Behavior of thermally restrained RC beams in case of fire

The thermal deformation of a reinforced concrete (RC) beam in case of fire, when prevented by the surrounding structure, induce axial forces and/or bending moments in the structural element changing its resistance. A few experimental studies on this subject address the analysis of simply supported beams, and, in some cases, when thermal restraint is imposed, the level of applied stiffness is not clearly quantified. Trying to fill this gap of knowledge, this paper reports a series of fire resistance tests on axially and/or rotationally restrained RC beams under flexural bending. The main objectives of this research were to verify the failure modes and fire resistance of the RC beams comparing the behavior of restrained with those unrestrained. Other important aspects analyzed were the evolution of temperatures in the cross section, the magnitude of the restraining forces and the vertical displacements developed. The results showed that the performance of RC beams can significantly be affected by the thermal restraint, since in some cases an increase of up to 100% in the fire resistance was registered.