Reliability considerations of modern design codes for CFST columns

Abstract Concrete filled steel tubular (CFST) columns have been increasingly used in tall buildings and bridges due to offering excellent structural and economic benefits. Current design codes for such columns exhibit certain limits in terms of material strengths and section slenderness. This paper aims to evaluate the reliability and the applicability of the current design equations in American code AISC 360–16, European code EC 4 and Australian/New Zealand code ASNZS 2327 for the design of the columns beyond their material and slenderness limits. A comprehensive database with over 3200 tests was collected to develop the statistics of the model errors for different types of columns. Monte Carlo and subset simulation techniques were developed based on Markov Chain Monte Carlo algorithms, to accurately and efficiently predict the reliability index of structures with small failure probability because they account for all uncertainties in material and geometric properties, loads and model errors. The results from the reliability analysis indicate that the reliability index of the concentric column designed by three considered codes is much higher than that of the eccentric column (i.e. beam-column). The results from a parametric study suggest that all three codes can be safely extended to the design of columns beyond the current material and section slenderness code limits.