Stiffness of welded T-joints with CHS chord members and passing-through longitudinal plates

In steel braced frames used in low-rise buildings, the connection between a longitudinal branch plate and a hollow structural section member is a useful structural detail for mounting braces. However, this joint can result in low stiffness, causing significant deformation of the tube's connecting face. This may necessitate using a thicker tube in the design phase, thus compromising the benefits of using a hollow section. To address this issue, employing connections with passing-through plates offers an attractive alternative to enhance the stiffness of such joints. Notably, current provisions and research investigations lack formulations for predicting the stiffness of these joints, focusing only on their strength. Within such a framework, this study develops formulations to estimate the initial stiffness of T-joints between Circular Hollow Section (CHS) profiles and axially loaded passing-through longitudinal plates. The research involved a selection of experimental data from studies available in the literature and validated a Finite Element (FE) model. Subsequent parametric analyses on 65 geometric configurations of connections were carried out through numerical simulations. Finally, analytical formulations, based on the application of Clapeyron’s theorem to simplified mechanical schemes, were developed to predict the initial stiffness of the analysed T-joints. These equations, validated against numerical results from the parametric study, showed a mean ratio of the predicted stiffness to the numerically simulated stiffness of about 1.00 and a maximum coefficient of variation equal to 7 %.