Research Projects

The strength and ductility of the three components of a welded joint, base metal, heat affected zone, and weld material, are crucial for steel structural systems like moment resisting frames under dynamic forces like earthquakes. Welded connections are expected to remain elastic, but under severe dynamic load, the strength and ductility of the weld material, heat affected zone, and base metal play a crucial role in avoiding brittle failure of the connection and the structural system. This proposal aims to develop an accurate micro-mechanics-based fracture model to understand and control the strength and ductility of these components. Initial efforts will focus on material characterization of base metal, HAZ, and weld metal under static and dynamic loads, including yield and ultimate strength, ductility, and three-dimensional fracture locus under static and cyclic loads. Component tests of fillet welded joints will be performed in two different load to un-welded notch configurations, under static and dynamic loads, to quantify the failure of the welds. The fracture model will be trained to predict the occurrence of brittle failure of weld considering residual stresses and variation of ductility at the weldment. The final validation will be performed through the sub-assembly test of a welded rigid beam-column joint assembly, considering energy dissipation by beam members, local slenderness of the cross section, rotation demands at the joint region, and residual stresses developed in the actual joint. This study will also help develop design procedures for welded beam-column joints in the Indian steel and fabrication context, with details regarding welding procedures and consumables to yield ideal performance during severe seismic events.