Seismic behavior of substandard extended rectangular RC columns jacketed with sprayed GFRM

Abstract

In earthquake prone areas, columns of many relatively old RC (reinforced concrete) structures do not comply with the current seismic design codes, particularly in developing countries. Low concrete strength, improper seismic detailing of transverse reinforcement and high axial stresses on the columns are common problems causing lack of sufficient ductility under seismic forces. External jacketing of substandard columns by spraying GFRM (glass fiber reinforced mortar) is a new, practical and feasible method to overcome these deficiencies, particularly for the cases where access to the structural members is limited. In this study, the effects of cross-sectional aspect ratio (h/b) of columns on effectiveness of external jacketing with sprayed GFRM are investigated experimentally. For this purpose, four full scale RC columns were tested under constant axial load (0.35f'cAg) and cyclic lateral displacement reversals before and after seismic retrofit with sprayed GFRM jacket. The cross-sectional aspect ratios of two columns were 2.0, whereas the cross-sectional aspect ratio was 4.0 for the other two columns. The structural responses of the columns are discussed through hysteretic and envelope load-displacement curves. The test results show that sprayed GFRM jacketing improves lateral ductility of the substandard columns significantly. It is also shown that the method is effective for the columns with high cross-sectional aspect ratios.