Fragility and hazard analysis of a welded steel Moment Resisting Frame

With the move towards performance and consequence-based design and assessment of structures under seismic loading, the engineering community is becoming increasingly convinced that design practices need to be developed and checked using probabilistic methods. In this article, a methodology for the probabilistic assessment of low-rise steel buildings is presented and applied to a welded Moment Resisting Frame (MRF). In light of recent field experience for this form of construction, emphasis is given to the modeling of connections, particularly with respect to fracture characteristics. The seismic behavior of the building is assessed by means of nonlinear dynamic time history analyses, using a set of ground motions scaled according to spectral acceleration. Randomness related both to structural properties and earthquake excitation is explicitly taken into account. Fragility curves are generated using the Monte Carlo (MC) simulation method coupled with the Latin Hypercube Sampling (LHS) technique, and the failure probabilities are presented in terms of drift angles at different performance levels. Furthermore, evaluation of the seismic risk through a hazard analysis is presented in order to compare present results with previous pertinent studies. The study reveals that structures experiencing brittle connection fractures undergo large deformations, resulting in a low reliability in terms of achieving code-related performance requirements.