Progressive Collapse Analysis Of Reinforced Concrete Curved Girder Bridge Based On Alternate Path Method

With the rapid development of urban traffic,the curved girder bridge has become one of the indispensable overpass types in the urban road network.As an important transportation hub,curved girder bridges are threatened by accidental loads such as impacts and explosions.Once progressive collapse is caused by local damage,they will cause huge loss of life and property.In view of the uncertainty of accidental loads and the danger of progressive collapse,how to reasonably consider the influence of accidental loads and carry out the study of progressive collapse of curved girder bridges has important practical significance.In this paper,the alternate path method is used to analyze the progressive collapse of the curved girder bridge.The mechanical behavior and collapse mode of the residual structure after the initial failure of the pier are studied,which provide a basis for the design of the curved girder against progressive collapse.The main research contents and conclusions of this paper are as follows:(1)According to the code for progressive collapse resistance of building structures and the structural characteristics of curved girder bridges,the allowable collapse range suitable for curved girder bridges is proposed.Combined with component failure criteria,progressive collapse evaluation of curved girder bridges can be carried out.(2)The finite element model of reinforced concrete curved girder bridge is established.Based on alternate path method,linear static analysis and linear dynamic analysis are made to study the progressive collapse of curved girder bridge.With the method of gradually increasing the load and by comparing the results of linear dynamic and linear static analysis,the value of dynamic amplification factor is suggested for curved girder bridge,which is taken as 2.0 for safety.(3)Based on alternate path method,nonlinear dynamic analysis is made to evaluate the progressive collapse mode of curved girder bridges,and the influence of dynamic effect of pier failure on internal forces of structures is studied.The results show that the dynamic effect of pier failure greatly amplifies the internal forces of the remaining structure.According to different working conditions,the bending moment of box girder increases by 4.0 ~ 6.5 times,and the position of maximum increase is within the failure span.The maximum axial force of piers increases by 2.0 ~ 3.0 times.The maximum increase was both for the adjacent piers and for the side piers.(4)The collapse modes of the remaining structure were analyzed according to plastic hinge development,superstructure displacement,pier displacement and damage state.The results show that the collapse mode under the middle pier failure is mainly vertical collapse and overturning collapse of the bridge deck,and the failure mode of girder is plastic hinge failure at end.The collapse mode under side pier failure is mainly characterized by the breakage of the cantilever girder at the end of side span and the failure of the falling beam,which then impacts the adjacent pier,causing serious damage or even collapse,and then causing domino progressive collapse.(5)The results of linear analysis and nonlinear dynamic analysis are compared.The results show that the linear analysis has the characteristics of simple analysis,short calculation time and reliability,but the development of structural plastic hinge and failure modes cannot be investigated.However,the results of nonlinear dynamic analysis are accurate,and can reflect the structural failure mode,but the analysis is complicated and cost long time.Therefore,linear analysis is suitable for preliminary judgment of structural safety,and nonlinear dynamic analysis is required by deeply analysis under dangerous working conditions.