Effect of Size and Shape of Concrete Column Elements Exposed to High Temperature

Abstract

Reinforced concrete (RC) structures and the structural elements (beams, columns, slabs) undergo degradation in strength and stiffness, when exposed to high temperature in the event of a fire breaking out in such structures. The concrete column elements tend to support the compressive loads transferred onto it from the floors and maintain the stability of the structure. The degradation in the compressive strength of concrete and degradation of yield strength of reinforcing steel present in the RC columns that get exposed to high temperature, in the event of a fire causes instability or collapse of the entire structure. In this work the variation of temperature across the cross section of reinforced concrete (RC) columns having various sizes and shapes (square and rectangular) exposed to different high temperatures (475 and 625 °C) and time of exposure (1 and 3 h) has been studied by carrying out a heat transfer analysis in Abaqus. The heat transfer analysis is carried out using heat transfer elements that possess the thermal properties of the materials (concrete and steel) that are temperature dependent. The depth of variation of a particular temperature for a particular time of exposure from the outer surface of the RC column upto the core having a particular size and shape is assessed. It is inferred from the analysis results, the time taken for a particular temperature to reach upto the core of the RC column is related to the size and shape of the concrete column. It is also learnt from the results, apart from increasing the concrete cover, a particular optimum size of a concrete column in cross section is necessarily to be provided while designing the column from thermal resistance point of view. As this optimum size of the column would delay the temperature reaching the core for a particular time of temperature exposure and would maintain a certain portion of concrete around the core portion to retain its original strength without causing failure of the column before the fire is put off.