Finite Element Analysis on the Effect of Fire for Specified Duration, on a Reinforced Concrete Beam with Varied Boundary Conditions

Concrete is a poor conductor of heat due to its incombustible nature and low thermal diffusivity, which guarantee a slow propagation of thermal transients within the structural members. Despite exhibiting a good behavior at high temperatures, it can suffer considerable damage when exposed to fire. The knowledge of high-temperature properties of concrete is critical for fire resistance assessment because the fire performance of structural members like beams depends on the properties of the constituent materials. To predict the conditions within the RC beams subjected to fire, knowledge is required of the behavior of concrete subjected to high temperatures. To ensure the safety of RC structural systems in the event of fire, concrete members should be designed against fire. The temperature dependent properties that are important for establishing an understanding of the fire-response of RC structures include thermal and material properties at elevated temperatures. In this research, a finite element model was developed using ALGOR® to study the impact of fire on an RC beams. This model provides information about temperature distributions in the beam for given initial and boundary conditions. Using finite element analysis, the entire beam was meshed into small segments called elements. The elements hold information about the physical properties of their corresponding materials. Each element was bounded by nodal points. Boundary conditions were included on the appropriate nodes in the model. The different boundary conditions on which the analysis was conducted are pin-roller, pin-pin, fixed on both ends and cantilever. All the results obtained from the analyses are time dependent, including displacement, stresses and strains. The location and magnitude of maximum stress, strain and displacement for each boundary condition were determined with the analysis. The maximum principal stress in each case when compared to the compressive strength of normal strength concrete, implied that failure has occurred in all the four cases i.e. pin-roller, pin-pin, fixed on both ends and cantilever. The results obtained from the Transient Heat Analysis were compared with the temperature distribution from other studies. It was found that the temperature distribution determined in Kodur et al is very similar to the temperature distribution which results from the transient heat transfer analysis.