Computational Structural Dynamic - Manolis Papadrakakis
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(2) Computational Structural Dynamics and Earthquake Engineering.
(3) Structures and Infrastructures Series ISSN 1747-7735. Book Series Editor:. Dan M. Frangopol Professor of Civil Engineering and Fazlur R. Khan Endowed Chair of Structural Engineering and Architecture Department of Civil and Environmental Engineering Center for Advanced Technology for Large Structural Systems (ATLSS Center) Lehigh University Bethlehem, PA, USA. Volume 2.
(4) Computational Structural Dynamics and Earthquake Engineering. E dited by. Manolis Papadrakakis1, Dimos C. Charmpis2, Nikos D. Lagaros1 & Yiannis Tsompanakis3 1. National Technical University of Athens, Athens, Greece University of Cyprus, Nicosia, Cyprus 3 Technical University of Crete, Chania, Greece 2.
(5) Colophon Book Series Editor : Dan M. Frangopol Volume Editors: Manolis Papadrakakis, Dimos C. Charmpis, Nikos D. Lagaros & Yiannis Tsompanakis Cover illustration: Minoan palace ruins, Knossos, Crete, Greece Nikos D. Lagaros September 2006 Taylor & Francis is an imprint of the Taylor & Francis Group, an informa business © 2009 Taylor & Francis Group, London, UK Typeset by Charon Tec Ltd (A Macmillan company), Chennai, India Printed and bound in Great Britain by Antony Rowe (a CPI Group company), Chippenham, Wiltshire All rights reserved. No part of this publication or the information contained herein may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, by photocopying, recording or otherwise, without written prior permission from the publishers. Although all care is taken to ensure integrity and the quality of this publication and the information herein, no responsibility is assumed by the publishers nor the author for any damage to the property or persons as a result of operation or use of this publication and/or the information contained herein. British Library Cataloguing in Publication Data A catalogue record for this book is available from the British Library Library of Congress Cataloging-in-Publication Data Computational structural dynamics and earthquake engineering / Manolis Papadrakakis ... [et al.]. p. cm. – (Structures and infrastructures series, ISSN 1747-7735) Includes bibliographical references and index. ISBN 978-0-415-45261-8 (hardcover : alk. paper) 1. Structural dynamics–Mathematics. 2. Earthquake engineering–Mathematics. 3. Engineering mathematics–Formulae. I. Papadrakakis, Manolis. II. Title. III. Series. TA654.C633 2009 624.1 71–dc22 2008044127 Published by: CRC Press/Balkema P.O. Box 447, 2300 AK Leiden,The Netherlands e-mail: [email protected] www.crcpress.com – www.taylorandfrancis.co.uk – www.balkema.nl ISBN13 978-0-415-45261-8(Hbk) ISBN13 978-0-203-88163-7(eBook) Structures and Infrastructures Series: ISSN 1747-7735 Volume 2.
(6) Table of Contents. Editorial About the Book Series Editor Foreword Preface Brief Curriculum Vitae of the Editors Contributors List Author Data. XI XIII XV XVII XXXI XXXIII XXXVII. PART 1. Computational Structural Dynamics 1. Computational stochastic dynamics – some lessons learned Gerhart I. Schuëller, University of Innsbruck, Innsbruck, Austria. 2. Finite element response sensitivity, probabilistic response and reliability analyses Joel P. Conte, University of California, San Diego, USA Michele Barbato, Louisiana State University, Louisiana, USA Quan Gu, AMEC Geomatrix, Newport Beach, USA. 3. 4. 3. 21. Energy-momentum algorithms for nonlinear solid dynamics and their assumed strain finite element formulation Francisco Armero, University of California, Berkeley, USA. 43. Energy conservation and high-frequency damping in numerical time integration Steen Krenk, Technical University of Denmark, Lyngby, Denmark. 57.
(7) VI T a b l e o f C o n t e n t s. 5. 6. 7. 8. 9. 10. 11. Computational elastoacoustics of uncertain complex systems and experimental validation Christian Soize, Université Paris-Est, Marne-la-Vallée, France Chahoui Chen, Université Paris-Est, Marne-la-Vallée, France Jean-François Durand, Université Paris-Est, Marne-la-Vallée, France Denis Duhamel, Ecole des Ponts, Marne la Vallee, France Laurent Gagliardini, PSA Peugeot-Citroen, Velizy-Villacoublay Cedex, France Structural dynamics design validation and optimisation of structures with imprecise parameters using the fuzzy finite element method David Moens, K.U.Leuven, Leuven, Belgium Dirk Vandepitte, K.U.Leuven, Leuven, Belgium Hilde De Gersem, K.U.Leuven, Leuven, Belgium Maarten De Munck, K.U.Leuven, Leuven, Belgium Wim Desmet, K.U.Leuven, Leuven, Belgium Morphological indicators and the prediction of the first natural frequency of a lightweight structure Willy Patrick De Wilde, Vrije Universiteit Brussel, Brussels, Belgium Jan Van Steirteghem, Besix Belgium, Brussels, Belgium Dynamic analysis of plates stiffened by parallel beams with deformable connection Evangelos J. Sapountzakis, National Technical University of Athens, Athens, Greece Vasilios G. Mokos, National Technical University of Athens, Athens, Greece Impacts on beams: Uncertainty in experiments and numerical simulation Werner Schiehlen, University of Stuttgart, Stuttgart, Germany Robert Seifried, University of Stuttgart, Stuttgart, Germany Rational derivation of conserving time integration schemes: The moving-mass case Elias Paraskevopoulos, Aristotle University Thessaloniki, Thessaloniki, Greece Christos Panagiotopoulos, Aristotle University Thessaloniki, Thessaloniki, Greece Demosthenes Talaslidis, Aristotle University Thessaloniki, Thessaloniki, Greece Classical and soft robust active control of smart beams Georgios K. Tairidis, Technical University of Crete, Chania, Greece Georgios E. Stavroulakis, Technical University of Crete, Chania, Greece Daniela G. Marinova, Technical University of Sofia, Sofia, Bulgaria Emmanuel C. Zacharenakis, Technological Educational Institute of Crete, Heraklion, Greece. 71. 85. 109. 123. 137. 149. 165.
(8) T a b l e o f C o n t e n t s VII. 12. Rail vibrations caused by ground stiffness transitions Håkan Lane, Chalmers University of Technology, Gothenburg, Sweden Per Kettil, Chalmers University of Technology, Gothenburg, Sweden Nils-Erik Wiberg, Chalmers University of Technology, Gothenburg, Sweden. 13. Development and applications of a staggered FEM-BEM methodology for ground vibrations due to moving train loads Dimitris C. Rizos, University of South Carolina, Columbia, USA John O’Brien, University of South Carolina, Columbia, USA Evangelia Leon, Geomech Group Inc., Columbia, USA. 14. Vibration monitoring as a diagnosis tool for structural condition assessment Guido De Roeck, K.U. Leuven, Leuven, Belgium Edwin Reynders, K.U. Leuven, Leuven, Belgium. 179. 189. 203. PART 11. Computational Earthquake Engineering 15. Multi-resolution distributed FEA simulation of a 54-story RC building Jun Ji, Kal Krishnan Consulting Services, Inc., Oakland, USA Oh-Sung Kwon, Missouri University of Science and Technology, Missouri, USA Amr S. Elnashai, University of Illinois at Urbana-Champaign, Illinois, USA Daniel A. Kuchma, University of Illinois at Urbana-Champaign, Illinois, USA. 223. 16. Simplified probabilistic seismic performance assessment of buildings Matjaž Dolšek, University of Ljubljana, Ljubljana, Slovenia Peter Fajfar, University of Ljubljana, Ljubljana, Slovenia. 241. 17. Computational simulation of the seismic response of buildings with energy dissipating devices Alex H. Barbat, Technical University of Catalonia, Barcelona, Spain Pablo Mata, Technical University of Catalonia, Barcelona, Spain Sergio Oller, Technical University of Catalonia, Barcelona, Spain Juan C. Vielma, Lisandro Alvarado University, Barquisimeto, Venezuela. 18. Structural health monitoring by Bayesian updating. 255. 275. Enrico Sibilio, Università di Roma TRE, Rome, Italy Marcello Ciampoli, Sapienza Università di Roma, Rome, Italy James L. Beck, California Institute of Technology, Pasadena, USA 19. A multiphase model with hypoplastic formulation of the solid phase and its application to earthquake engineering problems Konstantin Meskouris, RWTH Aachen University, Aachen, Germany Stefan Holler, Airbus Deutschland GmbH, Hamburg, Germany. 293.
