Research On Seismic Energy Failure Mechanism To Long-span Cable-stayed Birdge

Cable-stayed bridges as to compete with suspension bridge of long-span Bridgesare generally preferred by engineers. However we also need pay attention to large spanbridge anti-earthquake problem. Our country is one of the most earthquake-pronecountries,in order to reduce losses from the earthquake, seismic research coming withbridge construction develops gradually.The directive “Guidelines for seismic design ofHighway Bridges” was issued for bridges whose length are under150m,but specificanalysis for long-span bridges and further understanding of the seismic characteristicsare necessary. Earthquake motion is a kind of space motion, traveling wave effect,coherence effects and site effects need to be considered in the seismic analysis of spanstructures. Nonlinear factors also should be considered for some structures，Thesefactors determine the significance of the seismic research of long-span cable-stayedbridge.In order to provide reference for engineering design，based on specification,takinga long-span cable-stayed bridge as the research object to compared the earthquakeresponse under different excitations，and nonlinear effects was considered.The mainwork is as follows.①Energy significance of response spectrum and power spectrum was putforward,and chain theory frame for bridge seismic damage was established.②Finite element model of the cable-stayed bridge was established to get thevibration characteristics of parameters.③The location response spectrum were built on the basis of code responsespectrum combined with the bridge site conditions, six kinds of earthquake excitationcondition shown that a excitation direction inspire the largest contribution todisplacement response of this direction;midspan has the largest displacement wichbecome smaller as the excitation dimension increases gradually; transverse componentcan cause the main tower vertical displacement mutation;the largest moment is attower-beam combination,wich is about twice that of the middle;and main tower internalforces in the main beam at the horizontal position mutation.④Artificial seismic waves generated by the bridge location response spectrum，using support large mass method to do time history analysis considering traveling waveeffect and nonlinear effects; research shows that geometric nonlinear has small effect on seismic response of cable-stayed bridges, one-dimensional wave excitation can increasethe earthquake response of bridges while three-dimensional wave excitation can causegirder and main tower longitudinal displacement value decreases and verticaldisplacement displacement of the main girder appeared obvious asymmetry.⑤Transforming response spectrum to power spectrum,through different types ofsite considering uniform excitation compared with multi-point excitation to analyzes theeffect of seismic response of the bridge site.The research shows that the soft soil ofbridge location site the bigger the bridge respone values,multipoint excitation responsesare between uniform excitation responses; site effects give rise to the main beammidspan displacement mutation increases,wich is unfavorable for moment andfavorable for shear of the main tower.