Seismic retrofit of concrete columns using supplemental beams

Column strengthening is one of the most common practices used in the seismic retrofit of structures. Techniques such as concrete and steel jacketing have been widely applied in existing concrete buildings to improve the shear strengths and ductility of columns. Unfortunately, only few methods were found effective in increasing the flexural strengths of columns since the bending moment induced by an earthquake tends to reach a maximum at either the top or bottom of the column, and the strengthening attempts could easily be obstructed by existing building components near these locations. As an alternative, the retrofit could also be accomplished by lowering the flexural demand of the columns. In this study, two different frame configurations, both with soft story at its base, were retrofitted with supplemental beams which connected the existing columns between the top and bottom of these columns. With additional resisting moments provided by these beams, the flexural demands of the frame columns were significantly reduced.