Abstract In this paper, a finite element (FE) model integrating solid elements with the thermo‐mechanical‐time constitutive relationship of concrete and the thermo‐mechanical constitutive relationship of steel was developed to analyze the fire performance of continuous two‐way reinforced concrete (RC) slabs. Based on the validation of the FE model, the effects of load ratio, slab thickness, aspect ratio, and local fire conditions on the fire resistance of continuous two‐way RC slabs were investigated. Furthermore, the mechanism underlying the slab's top cracking while the fire‐exposed bottom remains relatively intact was clarified, and the relationship between the mechanical response stages of continuous two‐way RC slabs and the internal stress redistribution law was revealed. The analysis results indicate that: (1) The mechanical response of continuous two‐way RC slabs under fire undergoes four stages: elastic, elastoplastic, plastic, and tensile membrane stage. During the elastoplastic and plastic stages, an inverted arch effect develops, with biaxial compression at the fire‐exposed bottom and biaxial tension at the top. Consequently, tensile cracking is concentrated on the top surface, and the directly exposed bottom does not initiate cracking until the tensile membrane stage is reached. (2) Continuous RC slabs exhibit pronounced internal‐force redistribution under fire. The mid‐span moment and axial force shift from positive to negative. In the mid‐to‐late stages of fire exposure, the negative moment becomes stable and nearly uniform along the span, except within 1 m adjacent to each support line, enabling simplified moment distribution in elevated‐temperature design. (3) Increasing the aspect ratio L c / b c from 1:1 to 2:1 advances turning point C by 31 min, and delays the mid‐span axial‐force transition from tension to compression by 143 min. At the same load ratio, increasing slab thickness reduces the early‐stage displacement growth rate but increases the plastic displacement growth rate in the late heating stage, while also increasing the peak negative bending moment. Under local fire, adjacent unheated spans generate significant axial tensile forces. (4) Since both continuous and simply supported two‐way slabs exhibit the inverted arch effect and tensile membrane action, their fire resistance differs only marginally. In the analyzed cases, neither slab type fails within 4 h of fire exposure without fire protection.
Wang et al. (Thu,) studied this question.