Nonlinear analysis of steel tube initial stress effect in stell tube on bearing capacity for CFST arch bridges

Based on equilibrium equation of nonlinear problem and nonlinear geometric equation of spatial beam element,explicit formula of tangent stiffness matrix for spatial beam element was deduced,its constitutive relationship includes the initial stress and initial strain.According to structure character of dumbbell section,a combined spatial beam element is presented for computing and storing steel tube initial stress.Method of element division was described about bearing capacity analysis for concrete filled steel tubular(CFST) arch bridge.A special program was developed.The results calculated by program were in accordance with tests.A lot of bearing capacity calculation are performed,with regard to different coefficients of initial stress steel tube,different sectional steel ratios and different spans.Results show that initial stress of steel tube could reduce the capacity of CFST arch bridge,the reduction extent depends on the sectional type of arch rib,and the maximum reduction can exceed 30%.Finally,practical formulas of bearing capacity influence factor are given for the CFST arch bridge with three common sectional types.