Stability of Precast Concrete Tilt Panels in Fire
This report investigates the behaviour of slender cantilever concrete panels and concrete panels in steel frames exposed to elevated temperatures. This report also provides recommendations for the design of slender tilt-up wall panels for fire resistance. The current trend of tilt-up construction in industrial buildings utilises very tall and thin concrete wall panels that are reinforced with a single layer of reinforcing in the middle. These wall panels are cantilevered from the base and are not connected to a column or a portal frame. The panels are connected directly to the steel frame by a steel rafter or indirectly to the eaves tie. The analysis of this project was conducted using SAFIR, a non-linear finite element programme developed in the University of Liege, Belgium. Reinforced concrete walls subjected to a fire on one side will undergo non-uniform thermal expansion, causing the walls to bow. Free-standing concrete cantilever walls with slenderness ratios (Height to thickness ratio) in excess of 50 experience very large deflections when exposed to a fire on one side. The analyses have shown that these large deflections will lead to outward collapse of the walls onto the neighbouring property. Concrete cantilever walls connected to unbraced steel frames are dangerous as they cause the frame to sway and fall out onto the neighbouring property during a fire. Braced steel frames connected to the walls enhance the behaviour of the walls by preventing the large outward deflections of the panels. If bracing is available from the steel roof to prevent sway, the wall panels can be constructed up to 12 metres and slenderness ratios up to 96, without outward collapse or buckling failure of the wall panels. For the partially braced frames conducted in this study, the height of the wall panels should not exceed 9.0 metres and the slenderness ratios should not exceed 65. It is concluded that the deflections of the free standing cantilever walls should be controlled. Slender cantilever walls should be connected to a braced steel frame with well designed connections to the rafter and the eaves tie.