(9) VIII T a b l e o f C o n t e n t s. Christoph Butenweg, RWTH Aachen University, Aachen, Germany Daniel Meiners, RWTH Aachen University, Aachen, Germany 20. Mixed Lagrangian formulation in analysis of collapse of structures. 309. Andrei M. Reinhorn, University at Buffalo (SUNY), Buffalo, USA Mettupalayam V. Sivaselvan, University of Colorado at Boulder, Boulder, USA. Gary F. Dargush, University at Buffalo (SUNY), Buffalo, USA Oren Lavan, Technion – Israel Institute of Technology, Haifa, Israel 21. 22. Nonlinear models and nonlinear procedures for seismic analysis of reinforced concrete frame structures Enrico Spacone, University of Chieti-Pescara, Pescara, Italy Guido Camata, University of Chieti-Pescara, Pescara, Italy Marco Faggella, University of Chieti-Pescara, Pescara, Italy; University of California San Diego, California, USA Modelling inelastic buckling of reinforcing bars under earthquake loading. 323. 347. Michalis Fragiadakis, National Technical University of Athens, Athens, Greece; University of Thessaly, Volos, Greece. Rui Pinho, European School for Advanced Studies in Reduction of Seismic Risk (ROSE School), Pavia, Italy Stelios Antoniou, SeismoSoft—Software Solutions for Earthquake Engineering, Chalkida, Greece 23. 24. Analyzing steel moment-resisting connections using finite element modeling Chris P. Pantelides, University of Utah, Salt Lake City, USA Lawrence D. Reaveley, University of Utah, Salt Lake City, USA Scott M. Adan, Simpson Gumpertz & Heger Inc., San Francisco, USA Earthquake damage scenario software for urban areas. 363. 377. Atilla Ansal, Bogaziçi University, Istanbul, Turkey Aslı Kurtulu¸s, Bogaziçi University, Istanbul, Turkey Gökçe Tönük, Bogaziçi University, Istanbul, Turkey 25. 26. 27. Nonlinear performance assessment of bridges with Incremental Response Spectrum Analysis (IRSA) procedure ˙ M. Nuray Aydınoglu ˘ , Bogaziçi ˘ University, Istanbul, Turkey ˙ Göktürk Önem, Bogaziçi ˘ University, Istanbul, Turkey The equivalent modal damping concept and its use in seismic design of steel structures George A. Papagiannopoulos, University of Patras, Rio, Greece Dimitri E. Beskos, University of Patras, Rio, Greece Bayesian updating and model class selection of deteriorating hysteretic structural models using recorded seismic response James L. Beck, California Institute of Technology, Pasadena, USA Matthew M. Muto, California Institute of Technology, Pasadena, USA. 393. 401. 413.
(10) Table of Contents. 28. 29. IX. Parallel soil–foundation–structure interaction computations Boris Jeremi´c, University of California Davis, California, USA Guanzhou Jie, Wachovia Corporation, New York, USA. 427. Dynamic interaction of retaining walls and retained soil and structures. 447. Yiannis Tsompanakis, Technical University of Crete, Chania, Greece 30. 31. 32. Earthquake response of liquid tanks installed in saturated transversely isotropic soil Jae Kwan Kim, Seoul National University, Seoul, Korea Jin Ho Lee, Seoul National University, Seoul, Korea. 463. Advances in design optimization of reinforced concrete structural systems 477 Chara C. Mitropoulou, National Technical University of Athens, Athens, Greece Nikos P. Bakas, National Technical University of Athens, Athens, Greece Nikos D. Lagaros, National Technical University of Athens, Athens, Greece Manolis Papadrakakis, National Technical University of Athens, Athens, Greece Robust stochastic optimal control of seismically excited buildings. 507. Jorge E. Hurtado, Universidad Nacional de Colombia, Manizales, Colombia Naile Aguirre, Universidad Nacional de Colombia, Manizales, Colombia 33. 34. A multi-objective robust criterion for tuned mass dampers optimal design Giuseppe Carlo Marano, Technical University of Bari, Taranto, Italy Rita Greco, Technical University of Bari, Taranto, Italy Sara Sgobba, Technical University of Bari, Taranto, Italy. 531. Performance-based seismic optimization implementing neural networks. 547. Oscar Möller, University of Rosario, Rosario, Argentina Laura Quiroz, University of Rosario, Rosario, Argentina Marcelo Rubinstein, University of Rosario, Rosario, Argentina Ricardo O. Foschi, University of British Columbia, Vancouver, Canada 35. A very efficient computational procedure for the reliability-based optimization of uncertain stochastic linear dynamical systems Hector A. Jensen, Santa Maria University, Valparaiso, Chile Marcos A. Valdebenito, University of Innsbruck, Innsbruck, Austria References Author index Subject index. 565. 579 611 613.
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(12) Editorial. Welcome to the New Book Series Structures and Infrastructures. Our knowledge to model, analyze, design, maintain, manage and predict the lifecycle performance of structures and infrastructures is continually growing. However, the complexity of these systems continues to increase and an integrated approach is necessary to understand the effect of technological, environmental, economical, social and political interactions on the life-cycle performance of engineering structures and infrastructures. In order to accomplish this, methods have to be developed to systematically analyze structure and infrastructure systems, and models have to be formulated for evaluating and comparing the risks and benefits associated with various alternatives. We must maximize the life-cycle benefits of these systems to serve the needs of our society by selecting the best balance of the safety, economy and sustainability requirements despite imperfect information and knowledge. In recognition of the need for such methods and models, the aim of this Book Series is to present research, developments, and applications written by experts on the most advanced technologies for analyzing, predicting and optimizing the performance of structures and infrastructures such as buildings, bridges, dams, underground construction, offshore platforms, pipelines, naval vessels, ocean structures, nuclear power plants, and also airplanes, aerospace and automotive structures. The scope of this Book Series covers the entire spectrum of structures and infrastructures. Thus it includes, but is not restricted to, mathematical modeling, computer and experimental methods, practical applications in the areas of assessment and evaluation, construction and design for durability, decision making, deterioration modeling and aging, failure analysis, field testing, structural health monitoring, financial planning, inspection and diagnostics, life-cycle analysis and prediction, loads, maintenance strategies, management systems, nondestructive testing, optimization of maintenance and management, specifications and codes, structural safety and reliability, system analysis, time-dependent performance, rehabilitation, repair, replacement, reliability and risk management, service life prediction, strengthening and whole life costing. This Book Series is intended for an audience of researchers, practitioners, and students world-wide with a background in civil, aerospace, mechanical, marine and automotive engineering, as well as people working in infrastructure maintenance, monitoring, management and cost analysis of structures and infrastructures. Some volumes are monographs defining the current state of the art and/or practice in the field, and some are textbooks to be used in undergraduate (mostly seniors), graduate and.
