Evaluation of Failure Criteria in RC Structural Elements Due to Additional Internal Stresses Developed in Structural Elements Due to Temperature Exposure

Abstract

AbstractReinforced concrete structural elements such as beams, columns, slabs and shear walls, present in multi-storeyed buildings, undergo damage in the form of stiffness and strength degradation when exposed to high temperature in the event of a fire breakout in such buildings. The physical properties of concrete such as the elastic modulus, compressive and tensile strengths reduce with increase in temperature and time of exposure when compared to the corresponding properties of reinforcing steel. Constrained structural elements in framed structures when exposed to temperature are restricted from expanding. This constraint towards expansion in structural elements causes additional compressive stresses to be induced in them when exposed to temperature. This additional compressive stress that is induced in structural elements adds upon the internal stresses developed due to gravity loads causing an additional stress condition in the structural elements. When the total stress in concrete and reinforcing steel in compression or tension exceeds the maximum material strength values, the structural elements tend to fail. In this work, two temperatures of 300 ℃ and 450 ℃ are separately considered and applied on a 3D RC frame model along with the dead and live loads. The behaviour and additional internal stress increase in the structural elements such as the RC beams and RC columns are studied based on the internal stresses induced in these elements due to temperature exposure. Computations are carried out to ascertain the total internal stresses developed in the structural elements due to gravity loads and temperature and are compared with the maximum material strength values. Through this analytical approach, based on the values of the total internal stresses developed in the structural elements, comparative evaluation is carried out to identify structural members that have failed when the total internal stress exceeds the maximum material strength.KeywordsReinforced concreteStiffness degradationStrength degradationHigh-temperature fire exposureInduced internal stresses