Effects of bay spacing on collapse safety of steel moment resisting frames

To establish the relationship between the building seismic response and the damage level experienced by individual structural members at the target performance levels is challenging. Thus, the main focus of this study is to underline the effect of bay spacing and that of ground motion type expressed by the Trifunac duration on the seismic performance of steel moment resisting frame (MRF) buildings analyzed from yielding to failure. The selected case study is a 10-storey moderately ductile MRF building located in Vancouver, B.C., Canada, on site class C. Three variants of the building with different bay spacing, L1 are considered (e.g. L1= 6.0 m, 7.5 m and 9.0 m), while the floor area remains constant. All buildings are designed according to the current building code of Canada and the Steel Design standard. The numerical model is developed in OpenSees. A proposed fiber-based hinge damage accumulation model that is able to replicate the strength and stiffness degradation of I-shaped beams of steel MRFs is considered. This damage accumulation model was developed to replicate the effect of low-cycle fatigue encountered at the location of plastic hinges of MRF’s beams and was calibrated against experimental test results from the literature. All prototype buildings are subjected to crustal and subduction ground motions. A proxy for subduction records were those from the Mw9 Tohoku event. The selected engineering demand parameters are interstorey drift and residual interstorey drift. Results obtained from the IDA curves show that the maximum interstorey drift corresponding to significant damage of an MRF’s beam is strongly related to the Trifunac duration of ground motions and slightly dependent on bay spacing. Conversely, the maximum interstorey drift associated to a residual interstorey drift of 1.0% hs is almost independent of the bay spacing and Trifunac duration. Further, all studied buildings are able to pass the collapse safety acceptance criteria under both sets of ground motions, while the bay spacing is not a sensitive parameter. However, precaution should be given when designing buildings in high risk seismic zones prone to subduction earthquake.