The effect of reinforcement ratios on composite slabs in fire

Public-domain software currently allows designers to incorporate the enhancement of fire resistance due to tensile membrane action of composite slabs into their analysis of building behaviour in fire. Based on the Bailey–BRE Method, it enhances slab capacity by optimising reinforcement size in order to carry its fire limit state loading at the required fire resistance time. The method assumes that protected edge beams maintain vertical support of the slab at its boundaries, only allowing for failure of compartmentation integrity by tensile fracture of mid-panel reinforcement or by concrete crushing at the corners. However, these beams deflect under their increased loading in fire, which can cause premature structural failure of the panel. It is imperative to determine the real contribution of reinforcement to tensile membrane action, considering the loss of edge support. This paper presents a series of finite element studies conducted with Vulcan, compared with the generic simplified method and the public-domain software, to determine the influence of reinforcement on the failure of slab panels at elevated temperatures.-strength bolts after fire and that the effects of natural cooling are very different from those of water cooling.