CONTRIBUTION OF GRAVITY FRAMES TO SEISMIC PERFORMANCE OF STEEL MOMENT RESISTING FRAMES

Abstract

Traditionally, lateral stiffness and strength of the gravity frames in steel buildings are neglected in structural analysis. Duringthe past earthquakes, such as Northridge, USA, 1994 and Kobe, Japan, 1995, unexpected failures were detected at beam-tocolumn connections of steel moment resisting frames (MRFs). In the aftermath of these earthquakes, extensive research hasbeen carried out to reveal the causes of these failures. Based on the detailed observations, it is likely that the reserve capacityprovided by the gravity frames prevented the highly damaged steel buildings from collapsing, since majority of the momentresisting connections failed prematurely during the Northridge earthquake (1994). Even though the influence of gravity frames(GFs) on structural behavior can be substantial, little attention is paid to evaluate its impact on structural response. With thispaper, the contribution of interior GFs in seismic performance of special moment resisting steel frames (SMRFs) is evaluated.For this purpose, 4- and 9-story SMRFs were designed in accordance with the requirements of Draft Turkish Seismic Code(2016). The frames are, then, subjected to incremental dynamic analysis. To evaluate the contribution of the interior GFs onthe overall seismic performance of structural system, inelastic behavior of shear tab (simple) connections at beam-to-gravityonly columns were idealized as semi-rigid joints. A general purpose structural analysis software, ETABS, is utilized for theanalyses. The results of the study are presented in terms of story drifts, base shear vs. roof displacement.