Behaviour of cold-formed composite beam with bent-up bar as shear connector encased with self-compacting concrete

Abstract

Composite construction is well-known to be an economical solution by utilizing composite action developed between steel and concrete which has resulted in significant savings in steel weight and reduction in overall beam depth. The advantages of composite construction have contributed to the dominance of multi-storey buildings for medium-rise construction in some countries. However, the use of composite beam with cold-formed steel (CFS) lipped channel section is yet to be established as the structural behaviour of such beam is not well understood. Therefore, this study presents and discusses the behaviour of composite beam proposed for cold-formed steel section attached to profiled metal decking slab with an innovative shear connector. The composite beam comprises of a profiled deck slab arranged perpendicular to two CFS lipped channel sections acting as beam members infilled with self-compacting concrete (SCC), and a U-shaped ribbed rebar as shear connector. The study comprised of two components: experimental and theoretical works. The experimental work consists of fourteen full-scale specimens of the same dimensions (4300 mm x 1500 mm) which were prepared and tested for four-point bending test to investigate the structural behaviour and failure modes of the proposed composite beam system. The specimens are varied based on beam depth (250/150 mm), reinforcement ratio (2.5/1.9), size of shear connector (16/12 mm diameter), beam configuration (back-to-back/toe-to-toe) and types of slab (composite/solid) to study the influences on the ultimate load capacity of the composite specimens. The results showed that slab type, beam configuration, shear connector size and beam depth have significant influences on the ultimate load capacity. Changing from solid slab to composite slab could save about 25% of concrete volume. However, this change could also result in reduction of the ultimate moment resistance (34.1%) based on beam configuration. The results also show that the effective area ratio reduced with an increase in the beam depth. It was noted from all parameters that beam configuration has greater influences on the ultimate moment resistance. Parameter such as back-to-back arrangement has recorded higher increment ranging from 23.3-42.8%. In all specimens, shear connector of size 12 mm proven to be the optimum design configuration and provides a preferable flexible failure mode as compared to concrete brittle failure of shear connector size 16mm. It can be concluded that the proposed composite beam with cold-formed steel section is strong enough to be used as main beam. From the comparison between the experimental result and theoretical prediction using conventional method in EC4. It is found out that the conventional method was not able to predict the ultimate capacity of this composite beam. Hence, a modification had been made to the existing formula. Close agreement is recorded between experimental result and the proposed theoretical model in calculating the ultimate moment resistance of the proposed composite beam.