Shear capacity of high strength RC beams subjected to high temperature heating

Abstract

High temperature rise of 1,000 degrees or more was applied to high strength RC members (compressive strength of more than 90 MPa) and the remaining shear capacity was experimentally investigated to confirm resilience after fire accidents. The spalling of concrete close to the corner parts of the members and their web was observed, and widely dispersed cracks were seen. The whole surface of the RC beams was equally exposed to the fire. The shear capacity after fire exposure was found to be a little reduced without change of shear failure mode.With these experimental facts, the authors examined their multi-scale simulation model of structural concrete, which has been verified and validated under the normal climate conditions, but never been put to the task of performance assessment of RC members subjected to fire. The simulation platform, which takes into account the release of chemically bound water, the ensuing internal vapor pressure and decayed micro-pore structure, self-equilibrated stresses, spalling of concrete and rehydration, was validated and its reliability is quantitatively discussed in both scientific and practical terms. Based upon the verification and validation, non-uniform heating cases were discussed with a computational approach. Provided that beams are subjected to high temperature from the single side of arranged reinforcement, the shear capacity of RC beams is predicted to rise owing to the loss of bond between the reinforcement and the web concrete because of spalling of the cover concrete. It is surmised that heating of the side surfaces has the greatest negative effect on shear capacity due to degrade the fixing parts. Reduction of shear capacity may be mitigated by taking measures to protect the fixing parts from damage.