Analysis And Research On Main Beam Design Parameters Of Composite Continuous Beamarch Rigid Frame Bridge

In the construction project of urban highway bridges,the beam-arch combination continuous rigid frame bridge has been emerged.The main idea is to empty part of box girder webs,so that the upper main beam tends to be stressed by the beam structure and the lower main beam tends to be stressed by the arch structure.This bridge is expected to overcome the deflection and cracking problems of conventional continuous rigid frame bridges and enhance the spanning ability.Therefore,based on the background engineering of Chongqing Lijia Bridge,this paper mainly studies the design parameters from the following aspects for the structural design and stress characteristics of the beam-arch composite rigid frame bridge:(1)Relying on background engineering,the finite element model was established by Midas Civil and the internal force distribution characteristics of the upper and lower beams and the triangle fusion zone were obtained through static analysis.Combined analysis of structural characteristics of similar bridges,points out its similarities and differences with similar bridges and the coupling between the parameters is analyzed.Screen out the parameters that reflect the characteristics of the bridge design,such as the side-to-span ratio,the net-span ratio,the the bottom curve power of the lower beam,the high-span ratio of the lower beam,and the height of the mid-span.The results show that the maximum negative bending moment of the continuous rigid frame bridge with beam and arch appears in the fusion area of the upper and lower beams,and the value is also smaller than that of the continuous rigid frame bridge with the same span.(2)Establish a calculation model of a three-span beam-arch composite continuous rigid frame bridge,using the above parameters as research variables,the change trend of internal force,stress,natural frequency of each key sections under constant load is obtained,and a reasonable parameter value range is proposed.Define the bending moment ratio and discuss the change of the internal force distribution of the structure under the influence of live load.The results show that different design parameters have different effects and trends on the mechanical performance of the structure;the dead load plays a decisive role in the internal force distribution of the structure;it is recommended that the edge-to-span ratio should be 0.55 ～ 0.59,the net vector span ratio should be 0.09～ 0.12,and the lower beam height span ratio should be 1 / 64 ～ 1/42,the bottom curve power is 2.0 ～ 2.5 times,the mid-span beam height is 1 / 60 L ～ 1 / 42 L.(3)Aiming at the traditional method of multi-objective optimization,a weighted power coefficient method considering the weight of each internal force index is proposed.Orthogonal test analysis was used to obtain 16 sets of design parameter test combinations through the orthogonal table for the above four important parameters,and the design parameters were optimized with the maximum weighted power factor as the optimization goal.The results show that: when the mid-span ratio is 0.58,the net-span ratio is 0.12,the height-span ratio of the lower beam is 1/57,and the the bottom curve power of the lower beam is 2.0 times,the total power factor after the weighting of this design parameter combination is the largest;compared with the original design,the maximum negative bending moment of the lower beam is reduced by 29.58% and the mid-span deflection is reduced by 6.29%.