Residual self-tapping screw withdrawal resistance in steel-to-wood connections under cyclic moisture content load

This paper investigates the residual withdrawal resistance of fully-threaded (FT) and partially-threaded (PT) self-tapping screws (STSs) in steel-to-wood (S2W) connections subjected to cyclic moisture content (MC) load through both finite element (FE) modelling and an analytical ordinary differential equation (ODE) model. In the FE modelling, both installation-induced and MC loads were considered, with three MC cycles: 12%−16%−12%, 12%−21%−12%, and 12%−30%−12%. In contrast, the analytical ODE model considered only the effect of the MC load. Results reveal that the installation-induced loads can be neglected when quantifying the reduction in STS withdrawal resistance caused by wetting. While MC cycle with low MC increase, e.g., 12%−16%−12%, has negligible influence on the STS withdrawal resistance, MC cycles with moderate to large MC increases (e.g., 12%−21%−12%, and 12%−30%−12%) would significantly reduce the withdrawal resistance of STSs, especially for PT STSs (across all considered lengths from 80 mm to 400 mm) and FT STSs with short screw lengths (specifically, 80 and 120 mm). Moreover, the analytical ODE model proposed in this study can reasonably estimate the STS withdrawal resistance and therefore serve as an alternative to FE modelling.