Flexural capacity whole process calculation method for T‐shaped prefabricated composite reinforced‐concrete beams after fire exposure

Abstract To accurately evaluate the residual bearing capacity of concrete T‐shaped composite beams following fire exposure, the effects of key parameters, including protective layer thickness, thickness of precast slabs, and the strength of cast concrete slabs, are considered. A comprehensive numerical analysis method was developed, incorporating equilibrium conditions, material constitutive relationships, and sectional analysis theory, to predict the post‐fire flexural behavior throughout the loading process. The validity of the proposed method was confirmed through comparison with fire experimental results. The results demonstrate that the comprehensive numerical analysis method, in which T‐shaped composite beams are classified for separate analysis, allows for accurate prediction of the yield load and ultimate load within error margins of 11% and 6%, respectively; a high degree of agreement has been observed between the theoretically whole flexural failure process and the actual structural behavior, demonstrating a high level of accuracy. During the failure process, the neutral axis was observed to shift gradually downward, suggesting a potential transition from the first type (the neutral axis is located within the flange) to the second type (the neutral axis is located outside the flange) of beam failure behavior. The flexural capacity of T‐shaped composite beams decreases with longer fire exposure and increases with greater precast slab thickness.