In-plane Creep Buckling Analysis On Slender Concrete-filled Steel Tubul Ararches

In China, the first concrete-filled steel tubular(CFST) arch bridge was built in the 1990 s. From then on, the development of CFST arch bridges in China has been fairly fast with more than 300 CFST arch bridges built up to date. The longest CFST arch bridge has a span longer than 500 meters. Due to the excellent static responses of CFST to axial compressive loading, most of the CFST arches are slender and are more prone to creep-buckling problems as the time effects have more pronounced influences on the static behavior of the arches. Unfortunately, the available designing code has not considered the time effects on ultimate capacity of CFST arches, while related research is only in the starting stage.In this context, this thesis conducted finite element analysis using ABAQUS to investigate how time effects influence the in-plane static responses and creep buckling behaviour of circular corss-sectional parabolic CFST arches with fixed ends which subjected to loads uniformly distributed along the arch span. M odified EC2 model and step-by-step method were introduced to ABAQUS via UMAT to consider the creep and shrinkage of CFST. Geometric and material nonlinearities were also taken into accounted in the analysis. The analysis results were c ompared with the available experimental data from four in-plane buckling tests on circular corss-sectional parabolic CFST arches to verify the reliability of the analysis method.With the finite element model, parametric analysis was carried out to investigate time effects on the static responses, including displacements, stress distribution, contribution between concrete core and steel tube to resist distributed loading, and inner forces distribution, of circular corss-sectional parabolic CFST arches with fixed ends which subjected to loads uniformly distributed along the arch span. Considered parameters include slenderness ratio, steel ratio, span-to-rise ratio and sthength of concrete and steel, et al. It was found that time effects had considerable influences on the static responses of CFST arches, which can lead to up to 124% increase in vertical displacements. Among the considered parameters, steel ratio are the main factors that affect the long-term responses of CFST arches.Parametric analysis was also carried out to investigate the in-plane creep buckling behaviour of CFST arches. Based on the analysis results, designing equations were proposed to predict the reduction of the peak loading for CFST arches induced by time-dependent pre-buckling deformations. It was found that time effects had considerable influence on the in-plane stability of CFST arches. Within the parameter ranges considered in this paper, when subjected to sustained loading at the level of 0.5 of intantaneous ultimate loading for 100 years, the in-plane capacity for CFST arches can be reduced by up to 12% in comparison of the instantaneous values. steel ratio are the main factors that affect the in-plane creep buckling behaviour of CFST arches. The proposed designing equations can well predict the reduction of the peak loading for the arches induced by time effects, with the correlation coefficient of 7.8%.