(13) XII. Editorial. postgraduate courses. This Book Series is affiliated to Structure and Infrastructure Engineering (http://www.informaworld.com/sie), an international peer-reviewed journal which is included in the Science Citation Index. If you like to contribute to this Book Series as an author or editor, please contact the Book Series Editor ([email protected]) or the Publisher (pub.NL@ taylorandfrancis.com). A book proposal form can be downloaded at www.balkema.nl. It is now up to you, authors, editors, and readers, to make Structures and Infrastructures a success. Dan M. Frangopol Book Series Editor.
(14) About the Book Series Editor. Dr. Dan M. Frangopol is the first holder of the Fazlur R. Khan Endowed Chair of Structural Engineering and Architecture at Lehigh University, Bethlehem, Pennsylvania, USA, and a Professor in the Department of Civil and Environmental Engineering at Lehigh University. He is also an Emeritus Professor of Civil Engineering at the University of Colorado at Boulder, USA, where he taught for more than two decades (1983–2006). Before joining the University of Colorado, he worked for four years (1979–1983) in structural design with A. Lipski Consulting Engineers in Brussels, Belgium. In 1976, he received his doctorate in Applied Sciences from the University of Liège, Belgium, and holds two honorary doctorates (Doctor Honoris Causa) from the Technical University of Civil Engineering in Bucharest, Romania, and the University of Liège, Belgium. He is a Fellow of the American Society of Civil Engineers (ASCE), American Concrete Institute (ACI), and International Association for Bridge and Structural Engineering (IABSE). He is also an Honorary Member of both the Romanian Academy of Technical Sciences and the Portuguese Association for Bridge Maintenance and Safety. He is the initiator and organizer of the Fazlur R. Khan Lecture Series (www.lehigh.edu/frkseries) at Lehigh University. Dan Frangopol is an experienced researcher and consultant to industry and government agencies, both nationally and abroad. His main areas of expertise are structural reliability, structural optimization, bridge engineering, and life-cycle analysis, design, maintenance, monitoring, and management of structures and infrastructures. He is the Founding President of the International Association for Bridge Maintenance and Safety (IABMAS, www.iabmas.org) and of the International Association for Life-Cycle Civil Engineering (IALCCE, www.ialcce.org), and Past Director of the Consortium on Advanced Life-Cycle Engineering for Sustainable Civil Environments (COALESCE). He is also the Chair of the Executive Board of the International Association for Structural Safety and Reliability (IASSAR, www.columbia.edu/cu/civileng/iassar) and the Vice-President of the International Society for Health Monitoring of Intelligent Infrastructures (ISHMII, www.ishmii.org). Dan Frangopol is the recipient of several prestigious awards including the 2008 IALCCE Senior Award, the 2007 ASCE Ernest Howard Award, the 2006 IABSE OPAC Award, the 2006 Elsevier Munro Prize, the.
(15) XIV A b o u t t h e B o o k S e r i e s E d i t o r. 2006 T. Y. Lin Medal, the 2005 ASCE Nathan M. Newmark Medal, the 2004 Kajima Research Award, the 2003 ASCE Moisseiff Award, the 2002 JSPS Fellowship Award for Research in Japan, the 2001 ASCE J. James R. Croes Medal, the 2001 IASSAR Research Prize, the 1998 and 2004 ASCE State-of-the-Art of Civil Engineering Award, and the 1996 Distinguished Probabilistic Methods Educator Award of the Society of Automotive Engineers (SAE). Dan Frangopol is the Founding Editor-in-Chief of Structure and Infrastructure Engineering (Taylor & Francis, www.informaworld.com/sie) an international peerreviewed journal, which is included in the Science Citation Index. This journal is dedicated to recent advances in maintenance, management, and life-cycle performance of a wide range of structures and infrastructures. He is the author or co-author of over 400 refereed publications, and co-author, editor or co-editor of more than 20 books published by ASCE, Balkema, CIMNE, CRC Press, Elsevier, McGraw-Hill, Taylor & Francis, and Thomas Telford and an editorial board member of several international journals. Additionally, he has chaired and organized several national and international structural engineering conferences and workshops. Dan Frangopol has supervised over 70 Ph.D. and M.Sc. students. Many of his former students are professors at major universities in the United States, Asia, Europe, and South America, and several are prominent in professional practice and research laboratories. For additional information on Dan M. Frangopol’s activities, please visit www.lehigh.edu/∼dmf206/.
(16) Foreword. The purpose of this book is to present recent research findings in the fields of computational structural dynamics and earthquake engineering. The first part (Chapters 1 to 14) is devoted to computational structural dynamics, and the second part (Chapters 15 to 35) deals with computational earthquake engineering. To provide the reader with a good overview of pertinent literature, all cited references and additional references on the topics presented are collected in a comprehensive list of references. The Book Series Editor would like to express his appreciation to the Editors and all Authors who contributed to this book. It is his hope that this second volume in the Structures and Infrastructures Book Series will generate a lot of interest in the Computational Mechanics, Structural Dynamics, and Earthquake Engineering Communities. Dan M. Frangopol Book Series Editor Bethlehem, Pennsylvania August 30, 2008.
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(18) Preface. The increasing necessity to solve complex problems in Structural Dynamics and Earthquake Engineering requires the development of new ideas, innovative methods and numerical tools for providing accurate numerical solutions in affordable computing times. The purpose of this book is to present the latest research developments in the scientific fields of Computational Dynamics, Stochastic Dynamics, Structural Dynamics and Earthquake Engineering. This volume consists of state-of-the-art contributions. The selected chapters are revised and extended versions of the papers which were presented as plenary, semi-plenary and keynote lectures at the recent thematic Compdyn 2007 Conference. The book is addressed to people working in universities, engineering practice and industry. It will be useful for academic staff, researchers, post-graduate and research students active in areas of civil, mechanical, naval, aerospace engineering. Furthermore, the book is addressed to professional engineers confronted with complicated problems that need cost-effective designs. The potential readers will extend their knowledge in the aforementioned research fields. They will find this book very helpful in order to enhance their knowledge, to provide a foundation for further study, to indicate novel research areas, or areas where further developments are necessary and to deal with applications of advanced complexity. This volume is a “multi-collective’’ book of thirty-five, high-quality and selfcontained chapters, which present state-of-the-art theoretical advances and applications in various fields of Computational Structural Dynamics and Earthquake Engineering. The chapters in the first part of the book are focused on Computational Structural Dynamics theory and applications, while the chapters in the second part deal with advances in Earthquake Engineering theory and applications. The communities of Structural Dynamics and Earthquake Engineering will benefit from this publication, since they will be acquainted with advanced computational methods and software tools which can highly assist them in tackling complex problems in dynamic/seismic analysis and design. In addition, the book will also give the Computational Mechanics community the opportunity to become more familiar with very important application areas of great social impact. In the sequence, short descriptions of the chapters are presented. The aim of the introductory chapter by Schuëller (Chapter 1) is to review some of the most relevant lessons learned for solving reliability problems in structural dynamics. The emphasis is given on studying the effects of dimensionality of a reliability problem as well as the effects of structural nonlinearities when applying different reliability.
