Study On Response And Shock Absorption Measures For Long-Span Bridge Under The Long-Period Ground Motion

Low peak acceleration and long duration are the characteristics of long-period ground motion. The history records have show that magnitude, epicentral distance and local site condition have great effect on the occurrence of long-period ground motion.Through summarize this paper thinks that sites with deep overlying soil may occur long-period ground motion if there are large seismotectonic around it in the distance of far-field effect can be arise. Long-period ground motion may cause flexible structures such as long-span bridges and super high-rise buildings to occur large displacement, high velocity and greatly rocking. Unexpected failure or damage may be arise.In order to study the effect of long-period ground motion on long-span bridge, one suspension bridge and two cable-stayed bridges were take as the examples in this paper. Four general seismic waves and two long-period seismic waves were selected to excit the structures form longitudinal and transverse. The results of nonlinear time-history analysis show that the adverse effect of long-period ground motion on long-span bridges' dynamic response is very significantly. Not only deck displacement and tower top displacement are much larger under long-period ground motion than under general ground motion, but also the force of tower may be larger. Particularly on node location such as crossbeam or crossing point. Therefore, this paper thinks that if a long-span bridge was builded on the site which may occur long-period ground motion, adverse effect of long-period ground motion should be considered.Take a cable-stayed bridge as an example, the effectiveness of elastic link device and viscous damper under long-period ground motion was analyzed in this paper. The results show that elastic link device may be invalid under long-period ground motion, furthermore, it may increase the displacement and internal force. So elastic link device not suitable for long-span bridges which build on the site may occur long-period ground motion. In contrast, viscous damper have good shock absorption effect under this two kinds of ground motion.