| In recent years,the damage to bridge structure caused by vertical earthquake has attracted much attention.The near-field seismic damage shows it is more reasonable to understand seismic damage to some bridges from vertical seismic.Vertical earthquake will throw up the main beam and make it separate from the bearing.When the main beam falls,it will collapse with the bearing and thus cause damage to the bridge structure.In this paper,in view of the vertical collision problem of unequal span bridge,the analytical solution of multiple collision response of unequal span bridge under vertical earthquake action is derived by using the eigenfunction expansion method,and the basic characteristics of vertical collision of unequal span bridge are studied.The main research work is as follows:(1)Regarding to the problem of multiple collisions response,the dynamic model of "unequal span beam-spring-rod" is established.The analytical solution of multiple impact response of unequal span bridge under vertical seismic excitation is derived by using eigenfunction expansion method.(2)Aiming at the problem of multiple impact response of unequal span bridge under artificial harmonic vertical earthquake,the analytical solution of seismic response of unequal span bridge structure in collision contact process and separation process is derived.The impact force and displacement response under different excitation periods are calculated,and the effect of excitation periods on vertical impact is discussed.(3)The effects of seismic excitation period,beam span ratio,bearing stiffness and pier height on vertical collision are studied.It is found that when the excitation period is close to the natural period of unequal span bridges,multiple collisions occur.Among them,beam span ratio has great influence on collision characteristics.(4)A three-dimensional finite element model of unequal span bridge with is established.Based on the finite element model,the effect of actual vertical earthquake and transverse earthquake on vertical impact characteristics is studied.The results show that the value of contact force and the number of collisions increase in the transverse earthquake.In addition,the arrival time difference between horizontal and vertical earthquakes also affects the number of collisions and the maximum collision force. |