(19) XVIII P r e f a c e. methods. In particular, a critical appraisal on the role of the design point in estimating failure probabilities is carried out. The range of applicability of approximate methods is examined, as these methods rely to a large extent on the design point for producing reliability estimates. The discussion is based on the observations generated through the resolution of a series of numerical examples rather than from a theoretical point of view, given the inherent complex nature of structural reliability problems involving nonlinearities. The examples addressed show that the design point and its vicinity contribute significantly to the failure probability integral (PF ) for low dimensional problems. In contrast, when the number of random variables is large the design point and its vicinity do not play an important role in estimating PF . In addition, the examples examined indicate that the shape of the failure region in reliability problems involving structural nonlinearities can be rather involved, thus preventing its approximation by means of the so-called First Order Reliability Method (FORM). In view of the evidence presented in this chapter, the use of techniques such as FORM seems advisable only for problems with few uncertain parameters, involving weak nonlinearities. For high dimensional problems involving weak or strong nonlinearities, simulation techniques like direct Monte Carlo simulation, Subset simulation or Line Sampling should be applied. Conte, Barbato and Gu (Chapter 2) present the recent developments in finite element (FE) response sensitivity analysis based on the Direct Differentiation Method (DDM) for displacement-based, force-based, and three-field mixed finite elements. First-Order Second-Moment (FOSM) approximations of the first- and second-order statistics of the response of structural systems with random/uncertain parameters and subjected to deterministic quasi-static and/or dynamic loads are obtained using DDM-based FE response sensitivities and compared to Monte Carlo simulation results. The probability of a structural response quantity exceeding a specified threshold level is evaluated using the First-Order Reliability Method (FORM) combined with DDM-based FE response sensitivities in the search for the “design point(s)’’ (DPs). Both time-invariant and time-variant problems are considered. The geometry of limit-state surfaces near the DP(s) is explored in subspaces defined by planes of major principal curvatures. This geometry explains the lack of accuracy of FORM-based solutions in some cases and suggests the development of new improved solution strategies, e.g., the Design Point – Response Surface – Simulation (DP-RS-Sim) method. The examples presented in this study include both structural systems and soil-foundation-structure interaction systems and are based on two types of analyses which are used extensively in earthquake engineering, namely pushover analysis and time history analysis. Armero (Chapter 3) describes a new strain finite element formulation (or B-bar method) for the locking-free simulation of nearly incompressible elastic and inelastic solids in the finite deformation dynamic range that also preserves the conservation/dissipation properties of the so-called energy-dissipative momentum-conserving (EDMC) time-stepping algorithms. The general setting of finite strain plasticity is considered, including hyperelastic models as a particular case. The main motivation of this work is to avoid the nonlinear numerical instabilities observed in classical numerical schemes with unbounded growth of the energy (even in the plastic case) by introducing the exact dissipation/conservation of the energy in the discrete system by design. The incorporation of the conservation laws of linear and angular momenta, and the preservation of the associated relative equilibria, is also obtained. The chapter identifies.
(20) Preface. XIX. the conditions that the linearized strain operator has to satisfy for the preservation of these properties in time. These conditions require the definition of the assumed strain operator, originally developed with spatial considerations only, accounting for the temporal discretization in the definition of the associated strain variations. As a result, a fully discrete system in space and time is defined that shows exactly all these conservation/dissipation laws of the underlying physical system, including the exact plastic dissipation of the energy, with exact energy conservation for elastic steps. Numerical simulations are presented to illustrate the performance of the new formulation. Momentum and energy conserving time integration procedures are receiving increased interest due to the central role of conservation properties in relation to the problems under investigation. However, most problems in structural dynamics are based on models that are first discretized in space, and this often leads to a fairly large number of high-frequency modes, that are not represented well by the model. It is desirable to cure this problem by devising algorithms that include the possibility of introducing algorithmic energy dissipation of the high-frequency modes. The problem is well known from classic collocation based algorithms - notably various forms of the Newmark algorithm where the equation of motion is supplemented by approximate relations between displacement, velocity and acceleration. In the chapter by Krenk (Chapter 4) an efficient adjustment of the algorithmic parameters is used to introduce the so-called damping, and an improved form leading only to high-frequency damping that can be obtained by suitable averaging of the equilibrium equation at consecutive time steps. Conservative time integration algorithms are obtained by use of an integral of the equation of motion and the acceleration therefore does not appear as an independent parameter of these algorithms. Typically they do not contain algorithmic parameters either. Algorithmic damping can then be introduced in two ways: either by introducing artificial damping in terms of the displacement and velocity vectors, or by introducing additional variables to represent damping. The chapter by Soize, Chen, Durand, Duhamel and Gagliardini (Chapter 5) deals with the robustness of uncertain computational elastoacoustic models in low- and medium-frequency ranges. The elastoacoustic system is made up of a heterogeneous viscoelastic structure coupled with an internal acoustic cavity filled with a dissipative acoustic fluid. A reduced mean elastoacoustic model is deduced from the mean finite element model by using the modal approach with the structural modes of the structure and the acoustic modes of the acoustic cavity. Data uncertainties and model uncertainties are taken into account by using a nonparametric probabilistic approach for the structure, for the acoustic cavity and for the vibroacoustic coupling interface. The main objectives of this paper are (i) to present experimental validation of the nonparametric probabilistic approach of model uncertainties and to propose methods to perform the experimental identification of the probabilistic model parameters, (ii) to analyze the robustness of computational elastoacoustic models with respect to model and data uncertainties, (iii) to study uncertainty propagation through complex elastoacoustic systems. To illustrate the efficiency of their computational stochastic elastoacoustic model the authors analyze various experimental configurations. The theme of the contribution by Moens, Vandepitte, DeGersem, DeMunck and Desmet (Chapter 6) is structural dynamics design validation and optimization with imprecise parameters using the fuzzy finite element method. After initial research in the field of fuzzy finite elements has started in the middle of the nineties, different aspects.
(21) XX. Preface. of the problem have been considered, and continuous development has improved not only the capabilities but also the performance of the procedures. The improvement of the performance of fuzzy finite element analysis is still a big challenge. Vertex analysis with n uncertain parameters requires 2n deterministic analysis runs for each α-level that is considered. Another approach is optimization, which is capable of predicting absolute maxima and minima. Unlike vertex analysis, the performance of optimization procedures is unpredictable. Structural dynamics is a specific type of problem that can also be tackled with interval or fuzzy finite elements and there is currently no generally applicable consistent approach to take into account the effect of parameter uncertainties on Component Mode Synthesis (CMS) reduction schemes. Several approximation procedures have been proposed, but they are sensitive to the particular case that is considered. This chapter presents two recent enhancements to the hybrid optimization and interval arithmetic procedure for fuzzy envelope FRF calculation: a Response Surface Modeling (RSM) method and a new CMS procedure. The result is a highly efficient procedure for interval and especially fuzzy finite element analysis. De Wilde and Steirteghem (Chapter 7) deal with a number of dimensionless morphological indicators that represent a property of a structure and depend only on a small number of variables. These indicators allow for optimization at the stage of conceptual design. The most important indicators are the indicator of volume, related to the strength of the structure, and the indicator of displacement, related to the stiffness of the structure. These indicators, in their most simple appearance, are functions only of the geometrical slenderness of the structure, under the assumption that the structure is not subjected to second order effects and that shear effects are not predominant. The indicator of volume allows choosing the structural typology with a minimum of volume of material. When using the indicator of volume at the stage of conceptual design, important areas of slenderness appear to bring about problems of resonance. This is particularly the case for structures which have predominant co-vibrating loads, have large spans and are using a material with a small stiffness/strength ratio. To further illustrate this situation, a real-world example is discussed and some general design guidelines are proposed. In the work by Sapountzakis and Mokos (Chapter 8) a general solution for the dynamic analysis of plates stiffened by arbitrarily placed parallel beams with deformable connection is presented. According to the proposed model, the stiffening beams are isolated from the plate by sections in the lower outer surface of the plate, taking into account the arising tractions in all directions at the fictitious interfaces. These tractions are integrated with respect to each half of the interface width resulting two interface lines. Their unknown distribution is established by applying continuity conditions in all directions taking into account their relation with the interface slip through the shear connector stiffness. Any distribution of connectors in each direction can be efficiently handled. The proposed model permits the evaluation of the shear forces at the interfaces in both directions. Three finite element models using beam, shell or solid finite elements are presented for the verification of the accuracy of the results. Schiehlen and Seifried (Chapter 9) elaborately describe the impact on beams that results in large rigid body motions and small structural waves. Such mechanical systems are often modeled as multibody systems to describe the large nonlinear motion where the impacts are treated by the coefficient of restitution. The coefficient of restitution is considered as deterministic number depending on the material, the shape and the.
