The influence of gravity column continuity on the seismic performance of special steel moment frame structures

• The influence of gravity columns on seismic performance is investigated.
• Gravity columns delay collapse of special moment frame structures.
• Gravity columns reduce the probability of developing soft story mechanisms..
• Splice location and strength are important parameters in performance enhancements attributed to gravity columns.
• Nonlinear static and nonlinear dynamic analysis may be simplified by lumping gravity columns into a single continuous elastic column.

This paper investigates the influence of the stiffness and strength of gravity columns on the collapse performance of buildings that utilize steel special moment frames as the main seismic lateral load resisting system. The research centers on the development of a simple lumped column approach, where all the gravity columns are combined into one elastic, continuous, and pinned-base element. Once this approach was validated, 2-, 4- and 8-story buildings that were originally analyzed without the influence of gravity columns in the ATC 76-1 project were re-analyzed including gravity columns. The FEMA P-695 methodology was used to assess the collapse performance. The effect of having a different number of gravity columns and different column sections was modeled by varying the moment of inertia of the lumped gravity column. The results show that the gravity columns have a profound influence on the collapse performance of buildings, especially for taller structures. Moreover, it was found that the correlation between the results of the nonlinear static analyses and the nonlinear dynamic analysis, based on collapse evaluation, provides insight into the choice of an optimal section for the lumped column. This means, in turn, that the designer can determine the number and the size of gravity columns that are required to significantly improve the building's collapse performance.