Experimental and analytical study of hybrid steel-timber beams in bending

The combination of timber elements and steel beams can be of high interest for mechanical performances including instabilities and fire protection. In this paper, experiments and numerical modelling are performed to analyse the behavior of various configurations of steel-timber beams in bending. Two timber beams are connected to the web and the flanges of the steel beam. In order to define the material properties of the tested elements, each component (wood and steel) has been tested separately. Then, timber and steel beams have been connected and tested up to failure. The observed behavior shows a limited effect of hybridation in the elastic domain. However, the effect is significant at the ultimate stage. Actually, the combination of timber and steel elements improves the resistance to lateral torsional buckling and local buckling of the steel beam. The stiffness and the strength of these innovative hybrid structures are estimated at SLS and ULS respectively using approaches similar to those proposed in European design rules. The analytical values are close to those obtained from tests even with the failure reached by instability of steel element. However, it appears that for hybrid beams the calculated value of elastic critical bending moment for lateral-torsional buckling needs to be improved. These results highlight the potential of the steel-timber hybrid elements for further developments.