Experimental tests on full-scale RC unretrofitted frame and retrofitted with buckling restrained braces

The results of experimental tests carried out on reinforced concrete (RC) full-scale 2-storey 2-bays framed buildings are presented. The unretrofitted frame was designed for gravity loads only and without seismic details; such frame was assumed as a benchmark system in this study. A similar RC frame was retrofitted with buckling-restrained braces (BRBs). The earthquake structural performance of both prototypes was investigated experimentally using displacement-controlled pushover static and cyclic lateral loads. Modal response properties of the prototypes were also determined before and after the occurrence of structural damage. The results of the dynamic response analyses were utilized to assess the existing design rules for the estimation of the elastic and inelastic period of vibrations. Similarly, the values of equivalent damping were compared with code-base relationships. It was found that the existing formulations need major revisions when they are used to predict the structural response of as-built RC framed buildings. The equivalent damping ratio xi eq was augmented by more than 50% when the BRBs was employed as bracing system. For the retrofitted frame, the overstrength O and the ductility mu are 1.6 and 4.1, respectively; the estimated R-factor is 6.5. The use of BRBs is thus a viable means to enhance efficiently the lateral stiffness and strength, the energy absorption and dissipation capacity of the existing RC substandard frame buildings. The foundation systems and the existing members of the superstructure are generally not overstressed as the seismic demand imposed on them can be controlled by the axial stiffness and the yielding force of the BRBs