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Following the San Fernando, California earthquake of February 9, 1971 about 1100 structures of the 13,000 in the highway system were found to be in need of retrofitting work to increase their seismic resistance. Retrofitting is now complete for over half of this number. All identified seismic retrofitting on State Highway System structures should be completed by 1988.
Mitigating the effects of earthquakes is crucial to bridge design. With chapters culled from the best-selling Bridge Engineering Handbook, this volume sets forth the principles and applications of seismic design, from the necessary geotechnical and dynamic analysis background to seismic isolation and energy dissipation, active control, and retrofit
Following the San Fernando, California earthquake of February 9, 1971, some 1300 structures of the 13,000 on the highway system were identified as being in need of retrofitting in order to increase their seismic resistance. The Phase I program goal was to tie bridge superstructure components together at superstructure hinges and bearing supports so as to prevent bridge spans from separating. This fifty million dollar program is now essentially complete. The Whittier Narrows Earthquake of October 1, 1987 revealed a need to retrofit substructures, primarily columns. At the 605/5 separation structure, severe shaking caused incipient column shear failures. Accordingly, a ten year substructure retrofit program involving 800 substructures was started. The Loma Prieta Earthquake of October 17, 1989 tragically demonstrated the extreme vulnerability of multi-level, multi-column, long viaducts designed to the 1950s state-of-the-art and constructed in soft soils (bay mud). As a result, California has accelerated its substructure retrofit program to a three-year time frame. Several substructure retrofit techniques, including column encasement, footing enhancement, base isolation, and energy absorption are also being used or investigated. The cost of retrofitting a bridge completely is a small percentage of the cost of the facility or the cost arising from a seismically induced failure. For the covering abstract of the Conference see IRRD Abstract No. 807839.
"TRB's National Cooperative Highway Research Program (NCHRP) Synthesis 440, Performance-Based Seismic Bridge Design (PBSD) summarizes the current state of knowledge and practice for PBSD. PBSD is the process that links decision making for facility design with seismic input, facility response, and potential facility damage. The goal of PBSD is to provide decision makers and stakeholders with data that will enable them to allocate resources for construction based on levels of desired seismic performance"--Publisher's description.
Focuses on threats that earthquakes pose to the nation1s bridges.
The primary objectives of the report are to (1) provide current information on the theory and techniques for seismic analysis of highway bridges, including background material on basic structural dynamics, (2) identify the appropriate criteria necessary to decide if a bridge needs retrofitting and the type of retrofit measures to employ, and (3) demonstrate design details and installation specifications for retrofitting existing highway bridges to minimize earthquake damage. This report is in two volumes: Vol 1 "Earthquake and Structrural Analysis" Vol. 2 "Design Manual". Volume two is a design manual and contains illustrations of various retrofit concepts and specific design procedures which can be applied to existing bridges.
Because of their structural simplicity, bridges tend to beparticularly vulnerable to damage and even collapse when subjectedto earthquakes or other forms of seismic activity. Recentearthquakes, such as the ones in Kobe, Japan, and Oakland,California, have led to a heightened awareness of seismic risk andhave revolutionized bridge design and retrofit philosophies. In Seismic Design and Retrofit of Bridges, three of the world's topauthorities on the subject have collaborated to produce the mostexhaustive reference on seismic bridge design currently available.Following a detailed examination of the seismic effects of actualearthquakes on local area bridges, the authors demonstrate designstrategies that will make these and similar structures optimallyresistant to the damaging effects of future seismicdisturbances. Relying heavily on worldwide research associated with recentquakes, Seismic Design and Retrofit of Bridges begins with anin-depth treatment of seismic design philosophy as it applies tobridges. The authors then describe the various geotechnicalconsiderations specific to bridge design, such as soil-structureinteraction and traveling wave effects. Subsequent chapters coverconceptual and actual design of various bridge superstructures, andmodeling and analysis of these structures. As the basis for their design strategies, the authors' focus is onthe widely accepted capacity design approach, in which particularlyvulnerable locations of potentially inelastic flexural deformationare identified and strengthened to accommodate a greater degree ofstress. The text illustrates how accurate application of thecapacity design philosophy to the design of new bridges results instructures that can be expected to survive most earthquakes withonly minor, repairable damage. Because the majority of today's bridges were built before thecapacity design approach was understood, the authors also devoteseveral chapters to the seismic assessment of existing bridges,with the aim of designing and implementing retrofit measures toprotect them against the damaging effects of future earthquakes.These retrofitting techniques, though not considered appropriate inthe design of new bridges, are given considerable emphasis, sincethey currently offer the best solution for the preservation ofthese vital and often historically valued thoroughfares. Practical and applications-oriented, Seismic Design and Retrofit ofBridges is enhanced with over 300 photos and line drawings toillustrate key concepts and detailed design procedures. As the onlytext currently available on the vital topic of seismic bridgedesign, it provides an indispensable reference for civil,structural, and geotechnical engineers, as well as students inrelated engineering courses. A state-of-the-art text on earthquake-proof design and retrofit ofbridges Seismic Design and Retrofit of Bridges fills the urgent need for acomprehensive and up-to-date text on seismic-ally resistant bridgedesign. The authors, all recognized leaders in the field,systematically cover all aspects of bridge design related toseismic resistance for both new and existing bridges. * A complete overview of current design philosophy for bridges,with related seismic and geotechnical considerations * Coverage of conceptual design constraints and their relationshipto current design alternatives * Modeling and analysis of bridge structures * An exhaustive look at common building materials and theirresponse to seismic activity * A hands-on approach to the capacity design process * Use of isolation and dissipation devices in bridge design * Important coverage of seismic assessment and retrofit design ofexisting bridges
Much of Utah's population dwells in a seismically active region, and many of the bridges connecting transportation lifelines predate the rigorous seismic design standards that have been developed in the past 10-20 years. Other states in the west have instituted seismic retrofit programs in response to damage to transportation networks in past California earthquakes. In a parallel report, seismic retrofit guidelines were developed for Utah based on the Seismic Retrofitting Manual for Highway Structures published by FHWA. In this report, representative case study bridges are evaluated in detail using the guidelines. The case study evaluations include the following for each bridge: 1- selection and presentation of analysis method, 2- development of numerical model in LARSA 4D and/or additional programs as needed, 3- evaluation of the seismic response of the unretrofitted bridge, 4- design of a possible retrofit scheme. The bridges evaluated include a four-span simply supported prestressed concrete girder bridge, a four-span continuous concrete T-beam, and an eight-span curved steel girder bridge with in-span pin and hanger joints.