Non-linear analysis of the low-cycle fracture behaviour of isolated Tee stub connections

The present work deals with the numerical analysis of the low-cycle fracture behaviour of isolated Tee stub connections with partial fillet welds. The overall objective of the research is to assess the seismic performance of bolted partial strength beam-to-column joints under seismic loading; but first, the complexity of these joints is approached after understanding the behaviour of more simple geometries which govern the response. In fact, the study focuses on the low-cycle fracture behaviour of Tee stub connections that are elemental components of extended end plate connections with partial fillet welds. First, the general experimental program dealing with bolted end plate joints and component parts is presented. The program comprises sets of constant and variable displacement amplitude cyclic tests both on complete specimens and on components. Test results have shown good performance of bolted extended end plate moment joints under cyclic loading as well as that of fillet welds that represent an economic solution for thin and moderate extended end plates. Then, the connection material is characterized from a microstructural and fracture mechanics standpoint. Successively, detailed three-dimensional non-linear finite element analyses are carried out in order to tune model material parameters; whilst two-dimensional inelastic analyses are performed in a monotonic and cyclic loading regime to validate connection finite element models. Lastly, a parametric study is conducted in order to define details able to reduce loading-induced toughness demands. Analyses have inferred that fracture driving force demands, quantified in terms of crack tip opening displacements, are reduced by using fillet welds matching the end plate material, by limiting welding-induced residual stresses and by increasing the yield-to-ultimate strength ratio compatibly with plastic analysis requirements.