Analysis Of High-order Vibration Mode Effect And Study On Seismic Reduction Of Long-span Steel Truss Arch Bridge

In recent years,large-span steel truss arch bridges have been constructed in mountainous areas of Western China due to their advantages of light weight,large span capacity and beautiful shape.However,most of them are in high-intensity seismic areas in Western China.Seismic action often controls the design of arch bridges.The seismic response of long-span steel truss arch bridge is complex,which is mainly reflected in the influence of high-order modes on its seismic response can not be ignored,and the ductility design is difficult due to the large axial compression of the main arch ring.Therefore,in the seismic design of long-span steel truss arch bridge,effective seismic isolation measures should be adopted to reduce the seismic response on the basis of correct seismic response analysis,so as to keep the main arch ring in the elastic range as far as possible.In view of this,this paper mainly carries out the following work:(1)Based on a large number of domestic and foreign literatures,the dynamic characteristics,seismic response characteristics and seismic isolation technology of long-span steel truss arch bridges are summarized.Taking a 1-490 m deck steel truss arch bridge as the research object,the finite element calculation model of the whole bridge is established by using Midas/Civil finite element software,and the main dynamic characteristics of the bridge are analyzed.(2)Based on the formula for calculating the inertia force of structural particle by mode decomposition response spectrum method,a method for separating the seismic response corresponding to a particular mode from the overall seismic response of the structure is proposed by combining the response spectrum analysis with the static analysis.This method lays a foundation for the study of the influence of high-order modes on the seismic response of long-span steel truss arch bridges in this paper.(3)Based on the method of separating the contribution of specific modes to the seismic response of structures,the seismic response of long-span steel truss arch bridges under different seismic excitations is studied in depth.The results show that under transverse seismic excitation,the influence of higher modes on shear force is more significant than that of axial force and bending moment;under longitudinal seismic excitation,the coupling response of shear multi-modes is obvious;and under vertical seismic excitation,the influence of higher order modes on the axial force is significant.(4)Considering two-dimensional seismic excitation,the elastic seismic response of the bridge under rare earthquakes is analyzed by time-history response analysis method.The stress distribution maps of the upper and lower chords of the main arch ring are obtained,and the weak parts of the bridge are determined.(5)Based on the concept of "fuse" seismic design,buckling restrained braces are introduced as shock absorbers in long-span steel truss arch bridges.The reasonable layout and selection principle of buckling restrained braces are given,and their shock absorption effects are studied by using the method of non-linear time-history response analysis.The results show that the seismic response of the upper and lower chords of arch ribs can be effectively reduced by using buckling restrained braces as energy dissipation elements in long-span steel truss arch bridges.