Gravity Stiffness Method Of Suspension Bridge Pre-Including Horizontal Component Of Cable Tension Due To Live Loads

As the span of suspension bridges are constantly growing larger and larger, especially those large-span suspension bridges which use flat steel box beams as their stiffening girders, the stiffness of stiffening girder generally only accounts for one several tenth, or even one several hundredth, of that of the entire bridge. Hence, if the stiffness of stiffening girder is neglected and the suspension bridge is directly considered as a simple cable structure in our analysis, it will simplify the analysis. This kind of method, which applies approximate analysis method to suspension bridge, is the gravity stiffness method. The elastic elongation of cables by the live load are considered indirectly with past calculation methods which recalculate the calculated result by revising the parameters, while with the calculation method in the article, the elastic elongation of cables by the dead and live load are taken into consideration directly when the horizontal axial force is calculated. It is no need to revise the calculated result.The key work of the article is shown in detail in the following aspects:The article intends to specify the concept of gravity stiffness through shear force and bending moment of simple-supported beam that has the same span as the cable. It theoretically defines the gravity stiffness, and explains the calculation principles of gravity stiffness method. Also, it uncovers the relationship between the shear force and the horizontal axial force of cable, and the relationship between the bending moment and the cable deformation.We take the elastic elongation of cables by the dead and live load into consideration directly, establish the equation in accordance with that the non-stress length of cable is a constant, and work out the horizontal axial force when the structure regains its equilibrium after the action of external loads. Select real calculation cases and use gravity stiffness method to calculate the internal force and deformation of the suspension bridge structure, compare and analyze the calculated results with the results calculated by ANSYS which is a finite element software based on the Theory of Finite Displacement, give the calculation error, and evaluate the applicability of calculation methods according to the calculation error.The article intends to take the completion status as the initial state, and work out the increment of cable deformation caused by the action of live load, and neglecting the elongation and tilt of hangers, the deformation increment of cable is the deformation of stiffening girder; then, calculate the bending moment of stiffening girder. When using gravity stiffness method to calculate the bending moment of stiffening girder, we need to apply iterative calculation until it converges, so as to get a more reasonable result for the forecast.It adopts the LINK10 element of common software ANSYS, to stimulate the cable and boom, use BEANO element to stimulate the stiffening girder, and establish the calculation models for suspension bridges of the above calculation cases, so as to analyze and calculate the internal force and deformation of its structure.The article adopts respectively the gravity stiffness method and FEM to calculate the internal force and deformation of suspension bridge structure. Through the calculation course being retrospected and summarized, the calculation results being analyzed and studied , the conclusion as follows can be made:(1) The internal force and deformation results of large-span suspension bridges calculated by the gravity stiffness method are reasonable. Especially, it is in the initial design stage that the method is practical.(2) Under the action of external loads, suspension bridge structure system will regain a new equilibrium state in some new place.(3) When the suspension bridge structure is in the new equilibrium state, the reasonable outcomes can be achieved on condition that dead load, live load and horizontal force of cables in the new state, as well as other factors that have effect on internal force and deformation, must be taken into consideration comprehensively.