Study On Collapse Failure And Control Of Concrete Continuous Girder Bridge Under Strong Earthquake

In this paper,the two-span reinforced concrete continuous girder bridge was taken as the research subject.The nonlinear dynamic catastrophe mechanism and collapse control method of multi-span continuous girder bridge under multi-dimensional ground motion were explored,based on shaking table test and numerical simulation.The main work of this thesis included:(1)A continuous beam bridge model under multi-dimensional ground motion inputs was tested on shaking table.(2)The spatial nonlinear finite element model of multi-span continuous girder bridge was established based on implicit integration and explicit integration technique,and the nonlinear dynamic time history response analysis of different ground motion inputs was carried out.(3)The mechanical properties of high damping rubber bearing were experimental investigated.(4)The collapse failure analysis of multi-span continuous girder bridge under multi-dimensional earthquake motions was carried out,and the whole process of damage evolution,local and whole collapse were explored.(5)The control effects of three kinds of collapse control methods,which were the high damping rubber bearing,the fluid viscous damper and the lock up speed locking device,were compared and analyzed.The following observations and conclusions were made:(1)Simply supported pier vibration under the longitudinal short period shaking wave was stronger than that of the fixed pier,while the fixed pier vibration under the longitudinal long-period ground motion was greater than that of the simply supported pier for continuous girder bridge with laminated rubber bearings.The lateral relative displacement between the girder and the pier was larger than that under longitudinal shaking wave.The relative displacement of the upper and lower structures due to the long-period ground motion was larger than that under the short period ground motion.The peak value of relative displacement did not appear when the pier and the girder shock violently and their amplitudes were maximum.(2)The acceleration response of the girder increased slightly with the isolation of the high damping rubber bearing,while the acceleration response of the substructure was weakened.The damping effect was particularly notable of the simple supported pier.At the same time,the relative displacement between the upper and lower structures and the risk of the falling girder were reduced.The bilinear hysteretic model of high damping rubber bearing is proposed,which can be applied to the seismic response analysis of such bearing isolated bridge.(3)Based on the principle of energy balance,a bridge structural collapse criterion was proposed.Potential moment of structural damage or failure could be deduced by ratio of total energy to external work of force ? at t moment.It was suggested that when the energy ratio was less than 85%,the collapse stage could be determined.(4)There were two kinds of collapse failure modes of the continuous girder bridge under great earthquakes:the first is the failure of the middle pier and then the main girder falling;the mode two is the overall falling girder caused by the relative displacement between the pier and the girder.It is proved that index D could evaluate the damage state of two-span continuous girder bridge model reasonably.(5)Three kinds of methods,which were the high damping rubber bearing,the fluid viscous damper and lock up speed locking device,could improve collapse resistant capacity of continuous girder bridge under great earthquake.The liquid viscous damper and the speed locking device could more effectively control the displacement of the main girder than the high damping rubber bearing.(6)The proposed design strategy of anti-collapse involved three stages:conceptual design,anti-integral collapse design,anti-progressive collapse design.Anti-integral collapse design was divided into two kinds:ductility design and recoverable design.In the stage of concept design of continuous girder bridge,the high damping rubber bearing could control collapse under short period earthquake motion,while the liquid viscous damper or speed locking device could control collapse under long period earthquake motion.