . . . . . . . . . . . . . . 6846.10.1 Seismic Retrofitting of SPEAR Test-Structure

with RC or FRP Jackets . . . . . . . . . . . . . . . . . 6846.10.2 Seismic Retrofitting of Theatre Building with

RC and FRP Jackets and New Walls . . . . . . . . . . . 686

Epilogue: Some Ideas for Performance- and Displacement-BasedSeismic Design of New Buildings . . . . . . . . . . . . . . . . . . . . . . 695

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 703

Colour Plates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 717

Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 735