Experimental investigation of the flexural behaviour of innovative steel–timber composite beams featuring built-up cold-formed steel girders and LVL slabs

This paper investigates the structural behaviour of innovative steel–timber composite (STC) beams with cold-formed (CF) girders. Each beam consists of two back-to-back CF steel channels forming a built-up I-section, connected to a Laminated Veneer Lumber (LVL) slab with bolts. Thanks to the use of bolted shear connections, the composite beams are demountable. The flexural behaviour of eight simply supported beams was evaluated in four-point bending tests. Four groups of composite beams of different shear connection distribution were analysed. Significant load-bearing and deformation capabilities of the analysed beams were observed. Shear connection spacing had an impact on the load-bearing capacity of the analysed beams. The bolts used in shear connections did not fracture in any of the beams, despite the fact that the slip values exceeded 11 mm for the maximum load in the beam with the lowest degree of the shear connection. The values of the mid-span deflections exceeded L/24 for the maximum load, highlighting the large deformation capacity of the beams. Furthermore, the Gamma method was used to estimate the elastic resistance of the STC beams, while the method for steel–concrete composite beams with partial shear connections was used to estimate the plastic resistance. In the second method, the effective shear resistance of shear connectors was taken into account. The elastic bending resistance of the analysed beams from the Gamma method differed not more than 4% from the resistance obtained in the experimental tests. The calculated plastic bending resistance was 4–16% lower than the experimental values based on the test-informed comparison.