Effect of fracture on the reliability of a moment resisting frame under earthquake loading

The fractures observed following the Northridge earthquake in welded beam-to-column connections have been linked to a number of different material and manufacturing parameters such as fracture toughness, crack size and yield strength all of which are in general random. In a previous study of a simple sway frame, where randomness of the above variables was considered, fracture of the connections was found to result in the reduction of the frame’s lateral stiffness with an accompanying reduction of the natural frequency of the frame. In this paper, the linear elastic behaviour of a multi degree-of-freedom frame under earthquake loading is examined probabilistically as an extension of the previous investigation. The results demonstrate that most of the connections fail early on in the seismic event and that fracture probabilities are heavily dependant on the storey on which they are located. Removal of the backing bar is found to reduce the failure probability of the connection without, however, being able to prevent fracture when used as a sole measure