Residual area method for heat transfer analysis of concrete-encased I-sections in fire

A design concept called the residual area method is proposed to calculate the equivalent thickness of concrete for temperature analysis of concrete-encased I-sections in fire. The design of the equivalent concrete thickness is based on a regression analysis which is verified by experimental results. The significance of the coefficients of the regression analysis is assessed through statistical means (R² values and F-tests), and shown to be reasonably satisfactory. The steel temperature response of concrete-encased I-sections subjected to fire is characterized by three temperature variables. The proposed method makes use of the EC 3 provisions to formulate the temperature response of each representative point along the steel profile using a 1D heat transfer model. Apart from standard fire conditions, the proposed method is applied to concrete-encased I-sections exposed to hydrocarbon, external and parametric fire curves. The results demonstrate that the residual area method is intrinsic to the geometric configurations (cross sections) of concrete-encased I-sections, but independent of heating conditions. The proposed method has been further verified by three series of specimens, and the predictions are compared against the results obtained from finite element analysis.