Experimental and theoretical investigation of long-term performance of steel-timber composite beams

The structural performance of the steel-timber composite floors under sustained long-term loads was investigated by laboratory tests over a period of 22 months. The long-term deflections, end-slips, and strain distributions over the cross-section were measured and reported for six beams with a loading span of 5.8 m. Effects of different shear connectors, arrangement of the timber panels and timber slab segmentations and the magnitude of applied loads were studied. The timber slab segmentation had a detrimental effect on the short- and long-term stiffness of the tested beams. The long-term effects (after 22 months) led to a maximum 19% increase in the midspan deflections. Furthermore, the moisture transport, variation of mechanical properties with respect to moisture content, long-term compressive deformation of the panels and long-term slip moduli of the shear connectors were investigated to provide a thorough understating of the long-term behaviour of the steel-timber composite system. A simplified analytical model for estimating the flexural stiffness of the steel-timber composite beams was proposed and employed to estimate an overall creep deformation factor for the composite beams. The creep deformation factor of the tested beams was in the range of 0.29–0.39 depending on the shear connector type and timber slab orientation.