Numerical model to determine shear capacity of reinforced concrete deep beams exposed to fire

This paper introduces a preliminary numerical model used for simulation of reinforced concrete (RC) deep beams subjected to ambient and elevated temperature. A model for deep beams at ambient temperature condition is first proposed. Calibration of the model is achieved by comparing numerical predictions with test data collected from published literature. Subsequently, modifications to the model are adopted, including adjustments of material constitutive models, and considerations of thermal gradient and thermal restraint. Results from this study demonstrate that failure mode changes from shear to flexural-shear failure when temperature effect is considered. Strength reductions up to 67% are observed when the beam models are heated. Furthermore, diagonal concrete struts become wider in restrained beams compared to unrestrained beams. Improvement on beam strength and stiffness from unrestrained beams and change of failure mode to strut splitting are noted. The study also indicates that the strut-and-tie design approach in ACI 318 gives over-conservative predictions on shear strength of deep beams exposed to fire.