THE SIDE-EFFECTS OF RETROFITTING RC FRAMES WITH STEEL X-BRACES

In this paper, the side-effects of retrofitting an existing RC frame with X-braces on the global performance of the retrofitted frames are investigated. Extensive nonlinear time history analyses of the frame-brace system have been conducted to study the changes in load paths and demand levels of the RC frames. For this purpose, 20 representing earthquake records have been utilised and applied to three different frame-brace systems, representing low-rise, medium-rise and high-rise frames. It is found that in mid-rise to high-rise buildings, the effectiveness of the bracing system in reducing the maximum lateral displacements reduces as the number of storeys increases. Also, as the height of the frame is increased, the demand base shear after retrofitting is increased. However, the rate of increase in base shear is reduced as the height of frame increases. As a general conclusion, it is noted that; retrofitting low-rise RC frames with steel X bracing is beneficial to the frame in almost every aspect; however, for mid to high-rise frames, the adverse effects of retrofitting, particularly on columns attached to the bracing system, are noticeable and should be taken into consideration.

Keywords:

Seismic retrofitting , Steel X-bracing , RC frame , RC joints , Seismic response