Effects of gravity loads on seismic response of steel framed structures

Abstract

It is clear that current earthquake resistant design philosophy implicitly relies on the inelastic deformations to dissipate most of the input earthquake energy imparted into a building structure. Thus, most of building structures are expected to undergo inelastic deformations during a major earthquak. The amount and distribution of these inelastic deformations are substantially dependent on the relative strength of each structural member and dynamic characteristics of earthquake ground motions. In this thesis, seismic performance of ductile moment resisting frame structures designed based on the strong column-weak girder (SC-WG) criteria was investigated from the point of view of limiting ductility demands within desired levels. In addition, the effect of gravity load on seismic response of multistory framed structures, and its implications for earthquake resistant design were evaluated. Six earthquake ground motions were used as input ground motions which can be categorized into three groups accouding to their peak ground acceleration to peak ground velocity ratios. Even though overall ductility demand is reduced considerably due to the imposition of the SC-WG criteria, maximum of ductility demands are generally not affected by this criteria, which indicates that the localized concentration of ductility demands could not be controlled by the imposition of the SC-WG criteria. This is pronounced in the case of more ductile structures, more damaging earthquake ground motions. The localized maximum is generally induced in the lower floors in a structure, which implies that response modification factor specified in current design code practice is too large. The peak ground acceleration to peak ground velocity ratio can be a simple and efficient tool to distinguish damage potential of earthquake ground motions and it can be easily implemented in code practice. In the earlier stage of strong earthquakes, gravity load results in different bending moments at both ends...