Wave Passage and Incoherence Effect on Dynamic Response of a Pre-Stressed Viaduct Under a Natural Earthquake

Abstract eng:
The aim of this study was to assess the influence of spatial variation of ground motion on a 4-span pre-stressed concrete viaduct (160 m long) subjected to an earthquake. A seismic shock recorded in January 2012 in Poland was used as the kinematic excitation of the viaduct. In the dynamic analysis two models of non-uniform kinematic excitation were used. Firstly, a model of excitation in which only the wave passage effect was taken into account was applied. Secondly, a model of excitation considering the incoherence effect only was assumed. In both models of non-uniform kinematic excitation ground motion records at one point and a seismic wave velocity had to be known to generate earthquake records for all supports of the structure. In the analysis of the incoherence effect an effective engineering method for conditional stochastic simulation of ground motions was performed in the time domain. The results obtained for both models of non-uniform kinematic excitation were compared to those obtained for the model of uniform excitation that assumed identical motion of viaduct supports. The analysis revealed that the dynamic response of the viaduct to the shock is strongly determined by the assumed model of kinematic excitation. If the model of non-uniform kinematic excitation is applied the dynamic response may differ even up to 60% in relation to the response obtained for the model of uniform excitation. To assess the influence of seismic wave velocity on the dynamic response of viaduct to the earthquake various wave velocities were implemented. The analysis proved that the dynamic response of the viaduct strongly depended on the wave velocity. In case of the model of non-uniform excitation including the wave passage effect only, the dynamic response of the structure declined with the decrease of wave velocity. It is a consequence of the reduction of the average amplitudes of kinematic excitation. In case of the model of non-uniform kinematic excitation considering the incoherence effect only, the dynamic response of the viaduct substantially increases with decreasing wave velocity. For low wave velocities the dynamic response of viaduct is considerably greater for the model including the incoherence effect than for the model of uniform excitation. This occurs due to the quasi-static effects which result from changes of subsoil geometry during seismic shocks. Therefore, the application of conventional model of uniform excitation may lead to underestimation and non-conservative assessment of the dynamic response of a long structure, especially for low wave velocities.

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