Seismic Pounding Analysis Of Girder Bridge Based On Endurance Time Method

Pounding is a typical earthquake-induced damage in bridge structures due to the difference of dynamic characteristics between adjacent segments,non-uniform seismic inputs and insufficient length of expansion joints.A complex physical and mechanical behavior that includes local plastic deformation,crack,spalling,friction of contact surface,transfer of energy and the propagation of stress waves occurs with an extremely short contact-separation process of earthquake-induced pounding in bridge structures.Because of the complexity and uncertainty,contact phenomenon is kept away from the bridge seismic design codes in China,and only the protective measures are raised to mitigate negative effects of pounding rather than considering it in designing stage.Hence,it is vitally significant to put forward a seismic design method which takes the pounding into consideration for bridge structures.Considering the feature that various structural responses under corresponding seismic intensity levels are obtained in a few dynamic time-history analyses of the endurance time method(ETM),this study applies this method into the pounding research of bridge structures subjected to seismic excitations.The application of the ET method is investigated and discussed by treating straight elevated bridges as the main research object,and the seismic design method of bridges considering pounding is proposed on the basis of the research results.The main research issues and findings are shown as follows:(1)According to the typical characteristic of ET method that the magnitude of response spectrum is proportional to the duration time at a set interval,an unconstrained nonlinear least squares optimization method is adopted to generate appropriate endurance time acceleration functions(ETAFs)corresponding to the seismic codified design response spectrum of bridge structures in China.(2)A finite element model of three-span simply-supported beam bridge is established by using the OpenSees software.The characteristics of dynamic response without pounding under the inputs of ETAFs are analyzed.It is found that amplitudes of various response continuously increase with endurance time.By comparing the results between the ET method and the incremental dynamic analysis(IDA),indicates that the ET method is capable of efficiently showing the dynamic response of bridge structures.(3)To consider the effect of pounding between adjacent segments owing to seismic inputs,a finite element model of bridge structure is established by introducing the pounding element,and the seisimc pounding analyses are conducted by the ET method.It is found that the linear relationship is shown between dynamic response considering pounding effects and endurance time.In-depth study and exploration in comparison between the ET method and IDA indicates that ET method is able to effectively express the seismic damage status of this bridge,with the inclusion of pounding effects.Based on analyses of seismic-induced pounding effects on this bridge using the ET method,a design method of seismic bridge considering negative pounding effects is put forward,combining with present code for seismic design.