Research On Design Parameters Optimization Of Beam-Arch Composite Rigid Frame Bridge Under Seismic Response

The beam-arch composite rigid frame bridge has the stress characteristics of the beam bridge and the arch bridge.The structure is light,slender,and light in weight,which can effectively solve the problems of box beam crack development and mid-and longterm deflection,and improve the spanning capacity.As a new type of bridge,less research on its dynamic direction.At the same time,in the seismic design of the beam-arch composite rigid frame bridge,there are certain accidents and blindness in determining the main design parameters,and the optimal design plan is often not obtained.Taking the Lijia Jialingjiang Bridge under construction as an example background,a systematic and effective design parameter optimization method was proposed around the seismic performance of the beam-arch composite rigid frame bridge,and the design parameters were optimized.The main work and conclusions are as follows:(1)The dynamic time history analysis method is used to analyze the seismic response of the beam-arch composite rigid frame bridge with the same span and the ordinary continuous rigid frame.By comparing the seismic response results of the two,it is found that the beam-arch composite rigid frame bridge The bottoms of piers and pier are weak parts compared with ordinary continuous rigid frame bridges,but the development process of plastic hinges,the change trend of internal force and displacement,and the peak value of internal force displacement of key parts of the two are obviously different.According to the seismic response characteristics of the beam-arch composite rigid frame bridge,four optimization parameters were selected: net-span ratio,side-to-middle span ratio,pier wall thickness,and lower chord arch wall thickness.(2)The optimization method of the design parameters of the beam-arch composite rigid frame bridge under seismic response is proposed: firstly,the design parameters are reasonably selected,the design parameters are orthogonally combined to establish the finite element model,and the orthogonal test model is subjected to Pushover analysis.Then describe the deformation capacity and damage index of the structure by the curvature demand capacity ratio and the stiffness degradation seismic damage model,determine the objective function,and obtain the multi-objective function value of the test model according to the minimum distance ideal point method in the evaluation function method,and obtain a positive The best result of the test combination.Finally,taking the orthogonal test results as samples,combining BP neural network and genetic algorithm to further optimize the design parameters.(3)The optimal design parameter combination under the orthogonal test is a netspan ratio of 1/7.2,a side-span ratio of 0.57,a pier wall thickness of 1.1m,and a lower chord arch wall thickness of 0.4m.From the range analysis,it can be seen that the influence degree of each design parameter on the test results from large to small is the pier wall thickness,the net-span ratio,the thickness of the lower chord arch wall,and the side-span ratio.By combining the orthogonal table,BP neural network and genetic algorithm to further optimize the design parameters,the optimization results obtained are a net-span ratio of 1/7.5,an edge-to-span ratio of 0.54,a pier wall thickness of 0.91 m,and a lower chord arch wall thickness of 0.47 m.Compared with the minimum multiobjective function value of 0.0164 obtained by orthogonal experiments,the final optimized multi-objective function value is 0.0094,and the multi-objective function value is reduced by 42.7%.