Behaviour and design of double angle beam-column connection in fire conditions

The behaviour of composite floor systems in fire depends significantly on the performance of connections supporting the beam. This paper discusses the performance of double-angle shear connections under fire conditions investigated using numerical analyses and suggests changes to connection design and detailing for their improved fire performance. Finite element models are used to perform sequentially coupled, heat transfer and stress analyses of composite beams with end connections. The analysis technique is validated against several experimental studies. Two major triggers for connection failure in fire are identified: (i) excessive deformation following web buckling during the heating phase and (ii) contraction of the beam during the cooling phase. It is observed that the flexibility of angles used in the connection causes prying action and leads to a localized increase in the weld force demand, which increases the likelihood of a premature failure of the welded joint. The beams that have bottom flange coped at the ends are found to be more susceptible to web buckling during the heating phase. The web buckling can be prevented by using stiffened angles. The failure during the cooling phase can be prevented by using slotted holes.