Elastic Plastic Fe Analyses of Sub Models of Connections in Steel Framed Moment Resisting Buildings Under Earthquake Loading

Abstract

Finite element analyses have been carried out to investigate the factors that contributed to failure of the welded connections in moment resisting steel framed building as involved in the Northridge earthquake. The particular structure chosen for analysis was a four-storey frame typical of ones in which a significant number of brittle fractures had been reported. Analyses have been carried out under both full dynamic earthquake and equivalent Uniform Building Code (UBC) static loading. Five different geometries of sub model were incorporated into the global model, these being the basic beam to column connection with no strengthening, the case with added continuity plates between the column flanges, the case with the beam flange width reduced (dog bone) and the cases with an additional haunch or additional cover plates. The results confirmed the general increase in severity of conditions towards the centre of the beam flange width. The stress distribution also confirmed that the position of the maximum stress coincided with the location of the fracture initiation. Connections strengthened with a haunch or cover plates were found to show a very good performance and much better than the dog bone and “pre-Northridge” connection. The material tensile properties also affect the crack tip severity at the crack tip. The absolute values of applied CTOD obtained from the FE analyses are entirely consistent with the occurrence of fracture in materials with fracture toughness levels of the order of 0.1 mm to 0.2 mm CTOD.