Reseaech Of The Most Unfavorable Seismic Incentives Input Direction For Curve Continuous Beam Bridge Based On The Component Synthetic Method

Curved beam bridges have complex stress states under spatial structures,and under seismic excitation,the stress system states of structural components are more complex under bending torsion coupling.Due to the randomness of seismic motion,there are significant differences in the responses received at the support points of the structure.Therefore,how to determine the most unfavorable input direction of curved beam bridges is a specific problem that needs to be solved and analyzed.Currently,seismic design of bridges in China often uses the comparison of seismic waves along multiple possible directions to determine the most unfavorable input direction.Moreover,this method requires a large computational workload and cumbersome data processing,making it difficult to master the determination of the most unfavorable seismic input direction of curved beam bridges.How to effectively determine the most unfavorable seismic input direction of curved beam bridges requires us to conduct good research and analysis.On the basis of the component force method based on response spectrum,this article proposes the component force method of nonlinear response spectrum to determine the most unfavorable input direction for seismic excitation of curved beam bridge structures.In response to the nonlinearity of isolation bearings and the elastic-plastic nonlinearity of bridge piers,the component resultant force method of nonlinear response spectrum is used to determine the most unfavorable seismic direction of a three-span curved continuous steel beam bridge,and a comparative analysis is conducted with the most unfavorable seismic direction determined by nonlinear time history response.The main research work of this paper is as follows:(1)A component resultant force method based on nonlinear response spectrum was proposed.The nonlinear response spectrum is equivalently linearized and reduced using Midas/Civil software.The reduction of the nonlinear response spectrum is based on the displacement ductility coefficient of the structural component,which is the ratio of the ultimate displacement of the component under load to the yield displacement of the component.The formula derivation of the component resultant force method based on nonlinear response spectrum was carried out,and a calculation program using Matlab for the most unfavorable input direction of curved beam bridges based on component resultant force was developed.This program can calculate the peak modal response of seismic excitation on the X and Y axes,and obtain the maximum combined response of components under seismic excitation,in order to determine the most unfavorable input direction of curved beam bridges.(2)The combined force method of components considering the nonlinearity of seismic isolation bearings.Using the integral friction pendulum type seismic isolation ball bearing as the research object,a detailed finite element simulation was conducted on the seismic isolation bearing,with parameter values taken into account.The equivalent linearization method was used to consider the nonlinear characteristics of the structure.The Matlab program developed in this article was used to calculate and analyze the displacement and internal force responses of the mid span section,3 # pier,4 # pier support,4 # pier top,and pier bottom of the component combined force method based on the nonlinear response spectrum of seismic isolation bearings under longitudinal and transverse seismic excitations.Compared with the response values of non-linear time history analysis,except for some values with significant errors,other values are relatively close;Select the least favorable input direction with a smaller deviation and analyze the reasons for the larger deviation.Research has found that when the vertical load values on the upper part of the bridge are the same,the force on the support of the curved beam bridge is greater on the outer side than on the inner side,and the more it shifts towards the outer side of the support,the greater the force on the support,showing a gradual increase.And there is the following rule: when subjected to seismic excitation along the bridge,the most unfavorable input direction angles frequently alternate between,and the above characteristics of curved beam bridges become more significant.When,is the most unfavorable seismic input direction along the bridge for curved continuous beam bridges;When,for curved continuous beam bridges,the most unfavorable seismic input direction is in the transverse direction of the bridge.(3)The component force method considering the elastic-plastic behavior of bridge piers.The elastic-plastic fiber surface model was selected for the nonlinear consideration of bridge piers,and its mechanical parameters were first defined for the stress-strain curves of constrained concrete,steel bars,and unconstrained concrete.The Matlab program developed in this article was used to calculate and analyze the displacement and internal force responses of the component combined force method considering the nonlinear response spectrum of bridge pier elastic-plastic under longitudinal and transverse seismic excitations at the top and bottom of 3# and 4 # piers.Compared with the response values of nonlinear time history analysis,except for some values with significant errors,other values are relatively close.Compared with nonlinear time-history response,it was found that the component resultant force method considering the nonlinearity of seismic isolation bearings and the component resultant force method based on the elastic-plastic response spectrum of bridge piers determine the most unfavorable input direction of seismic motion,with less computational complexity and higher rationality.Research has found that the most unfavorable input direction determined by the component resultant force method based on nonlinear response spectrum is close to that determined by the nonlinear time-history response analysis method.Select the least favorable input direction with a smaller deviation.At that time,the displacement response value of the top of Pier 3 based on the component combined force method was the highest under seismic excitation,which was the most unfavorable input direction for curved continuous beam bridges.The combined force method based on nonlinear response spectrum,proposed mainly for unidirectional seismic excitation,can effectively solve the problems of large calculation volume and cumbersome data for curved continuous beam bridges under nonlinear time-history seismic excitation.At the same time,it solves the problems of elastic and elastic-plastic seismic analysis,breaking through the limitations of traditional response spectrum and time-history seismic analysis methods in terms of calculation scale and efficiency,and has ideal calculation accuracy and efficiency.Compared with nonlinear time-history response,it was found that the component resultant force method considering the nonlinearity of seismic isolation bearings and the component resultant force method based on the elastic-plastic response spectrum of bridge piers determine the most unfavorable input direction of seismic motion,with less computational complexity and higher rationality.