Temperature and stress of RC T-beam under different heating curves

Abstract

Reinforced concrete (RC) structures are usually exposed to fire in actual engineering. A three-dimensional nonlinear finite element model was developed to predict the thermal and mechanical behaviors of RC T-beam under three kinds of temperature-time curves, including RABT, ISO 834 and HC (hydrocarbon). In the thermal analysis, concrete and steel reinforcement were simulated using DC3D8 (eight node linear heat transfer brick element) and DC1D2 (two node bar element), respectively. By repeated trial calculation, the element size of 35 mm × 35 mm × 35 mm was adopted. A subsequent thermal-mechanical coupling procedure was performed, and the mesh size of the beam was the same as the previous model, but the thermal elements of DC3D8 and DC1D2 were replaced with the stress elements of C3D8R (eight-node continuum element with reduced integration) and T3D2（two-node link element), respectively. The numerical results indicated that: (a) heat transfer delayed in the process of heating, and the ISO 834 curve was much more significant due to its slower heating rate; (b) larger heating rate led to higher temperature gradient and larger stress change rate of the concrete and the steel bar; (c) at the initial stage of heating, the tensile stress of the concrete on the lower surface of the beam decreased until it became compressive, and the tensile stress of the steel bar decreased; as the fire exposure time increased, the compressive stress of the concrete decreased and then became tensile stress, and the tensile stress of the steel bar increased again and then decreased, finally the beam reached the strength capacity; (d) compared with HC and ISO 834, RABT curve had more significant influence on the temperature and stress of the T-beam. The research results could give some references to the fire safety design of RC T-beam.