American Society of Civil Engineers

Implications of Design Assumptions on Capacity Estimates and Demand Predictions of Multispan Curved Bridges

by Aman Mwafy, (corresponding author), (Sr. Res. Fellow, Univ. of Illinois at Urbana-Champaign, Urbana, IL 61801, Asst. Prof. (on leave), Univ. of Zagazig, Egypt E-mail:, Amr Elnashai, F.ASCE, (Bill and Elaine Hall Endowed Prof. of Civ. Engrg., Dir. of the Mid-America Earthquake Ctr., Univ. of Illinois at Urbana-Champaign, Urbana, IL 61801. E-mail:, and W.-H. Yen, (Program Mgr. of Seismic Hazard Mitigation, Ofc. of Infrastructure, R&D Federal Highway Administration, McLean, VA 22101. E-mail:

Journal of Bridge Engineering, Vol. 12, No. 6, November/December 2007, pp. 710-726, (doi:

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Document type: Journal Paper
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.

ASCE Subject Headings:
Continuous bridges
Earthquake loads
Nonlinear analysis
Span bridges
Three-dimensional models