Influence of Incoherence and Wave Passage Effects on Seismic Performances of Long Immersed Tunnel

This paper conducts time history analysis to explore the influence of spatially varying earthquake ground motion (SVEGM) on seismic responses of the long immersed tunnel. Incoherence effect and wave passage effect are mainly focused here. Moreover, three coherency models are adopted to investigate the sensitivity of the computed responses to the models. The calculation results show that SVEGM enlarges seismic responses of the immersed tunnel significantly than uniform excitation. Considering wave passage effect and incoherence effect simultaneously makes the seismic responses increase more sharply than considering the latter only. The deformation of Gina gasket is barely sensitive to coherency model, while the axial compression force is sensitive to coherency model. It indicates suppressing that the fundamental mode and dominating higher-mode response are the hallmark of multi-support excitation. The great differences of three models decay with separation at low frequencies and their coherency in frequency domain are the main reasons that cause the variations of the axial compression forces.

Wave-Passage Effect of Earthquake Loadings on Long Structures

The wave-passage effect of earthquake loadings on long-span structures is studied through use of a multiply-supported single-degree-of-freedom (SDOF) system excited by traveling seismic ground motions. The absolute acceleration response of the SDOF system is represented in the analytical form in the time domain. The frequency-domain analysis results indicate that the wave-passage effect may reduce the absolute acceleration response and the earthquake loading acting on the multiply-supported SDOF system. Further, for different velocities of wave-passage, the response spectra are calculated to represent the reduction of the maximum earthquake loading on the long-span system caused by the wave-passage effect. The computation results of the response spectra indicate that the reduction of the maximum earthquake loading is fluctuant, but has a general tendency to decrease with the increase in the apparent wave velocity and the structural natural period.