Design strength of concrete-filled steel columns

The purpose of this paper is to recalibrate the capacity reduction factors, estimate the reliability of current equations, and investigate the effect of these factors in AS 5100.6, the Australian Bridge Standard for concrete-filled steel tubular columns. This work has important ramifications for other international codes of practice as the Australian code has the identical or similar underlying design philosophy with Eurocode 4, AISC and the code of practice in Hong Kong. The method developed by Johnson and Huang is extensively applied to the Australian code format to recalibrate the capacity factors in AS 5100 for a target reliability of β = 3.04 based on an extensive database of 1,583 test results covering a wide range of input parameter values. In addition, an inverse analysis procedure based on Johnson and Huang's method is proposed to estimate the reliability of design equations with known capacity factors. The analysis results show that the interaction between the concrete and steel needs to be considered for the current capacity factors in AS 5100. The results also show that the current capacity factors provide greater reliability than the target reliability suggested in AS 5104:2005/ISO 2394:1998, but after considering the additional uncertainties created due to the application of multiple capacity factors, the reliability was almost the same as the recommended value. In conclusion, the current capacity factor values in AS 5100 are adequate with regards to safety and can be maintained, but better optimised values would be preferable to improve the cost-safety balance.