A Case Study on Performance of Isolated Bridges under Near-Fault Ground Motion
This paper presents a numerical investigation on the seismic performance of a benchmark bridge with different optimal isolation systems under near fault ground motion. Usually, very large displacements make seismic isolation an unfeasible solution due to boundary conditions, especially in case of existing bridges or high risk seismic regions. Hence, near-fault ground motions are most likely to affect either structures with long natural period range like isolated structures or structures sensitive to velocity content such as viscously damped structures. The work is aimed at analyzing the seismic performance of a three-span continuous bridge designed with different isolation systems having different levels of damping. The case study was analyzed in different configurations including: (a) simply supported, (b) isolated with lead rubber bearings (LRBs), (c) isolated with rubber isolators and 10% classical damping (HDLRBs), and (d) isolated with rubber isolators and 70% supplemental damping ratio. Case (d) represents an alternative control strategy that combines the effect of seismic isolation with additional supplemental damping trying to take advantages from both solutions. The bridge is modeled in SAP2000 and solved by time history direct-integration analyses under a set of six recorded near-fault ground motions. In addition to this, a set of analysis under Italian code provided seismic action is also conducted, in order to evaluate the effectiveness of the suggested optimal control strategies under far field seismic action. Results of the analysis demonstrated that an isolated bridge equipped with HDLRBs and a total equivalent damping ratio of 70% represents a very effective design solution for both mitigation of displacement demand at the isolation level and base shear reduction in the piers also in case of near fault ground motion.
Digital Object Identifier (DOI): doi.org/10.5281/zenodo.1129894Procedia APA BibTeX Chicago EndNote Harvard JSON MLA RIS XML ISO 690 PDF Downloads 669
 A. Martelli, and M. Forni, (2010), “Seismic Isolation and Protection Systems. The Journal of the Anti-Seismic Systems International Society, 1(1)
 F. Naeim, “Design of Seismic Isolated Structures: From Theory to Practice”, Earthquake Spectra, 16(3), 709–710, 2000.
 W.I. Liao, C.H. Loh, and B.H. Lee, “Comparison of dynamic response of isolated and non-isolated continuous girder bridges subjected to near-fault ground motions”, Engineering Structures, 26 (14), 2173-2183, 2004.
 R. S. Jangid, and J.M. Kelly, “Base isolation for near-fault motions”, Earthquake Engineering and Structural Dynamics, 30 (5), 691-707, 2001.
 J. Shen, M.H. Tsai, K.C. Chang, and G.C. Lee, “Performance of a seismically isolated bridge under near-fault earthquake ground motions”, Journal of Structural Engineering, 130 (6), 861-868, 2004.
 M. H. Jònsson, B. Bessason, and E. Haflidason, “Earthquake response of a base-isolated bridge subjected to strong near-fault ground motion”, Soil Dynamics and Earthquake Engineering, 30 (6), 447-455, 2010.
 J. F. Hall, T. H. Heaton, M. W. Halling, and D.J. Wald, “Near-source ground motion and its effect on flexible buildings”, Earthquake Spectra, 11(4), 569–605, 1995.
 O. E. Ozbulut, and S. Hurlebaus, “Optimal design of superelastic-friction base isolators for seismic protection of highway bridges against near-field earthquakes”, Earthquake Engineering and Structural Dynamics, 40, 273-291, 2010.
 S.S. Sahasrabudhe, and S. Nagarajaiah, “Semi-active control of sliding isolated bridges using MR dampers: an experimental and numerical study”, Earthquake Engineering and Structural Dynamics, 34(8), 965-983, 2005.
 R.S. Jangid, “Optimum lead-rubber isolation bearings for near-fault motions”, Engineering Structures, 29 (10), 2503-2513, 2007.
 N. Makris, and S.P. Chang, “Effect of viscous, viscoplastic and friction damping on the response of seismic isolated structures”, Earthquake Engineering and Structural Dynamics, 29, 85-107, 2000.
 D. Losanno, M. Spizzuoco, and G. Serino, “Optimal design of the seismic protection system for isolated bridges”, Eartquakes and Structures, 6, 969–999, 2014.
 Y. P. Wang, L. L. Chung, and W. H. Liao, “Seismic response analysis of bridges isolated with friction pendulum bearings”, Earthquake Engineering and Structural Dynamics, 27 (10), 1069-1093, 1998.
 NTC, “Nuove norme tecniche per le costruzioni”, DM 14 gennaio 2008, Gazzetta Ufficiale n. 29 del 4 febbraio 2008 – Supplemento Ordinario n. 30, Italy, 2008.
 I. Iervolino, C. Galasso, and E. Cosenza, “REXEL: computer aided record selection for code–based seismic structural analysis”, Bulletin of Earthquake Engineering, 8 (2), 399-362, 2010.