| With the continuous improvement of China's transportation system,the number of highway bridges in mountainous areas has gradually increased.The prestressed concrete continuous rigid frame bridge has become the dominant bridge type when the main span is around 100-250 m.However,in the long-term enginerring practice,it has been found that there are some deflaws and problems such as heavy dead load,large midspan deflection,root web cracking,mid span floor cracking and so on.Therefore,more attention has been paid to beam-arch composite rigid frame bridge formed by hollowing out the concrete web of rigid frame bridge girder near pier.Based on the investigation of the design parameters of the existing beam-arch composite continuous rigid frame bridge and the review of the relevant research of this type of bridge,this paper presents the evolution process of the beam-arch composite system,explores the reasonable structure of the beam-arch composite rigid frame system bridge,puts forward a novel type beam-arch joint structure,and carries out experiments to compare the influence of the web hollowing ratio and the cantilever-type transition structure on the mechanical performance of the beam-arch corner joints.To explore the mechanical performance of the joint,the bearing capacity calculation method of the corner joint of the arch-beam joint is proposed.The main research work of this paper is as follows:1.Based on the topological evolution principle,the evolution process of beam-arch composite continuous rigid frame bridge system is revealed.The strut-and-tie model is ultilized to analyze the system,and the structural rationality of the beam-arch composite rigid frame system is analyzed.By comparing the mechanical properties of different structural systems,the advantages of the beam-arch composite rigid frame system in the long-span bridge structure are clarified.A theoretical analysis mechanical model with reasonable consideration of the axial stiffness of the main beam and the lower curve of the lower chord are established,and the mechanical expressions of key parameters such as negative bending moment and mid-span displacement of pier top are given.Based on specific conditions,the influence of rise span ratio,horizontal length of hollowing section rigid frame,side to middle span ratio,mid span girder stiffness and axial stiffness of lower chord on the displacement and internal force of key points are explored.2.Based on the finite element theory and C# language,a finite element analysis system for the structure of beam-arch composite rigid frame bridge is developed,and a finite element model which can consider the longitudinal layout of the whole bridge,arch curve structure,variable section detail size,lower foundation stiffness,steel tendon tension release and other factors is established.With the model,the influence the reasonable structure of the completed bridge and the reasonable layout of cables under the short-term construction state are investigated.Through univariate analysis and multivariate orthogonal analysis,the reasonable values of rise span ratio,hollowing web ratio,side to middle span ratio and section height of beam are obtained,and the reasonable structure of beam-arch composite rigid frame system bridge is discussed.The optimization analysis of temporary cable layout in construction process is carried out,and a "uniform progressive" optimization method is proposed for the optimization of temporary cables of main girder in open web section of beam-arch composite rigid frame bridge Practical cable force optimization method.3.A novel type arch-beam joint is proposed,and three model tests are carried out to investigate the crack development and distribution,load displacement curve,load strain relationship,ultimate bearing capacity and failure mode of the joint under normal service operation and ultimate failure condition.The effectson bearing capacity,deformation capacity and failure modeof the novel structure,cantilever-type transition structure and that with variable hollowingweb ratio are compared.The results show that the structure is linear elastic when the structure is under normal service operation.When the structure failed,the failure node of the specimen is mainly the bending shear failure of the upper chord beam after the upper and lower chords are widely seperately;the bearing capacity of the novel type beam-arch joint structure is higher,and the cantilever-type transition structure is beneficial to alleviate the local stress concentration phenomenon,and increasing the hollowing web ratio can significantly improve the ductility of the structure.4.The refined finite element model of arch-beam joint is established,and the the whole loading process is simulated.The test results are verified and the shear mechanism is analyzed.The force boundary conditions of local finite element model are constructed by using the method of influence matrix analysis on according to the principle of von Mises stress similarity tracking,and at the same time,the finite element of ultimate bearing capacity of arch-beam joint based on plastic damage model is developed.The results show that for 18 possible adverse load cases,the maximum positive moment combination of the top chord beam is the most criticalto the load case;the failure of the arch-beam joint starts at the tensile failure of the bottom slab concrete of the top chord beam,and then the failure surface gradually expands as the maximum positive moment combination of the top chord beam increasing;finally failed due to the concrete crush of top deck of the top chord beam.The failure mode of structure is classic bending failure.Under the most unfavorable load condition,the ultimate bearing factor of the arch-beam joint is greater than 2.0,which has a high safety reserve.5.18 groups of 54 nonlinear finite element models are established,and the influence of concrete strength,steel strength and web hollowing ratio on the mechanical properties of arch-beam joint is investigated and discussed by parametric analysis.Based on the shear bending mechanism of arch-beam joints,the calculation methods of Chinese,European and American codes are compared and analyzed.The limitations of the codes for the calculation of the structural bearing capacity of the arch-beam joint are addressed.The bending failure and bending shear failure of the upper chord are the main failure modes,and the calculation method of the bearing capacity of the arch-beam joint considering the reinforcement ratio,the ratio of reinforcement and the angle between the beam and the arch are proposed,with structural requirements of the bottom chord and mid span beam section suggested. |
PDF Full Text Request