Implications of Design Assumptions on Capacity Estimates and Demand Predictions of Multispan Curved Bridges
Publication: Journal of Bridge Engineering
Volume 12, Issue 6
Abstract
The paper presents a detailed seismic performance assessment of a complex bridge designed as a reference application of modern codes for the Federal Highway Administration. The assessment utilizes state-of-the-art assessment tools and response metrics. The impact of design assumptions on the capacity estimates and demand predictions of the multispan curved bridge is investigated. The level of attention to detail is significantly higher than can be achieved in a mass parametric study of a population of bridges. The objective of in-depth assessment is achieved through investigation of the bridge using two models. The first represents the bridge as designed (including features assumed in the design process) while the second represents the bridge as built (actual expected characteristics). Three-dimensional detailed dynamic response simulations of the investigated bridge, including soil-structure interaction, are undertaken. The behavior of the as-designed bridge is investigated using two different analytical platforms for elastic and inelastic analysis, for the purposes of verification. A third idealization is adopted to investigate the as-built bridge’s behavior by realistically modeling bridge bearings, structural gaps, and materials. A comprehensive list of local and global, action and deformation performance indicators, including bearing slippage and inter-segment collision, are selected to monitor the response to earthquake ground motion. The comparative study has indicated that the lateral capacity and dynamic characteristics of the as-designed bridge are significantly different from the as-built bridge’s behavior. The potential of pushover analysis in identifying structural deficiencies, estimating capacities, and providing insight into the pertinent limit state criteria is demonstrated. Comparison of seismic demand with available capacity shows that seemingly conservative design assumptions, such as ignoring friction at the bearings, may lead to an erroneous and potentially nonconservative response expectation. The recommendations assist be given to design engineers seeking to achieve realistic predictions of seismic behavior and thus contribute to uncertainty reduction in the ensuing design.
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Acknowledgments
This study was funded by the U.S. Federal Highway Administration (FHWA) through the Mid-America Earthquake (MAE) Center, University of Illinois at Urbana-Champaign. The MAE Center is an engineering research center funded by the National Science Foundation under cooperative agreement reference EEC 97-01785. The writers are grateful to Professor Glenn Rix, Georgia Institute of Technology, for his advice on earthquake input motions.
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Information & Authors
Information
Published In
Journal of Bridge Engineering
Volume 12 • Issue 6 • November 2007
Pages: 710 - 726
Copyright
© 2007 ASCE.
History
Received: Feb 2, 2006
Accepted: Oct 16, 2006
Published online: Nov 1, 2007
Published in print: Nov 2007
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