Funded by NSF’s Pacific Earthquake Engineering Research Center. Investigators – R. W. Boulanger, Y. H. Chai, C. J. Curras, T. C. Hutchinson and I. M. Idriss.
Abstract: Tall bridge structures supported on soft soils are particularly vulnerable to near-fault ground motions due to the long-period characteristic of these structures. The large velocity pulses in the near-fault ground motion tend to subject the structure to a very large displacement ductility demand which, in the case of full-ductility structure, would occur in the columns or pier-walls of the structure. Unacceptably large residual deformations may also occur in the structure after an earthquake. The extent of the these deformations depends on the amplitude, period and shape of the large pulses in the ground motion, and the lateral strength and period of the structure which are inherently coupled with the condition of the supporting soil, particularly for soft soils. For very large magnitude earthquakes, the duration of the intense ground motion can be significantly lengthened due to a large fault rupture, and the long-duration ground motion is important for the dynamic stability of tall bridge structures. As current design of tall bridge structures often result in relatively low lateral strength for these structures, the combination of low strength and large lateral displacement leads to a situation where P-D effect becomes very important. As P-D effects reduce the effective lateral strength of the structure, the structure response tends to be characterized by progressive yielding in one direction. The asymmetric accumulation of inelastic deformations in one direction becomes increasingly important as the duration of the ground motion is increased. Since the hysteretic characteristics of yielding elements have a pronounced influence on the ductility demand and residual deformation, the response of tall bridge structures can be expected to be significantly affected by the nonlinear interaction of the supporting soil with the structure. This project will investigate the influence of long-period and long-duration ground motions on tall bridge structures. The software FEAP coupled with FEDEAS (Finite Elements for Design, Evaluation and Analysis of Structures) is being used for the analysis.
Key Publications:
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T. C. Hutchinson, Y. H. Chai, R. W. Boulanger and I. M. Idriss (2004). “Estimating Inelastic Displacements for Design: Extended Pile-Shaft-Supported Bridge Structures”, Earthquake Spectra, Vol. 20, No. 4, pp. 1081-1094.
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T. C. Hutchinson, Y. H. Chai, R. W. Boulanger and I. M. Idriss (2004). “Inelastic Seismic Response of Extended Pile-Shaft-Supported Bridge Structures”, Earthquake Spectra, Vol. 20, No. 4, pp. 1054-1080.