Seismic Analysis Of Large-span Cable-stayed Bridge Under Compicated Conditions

The seismic design of large-span cable-stayed bridge has been a topicwith special focus in current research for its complicated constructionconditions. In this paper, the method of seismic ground motion inputing,soil-structure interaction and the hydrodynamic effect of large-spancable-stayed bridge are studied.The results are shown that:1. In the fixed-foundation ground motion input mode, the influence oftravelling wave effect on a seven-span cable-stayed bridge with fully floatingstructure system is considered by way of introducing a 'time difference' intothe ground motion time history of each support point of bridge. The dynamicresoponse of key parts of cable-stayed bridge to the seismic travelling waveand seismic uniform excitation are given. By comparing with the dynamicresponse of cable-stayed bridge to seismic uniform excitation, the differenceof that of cable-stayed bridge to seismic travelling wave excitation isdiscussed. The effects of latter are stated, and the effective seismicfortification measures are suggested.2. The seismic analysis of large-span cable-stayed bridge with multispans is a multi-source scattering problem in numerical wave field. Based ontwo typical single-source visco-elastic artificial boundary, that are, LiuJingbo's boundary which is set up on a basis of cylindrical evanescent waveand Du Xiuli's boundary which is set up on a basis of plane wave and thesuperposition of far-field scattering wave, a multi-source weigthingconcentrated visco-elastic artificial boundary by using stacking principle ofwave fields. The formulas for calculating its spring coefficient and dampingcoefficient are givien. The accuracy and the stability of this boundaryconditions discussed by giving verification examples such as the2D eccentricsingle-point source problem, the2D eccentric multi-point source problem andthe2D multi-source scattering problem.3. Based on the structure-foundation integral model which is set up byadopting direct method and the multi-source weigthing concentratedvisco-elastic artificial boundary, the visco-elastic artificial boundary groundmotion input mode for bridge is realized. The influence of soil-structureinteraction on the dynamic resoponse of cable-stayed bridge with fullyfloating structure system is analyzed. By comparing the seismic resoponse ofcable-stayed bridge in visco-elastic artificial boundary ground motion inputmode to that in the fixed-foundation ground motion input mode, the differenceof the dynamic resoponse of key parts of cable-stayed bridge in two input modes are discussed. The limitations of the fixed-foundation ground motioninput mode by introducing a 'time difference' into the ground motion timehistory of each support point of bridge are analyzed. The ground motion inputmode based on multi-source weigthing concentrated visco-elastic artificialboundary and the structure-foundation integral model are proposed fordynamic ananlysis of large-span cable-stayed bridge under complicatedconditions.4. The hydrodynamic effects on cable-stayed bridge with fully floatingstructure system in two different ground motion input modes are modeled byadded mass. The difference of the seismic resoponse of key parts ofcable-stayed bridge in two input modes are compared, which demonstratesthat it is necessary for seismic analysis and design of large-span cable-stayedbridge to consider the coupling interaction of hydrodynamic effect andsoil-structure interaction.