Study On The Spatial Seismic Responses Of Long Span Self-anchored Suspension Bridge

Self-anchored suspension bridge,having a beautiful appearance,competitive in cost,is being more used recently.With the increasing of the span the demand of aseismic is becoming more important,so it is very necessary for us to research its dynamic property and seismic response.Some basic theories of certain seismic analysis were reviewed firstly in this paper.Then a new time-history analysis method is introduced based on the combination of Large Mass Method Theory and Clough Pseudo Static Displacement Theory,the equation of motion is derived,and the practical numerical method of this theory is obtained.A spatial finite method analysis model was built for a long span self-anchored suspension bridge with a span of 400 m—The Jin Zhou Bay Strait Bridge in Dalian City Liaoning Province.With the aids of a FEA programs,the first 100 natural frequencies and their according mode shapes were obtained. The response spectrum analysis was performed to assess the seismic response primarily.Then three modified nature wave was generated as calculation records.Taking account of the flex slot between main bridge and bridge approach,the time history analysis was performed and the results were compared to the spectrum analysis.The correctness of the time history analysis is also proved.The influence of travelling wave to the long span self-anchored suspension bridge is studied.The displacement of bridge is increased,but the increment is small.The bending moment of the main tower bottom have a big increment.The bending moment of the middle main girder span is increased as multiple,but which is much smaller than the 1/4 span bending moment;the axial force is influenced little.The influence to the bridge is obvious when taking account of the seismic soil pile superstructure interaction.The displacement of the bridge increased orderly and obviously;the bending moment of the main tower bottom have a big decrease.When taking account of vertical seismic force,the main tower axial force and bending moment both increased,the main girder bending moment have a big increase. Because of the higher stiffness of the long span self-anchored suspension bridge,especially the higher main girder axial force,the influence of travelling wave,the seismic soil pile superstructure interaction and vertical seismic force to the bridge is obvious.