| Because the contradiction between hoisting weight and span of concrete filled steel tube (CFST) arch bridges was comparatively resolved, CFST arch bridges have become one of most rapid development bridge structures in last ten years. To 2005, a CFST arch bridge with a span of 460 meters, Wushan Yangtze River Bridge, has been built in Chongqing, China. Furthermore, the span and amount of this type of bridge are still increasing. Compared with the engineering practice, the design theories are relatively backward, such as a question of bearing capacity influence of steel tube initial stress to the CFST arch bridge is just one of them. CFST arch bridge is a steel-concrete composite structure, the sections of which are formed by the core concrete cast step–by–step. Before the formation of CFST arch bridge, steel tube will withstand itself weight and wet concrete weight, this lead to the steel tube initial stress produce inevitably. The initial stress forces the steel tube to prior reach the yield point of material, which will affect the capacity of CFST arch bridge. However,research on initial stress has not been carried out deeply and systematically so far.Based on"The influence research of steel tube initial stress to an arch bridge structural behavior and bearing capacity", which is the item of Western transportation science and technology project"Key technologies research on design, construction and maintenance of CFST arch bridge"(contract No. 2003318814202) , the following researches have been completed in the dissertation:1.The computation of ultimate bearing capacity of CFST arch bridge will be completed by spatial beam element. In order to reflect effect of the steel tube initial stress to the arch bridge capacity, based on spatial beam element nonlinear geometry equation and virtual work principle, explicit tangent stiffness matrix of spatial beam element contained the initial stress and the initial strain in general elastic configuration relationship has been deduced. Furthermore, in order to consider the effect of confined effect produced by steel tube and core concrete after once steel tube yield ahead of time enter the elastic-plasticity status, a new method of synthesis application of solid– spatial beam element and general spatial beam element to compute bearing capacity was put forward, and solid-spatial beam element stiffness matrix included the initial stress and corresponding transformation matrix were also inferred.2. The formulas of initial stress for single-tube, dumbbell and 4-tube latticed CFST arch bridge were in detail deduced,and the flow chart of initial stress calculation was also given in the dissertation.3. According to linear creep theory, creep stress formulas of both axis and small eccentric CFST compression members were derived. Creep degree introduction of the most common forms of degradation nucleus Dirichlet series was adopted. The recurrence formulas and the finite element equations which could be calculated the creep deformation of core concrete of CFST arch bridge was developed. An application of conjugate gradient method to fit concrete creep coefficient is in good agreement with experimental results.4. There are 8 CFST members bearing capacity tests with different initial stress factor and eccentric distances having been launched.5. A generalized analysis program which could be considered steel tube initial stress influence of CFST arch bridge is developed. The correct and accuracy of the program were verified by the experimental results of the axis, eccentric compression initial stress CFST member and a model of CFST arch bridge. On the basis of these, the ultimate capacity analysis of single-tube, dumbbell and four limbs latticed CFST arch bridges including different initial stress factorβ, span as well as sectional steel ratioαhave been performed. In addition, the effect of rise-span ratio to capacity influence factor K pof CFST arch bridge has also discussed.6. The formulas of bearing capacity influence factor have been separately given for single-tube, dumbbell and four limbs latticed CFST arch bridge by use of the recurrence analytic method, and extents of initial stress factor has also respectively given.7. The analytical results show that steel tube initial stress can reduce bearing capacity of CFST arch bridge. However, the reduced extents have connection with not only steel tube initial stress factorβ, sectional steel ratioαand span etc., but also section type of arch rib. The maximum reduction reaches more than 10%. If the reduction extent of bearing capacity does not exceed 10%, thus initial stress factor of single-tube, dumbbells and four limbs latticed CFST arch bridge should be separately limited to 0.3, 0.6 and 0.6. Therefore, when extent of steel tube initial stress was set, it must depend on the corresponding section type of CFST arch bridge. At present, the initial stress control factor 0.6 is quite appropriate when the dumbbell and four limbs latticed CFST arch bridge were designed in domestic. However, same initial stress control factor 0.6 of single-tube CFST arch bridge is bigger, this will lead to its bearing capacity reduce 20%. 8. Most of CFST arch bridges are large-span structures. Geometry nonlinear has an obvious effect on the bearing capacity. Therefore, when bearing capacity analysis of steel tube initial stress to CFST arch bridge was performed, both material nonlinear and geometry nonlinear should be simultaneously included.
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