American Society of Civil Engineers


Equivalent Modal Damping of Short-Span Bridges Subjected to Strong Motion


by Sungchil Lee, Ph.D., (Assistant Researcher, Dept. of Civil and Environmental Engineering, Univ. of California, Irvine, CA 92617. E-mail: sungcl@uci.edu), Maria Q. Feng, M.ASCE, (Professor, Dept. of Civil and Environmental Engineering, Univ. of California, Irvine, CA 92617. E-mail: mfeng@uci.edu), Seung-Jun Kwon, Ph.D., (Assistant Researcher, Dept. of Civil and Environmental Engineering, Univ. of California, Irvine, CA 92617. E-mail: juni98@yonsei.ac.kr), and Seok-Hee Hong, (Vice President, Naekyung Eng. Co., Anyang-Si, Kyungki-Do, Korea 431-060. E-mail: nk2900@empal.com)

Journal of Bridge Engineering, Vol. 16, No. 2, March/April 2011, pp. 316-323, (doi:  http://dx.doi.org/10.1061/(ASCE)BE.1943-5592.0000149)

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Document type: Journal Paper
Abstract: In this paper four different methods are investigated for estimating the equivalent modal damping ratios of a short-span bridge under strong ground motion by considering the energy dissipation at the boundary. The Painter Street Overcrossing (PSO) is investigated because of seismic data availability. Computed responses using the response-spectrum method with the equivalent damping ratios estimates are compared with the recorded responses. The results show that the four methods provide reasonable estimation of equivalent modal damping ratios and that neglecting off-diagonal elements in the damping matrix is the most efficient and practical method. The equivalent damping ratio of the PSO was nearly 25% under an earthquake with peak ground acceleration of 0.55g, which is much higher than the conventional assumption of 5%.


ASCE Subject Headings:
Span bridges
Response spectra
Modal analysis
Vibration
California

Author Keywords:
Bridges
Response spectra
Modal analysis