Long-term coupled analysis of steel-timber composite (STC) beams

Abstract

In this paper, the long-term behaviour of steel-timber composite (STC) beams under sustained load is numerically investigated. The long-term constitutive law of timber that accounts for the effect of elastic modulus change due to the moisture content (MC) variation, creep, mechano-sorption, inelastic shrinkage/swelling, and thermal strain is adopted from the literature to develop a 1D fibre element model for long-term analysis of the timber components. The time-dependent behaviour of shear connectors is considered in the formulation by a time-dependent shear-slip model calibrated against the results of long-term pushout tests. A 3D diffusion analysis based on finite difference (FD) scheme is coupled with the 1D fibre element model to simulate the variation of MC and temperature within the timber section due to variations in the ambient relative humidity and temperature. The coupled hygro-thermo-mechanical model is verified against experimental and numerical models available in the literature and incorporated into the 1D composite fibre element formulation to simulate long-term behaviour of the STC beams under variable environmental condition. The accuracy of the analytical tool is verified against available experimental data and the model is used to estimate the creep coefficient of the STC floors for a service life of 50-year. Furthermore, the evolution of nonlinear time-dependent stress–strain in timber and shear forces in shear connectors are comprehensively investigated and discussed, and the influence of service load level, panel width, and shear connectors’ spacing on the long-term performance of the STC floors are highlighted. The results of parametric studies suggest a creep coefficient of 0.35 for 50-years’ design life of STC beams (applicable to a wide range of shear connectors).