A Study On The Mechanical Behavior Of Stiffened Steel Pipe-Section Bridge Piers

Steel structures are widely used in civil structures with good seismic requirements, due to its high intensity, light weighted, good aseismic performance and many other advantages. Steel piers are always applied to city viaducts, expressway bridges, footbridges and other fields. The traditional reinforced concrete piers suffer quite lots of damages during the earthquake, because of its heavy self-weight and poor ductility. Compared with reinforced concrete piers, steel piers have better strength and aseismic behavior. In the earthquake, the failure of steel pier is mainly due to the presence of the local buckling of the steel plates near the bottom of the pier. In order to improve the ductility behavior and hysteretic performance of steel piers, this thesis aims to set some longitudinal stiffeners near the bottom of the piers.On the basis of summarizing numerical simulation and experimental research results of stiffened steel pipe-section bridge piers, this thesis studies the ultimate strength, ductility behavior, energy-absorption ability of stiffened steel pipe-section bridge piers subjected to a constant vertical load and cyclic horizontal loading, through establishing nonlinear finite element analytical models. In addition, the effect of radius-thickness ratio, number of longitudinal stiffeners, longitudinal stiffener's slenderness ratio on the ductility behavior of the steel piers are investigated, and the empirical formulas for predicting the ductility behavior of this kind of steel piers are proposed, which can achieve the purpose to make research results of the nonlinear analysis be conveniently applied for engineering practice. The main contents of this thesis include the following four parts. Numerical analysis to simulate the test result of stiffened steel pipe-section bridge piers are carried out by employing accurate finite element analytical model. By comparing the analytical results of ultimate strength, ductility behavior, failure mode, and energy-absorption with the test results, it is observed that the proposed finite element analytical model is accurate and reasonable.The new types of pipe section to set 4 stiffeners, 6 stiffeners, and 8 stiffeners respectively, near the bottom of bridge pier, are presented. The finite element analysis method is employed to predict the ultimate strength, ductility behavior, failure mode, and energy-absorption capacity of 39 steel pipe section bridge piers.Compared with the research results of un-stiffened steel pipe section bridge piers, the ultimate strength, ductility behavior, and failure mode of stiffened steel piers are investigated into details. Furthermore, the effect of radius-thickness ratio, number of longitudinal stiffeners, and the longitudinal stiffener's slenderness ratio on the ductility behavior and energy-absorption capacity of the steel piers is studied. The analytical results show that with the decrease in radius-thickness ratio and longitudinal stiffener's slenderness ratio, the ductility behavior and energy-absorption capacity of steel pier have been greatly improved.Based on the consideration of the effects of various geometric parameters of steel piers, empirical formulas to predict the ultimate strength and ductility behavior of the stiffened steel pipe section piers are proposed.In this thesis, the nonlinear finite element analysis method is employed to systematically analyze the mechanical behavior of stiffened steel pipe-section bridge piers, but many issues which are discussed at the end of this thesis, are still required to be further investigated.