(22) Preface. XXI. velocity of the colliding bodies. However, in experiments and computations it was observed that for a sphere striking a beam the coefficient of restitution is uncertain due to multiple impacts resulting in chaotic behavior. For the evaluation of the numerical and experimental data a statistical approach is proposed providing mean value and dispersion of the coefficient of restitution depending on four classes of the velocity. It is shown that these parameters allow characterizing the uncertainty. The statistical range is increasing with the relative velocity of the impact. However, the mean value or midrange point, respectively, may be used to solve the structural dynamics beam problem. A rational approach is proposed by Paraskevopoulos, Panagiotopoulos and Talaslidis (Chapter 10) for the time integration of the dynamic equations arising in nonlinear structural problems, which employs a series of innovative concepts, e.g.: independent assumptions for the velocities and momentum type variables, use of different approximations for the test functions and the variables itself, and abandonment of the convention concerning the vanishing of the test functions at the time boundaries. The presented methodology offers a systematic and mathematically consistent procedure for time integration, ensures consistency and stability, and avoids flaws of existing techniques. Conservation properties are examined employing a form of Noether’s Theorem. Furthermore, existing integration schemes may be theoretically justified by the present approach. The methodology is applied to the analysis of systems under moving loads and masses. Since this class of problems contains Dirac’s delta function and its time derivatives, the effective numerical treatment of the governing equations offers a challenging problem. Tairidis, Stavroulakis, Marinova and Zacharenakis (Chapter 11) describe how smart structures are incorporated into control schemes that allow them to react against disturbances. In mechanics, suppression of mechanical vibrations with possible applications on noise and vibration isolation is a very important field. Smart structures that include sensors and actuators are able to react to the environment due to coupling with some active control mechanism. The intelligence is introduced by a structural control scheme. A model problem of a smart beam with embedded piezoelectric sensors and actuators is used in this study. Vibration suppression is realized by using active control. Classical mathematical control usually gives good results for linear feedback laws under given assumptions. The design of nonlinear controllers based on fuzzy inference rules is proposed and tested. From the numerical results it can be observed that further vibration reduction can be accomplished. Nevertheless, the problems concerning velocities and accelerations remain. The performance of the fuzzy control system can be further reduced by fine-tuning the parameters of the fuzzy system (membership functions, rules, etc) by using neural networks or a global optimization scheme such as the Particle Swarm Optimization (PSO) method. The essence of railway dynamics is the transfer of forces at the wheel rail interface. The energy from the motion of the train is taken up as elastic deformation in the track structure consisting of the rail, sleepers, dry crust, ballast and soil. Spatial changes in the material properties of the track and subground may lead to variations in the contact forces at the wheel-rail interface. A shift from one material to another can potentially induce transition radiation vibration modes. The phenomenon has been observed in situations where the train goes onto a bridge. In the chapter by Lane, Kettil and Wiberg (Chapter 12) an advanced numerical model of the entire train-track-subgrade dynamic.
(23) XXII. Preface. system with moving finite elements has been used to study the influence of material stiffness transitions in the subground. While the properties of the ballast and the rail were kept constant, the Young’s moduli of the two layers of clay representing the soil underwent a linear change over a short distance. Both transitions from soft to stiff and from stiff to soft soil were considered. The results indicate that the main effect of the transition is a temporary variation followed by a transient low-frequent vibration. High speed rail transportation is quickly becoming a popular form of mass transit through-out the world. High Speed Trains (HST) pertain to passenger trains traveling in excess of 160 km/h, and as fast as 500 km/h. Potential problems arise when high speed trains travel over soft soils having relatively low wave velocities. In the chapter by Rizos, O’Brien and Leon (Chapter 13) an efficient methodology for the analysis of vibrations in a railroad track system, induced by the passage of conventional and high speed trains, is presented. The methodology is based on an efficient coupling of the Boundary Element method (BEM) with the Finite Element Method (FEM) in the direct time domain. BEM is based on the 4th order B-Spline fundamental solutions for 3-D elastodynamics and the concept of B-Spline impulse response functions. The BEM is used for the modeling of the soil-tie system and the FEM for the modeling of the flexible rail system. Soil-Structure Interaction and traveling wave effects are inherently accounted for and normalizations and scaling procedures are adopted. The proposed methodology allows for selection of different time steps in order to fulfil stability requirements of each solver. Numerical applications demonstrate the accuracy and versatility of the method. The chapter by De Roeck and Reynders (Chapter 14) gives an overview of the necessary conditions for a successful structural condition assessment by vibration measurements and concentrates on finite element (FE) updating, a versatile method for damage identification. First a critical overview is given about the advantages and disadvantages of the different excitation sources: forced, ambient and impact excitation. At the expense of building an elaborate FE-model of the structure, all acquired data can be used: natural frequencies, scaled or unscaled mode shapes and modal strains. Potential damage is simulated in the finite element model using a parametric representation and a constrained optimization problem is solved with the objective function defined as a sum of squared differences. Two bridge examples illustrate the use of finite element updating for damage assessment. Finally, a detailed set of conclusions are highlighted which can be considered as guidelines for engineering practice in vibration monitoring. There is a dearth of accurate, efficient and reliable analytical approaches for the inelastic static and dynamic analyses of complex reinforced concrete and composite high-rise buildings under extreme loads taking into account shear-flexure-axial interaction, crack propagation and other detailed features of concrete response. In the work of Ji, Kwon, Elnashai and Kuchma (Chapter 15), a new approach termed Multi-resolution Distributed Finite Element Analysis (MDFEA) is proposed and used to analyze a reference RC high-rise building with a dual core wall-frame system. The features of the new framework are demonstrated through the analysis of a complex 54-story reinforced concrete building. In this distributed analysis framework, the capabilities of a frame analysis tool and a continuum analysis tool are combined using a suitable simulation coordinator software. The static and dynamic responses of the building are predicted using MDFEA and compared with those predicted by conventional frame analysis. The comparisons from both pushover and response history analysis highlight that due.
(24) Preface. XXIII. to the influence of shear, the use of the multi-resolution approach is able to capture critical aspects of the behavior more sufficiently than some traditional methodologies performing pure frame analysis. The integrated MDFEA framework is generic, thus it enables the use of the best features of any computational tools so as to accurately and efficiently predict the inelastic static and dynamic response of complex structures subjected to extreme loads. A simplified method for the probabilistic seismic performance assessment of building structures is presented by Dolšek and Fajfar (Chapter 16). The method is basically the SAC-FEMA approach, in which the most demanding part, i.e. the Incremental Dynamic Analysis (IDA), is replaced by the incremental N2 method, which is based on nonlinear pushover analysis and the response spectrum approach and has been implemented in Eurocode 8. In this work the method is applied to a bare and an infilled reinforced concrete frame, for which pseudo-dynamical laboratory test results are available. The most common analytical modeling technique, which employs compressive diagonal struts for modeling of masonry infill, and one-component lumped plasticity elements for modeling the flexural behavior of beams and columns, was applied. The mathematical models developed are validated by comparing the results of nonlinear dynamic analyses with the test results. The probabilities of exceedance of the near collapse limit state are estimated and discussed. The results of analyses indicate that the infills can completely change the distribution of damage throughout the structure. The probability of failure of the infilled frame is smaller than that of the bare frame, however for both structures the probability of failure is larger than acceptable. Barbat, Oller, Mata and Vielma (Chapter 17) study the nonlinear dynamic response of reinforced concrete (RC) buildings with energy dissipating devices using advanced computational techniques. A fully geometric and constitutive nonlinear model is used for describing the dynamic behavior of structures. The equations of motion are expressed in terms of cross sectional forces and strains and its weak form is solved using the displacement based finite element method. A suitable version of Newmark’s scheme is used in updating the kinematics variables in a classical Newton type iterative scheme. Material points of the cross section are assumed to be composed of several simple materials with their own constitutive laws. The mixing theory is used to treat the resulting composite. A specific finite element based on the beam theory is proposed for the dissipators including constitutive relations. In addition, several numerical tests are carried out to validate the proposed model. In the contribution by Sibilio, Ciampoli and Beck (Chapter 18), a complete procedure for structural health monitoring, that is, for both damage detection and reliability assessment of a structure subject to seismic excitation, is briefly illustrated and applied to an example case. The problem of damage detection is dealt with by an identification technique with unknown input. A Bayesian model updating procedure is adopted to quantify the damage to the structure based on data from monitoring. Bayesian updating is based on an adaptive Markov Chain Monte Carlo method: the knowledge of the modal quantities of the undamaged and damaged structure is used to update the stiffness parameters that are chosen as the damage indicators. An advanced simulation technique, the so-called Subset Simulation, is then used to assess the probability of exceeding any structural response level, that is, the risk for the damaged structure. The procedure is formulated in a unified probabilistic framework that takes into account.
