Stress transfer and failure mechanisms in steel-concrete trussed beams: Experimental investigation on slab-thick and full-thick beams

This study presents the results of an experimental investigation on semi-precast Hybrid Steel Trussed-Concrete Beams (HSTCBs) for analyzing the failure modes and the stress transfer mechanism between concrete and embedded steel elements (plate and truss). The available literature presents previous studies carried out by the authors mainly focused on the understanding of the local transfer mechanism by means of push-out tests. Conversely, in this paper original the results of laboratory tests conducted on six specimens of full-size HSTCBs subjected to four-point bending, with variation in the shear span, are reported on. From these results, the authors are able to assess the failure modes of each beam and, finally, the transfer length necessary to ensure a full-strength connection. In the experimental campaign, two beam typologies are considered: Slab Thick Beams (STBs) and Full Thick Beams (FTBs). Both global and local response are monitored, the former in terms of load-midspan deflection curves and the latter in terms of strain measurements from Strain Gauges (SGs) placed on steel elements and concrete. Finally, some of the most relevant analytical models available in the literature and/or deduced from codes are used for interpreting the load-carrying capacity of slab and full thick beams as well as the failure modes experimentally observed, i.e. failure due either to flexure or shear, or failure of connections.