Influence of concrete slabs on lateral torsional buckling of steel beams

The use of pre-cast concrete floor slabs in steel framed structures is quite common. In the de-sign of the steel beams, the lateral restraining effect of the pre-cast concrete slab is normally safely neglected. However, the concrete slab will provide some horizontal restraint, even without special provisions such as dowels being present. It may even be that the restraint provided by the floor slab prevents lateral torsional buckling. To investigate the restraining effect of a concrete slab on the top flange of a steel beam subject to lateral torsional buckling, two experimental load tests were performed. The first test is a so called reference test where a steel beam with lateral restraints at the supports only (fork conditions), was loaded in four point bending. In a second test, a single 1.2 m wide non-connected concrete slab was placed on a strip of rubber at mid span of the steel beam with the same support conditions. The tests were carried out on 7.2 m long IPE240, S235 beams subject to identical loading conditions. The test results have been compared with results obtained from Finite Element simulations and theoretical analyses. It was observed that the non-connected pre-cast concrete slab, placed on top of the steel beam, performed as a lateral support against lateral torsional buckling such that the beam almost reached its full plastic mechanism capacity. This preliminary study shows promising results. Further research is planned to quantify the restraining effect of floor slabs on the lateral tor-sional buckling behaviour of steel floor beams