The structural behaviour of hybrid steel-trussed concrete beams: A literature review of experimental tests and theoretical models.

Hybrid Steel-Trussed Concrete Beams (HSTCBs), introduced in civil construction around the 70s, combine a steel truss within an in-situ cast concrete core, often with a steel or concrete bottom plate. Initially favoured in industrial buildings for their semi-prefabricated construction and ability to span large distances with contained depths, HSTCBs have subsequently attracted scientific interest in residential construction, focusing on static and seismic response. The technical literature on this topic highlights that HSTCBs do not follow the same mechanical rules of RC or steel-concrete composite beams, necessitating specific insights into their behaviour under flexure, shear, and seismic conditions. This review aims to collect the major scientific results obtained in the last twenty-five years by several researchers in Italy and abroad, beside the outcomes of some relevant earlier studies. The reviewed papers encompass findings from experimental campaigns on weldings, push-out test specimens, simply supported beams and beam-to-column joints. Some of these studies also incorporate proposals for analytical formulations aimed at offering design-oriented and code-compliant prediction models, alongside finite element simulations to replicate the strengthening mechanisms. Following a thorough synthesis of the primary findings to date, the literature review underscores notable gaps in knowledge and still open issues, particularly concerning long-term performance and size-effect laws.