Study on thermodynamic properties of RC beams considering elevated temperature and spalling effect

In order to study the effect of high temperatures on the thermomechanical properties of RC beams, fire and mechanical tests were carried out on four fully-dimensioned simply supported beams. A numerical analysis model based on the measured information was developed, and it was validated through experimental tests and theoretical calculations. The effects of fire exposure time, different physical parameters and concrete spalling parameters on the thermodynamic properties were further analyzed. The results show that the measured vibration frequencies appear a fluctuating trend of decay with increasing fire exposure time. The simulated frequency decays as a power function of fire exposure time. The frequency decreases with increasing span-to-height ratio and increases with section width, elasticity modulus of concrete and reinforcement ratio, respectively. Cross-sectional temperature field is most significantly affected by spalling depth, which increases rapidly with its increasing. With the increase in spalling area ratio, the increase in the temperature field gradually becomes smaller. The effect of spalling area ratio was relatively stable after more than 15%. The flexural bearing capacity shows a linear decrease trend with the increase in spalling depth. With the increase in spalling area ratio, it shows a power function of the decreasing trend.