Regresar

The influence of the gravity system framing on the seismic performance of special steel moment frames

Abstract:

It is common practice to neglect the gravity framing system when seismic analysis is performed on building structures. Yet, past earthquakes such as the 1994 Northridge earthquake have demonstrated that the gravity system can act as an essential back up system when the main lateral resisting frame loses strength. This study focuses on the benefits of including the gravity system on the expected seismic performance of special steel moment frames (SMFs). The 2-, 4- and 8-story SMFs from the ATC 76-1 project are reanalyzed with and without the gravity system using the FEMA P-695 procedure. The gravity system is incorporated using partially restrained (PR) connections idealized using ASCE 41-13, a bilinear hysteresis model, and assuming that the strength of the PR connections is a percentage (0, 35, 50 and 70%) of the plastic capacity of the beam. Nonlinear dynamic (response history) analysis is used to compare the influence of the gravity system on the interstory drifts, residual displacements and base shear for the Maximum Considered (MCE) and Design Basis (DBE) Earthquakes, as well as the influence of the gravity system on the collapse margin ratio (CMR). The results indicated that the gravity system has a significant impact on drifts, residual displacements, and the probability of collapse, even when a minimum strength in the gravity framing connections is assumed.