Geometric Nonlinear Calculation Method For Long Span Arch Bridges Coupled With Bidirectional Deformation

Large-span arch bridges are affected by geometric nonlinearities,and the existence of additional bending moment reduces the bearing capacity of the arch,which leads to the problem of how to accurately calculate the geometric nonlinear internal forces of arch bridges.However,the existing theoretical methods for calculating geometric nonlinear internal forces of arch bridges are not yet perfect,the calculation efficiency of finite element analysis is low,and the complex internal force evolution regulation and structural stress state are difficult to reflect accurately.To address these problems,this thesis proposes an accurate calculation method for geometric nonlinear internal forces of largespan arch bridges,deduce the accurate calculation theory for bidirectional deformation geometric nonlinear internal forces of hingeless arches with suspended chain lines.Model tests of concrete-filled steel tube arch bridge and stiffening skeleton arch is carried out to verify the accuracy and reasonableness of the algorithm theory.Finally,the normative values and finite element values of the geometric nonlinear bending moment of are compared with the theoretical values,and it is discussed to the current calculated reasonableness of the geometric nonlinear internal forces.The research contents and findings of this thesis are as follows:(1)The geometric nonlinear analysis mechanism of the arch bridge considering the bidirectional bearing characteristics is established,and the essential differences between the geometric nonlinear analysis mechanism of the arch and the eccentric compressed column are discussed.The results show that the geometric nonlinear internal force influencing parameters are multifaceted,and it is difficult to reflect the geometric nonlinear force state of the whole arch by using the unified eccentricity increase coefficient,and the calculation formulas of the eccentricity increase coefficient have different forms,the calculation results are different,and the value of η is difficult to be taken.(2)Coupling the horizontal deformation and vertical reaction force as well as the vertical deformation and horizontal thrust action,the theoretical analytical formula of arch internal force-deformation relationship is constructed,the endowment mechanism of internal force and deformation is clarified,and the evolution regulation of internal force and deformation of arch structure is revealed.Matlab is used for theoretical programming to realize efficient and fast automatic and accurate calculation of nonlinear internal forces in arch geometry,which overcomes the shortcomings of low efficiency of finite element calculation,and provides a new path for accurate analysis of internal forces and deformation of large span arch bridges.(3)The model test of large-span arch bridge was carried out to measure the geometric nonlinear internal forces during loading,which accurately reflects the structural stress state of the arch.The maximum difference between the test value and the theoretical value is within 10%,which verifies the accuracy and reasonableness of the accurate calculation method of geometric nonlinear internal force with large span arch bridge.(4)The JTG3362-2018 normative and finite element geometric nonlinear internal force values of steel pipe concrete arches are close to the theoretical values.the JTG/T D65-06-2015 normative is about 5.8% larger than the theoretical value on average,and the GB50010-2010 normative is about 13.25% larger than the theoretical value on average,and the calculation results are conservative.The geometric nonlinear internal force value of the GB50010-2010 specification for the stiff skeleton arch is closer to the theoretical value.the JTG3362-2018 specification is about 7.25% smaller than the theoretical value on average,the JTG/T D65-06-2015 specification is about 10.89%smaller than the theoretical value on average,and the finite element value is about 11.48%smaller than the theoretical value on average,and the consideration of the influence of geometric nonlinearity is The degree is not enough.