Modelling the behaviour of concrete-encased concrete-filled steel tube (CFST) columns subjected to full-range fire

Abstract

This paper presents an advanced finite element analysis (FEA) model to predict the fire behaviour of concrete-encased concrete-filled steel tube (CSFT) columns. The sequentially coupled thermal-stress analysis method provided in the software package ABAQUS was used. Full-range fire simulation given in this paper included four phases, i.e. loading (to a certain load level) at ambient temperature, standard fire exposure (heating) with the load applied, cooling down phase and postfire loading up to final failure. Calibrated empirical models for steel tube, unconfined and confined concrete (confined by steel tube and by reinforcement, respectively) over the four phases were chosen separately and applied to the FEA model. Numerical results from the model were compared with previously reported results of the experiments on the concrete-encased CFST columns, in terms of ultimate strength at ambient temperature, temperature field, failure modes, fire resistance, axial deformation versus time relationships, load versus axial deformation relationships and postfire residual strength. It is found that acceptable agreement was reached between the predictions and experimental observations, although some aspects could be further improved. Sensitivity analyses on several identified parameters of the modelling were conducted. Recommendations on simulating the full range fire behaviour of concrete-encased CFST columns were proposed based on the numerical study presented in this paper. In addition, the calculated internal force of the tested specimens was extracted and analysed, which confirmed the design concept of the composite action of concrete-encased CFST columns in fire.