(25) XXIV. Preface. any kind of uncertainty involved in the various phases of the analysis. It is observed that the Bayesian approach is really efficient in characterizing the structural damage and its effects in probabilistic terms. The main reason is that this approach gives as final result the probability density functions of the identified parameters, which in turn can be used in any structural reliability assessment. Moreover, Subset Simulation requires a much smaller number of samples than Monte Carlo simulation; this advantage is essential, especially for structures which exhibit a strongly nonlinear behaviour when subjected to seismic excitation. A multiphase model including a hypoplastic formulation of the solid phase is presented and its application to earthquake engineering problems is discussed by Meskouris, Holler, Butenweg and Meiners (Chapter 19). This advanced soil model, which is based on the theory of porous media, comprises three distinct phases namely: solid, fluid and gas phase. For each of these phases the compressibility of the respective medium is taken into account in the mathematical formulation of the model. Due to the hypoplastic formulation including intergranular strain, the model is capable of predicting soil behaviour even under cyclic loading and therefore offers a possibility to further investigate complex dynamical phenomena such as ground liquefaction. The presented mutliphase model is capable of simulating consolidation, saturation and drainage processes and can realistically predict permanent ground displacements. Although the compressibilities of fluid and gas phases do not have a strong impact on the flow characteristics and the load bearing capacity of soils, they were still taken into account to provide further application possibilities for the model. Additionally, the model allows the implementation of arbitrary constitutive equations for the solid phase and also allows coupling to existing solid elements. The accuracy of the numerical approximation has been shown by comparison to experimental data. The model is numerically realized by means of the finite element method, it is implemented into the finite element code ANSYS and also allows the simulation of soil-structure interaction problems. In the chapter by Reinhorn, Sivaselvan, Dargush and Lavan (Chapter 20) a Lagrangian approach is developed for analysis of frame structures near-collapse, which is a mixed method, where in addition to the displacements, the stress-resultants and other variables of state are primary unknowns. This formulation consists of two sets of equations: equilibrium and compatibility of displacement rates (velocities), while its primary unknowns are forces and velocities. For numerical solution, a discrete variational integrator is derived. This integrator inherits the energy and momentum conservation characteristics. The integration of each step is a constrained minimization problem and it is solved using an Augmented Lagrangian algorithm. The presented examples show that this method can provide as good or better information than a widely used displacement based inelastic analysis solution. The results also show that the method is stable and efficient for large structures. However, the power of the method presented herein is in evaluating structures where various elements collapse, and forces and momentum have to be redistributed in the remaining system. Spacone, Camata and Faggella (Chapter 21) underline the potential of nonlinear models and nonlinear procedures for seismic analysis of reinforced concrete frame structures. Nonlinear methods of analysis for seismic vulnerability assessment of existing structures are attracting increasing attention due to their capacity to predict the actual seismic behavior better than linear methods. Their inclusion in modern design.
(26) Preface. XXV. codes such as Eurocode 8 is a major boost for their use in practical applications. Recent years have also seen steady advances in the modeling capabilities of reinforced concrete frames, particularly in the field of beam and column behavior. Advanced frame modeling tools are included in both research and commercial codes. As research and practicing engineers start applying nonlinear methods to real problems, questions arise regarding the application of the design code-provided procedures and the selection of the appropriate structural model given the objective limitations of the frame modeling capabilities today available. The scope of this chapter is to discuss some of the issues still open regarding the applications of the nonlinear methods of analysis to reinforced concrete structures, with the firm belief that an open discussion on these methods, their advantages and limitations will open the way to a more widespread use of advanced and more accurate methods of analysis. This way, the above issues will become clearer and any major deficiencies will be solved, especially through a strong interaction between practicing engineers and researchers. Past earthquakes have shown that a common failure mode of reinforced concrete (RC) members is buckling of the longitudinal reinforcement. In order to obtain an accurate prediction of strength and ductility, this effect should be taken into account during analysis. Buckling of the reinforcement is in essence a stability problem and therefore depends both on the geometry of the bar and on the material properties. To deal with this issue, Fragiadakis, Pinho and Antoniou (Chapter 22) propose a uniaxial material model for steel reinforcing bars subjected to a generalized loading history. The model of Monti and Nuti which is based on a set of experimental observations in order to account for buckling of the steel bars is examined. It has been noticed that in the case of partial unloading and then reloading, a common situation when a structure is subjected to seismic actions, the model might greatly overestimate the corresponding stress. An additional memory rule is thus proposed to eliminate this observed shortcoming. With the aid of the proposed modification, the Monti-Nuti model is proved to be capable of simulating accurately the capacity of reinforced concrete members. The rules presented are easy to implement and applicable to any model in the literature where a similar situation is identified. Two case studies are examined where the enhanced model was proven capable to produce realistic numerical results. Pantelides, Adan and Reaveley (Chapter 23) analyze steel moment-resisting connections using finite element modelling. They stress that in seismic structural design and rehabilitation deviations from the common practice require testing. The AISC seismic provisions for structural steel buildings recommend that usage and sizing of beam flange continuity plates across the column web shall be based on tests. FEMA 350 recommended seismic design criteria state that unless project-specific testing is performed to demonstrate that continuity plates are not required, moment-resisting connections should be provided with continuity plates when the thickness of the column flange is below a minimum value. Similarly, in order to qualify any new connection type for inclusion in the AISC prequalified connections for special and intermediate steel moment frames for seismic applications, testing has to be carried out to validate the design concept and to satisfy minimum performance criteria on strength and interstory drift angle capacity. In this study, nonlinear finite element analyses are performed to establish a correlation between measured and computed responses of two steel connections: (i) the reduced beam section (RBS) moment connection without continuity plates, and (ii) the bolted bracket (BB) moment connection. The connections.
