Research On The Behaviour Of Concrete Encased Concrete Filled Steel Tubular Columns Under Long-term Sustained Load With Preload Effects Considered

Abstract:Concrete-encased concrete-filled steel tube (CFST) has attracted the interests of structural engineers due to its good structural performance. It is necessary to provide the information on the composite members under long-term sustained load with preload effects considered, based on the study on the performance of concrete-encased CFST. This paper is anttempt to study the behaviour of CECFST columns subjected to long-term sustained loading with preload effects condidered. The mian content of CECFST columns with preload effects considered under long-term sustained loading can be summarized as follows:(1) To study the behaviour of CECFST short columns under long-trem loading, eight CECFST columns were tested under differert levels of sustained axial loads. The influence of loading ratio of column, steel tube ratio and outside concrete strength on the creep were investigated.(2) Uitimate state tests of twelve CECFST short columns without long-term sustained loading considered and eight CECFST short columns with long-term sustained loading considered were carried out to study long-term load effect on ultimate strength, peak strain, ductility and stiffness of CECFST short column.(3) To study the behaviour of CECFST short columns under long-trem sustained load with preload effects, eight CECFST columns were tested under long-term sustained loading with preload effects considered. The incremental deformation of steel tube, longitudinal reinforcement and outside concrete caused by time effects for CECFST specimens were measured and recorded in the tests. The influence of preload ratio, loading age and steel tube ratio on the creep were analyzed.(4) Uitimate state tests of twelve CECFST short columns and eight CFST short columns without long-term sustained loading and preload considered and eight CECFST short columns with long-term sustained loading and preload effect considered were carried out to analyse the effect of long-term loading and preload on ultimate strength, peak strain, ductility and stiffness of CECFST short column.