Structural Static Performance Research Of Diagonal-span Arch Bridge

Diagonal-span arch bridge is a new type of bridge developed in recent years. This bridge type using a spatial arrangement with a single arch oblique across the main beam, the two arch springers are respectively located at the upstream and downstream of the bridge, and spatial hangers are used to connect the arch with the mian beam. The emergence of this bridge type provides a new alternative for long-span curved bridge. As the special spatial arrangement, the inner forces of this bridge type are also more complicated than others. Based on the problems and difficulties encountered in the design of Tongtai Bridge in Zhang jia-kou, the following aspects are studyed in this paper:1. The solving method of the reasonable arch axisThe determination of reasonable arch axis is very important in the design of arch bridge. The arch axis is reasonable or not, is directly related to the aspects of security and economy. The appearance of special-shape arch bridge, such as skewed arch bridge and diagonal-span arch bridge, make solving the reasonable arch axis become more complex. Based on the assumption of the reasonable arch axis is a inverted segmented catenary under concentrated loads, this paper derives the second order differential equations of the reasonable arch axis, and solves the equations with numerical method to obtain the reasonable arch axis under the corresponding load cases; Arch rib can be simplified as a truss system based on the definition of reasonable arch axis when the arch rib is only exposed to axial force under the corresponding load case, according to this assumption, this paper proposed an approximate numerical method to solve the reasonable arch axis of the truss system. Combined with the actual engineering, verify the practicality of the numerical solution method of the second order differential equations and the simplified truss. For the diagonal span arch bridge, in the arch rib near the arch springer without hangers, the curvature of the arch axis is small, the arc axis relatively flat; in the middle of the arch rib, the hangers are centralized arrangement, the curvature of the arch axis is greater, parabola of higher degree can be used to fit the arch rib axis.2. The analysis of stability of diagonal-span arch bridge and its influence factorsAs a new type of bridge structure, curved diagonal-span arch bridge is developed in recent years, as for its typical characteristics of spatail arrangement the structural performance is very complex. This paper uses eigensolvers method and double nonlinear finite element method based on the theory of elastic-plastic to solve the stability of Tongtai Bridge respectively. Compared with conventional arch bridge, under the ultimate load the failure modes of diagonal-span arch bridge performed to be the combination of the in-plan and out-of-plan buckling modal. In the method using eigenvalue analysis, the Tongtai Bridge has large stability factors under different load cases. For Tongtai Bridge, the rib-plane bending stiffness and the rise-to-span ratio changes can greatly affect the overall stability of the structure. Compared with the conventional arch with the hangers are uniform layout, since the hangers of diagonal span arch are relatively arranged concentratly, the rise-to-span ratio of the diagonal-span arch bridge is greater than conventional arch bridge, generally about0.35is more reasonable. By studying stability of the two diagonal-span arch bridge we found that the two diagonal arch stability factors of the first class and second class stability coefficient ratios were4.8and6.16, the ratio is higher than the conventional arch bridge. Therefore, when the first category is adaped to analysis the overall stability on the diagonal-span arch bridge, compared with the conventional arch bridge, the diagonal-span arch bridge require higher first class stability factor.3. Analysis of reasonable finished state of diagonal-span arch bridgeBased on the energy principle with the consideration of spatial effects, this paper researched the application of unconstrained optimization method and constrained optimization method in solving a reasonable finished state of diagonal-span arch bridge; It discussed the applicability of the two optimization methods in solving hanger forces of reasonable finished state of diagonal-span arch bridge; Cable tension forces of reasonable finished state of diagonal-span arch bridge can not be solved by unconstrained optimization methods which only demand the minimum structural strain energy as the objective function, but relative uniform cable tension forces can be obtained by analysis of unconstrained optimization which objective function reconstructed through adding appropriate weighting factor. The constrained optimization method based on energy method can be effectively used to determine the reasonable finished state of diagonal-span arch bridge. By limiting the force of the key sections, the live load effects can be considered. Comparative study results show that for diagonal-span arch bridge in addition to the main beam bending strain energy, the main beam torsional strain energy can also be a main factor of reasonable finished state of diagonal-span arch bridge. Under the reasonable finished state, there is a big torque in the main beam and the arcrib, for the diagonal-span arch bridge the box-section should be used in main beam and the arcrib.4. Model experimental research of diagonal-span arch bridgeIn order to study the overall structure characteristics of the diagonal span arch bridge characteristics and verify the correctness of the design and calculation methods, based on the similarity theory, a full-bridge1:25reduced scale test model of Zhangjiakou Tongtai Bridge is built. Through the comparison of finite element analysis and experimental results verified that the design theory and calculation method used in this new type bridge structure is adpable. and the understanding of the structure characteristics of the diagonal span arch bridge has deepened. The conclutions provide the basis for the actual engineering design and provide a reference for the same type of bridge.