Experimental and analytical study of timber-timber composite (TTC) beams subjected to long-term loads

Eight TTC beams were fabricated by connecting cross-laminated timber (CLT) slab panels to laminated veneer lumber (LVL) or glued laminated timber (GLT) joists and the TTC beams were subjected to a constant sustained load and monitored over 540 days in an indoor uncontrolled environment. Benchmark experimental data for validation of numerical and analytical models were produced and effect of joist type (LVL or GLT), CLT slab thickness (60 mm or 100 mm) and orientation (crosswise or lengthwise), and type and size of shear connectors (8-or 12-mm screws) on the long-term performance of the TTC beams were studied. The creep deformation factors obtained from experimental results were in the range of 0.39-0.73. Simplified analytical models available in the literature were modified and utilised to predict the mid-span deflections of the TTC beams. The midspan deflections predicted by the simplified models had good agreement with the test data. The inelastic strains due to (differential) shrinkage between the slabs and joists had minor (less than 3%) influence on the long-term de-flections predicted by the models. The analytically estimated creep deformation factor for 50-year design life of the TTC floors was in the range of 0.55-1.26 that was slightly higher than the values obtained from the EC5 approach.