Analyses Of Fire Behaviors Of RC Beam-Slab Assemblies With Boundary Restraints

In the past decade, a great amount of research on fire performance of reinforced concrete(RC) beams(including isolated beams and beams with axial and rotational restraints at beam ends) has been conducted. In real fire scenarios, however, floor slabs also play an important role in the beams’ fire behaviors. But the structural behaviors of beam-slab assemblies in fire are not fully understood yet. Therefore, further study is still needed to explore the fire behaviors of the beam-slab assemblies. The research details of this paper are as follows:1. Based on many reasonable assumptions, abundant numerical analysis was conducted to establish the express of the rotational and lateral restraint stiffness at slab edge. Meanwhile, the express of the rotational and lateral restraint stiffness at beam end was revised. It presented that:(1) When calculating the rotational restraint stiffness at slab edge, it is accessible to adjust the adjacent beam’s rotational stiffness to take the adjacent slab into account; the adjusted factor increases with the slab height and the smaller the beam section is, the more significant the adjusted factor varies.(2) The express of rotational stiffness adjusted factor has good predicting accuracy.2. Using ABAQUSA(the general finite element software), a preliminary study was conducted to reveal the fire behaviors of beam-slab assemblies with boundary restraint which was also contrast with the fire behaviors of no slab restraint beam. It presented that:(1) At the beginning of heating, the mid-span deflection of both beam-slab assembly and no slab restraint beam are almost the same, and after that the former increased larger than the later.(2) With time increasing, the bending moment at beam end section of both beam-slab assembly and no slab restraint beam reached peak value rapidly and then decreased gradually. The bending moment peak value at slab edge of beam-slab assembly was smaller than that of beam end section, and decreased to 0 and increased at the opposite direction at the end of heating.(3) Compared with the beam-slab assembly, the no slab restraint beam’s peak value of bending moment at beam end section was smaller, and decreased faster after peak.(4) The axial force at beam end section of beam-slab assembly was smaller than that of slab edge section, it was also smaller than that of no slab restraint beam.3. Using ABAQUSA, the influence of beam end rotational stiffness ratio,beam end lateral stiffness ratio,slab edge rotational stiffness ratio and slab edge lateral stiffness ratio on the deformation and internal force of beam-slab assembly under elevated temperature was investigated. It presented that:(1) When the beam end lateral stiffness ratio was high, the peak value of beam end section’s bending moment and axial force increased and decreased respectively with beam end rotational stiffness ratio increasing.(2) The beam end lateral stiffness ratio showed great significant influence on the beam end section’s bending moment and axial force. The beam end section’s bending moment and axial force increased faster and higher under larger beam end lateral stiffness ratio. What’s more, the beam end section’s bending moment decreased faster after the peak, hit 0 and increased at the opposite direction eventually.(3) The slab edge rotational stiffness ratio almost had no influence on the mid-span deflection of the beam-slab assembly. In medium-term, with the increasing of the slab edge rotational stiffness ratio, the beam end section’s bending moment and axial force decreased significant. While in early stage and later stage, it had limited influence.(4) The slab edge lateral stiffness ratio showed limited impact on the deformation and internal force of the beam-slab assembly.