Investigation of Fire Effects on Columns of High-Rise Reinforced Concrete Buildings

The effects of firebreak in high-rise buildings seem essential to be investigated cautiously since world trade center towers incident. Consequently, many technological advancements were achieved and numerous researches were performed. Nevertheless, in 2017, Plasco building in Iran also was set ablaze and the consequence was the full destruction of the building, claiming lives of at least 20, injuring 70 and loss of thousands of jobs. Therefore, it is crucial to investigate the effects of fire in high-rise buildings more thoroughly in order to prevent progressive collapse, a phenomenon that caused the destruction of the two landmarks. Ordinarily, to achieve this goal, methods of analysing fire effects are developed. So by choosing a logical fire scenario, design fire is extracted from time-temperature relations of design codes. After determining the firing temperature at various times, effects of temperature increase on the material's mechanical properties are investigated. Important characteristics such as concrete compressive strength, concrete and steel modules of elasticity, tensile strength, the coefficient of thermal expansion and steel rebar yielding stress are affected by alterations of temperature. Finally, by analysing structural behaviour utilizing modelling programs and comparing results of different fire temperatures and stories in which fire occurs with the initial design of the building RCC frame, it can be concluded that axial forces increases in columns are the critical condition in fire situations and in case of fire break in distinct stories, lower floors will experience a sharper surge of axial forces.