Effect Of Initial Stress And Creep On Bearing Capacity Of Four-tube Concrete Filled Steel Tube Arch Bridge

The Concrete Filled Steel Tube (CFST) is a type of composite material composed of steel tube and core concrete. The CFST has been widely adopted in the arch bridge building due to its advantages of large bearing capacity, rapid construction and well anti-seismic performance.Most of long-span CFST arch bridges are used of the four-tube section. In construction of long-span arch bridge, the main methods are non-bracket construction technology or the swing technology. Under these methods, before the formation of CFST arch bridge, steel tube will withstand the weights of itself and the wet concrete; this will cause the initial stress of the steel tube inevitably. The initial stress forces the steel tube to prior reach the yield point of material, which will affect the bearing capacity of CFST arch bridge, so that it should be considered in the calculation of the CFST arch bridge's bearing capacity.The creep of the CFST arch bridge will also affect its dynamic performance, just like the common concrete. For the CFST, in the procedure of creep, the stress of the steel tube is increasing and the stress of concrete is degrading. However, as one of the most important problem in the researches of the CFST, the related studies and documents are still not enough.Aimed at the above problems, main work in this paper is listed as follow:(1) Discussed the methods of calculate the arch bridge's bearing capacity and chosen a proper constitutive relationships, based on the theories of material nonlinear and geometric nonlinear to analyses the CFST arch bridge's bearing capacity;(2) Based on the matrix displacement method, according to section's mechanical characteristic of arch-bridge when ultimate capacity reached, for comprehensively considering initial stress of steel tube and confined effect between steel tube and core concrete, the method which included both spatial solid-beam element and general spatial beam element with the initial stress to analyze the effect on initial stress to the bearing capacity of four-tube CSFT arch bridge was introduced;(3) Chosen the fitting creep computation schema after compared with the common computation methods. Based on this, experimental and program verification were made to the formulated program, the result shows that the program was well-meshed with the data of the experiment as well as the third program;(4) Chosen a through CFST arch-bridge as the calculation examples, built the finite element model. The calculation was concentrated at the influences of different factors on the structure such as the nonlinear, the initial stress, the concretes'pumping sequence and the creep. The analytical results show that in calculation of the CFST arch-bridge's bearing capacity, the double-nonlinear should be considered, the initial stress will affect the bearing capacity of CFST arch-bridge; the affect of the pumping sequences of concrete and the creep to the bearing capacity of CFST are inconspicuous;(5) The effects of different design parameters, like the grade of initial stress, span, steel ratio on the ultimate bearing capacity are studied. Based on the result of analysis, a limitation to initial stress of steel tube and a formula of the influence factor of bearing capacity of four-tube CFST arch-bridge was put forward.