(27) XXVI. Preface. were tested using cyclic quasi-static displacements applied at the beam tip and the comparison of measured and computed responses showed good correlation. Ansal, Kurtulus and Tönük (Chapter 24) present a specialized software to perform earthquake scenarios for estimating structural damage and human casualties. The first stage involves generation of microzonation maps for separately calculated regional seismic hazard. The seismic hazard can be probabilistic or deterministic where PGA and spectral accelerations or acceleration time histories are specified respectively for each cell on the engineering bedrock outcrop. In the second stage, representative soil profiles are defined for each cell and 1D site response analyses are conducted to calculate average PGAs and elastic acceleration response spectra on the ground surface. An envelope NEHRP spectrum is calculated for each cell based on site specific average acceleration spectrum to estimate short (T = 0.2 s) and long (T = 1 s) period spectral accelerations. In the third stage, vulnerability of the building stock is estimated with respect to number of buildings in each cell. A characteristic case study is discussed to demonstrate the applicability of the software. In the chapter by Aydınoglu ˘ and Önem (Chapter 25) the Incremental Response Spectrum Analysis (IRSA) procedure is introduced as an advanced multi-mode pushover analysis tool for the performance-based seismic assessment and design of buildings and bridges. The practical version of the procedure works directly with smoothed elastic response spectrum and makes use of the well-known equal displacement rule to scale modal displacement increments at each piecewise linear step, in which the traditional linear Response Spectrum Analysis (RSA) is implemented. Being a general analysis tool, IRSA is completely independent of the type of structure, as in its linear counterpart RSA. In this respect, IRSA is readily applicable to any type of bridge. In the present contribution, IRSA is applied to few types of highway bridges and its performance is checked against the results of the corresponding nonlinear response history analysis (NRHA) performed. It is shown that IRSA is capable of estimating bridge nonlinear demands with an acceptable accuracy for practical purposes. In the work of Papagiannopoulos and Beskos (Chapter 26) an efficient method is presented for the determination of the maximum structural response through a linear elastic spectrum analysis using equivalent modal damping values instead of the crude strength reduction factor. Geometrical and material non – linear structural effects are converted into equivalent time – invariant modal damping values. These equivalent damping values for the first few modes of the structure are numerically computed by first iteratively forming a frequency response transfer function until certain smoothness criteria are satisfied and then by solving a set of non – linear algebraic equations. A design – oriented scheme is developed in order to apply the equivalent modal damping concept to the seismic response analysis of multi-degree-of-freedom (MDOF) building structures. This scheme involves: a) the quantification of equivalent modal damping of a structure for predefined deformation limits and b) the use of spectrum analysis and modal synthesis for the calculation of the design base shear of the structure. For illustration purposes, curves providing equivalent damping as function of period for the first few modes as well as design acceleration versus period for given equivalent damping are constructed using a large number of steel moment resisting frames excited by various seismic motions. It is concluded that the proposed design scheme can be viewed as an alternative to the force based method of current seismic codes with equivalent modal damping values playing the role of the strength reduction factor..
(28) Preface. XXVII. Beck and Muto (Chapter 27) explain how identification of structural models from measured earthquake response can play a key role in structural health monitoring, structural control and improving performance-based design. System identification using data from strong seismic shaking is complicated by the nonlinear hysteretic response of structures where the restoring forces depend on the previous time history of the structural response rather than on an instantaneous finite-dimensional state. Furthermore, this inverse problem is ill-conditioned because even if some components in the structure show substantial yielding, others will exhibit nearly elastic response, producing no information about their yielding behavior. Classical least-squares or maximum likelihood estimation will not work with a realistic class of hysteretic models because it will be unidentifiable based on the data. In contrast, the combination of Bayesian updating and model class selection provides a powerful and rigorous approach to tackle this problem, especially when implemented using Markov Chain Monte Carlo simulation methods. The emergence of these methods in recent years has led to a renaissance in Bayesian methods across all disciplines in science and engineering because the high-dimensional integrations that are involved can now be readily evaluated. The power of these methods to handle ill-conditioned or unidentifiable system identification problems is demonstrated by using a recently-developed stochastic simulation algorithm, Transitional Markov Chain Monte Carlo, to perform Bayesian updating and model class selection on a class of Masing hysteretic structural models that are relatively simple yet can give realistic responses to seismic loading. Examples are given using deteriorating hysteretic building models with simulated seismic response data. The chapter by Jeremic and Jie (Chapter 28) focuses on two main topics. Firstly, it describes (in some detail) a parallel finite element computational method that is particularly well suited for elastic-plastic models. The method, named Plastic Domain Decomposition (PDD), dynamically balances computational loads for elastic-plastic finite element computations on distributed memory parallel computers. The PDD method uses the original algorithm with weighted graph partitioning that minimizes wall clock time for parallel, elastic-plastic computations. Excellent scalability of the method is shown on a variety of distributed memory parallel computers (from in house developed clusters to large national supercomputers). Secondly, the developed PDD method is applied to a problem of seismic soil-foundation-structure (SFS) interaction. Detailed 3D models of a prototype bridge (with up to 1.6 million DOFs) were developed and used for scalability studies. In addition to that, those detailed models were used to investigate seismic SFS interaction behavior of a conrete bridge founded on piles in soft and/or stiff soils. Results indicate that the interaction of a triad of dynamic characteristics of earthquake, soil and structure all have very important influence on overall seismic behavior of a soil-structure system. For example, it is shown that a long period earthquake motion has a detrimental effect on a stiff structure founded on soft soil. In contrast a short period earthquake motion has an even more detrimental effect on a stiff structure founded on stiff soil. Retaining systems, such as cantilever walls, are widely used worldwide for serving various purposes in structures and infrastructures (embankments, bridges, ports, etc). In the chapter by Tsompanakis (Chapter 29) the dynamic interaction of the retaining walls with the retained soil and the retained structures is investigated. This so-called phenomenon of dynamic wall–soil–structure interaction (DWSSI) is a rather.
(29) XXVIII. Preface. complicated issue that includes: (a) the dynamic interaction between a wall and a retained single soil layer (DWSI), and (b) the “standard’’ dynamic soil–structure interaction (DSSI) of a structure with its underlying soil. The aforementioned dynamic interaction issues are not properly considered in the modern seismic codes, thus, in the present work, using numerical two-dimensional simulations, the influence of the wall flexibility on the free-field ground shaking behind the wall is investigated. Emphasis is given on the impact of the wall’s presence on the amplification of the base acceleration on the retained soil layer, an amplification generally ignored by the seismic design norms. Consequently, a structure founded on the retained soil is included in the numerical models. Numerical results provide a clear indication of the direct interaction between a retaining wall and its retained structures. That fact justifies the necessity for a more elaborate consideration of this interrelated phenomenon on the seismic design, not only of the retaining walls but of the nearby structures as well. In the chapter by Kim and Lee (Chapter 30) a 3-D transmitting boundary in a cylindrical coordinate system is applied to obtain the earthquake response of a cylindrical liquid storage tank installed in the water-saturated transversely isotropic ground. The effects of the far-field region are represented by the transmitting boundary. Using finite elements, models are developed for the flexible tank wall and the near-field region of the ground. The motion of the contained liquid is modeled using boundary elements. Hybrid time domain-frequency domain analysis is used to obtain direct time-domain representation of the earthquake response of the system. Numerical results are given to illustrate this method of analysis. The results from the numerical analysis show that complex soil-structure interactions in water-saturated transversely isotropic ground can be modeled successfully. A rigorous two-phase transversely isotropic medium model has to be employed to accurately represent the dynamic behavior of a structure on the water-saturated transversely isotropic strata. In the work by Mitropoulou, Bakas, Lagaros and Papadrakakis (Chapter 31) a number of design approaches for 3D reinforced concrete (RC) buildings are formulated in the framework of structural optimization and they are assessed in terms of structural performance under earthquake loading. This chapter consists of two distinctive parts. In the first part the European seismic design code is evaluated with reference to the behavioral factor q. For each optimum design achieved for the various values of the behavioral factor, fragility curves are developed for four characteristic damage states. The optimum designs are compared based on limit-state probabilities of exceedance encountered for the design earthquake. In the second part, three design approaches for RC buildings are considered aiming at improving the torsional response of RC buildings. It is shown that the optimized designs obtained according to the minimum eccentricity of the rigidity centre behave better in frequent (50/50 hazard level) and occasional (10/50 hazard level) earthquakes, while the designs obtained according to the minimum eccentricity of the strength centre formulation was found better in rare (2/50 hazard level) events. Hurtado and Aguirre (Chapter 32) focus on the randomness of earthquake ground motions which constitutes one of the main problems in seismic design, as it increases the uncertainty and the effectiveness of design decisions. In advanced earthquakeresistant design an alternative to incorporate ground motion uncertainty is to perform a reliability-based optimization, consisting in minimizing the cost subject to keeping the failure probability less than a certain threshold. The use of structural passive or active.
