Hygro-mechanical analysis of timber-timber composite (TTC) beams in time-dependent environments: A 3D coupled finite element approach

The time-dependent behavior of timber-timber composite beams under constant loads within uncontrolled indoor environmental conditions is examined using a 3D fully coupled hygro-mechanical finite element model. These TTC beams are composed of glued laminated timber (GLT) or laminated veneer lumber (LVL) beams interconnected with cross-laminated timber (CLT) slab panels via coach (lag) screw shear connectors. A 3D hygro-mechanical material model, integrated into finite element software, is validated against a long-term experimental study spanning 735 days. A comprehensive sensitivity analysis is performed, exploring the influence of mesh size, time step, coefficient of hygro-expansion/contraction, and contact properties on the results of coupled finite element simulations. This results in the delineation of input parameters (i.e., mechanical properties of materials and screw-to-timber soft-contact model) that are suitable for practical hygro-mechanical simulations of Radiata Pine LVL, GLT, and European Spruce CLT materials. Smoothed temperature and relative humidity data are employed to enhance the convergence of coupled finite element simulations, especially for extended, long-term numerical simulations. Finally, the coupled finite element models are used to forecast midspan deflections in TTC beams over a prolonged duration, specifically after 4000 days.