ROSE SCHOOL European School for Advanced Studies in Reduction of Seismic Risk Bridge Isolation and Dissipation Devices
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I.U.S.S. Istituto Universitario Università degli Studi di Studi Superiori di Pavia ROSE SCHOOL European School for Advanced Studies in Reduction of Seismic Risk Bridge Isolation and Dissipation Devices: state of the art review of seismic response and modelling of modern seismic isolation and dissipation devices A Dissertation Submitted in Partial Fulfilment of the Requirements for the Master Degree in EARTHQUAKE ENGINEERING by Chiara Casarotti Supervisors: Dr. Rui Pinho, Prof. Gian Michele Calvi University of Pavia and ROSE School July 2004 The dissertation entitled “Bridge isolation and dissipation devices: state of the art review in bridge isolation, seismic response and modelling of bridge isolation and dissipation devices”, by Chiara Casarotti, has been approved in partial fulfilment of the requirements for the Master Degree in Earthquake Engineering. Dr. Rui Pinho Prof. Gian Michele Calvi ABSTRACT The basic principle of conventional earthquake-resistant design is to ensure an acceptable safety level while avoiding catastrophic failures and loss of life. When a structure does not collapse during a major earthquake, and the occupants can evacuate safely, it is considered that this structure has fulfilled its function even though it may never be functional again. Generally, this approach can be considered adequate for most types of structures. However for important structures, safer methods are required, while keeping economic factors in mind. For example, avoiding collapse is not sufficient for facilities that must remain functional immediately after an earthquake: hospitals, police stations, communication centers, strategically located bridges, and so on. Over the last 20 years, a large amount of research has been conducted into developing innovative earthquake-resistant systems in order to raise the safety level while keeping construction costs reasonable. Most of these systems are intended to dissipate the seismic energy introduced into the structure by supplemental damping mechanisms and/or to isolate the main structural elements from receiving this energy through isolation systems. Keywords: isolation, dissipation, bridge devices, bearings, dampers, isolators. ACKNOWLEDGEMENTS The author wishes to thank in particular Dr. Rui Pinho for all his guidance and support throughout the duration of the MSc program. In addition, the author is grateful to Professor Gian Michele Calvi, who gave the opportunity of being part of the school and to all members of the Rose School at the University of Pavia for their friendly and precious assistance. A particular thanks to all the students of the school, with whom I shared important moments of work and fun. I specially thank Sandra, for her invaluable friendship, assistance and support in any single moment of the great time we shared. TABLE OF CONTENTS Abstract i Acknowledgements ............................................................................................................................................................... iii Table of contents.................................................................................................................................................................... v List of figures.......................................................................................................................................................................... ix List of tables ..........................................................................................................................................................................xv 1. INTRODUCTION....................................................................................................................................................................... 1 1.1 The development of isolation concept in seimic design .......................................................................................... 1 1.1.1 Seismic isolation conceptual design and conventional approach............................................................... 2 1.1.2 Pros and cons of seismic isolation in the context of structural performance evaluation ...................... 3 1.1.3 Dissertation objectives....................................................................................................................................... 4 1.2 Dissertation outline......................................................................................................................................................... 4 2. BASIC ISSUES: SEISMIC DESIGN ISSUES, ENERGY CONCEPTS, FRICTION AND DISSIPATIVE MECHANISMS ............... 5 2.1 Bridge considerations...................................................................................................................................................... 5 2.2 Energy formulation of the seismic problem............................................................................................................... 6 2.3 Base concepts and linear theory of seismic isolation................................................................................................ 6 2.3.1 Effects of damping on the response of seismic isolated structures........................................................... 9 2.3.2 Near field effects on the response of seismic isolated structures...............................................................9 2.4 Property Modification Factors of seismic isolation bearings ................................................................................10 2.4.1 Variation of the coefficient of friction..........................................................................................................11 2.4.2 Representations of coulomb friction for dynamic analysis .......................................................................17 2.5 Dissipating and isolating devices ................................................................................................................................18 2.5.1 Antiseismic device typologies .........................................................................................................................19 2.5.2 Isolation/Dissipation systems issues.............................................................................................................22 3. DEVICE TYPOLOGIES: METALLIC AND FRICTION DAMPERS..........................................................................................25 3.1 Basic hysteretic behaviour and dynamic response with metallic/friction devices.............................................25 3.1.1 Response at resonance.....................................................................................................................................26 3.2 Friction dampers............................................................................................................................................................27 3.2.1 Advantages and disadvantages of friction dampers and environmental effects....................................27 3.2.2 Numerical simulation of friction dissipators................................................................................................28 3.2.3 Friction damper typologies: slotted-bolted connections............................................................................28 3.2.4 Friction damper typologies: Pall devices.......................................................................................................30 vi TABLE OF CONTENTS 3.2.5 Friction damper typologies: Sumitomo devices.......................................................................................... 30 3.3 Steel Hysteretic Dampers ............................................................................................................................................ 31 3.3.1 Numerical simulation of metallic dissipators............................................................................................... 32 3.3.2 Hysteretic Damper Typologies: E-shaped Devices.................................................................................... 33 3.3.3 Hysteretic damper typologies: C-shaped devices and EDU device......................................................... 34 3.3.4 Hysteretic damper typologies: ADAS and TADAS elements .................................................................. 36 3.3.5 Hysteretic damper typologies: lead extrusion devices................................................................................ 38 3.4 Design considerations .................................................................................................................................................. 39 3.4.1 Conceptual design: concepts of yield/slip shear and optimization criterion......................................... 39 3.4.2 Choice of bracing members and design procedure.................................................................................... 40 4. DEVICE TYPOLOGIES: VISCOUS AND VISCOELASTIC DAMPERS .................................................................................. 43 4.1 Viscous dampers ........................................................................................................................................................... 43 4.1.1 Basic hysteretic behaviour of viscous dampers........................................................................................... 44 4.1.2 Viscous damper typologies: the Taylor device ............................................................................................ 45 4.1.3 Design procedure