(30) Preface. XXIX. control necessarily implies a severe reduction of the allowable failure probabilities, thus making more expensive the application of reliability-based optimization. In addition, a major problem in applying Linear Quadratic Regulator (LQR) control is that it is subject to arbitrary selection of the relative weights of the story displacements and control forces. For these reasons it is convenient to apply a different strategy than the reliability-based design to overcome these difficulties and drawbacks. The concept of robust optimal design is used, which consists of minimizing the structural cost in such a way that the standard deviations of the responses are less than certain thresholds, thus yielding the optimal values of the weights with due regard to the uncertainties present in the system. The computation of the response standard deviations in view of the large uncertainties of the ground motion parameters is also discussed and the application of a practical procedure is suggested and illustrated for a passive control case. Marano, Sgobba and Greco (Chapter 33) propose a robust optimization criterion of mechanical parameters in the design of linear Tuned Mass Dampers (TMD) located at the top of a main structural system subject to random base accelerations. The dynamic input is modelled as a stationary filtered white noise random process. The aim is to properly consider non-uniform spectral contents that happen in many real physical vibration phenomena. The main structural system is described as a single linear degree of freedom, and it is assumed that uncertainty affects the system model. The problem parameters treated are described as random uncorrelated variables known only by the estimation of their means and variances. Robustness is formulated as a multiobjective optimization problem in which both the mean and variance of a conventional objective function are minimized simultaneously. Optimal Pareto fronts are obtained and results show a significant improvement in performance stability compared to a standard conventional solution. Möller, Quiroz, Rubinstein and Foschi (Chapter 34) present an efficient methodology for performing performance-based design in earthquake engineering. They take into account various structural and ground motion uncertainties in optimizing design parameters, satisfying multiple performance criteria with target reliabilities and minimizing an objective. This implies performing nonlinear structural dynamic analyses for earthquakes likely to occur at the site, in order to obtain the demand responses of interest. The responses are represented here via neural networks and used in the performance criteria for estimation of achieved reliabilities by Monte Carlo simulation. An optimization technique is implemented to obtain optimal parameters, using a gradient-free algorithm. A numerical application is presented for a reinforced, multistory concrete frame. The demand is simulated using artificially generated ground motions, with the peak ground acceleration corresponding to the city of Mendoza, Argentina. Performance requirements (operational, life safety or collapse) are specified in terms of damage severity, using maximum displacements, inter-story drifts, local and global damage indices while optimization objectives are minimum cost, minimum dimensions and/or minimum steel reinforcement. In the last contribution, Jensen and Valdebenito (Chapter 35) deal with an efficient computational procedure for the reliability-based optimization of uncertain stochastic linear dynamical systems. The reliability-based optimization problem is formulated as the minimization of an objective function for a specified failure probability. The probability that design conditions are satisfied within a given time interval is used as a measure of the system reliability. Approximation concepts are used to construct.
(31) XXX. Preface. high quality approximations of dynamic responses in terms of the design variables and uncertain structural parameters during the optimal design process. The approximations are combined with an efficient simulation technique to generate explicit approximations of reliability measures with respect to the design variables. In particular, an efficient importance sampling technique is used to estimate the failure probability. The effectiveness and feasibility of the suggested approach is demonstrated by a characteristic example problem. Concurrently, the effect of uncertainty in the system parameters on the performance and reliability of the final design is also investigated. Numerical results show that uncertainty in the structural parameters may cause significant changes in the performance and reliability of linear systems subject to stochastic loading. The proposed procedure dramatically reduces the number of exact dynamic analyses as well as reliability estimations required during the design process. The book editors would like to express their deep gratitude to all contributors for their active participation in the Compdyn07 Conference and for their time and effort devoted to the completion of their contributions for this volume. In addition, we are most appreciative to the Book Series Editor, Professor Dan M. Frangopol, for his kind invitation to edit this volume and for his constructive comments and suggestions offered during the publication process. Finally, the editors would like to thank all the personnel of Taylor and Francis Publishers, especially Germaine Seijger, Richard Gundel, Leon Bijnsdorp and Janjaap Blom, for their most valuable support for the publication of this book. Manolis Papadrakakis Dimos C. Charmpis Nikos D. Lagaros Yiannis Tsompanakis August 2008.
(32) Brief Curriculum Vitae of the Editors. Manolis Papadrakakis is Professor of computational structural mechanics in the School of Civil Engineering at the National Technical University of Athens, Greece. His main fields of interest are: large-scale, stochastic and adaptive finite element applications, nonlinear dynamics, structural optimization, soil-fluid-structure interaction and soft computing applications in structural engineering. He is co-Editor-in-chief of the Computer Methods in Applied Mechanics and Engineering journal, an Honorary Editor of the International Journal of Computational Methods, and an Editorial Board member of a number of other international scientific journals. He is also a member of both the Executive and the General Council of the International Association for Computational Mechanics, Chairman of the European Committee on Computational Solid and Structural Mechanics and Vice President of the John Argyris Foundation. He is also the President of the European Community on Computational Methods in Applied Sciences (ECCOMAS). Professor Papadrakakis has chaired many international conferences and presented numerous invited lectures. He has written and edited various books and published a large variety of scientific articles and book chapters. Dimos Charmpis is a Lecturer at the Department of Civil and Environmental Engineering of the University of Cyprus. His scientific interests cover various topics of Computational Mechanics and aim in the exploitation of innovative computing systems and numerical methods for the analysis and design of structures under static or dynamic/seismic loading. More specifically, his research work is related with finite element methods, reliability estimation and stochastic analysis, design optimization, soft computing applications and high performance computing. Dr. Charmpis has participated in several research projects funded by national or European Union sources focusing on computational methods for structural engineering applications. He has also experience from working in the private civil engineering sector in Greece. He has authored or co-authored several scientific publications, has served as.
(33) XXXII. Brief Curriculum Vitae of the Editors. board member and special sessions organizer in a number of international conferences and is a reviewer of research articles for international journals. Nikos D. Lagaros is Lecturer of structural dynamics and computational mechanics in the School of Civil Engineering of the National Technical University of Athens, Greece. His research activity is focused on the development and the application of novel computational methods and information technology to structural and earthquake engineering analysis and design. In addition, Dr. Lagaros has provided consulting and expertwitness services to private companies and federal government agencies in Greece. He also serves as a member of the editorial board and reviewer of various international scientific journals. He has published numerous scientific papers, and is the co-editor of a number of books, one of which is dealing with innovative soft computing applications in earthquake engineering and another is focused on probabilistic structural optimization. Nikos Lagaros is co-organizer and co-editor of COMPDYN 2007 and its selected papers volume. Yiannis Tsompanakis is Assistant Professor in the Department of Applied Sciences of the Technical University of Crete, Greece, where he teaches structural and computational mechanics as well as earthquake engineering lessons. His scientific interests include computational methods in structural and geotechnical earthquake engineering, structural optimization, probabilistic mechanics, structural assessment and the application of artificial intelligence methods in engineering. Dr. Tsompanakis has published many scientific papers and is the co-editor of several books in computational mechanics. He is involved in the organization of mini-symposia and special sessions in international conferences as well as special issues of scientific journals as guest editor. He serves as a board member in various conferences, co-organized the COMPDYN-2007 conference and acts as a co-editor of the resulting selected papers volume..
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