Time-dependent reliability analysis of CFST arches for in-plane stability considering concrete creep

CFST arches have been widely used in bridge engineering worldwide due to the light weight, the high compressive strength, the convenience of construction, and the aesthetic appearance. However, studies on the reliability of this type of bridges have been limited, especially on the time-dependent reliability. The time-dependent changes of the equilibrium configuration of CFST arches could lead to a buckling mode under a sustained load, which is lower than the stability bearing capacity under a short-term load. Therefore, time-dependent reliability levels for the in-plane creep stability bearing capacity of CFST arch ribs, the main members of CFST arch bridges, are investigated in this paper. The time-dependent limit state function for the in-plane creep stability of CFST arches considering the concrete creep is firstly established, in which a random process of the resistance is expressed as a simple time-dependent function. The time discretized-integrated approach and the first order reliability method are then combined to solve the reliability indices during different time intervals. It has been shown by the numerical results that with the deterioration of the in-plane stability bearing capacity induced by the concrete creep, the reliability of CFST arches decreases significantly. For different basic random variables, the outer diameter of the steel tubular has the most important influences on the reliability index, and it is followed by the elastic modulus of steel, the elastic modulus of concrete, the thickness of steel tubular. However, the influences of the creep coefficient vary with the steel ratios. With the increasing of the steel ratios, the sensitivity indices of the creep coefficient decreases sharply. Detailed parameter studies show that steel ratios have significant influences on the in-plane creep stability of CFST arches especially when the steel ratios are lower than 15%.