Effect of Fire on Confined Concrete Columns under Axial Loading

Abstract

The aim of this study is to numerically investigate the feasibility of confinement, the load carrying capacity and the temperature at which the confinement become obsolete for a RC column with dimensions of [200x200x
800 mm] subjected to a standard fire loads (ISO834) from four sides. The study was carried out using the research-oriented FE code ANSYS APDL. ANSYS can integrate the nonlinear behavior of concrete by accounting for both crushing under compression stresses and cracking under tensile stresses, and well as the bilinear behavior of the reinforcing steel.The Numerical program was subcategorized into two major groups. The first one consisted of thirteen models. Those models were analyzed under static loading conditions. The second group consisted of 72 models. The models in this group where subjected to both structural and thermal loading conditions. The structural loading was in a form of static service loads, while the thermal loading was in a form of standard fire curve that has been applied to the four faces of the column.The numerical results were compared with experimental results as far as possible, in order to verify the accuracy of the numerical models used. The numerical analysis aimed to study of the effect of many variables, i.e., the diameter of the lateral reinforcement, the diameter of the longitudinal reinforcement.The results revealed the accuracy of the analytical models when compared to the experimental studies. A positive effect was captured in terms of the load carrying capacity and delaying the failure time, i.e., loss in confinement effect, when increasing 1) the diameter of the longitudinal, 2) the diameter of the transverse reinforcement and Additionally, the results indicated an increase in the column loading time under thermal loading conditions when static design loads are applied. And when the percentage of failure load increased, the time of carrying columns of fire decreased.

Keywords: Finite Element Theory, Thermal Analysis, Reinforced Concrete Columns