Research On Ultimate Load-Carrying Capacity Of Concrete Filled Steel Tubular Truss Arch Bridges With Initial Stress

While constructing the concrete filled steel tubular (CFST) arch bridge, the initial stresses will be developed in the steel tube of CFST arch ribs, which are caused by the steel tube self-weight, concrete gravity and other construction payloads before formed the CFST composite structure. The presence of the initial stress will decrease ultimate load-carrying capacity of CFST arch bridge, and which will be more decreased by the spans and cross sections of arch bridges increased. However, few researches on ultimate load-carrying capacity of CFST truss shaped arch bridges with initial stress had been conducted. Otherwise, whether the method used to calculate the load-carrying capacity of CFST solid arch bridge can be applied directly to the truss shaped one is still need to further investigate. Therefore, in order to study the mechanic behaviour of CFST truss arch bridge with initial stress, the main work and conclusions in this paper are presented as following:(1)The survey and analysis of initial stress degree (ISD) of CFST arch bridges have been carried out. It shows that the ISD of CFST truss shaped arch bridges are largest than the ISD of single tubular arch bridges and dumbbell shaped ones. Otherwise, the ISD of single tubular arch bridges are minimal for three kind of shaped arch bridges. Furthermore, the formula for calculating the ISD of CFST arch bridges is given based on the survey results.(2)The experiment of truss shaped CFST columns with initial stress subjected to axial compression and the finite element method are conducted. The results demonstrate that the presence of the initial stress reduces the ultimate load-carrying capacity of truss shaped CFST columns; the finite element method can be used to simulate the ultimate load-carrying capacity of the truss shaped CFST columns with initial stress, alternatively.(3)The parametric analysis of the ultimate load-carrying capacity of truss shaped CFST columns with the initial stress are carried out, which shows that the ultimate load-carrying capacity of the truss shaped columns with initial stress will be decreased. The parameters of the ISD, slenderness ratio as well as eccentricity ratio have a coupling effect on the ultimate load-carrying capacity. Furthermore, the formula can be applied to calculate the ultimate load-carrying capacity of truss shape columns with initial stress.(4)The simplified formula of initial stress effect reduced factor of CFST solid rib structure is proposed, which is compared with the experimental results and several reduction factor theoretical calculation formulae. It shows that the simplified formula is more reasonable and can be suitable for calculating ultimate load-carrying load of the truss shaped columns.(5)The finite element models of Caoejiangpaojiang Bridge with and without initial stress are established by MIDAS software. The analytic results release that the initial stresses have a larger influence on the stress of steel tubular arch ribs and have a smaller influence on arch rib deformation and internal forces. The calculation results also mean that the internal forces of Caoejingpaojiang Bridge with initial stress can comply with the specification requires.