Keywords: earthquake, nonstationary, random vibration, multiple excitation.

Earthquakes are typical random vibrations and so the random vibration approach to structural aseismic designs has been gradually accepted by the earthquake engineering community, e.g by the European Committee for Standardization in terms of the Eurocode 8 (Part 2 : bridge) [1]. So far, however, only the comparatively simple stationary random vibration analysis of structures has been studied and applied using simple finite element models [2,3,4]. As for the nonstationary random response analysis, since it is considered even more complicated and difficult, so little research progress has been reported to tackle this issue. It is especially so if the structural models have many degrees of freedom and ground nodes (supports), and/or if the seismic spatial effects must be simultaneously taken into account.

In this paper, long-span structures subjected to multiple seismic nonstationary random excitations are investigated by using the PEM (pseudo excitation method) [5] in combination with the precise integration method [6]. The PEM is a complete CQC method because the cross-correlation terms between the participating modes and between the random excitations are both included in the computational results. Meanwhile, the quasi-static and dynamic components of the response and their coupling terms are also accurately included.

The nonstationary random response of a real long-span cable-stayed bridge, Yong-An bridge, built in Liaoning Province of China was computed using the proposed method. The finite element model has 1642 degrees of freedom and 5 supports, and 100 modes were taken for mode-superposition. The results are compared with those based on the stationary random analysis.

Using a Pentium-4 personal computer, the computational times required by the nonstationary analyses are about 7 minutes for the cases of uniform ground motion or with the wave passage effect taken into account, or about 40 minutes if the incoherence effect is included. This high efficiency is quite acceptable for practical engineering designs.

It is concluded from the numerical comparisons that for long-span bridges, not only the seismic spatial effect (in particular the wave passage effects), but also the nonstationary effects, may be quite important and should be taken into account in the aseismic designs. Previously, it was very complicated and difficult to account for such effects. By means of the proposed the PEM combined with the precise integration method, however, all these difficulties have been overcome. These spatial and nonstationary effects can now be included in the aseismic analysis conveniently, accurately and very efficiently.

1

European Committee for Standardization, "Eurocode 8, Structures in Seismic Regions - Design Part 2: Bridge", Brussels, European Committee for Standardization, 1995.

2

A.D. Kiureghian, A. Neuenhofer, "Response Spectrum Method for Multi-support Seismic Excitations", Earthquake Engineering and Structural Dynamics, 21(8), 713-740, 1992. doi:10.1002/eqe.4290210805

3

H.Z. Ernesto, E.H. Vanmarcke, "Seismic Random Vibration Analysis of Multi-support Structural Systems", Journal of Engineering Mechanics, ASCE, 120(5), 1107-1128, 1994. doi:10.1061/(ASCE)0733-9399(1994)120:5(1107)

4

M. Berrah, E. Kausel, "Response Spectrum Analysis of Structures Subjected to Spatially Varying Motions", Earthquake Engineering and Structure Dynamics, 21(6), 461-470, 1992. doi:10.1002/eqe.4290210601

5

J.H. Lin, Y.H. Zhang, "Pseudo Excitation Method of Random Vibration", Science Press, Beijing (in Chinese), 2004.

6

W.X. Zhong, "Duality System in Applied Mechanics and Optimal Control", Kluwer Academic Publishers, Boston, 2004.

purchase the full-text of this paper (price £20)

go to the previous paper
go to the next paper
return to the table of contents
return to the book description
purchase this book (price £135 +P&P)