Ultimate behaviour of bolted beam-to-column connections in large rotations

The moment-rotation capacity of a beam-to-column joint is critical to the ability of steel-framed structures to survive extreme loading, where catenary actions develop in their connecting beams leading to large joint rotations. Recent works have shown that EC3 Part 1–8 breaks down in the regime of large joint rotations since geometric nonlinearity – this is not considered in EC3 - may influence its behaviour leading to gross under- (or over-) prediction of its response. To fill this knowledge gap, a mechanical model of a double-split tee joint (Francavilla et al., 2016), that only considers material non-linearity, is extended here to include geometric non-linearity. The results of six full-scale joint tests, that developed significant catenary actions in the joint components are presented. The updated mechanical model will be shown to be highly accurate in predicting the ultimate joint rotation (φ) and the maximum bending moment capacity (M) of the joint. Comparison between the predicted parameters and experimental data gives a mean value of 1.04 (and a CoV equal to 0.07) for the ratio φth/φexp and a mean and CoV of 1.03 and 0.12, respectively, for the ratio Mth/Mexp. To demonstrate the fidelity of the model, predictions from a previous non-linear material model (MNM), disregarding geometric nonlinearity, will be compared to the current one (GMNM).