Seismic Behavior of Renovated RC Frame after Column Removal and Retrofitting with Steel X-Bracing and Jacketing

Abstract

Structural renovation is an economic choice to expand the space of existing frame buildings. To this end, removing a column and strengthening the adjacent beams and columns are required. The renovation should not only redistribute gravity loads but also sustain horizontal seismic actions in seismic regions. Therefore, in this paper, the seismic behavior of a 2-story 2-bay RC frame and a corresponding renovated RC frame after a column removal at the ground story, retrofitted by steel X-bracing at the second story with strengthened beams and columns at the renovated story, is experimentally investigated under cyclic loading. The results demonstrate that the lateral stiffness and peak capacity of the renovated frame are substantially larger than those of the original frame, but the ultimate deformation capacity of the renovated frame is smaller and the energy-dissipation capacity is similar to the original frame. Moreover, macro-based finite-element numerical models of the renovated frame are built, validated, and used for parametric studies. The numerical results suggest that this renovation should be used with the axial compression ratio of side columns in the braced story not greater than 0.5. Finally, this renovation is likely to introduce a soft lower story for a planar 2-bay 2-story frame. Consequently, it is necessary to control the dimensions of strengthened columns, and it is suggested that the elastic lateral stiffness ratio of the renovated story (i.e., with a larger space) to the braced story should be greater than 0.5.