Date of Award
M.S. in Engineering Science
University of Mississippi
Infrastructure constructed should be safe and reliable. Bridges are essential infra structure used by large mass of people on a daily basis. Out of 617,000 bridges across the United States, 42% are at least 50 years old, and 7.5% are considered structurally deficient as per Infrastructure report card. 178 million trips are made on these structurally deficient bridges every day in the US. Thus, a bridge should be designed, not only for Strength and Service limit states, but also for Extreme limit states which includes earthquake. New Madrid Seismic Zone (NMSZ), located in southeastern Missouri, northeastern Arkansas, western Tennessee, western Kentucky and southern Illinois, is the most active seismic area in the United States, east of the Rocky Mountains.
Within the influence of NMSZ is Mississippi because of which the bridges in Northern Mississippi falls into Region 3 Seismic Performance Category defined by AASHTO. During the past 20 years, seismic isolation using specially designed bearings has emerged as one of the most promising retrofitting strategies for improving the seismic performance of existing bridges. The objective of this paper to measure effectiveness of the seismic bearings in terms of reduction of bending forces developed in critical elements of newly constructed highway bridges in Northern Mississippi when subjected to simulated earthquake motion.
A full bridge model has been developed using frame elements for the substructure and cross frames while plate elements for the superstructure using a finite element software (SAP2000). Shear resistance of the bearings and lateral resistance of the soil are represented using linear springs whose effective stiffness is established from the literature review using an experimental study assessing the load-deformation response of the two selected seismic bearing types. Time history analysis has been performed based on the input motion applied to the soil spring. Input motion has been adapted and scaled according to Federal Emergency Management Agency (FEMA). A three shaft isolated bent model developed using Frame element is subjected to linear pushover analysis. Plastic hinge formation sequence and damage limit states in potential hinge locations were observed using this model. Modal analysis was performed on both of full bridge and isolated bent model.
Lateral response behavior simulated using the two models has been observed and compared to identify any significant influence of the deck and adjacent bents and abutments. The maximum internal force response at crucial bent served as the main benchmark for assessing the effectiveness of the seismic bearings. The research is focused on contrasting the maximum internal flexural responses computed in crucial shaft. According to the simulations, the selected seismic bearings reduced demand at the crucial shaft section of the selected bridge compared to the rigid case.
Gupta, Sandip, "Full Bridge Modeling to Evaluate Effectiveness of a Seismic Bearing on a Newly Constructed Bridge on I-55" (2023). Electronic Theses and Dissertations. 2512.