Developments and advanced applications of concrete-filled steel tubular (CFST) structures: Members

Strength, stiffness and ductility of concrete-filled steel columns under axial compression

Post-fire behaviour of reinforced concrete stub columns confined by circular steel tubes

Composite columns have superior strength and ductility performance, and they have become more widely accepted in the engineering applications. However, the filled tubular columns require more attention. This study aims to present a new formulation for the axial load carrying capacity (N
 u
 ) of circular concrete filled steel tubular (CFST) short columns having various geometrical and material properties. Although there have been some empirical relations for predicting N
 u
 in the literature, genetic algorithm based explicit formulation is not available. In the current study, 314 comprehensive experimental data samples presented in the previous studies were examined to prepare a data set for training and testing of the prediction model. The prediction parameters were selected as outer diameter of column (D), wall thickness (t), length of column (L), compressive strength of concrete (f
 c
 ), and yield strength of steel (f
 y
 ). The prediction model was obtained by means of gene expression programming (GEP). The proposed model was compared with available ones presented in the current design codes (ACI, Australian Standards, AISC, AIJ, Eurocode 4, DL/T, and CISC) and some existing empirical models proposed by researchers. The prediction performance of all models were also evaluated by the statistical parameters. The results indicated that the GEP model was much better than the available formulae, yielding higher correlation coefficient and lower error.

Ultimate capacity prediction of axially loaded CFST short columns

The post-fire behaviour of slender reinforced concrete columns confined by circular steel tubes is investigated experimentally and numerically in this paper. Experiments were performed firstly to explore the fundamental behaviour of steel tube confined reinforced concrete (STCRC) slender columns after exposure to the ISO 834 standard fire, including the cooling phase. Temperature distributions, load versus lateral displacement curves, strains in the steel tube and failure modes were obtained and discussed. Next, a 3D finite element model was developed with the program ABAQUS using a sequentially coupled thermal-stress analysis. After validation of the FE model, parametric studies were carried out to identify the influence of key parameters on the load-bearing capacity and buckling reduction factor of slender STCRC columns. The considered parameters were the heating time, cross-sectional dimension, slenderness ratio, material strength, steel tube to concrete area ratio and reinforcement ratio. Finally, a simplified design method was proposed for predicting load-bearing capacity of STCRC slender columns after exposure to standard fires.

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Guowang Huang

Papers

Effects of sustained axial load and cooling phase on post-fire behaviour of concrete-filled steel tubular stub columns