Evaluation of the shear capacity of RC beams in fire conditions

Based on the upper bound kinematic approach of the yield design theory, this paper presents a simplified approach for evaluating the shear capacity of reinforced concrete (RC) beams in fire conditions. The proposed method assumes rigid-block velocity fields of a beam under 4-point bending loading, and accounts for fire-induced strength reduction of materials as a function of temperature distribution across the beam cross-section. At first, to determine the shear capacity using a general velocity field in the beam, a simple convex optimization problem is numerically solved. Then, simplified analytical expressions corresponding to steel-yielding or concrete crushing velocity fields are provided, using two particular velocity fields, thus giving closed-form expressions in those particular cases. Such an approach allows for a direct and quick evaluation of the shear capacity of RC beams from the thermal analysis of their cross-section and is further compared to available experimental results.