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原文传递 Seismic Retrofitting and Design of Highway Bridges in New Jersey

题名：	Seismic Retrofitting and Design of Highway Bridges in New Jersey
作者：	M. Ala Saadeghvaziri, and Alireza Yazdani-Motlagh
关键词：	Seismic Design, Bridges, Seismic Retrofit, Multi-Span Simply Supported Bridges, Bearings, Soil-Structure Interaction
摘要：	This report presents the results of the second phase of a comprehensive analytical study on the seismic response of high way bridges in New Jersey. Most bridges in New Jersey are multi-span simply supported (MSSS) where due to impact at the joints the seismic response is highly nonlinear. Therefore, detailed seismic analysis of essential bridges should employ nonlinear computer models that consider the important behavioral characteristics. Among these are; behavior of steel bearings, impact between adjacent spans and between the end-span and the abutment, soil-structure interaction, frictional characteristics following bearing failure, plastic hinges and/or shear failure at the columns, and combined effect of horizontal and transverse ground motion excitations. In light of these , the overall objective of this phase of the study was to evaluate the nonlinear seismic response of actual bridges with emphasis on soil-structure interaction and three-dimensional effect of ground motion .Furthermore ,capacity /demand ratios for various components were derermined based on FHWA’s seismic retrofitting manual for highway bridges. The results indicate that even under low intensity earthquakes high impact forces will be generated within an MSSS bridge. As a result the steel bearings, which are employed in most bridges in New Jersey, will most likely fail. However, if the failure Is followed by stable Coulomb-Friction at the interface of the steel bearing and the steel girder or the interface of the bearing and concrete seat, it is not expected that the bridge will collapse. Actually, due to energy dissipation capacity of this mode of failure the response of the bridge will be constrained. Thus, the bridges investigated under this study can survive an earthquake with peak ground acceleration (PGA) of 0.18g, which is the maximum seismic coefficient for New Jersey based on AASHTO's Seismic Specifications. For a ground motion with PGA of 0.4g, the bridges considered will sustain shear failure of columns in addition to bearing failure. This in turn can cause collapse of the bridge. Soil-structure interaction and frictional coefficient at the failed bearings have significant effect on the response of MSSS bridges in the longitudinal direction. Considerations should be given to increasing seat lengths and strengthening concrete seat under the bearings to ensure stable behavior following bearing failure. Future research work may consider experimental work to support the analytical conclusions reported here, and further analytical work on development of pushover analysis methodology and nonlinear design spectrum for MSSS bridges.
报告类型：	科技报告