Methods of improving the survival temperature in fire of steel beam connected to CFT column using reverse channel connection

This paper presents the results of a numerical study, using ABAQUS, of the behaviour and methods of improving the survival temperatures in fire of steel beams to concrete filled tubular (CFT) columns using reverse channel connection. The beams are axially restrained by the connected columns and develop catenary action so their survival temperatures are primarily controlled by the joint tensile resistance and deformation capacity. Therefore, improving the beam survival temperature mainly relies on improving the joint performance. This study investigates five different joint types of reverse channel connection: extended endplate, flush endplate, flexible endplate, hybrid flush/flexible endplate and hybrid extended/flexible endplate. The connection details investigated include reverse channel web thickness, bolt diameter and grade, using fire-resistant (FR) steel for different joint components (reverse channel, end plate and bolts) and joint temperature control. The effects of changing the applied beam and column loads are also considered. It is concluded that by adopting some of the joint details to improve the joint tensile strength and deformation capacity, it is possible for the beams to develop substantial catenary action to survive very high temperatures. However, it is important that the additional catenary force in the beam is resisted by the connected columns.

► Most effective joint type to increase beam survival temperature. ► Methods of improving joint performance to increase beam survival temperatures. ► Demands on steel material performance at elevated temperatures. ► Guidance on column behaviour and design.