Preliminary Experiences and Basic Concepts on the Structural Performance of Hybrid Trussed Beams

The definition “hybrid trussed beams” indicates a particular type of steel-concrete structural elements which are composed by prefabricated steel trusses completed by in-situ casting of concrete (cast-in-place concrete). They can be classified among the partially prefabricated and composed structure. From their first ideation and introduction, that goes back in 1967 by means of S. Leone, the interest of the civil engineering for hybrid trussed beams has been continuously increasing and nowadays they cover a relevant part of the total demand of beam prefabrication in Italy and applications range from the more traditional residential and industrial constructions to the infrastructure realizations. The increasing appeal of hybrid trussed beams now claims the definition of a standard for their calculation and realization. Perhaps the theoretical studies and experimental investigations conduced in the past on this structures are partial and insufficient to give a complete and exhaustive explanation of their structural performance, specially for the aspects of ductility and shear resistance. An articulate experimental program have been planned at the University of Padova to give a contribution in this field. In this work the first results from tests conduced on simply supported beams to investigate the flexural and shear behavior of the hybrid trussed beams are reported. The tests have been conduced on a series of 8 classic beams (named REP® NOR beams) made with a lower steel plate. Four of these have been loaded as bare, without integrative casting, to simulate the working condition in the first phase. The remaining four were completed with the concrete casting and tested. Globally 10 destructive tests have been conduced, both in the shear and in bending fields. In the paper, after the description of the test setup, the experimental results will be listed. The basic concepts of the experimentally observed behavior of hybrid trussed beams are reported together with some preliminary proposals for their safe design.