Experimental Investigation of the Shear Response of Precast Steel-Concrete Trussed Beams

The results of an experimental campaign of three-point bending tests on precast composite beams, named hybrid steel–trussed concrete beams (HSTCBs), are provided. HSTCBs are typically constituted by a precast steel truss embedded in a block of concrete cast in place. Two series of specimens were manufactured, designed such that shear failure would occur, and tested under positive and negative bending moment. The experimental results obtained showed that fragile shear failure occurred in almost all cases, evidencing the crisis of the compressed concrete strut involved in the collapse mechanism. Yielding of the steel members provided ductility to the system, especially in those cases in which the mechanical properties of the concrete were adequate and allowed the failure of the strut to be delayed. Some of the more accredited expressions for prediction of shear resistance available in the literature were used to assess the shear capacity and compared against those experimentally obtained for all specimens. The existing formulas mainly refer to classical reinforced concrete (RC) beams, but analytical models recently developed for HSTCBs were considered for interpreting the test results. On the basis of the experimental outcomes and the results obtained from their analytical interpretation, comments and design considerations on the main parameters ruling the resisting mechanism occurring in the tested beam typology are provided.