Ultimate Bearing Capacity Of Reinforced Concrete Beam High Temperature Calculation And Fire Resistance Design Methods

Building fire is serious hazard to people's life and property safety. The researchers and the engineers have consistently focused their attention on the mechanical property at elevated temperature and fire safety design of the reinforced concrete structure, which is one of the most commonly use in construction. But up to present, there is not any national code related to fire resistance design of reinforced concrete structure. In this paper, the ultimate bearing capacity of reinforced concrete beam at elevated temperature and the method of fire resistance design were researched.1. The thermal parameter and mechanical property of concrete and steel bar at elevated temperature were compared in different documentation of domestic and foreign countries'. And then properly parameters were selected to analysis the temperature filed and the bearing capacity of reinforced concrete beam.2. The distribution of the temperature field is presented with ANSYS8.0. The parameters which influence the temperature field, such as the curve of temperature rising, the kind of aggregate, the sectional dimension and the burning time were analyzed. The distribution of temperature filed diagram for different sectional dimension and different burning time, and the position of 300℃and 800℃isothermal line and the simplified formula about the steel bar's temperature of reinforced concrete beam subjected to fire were discussed.3. The equivalent area of concrete section was deduced by taking the two step model to consider concrete at elevated temperature, and any formula was established to calculate the ultimate bearing capacity of reinforced concrete beam, and the corresponding program in FORTRAN90was built. By this program, the parameters, such as the sectional dimension, the strength of concrete and steel bar, the thickness of concrete cover and the ratio of reinforcement were discussed. The discussion indicated that the sectional dimension has to the ultimate bearing capacity of reinforced concrete beam, and width has more evident influence than height, and it cann't improve the fire resistance of beam in effect by improving the strength grade of concrete and steel bar, the thickness of concrete cover is a impotant parameter to influent the fire resistance of reinforced concrete beam, but when the thickness up to a extreme, the influence get less evidence, and the reinforcement ratio also cann't improve the fire resistance in effect, and the existence of compressive reinforcement bring any influence to the fire resistance of the beam.4. A design method based on calculation of reinforced concrete structure against fire was presented, in which the practical situation and fire load of the burning room was consided. The combination of load effects for designing against fire is discussed. And then the bearing capacity and stability of reinforced concrete beam at elevated temperature were checked by using above simplified method. A formula was deduced to calculate the rigidity of reinforced concrete beam at elevated temperature.