Stabilità di tralicci PREM in prima fase

The results of a numerical and analytical investigation on hybrid steel truss RC beams are described. Hybrid steel truss RC beams are beams where, during the construction phase and the concrete casting (Phase I), the steel truss system only carries the vertical loads. The steel truss of the beams may have different shapes, depending on the technology adopted, the span and the load. In this report, Steel trusses constituted by upper and diagonal bars and a steel plate at the bottom are considered. In construction phase, the verification against failure due to the safety against instability of the upper steel bars in compression or the diagonal elements is the most important design requirement. In the present study, four different beams are considered, with different steel trusses in Phase I condition. Finite Element modelizations of the beams are made and the failure loads are obtained, taking into account second-order effects due to large displacements. It is shown that the stability of the steel truss strongly depends on the lateral stiffness of the diagonal elements of the truss, as well as on the torsional rigidity of the lower steel plate. Starting from results of the numerical model, some design criteria are illustrated and discussed.