Experimental investigation of the effects of concrete strength and axial load ratio on the performances of CFRP-wrapped and externally collared RC short columns

Abstract

In this study, the seismic performances of 18 full-scale reinforced concrete short columns were evaluated under cyclic quasi-static loading. Concrete strength and axial load ratio were considered as parameters in performance tests of the columns. Based on these parameters, there were used six reference columns without any strengthening application. CFRP wrap and steel collar strengthening were applied to the other twelve columns. Longitudinal reinforcements of all test columns were the same. In order to demonstrate the efficiency of the strengthening applications more clearly, Ø10/100 stirrups were used in reference columns, while Ø10/150 stirrups were used in strengthened columns. The effectiveness of the applied strengthening methods based on changes in the concrete strength and axial load ratio, which are the two important parameters affecting the behaviour of RC short columns, were investigated. Reference columns were called as ideal columns with well transverse reinforcement detail. The performances of the strengthened columns were compared with ideal reference columns. The performances of the columns were examined in terms of crack development, hysteretic behaviour, strength, ductility, and energy dissipation. Increasing the concrete strength and axial load ratio increased the strength of the columns and directed the columns toward brittle behaviour. The columns were governed by a flexure-shear failure mode and the strengthening solutions herein were adopted aim at avoiding the shear interaction in order to achieve the ductile behaviour of the members. CFRP wrap and Collar strengthening applications significantly improved the performance of the columns. CFRP wrap and Collar strengthening increased the mean ductility values of the columns by 38.8%-108.6% and 61.7% −100.8%, respectively, compared to Reference columns. This resulted in an increase in energy dissipation values of up to 347.2% in the CFRP-wrapped columns and 379.3% in the collared columns.