Load-carrying capacity of circular recycled aggregate concrete-filled steel tubular stub columns under axial compression: Reliability analysis and design factor calibration

It has been well-reported that using steel tubes to confine recycled aggregate concrete (RAC) is an effective solution to strengthen the imperfection of RAC, namely RAC-filled steel tubes (RAC-FST). Yet to date available design codes applicable to the axial compressive behavior of RAC-FST stub columns are still limited, and very scarce studies have concentrated on investigating the structural safety. This paper presents a full-scope reliability-based design analysis for the load-carrying capacity of circular RAC-FST stub columns under axial compression. First, the performances of several code-based models were evaluated in terms of model uncertainty based on a reliable experimental database that comprises 94 circular RAC-FST stub columns, respectively. Then, the statistical characteristics for characteristic compressive strength of RAC were specially identified, and other uncertainties associated with steel strength, geometrical configurations, and loads were taken from available publications. Subsequently, the reliability of circular RAC-FST stub columns designed using existing design factors in current normal concrete filled steel tubes (CFST) codes was investigated in conjunction with Monte Carlo simulation (MCS) technique. Results indicated that in order to achieve the reasonable design of circular RAC-FST stub columns, existing design factors need to be calibrated. Accordingly, a combined partial factor directly reducing the whole resistance of composite cross-section was proposed, and the corresponding recommendations were provided based on the target reliability index-oriented calibration process.