Study On The Nonlinear Dynamic Response And Damage Feature Of Cable-stayed Bridge In Deep Water Excited By Cross-fault Earthquakes

Fault movement is the main reason for the earthquake formation. The distance to avoid active faults and recommended actions to cross active faults have been given in domestic and foreign seismic codes. Due to the restriction of topographic and geomorphic conditions, the design of line selection, construction cost and other objective conditions, the form of using a bridge to cross active fault is inevitable. In several major earthquakes in recent years, a number of bridges crossing the fault were severely damaged or collapsed completely. At present, the problem for seismic design of bridge in domestic and foreign is still in the initial research stage, there is a lack of reference literature and standardized regulations. With more and more bridges being constructed in the area of high seismic intensity, the seismic research of cross-fault bridge has important practical significance. A long-span cable-stayed bridge in deep water is taken as an example to carry out the research of cross-fault ground motion input, structural seismic response and injury problems. The main research work in this paper is as follows:(1) The research status of seismic analysis for cross-fault structure by different people was summarized systematically, and the deficiencies of research for cross-fault bridges were analyzed. According to the earthquake motion characteristic of strike-slip fault, the earthquake motions with different magnitudes in fault-normal (FN) direction and fault-parallel (FP) direction were synthesized with the combination of low frequency pulses and high frequency waves, and the cross-fault earthquake motion characteristic was compared in different directions. The results show, in both side of fault, the ground motions in FN direction are equal and in the same direction, the ground motions in FP direction are equal but in opposite directions; the predominant period of acceleration spectra and velocity spectra in FN direction is larger than those in FP direction.(2) Taking a long-span cable-stayed bridge with elevated pile cap in deep water as an example, the three-dimensional nonlinear detailed model was built based on OpenSees software, and the influences of soil-structure interaction and water depths to natural characteristics of cable-stayed bridge was analyzed. The result shows that:first several vibration modes of cable-stayed bridge are all the vibration shapes of girder, and has long vibration period;.In addition, because of the soil-structure interaction and the increase of water depth, the vibration period of cable-stayed bridge increase accordingly.(3) Based on synthetic cross-fault ground motion, the nonlinear dynamic analysis of cable-stayed bridge in deep water was studied by uniform excitation analysis in FN direction and by nonlinear non-uniform excitation analysis in FP direction. The influences of different magnitudes, water depths, cross-fault angles and locations to seismic response and damage distribution of tower were analyzed respectively. The results show that, considering the above factors, the maximum dynamic response and damage index appear at the bottom of tower. Therefore, the response characteristics of the tower bottom should be paid attention in seismic design of cable-stayed bridge in deep water excited by cross-fault earthquakes.(4) According to the change rule of dynamic response and damage index for cable-stayed bridge with different angles and locations of cross-fault, the reasonable angle and location of cross-fault for cable-stayed bridge is proposed to provide a theoretical support for the actual construction.