BEHAVIOR OF RC FRAME STRENGTHENED USING STRUCTURAL-STEEL BRACING

A retrofit strengthening technique for improving the seismic behavior of a nonductile reinforced concrete (RC) frame was investigated experimentally. The original frame contained deep, stiff spandrel beams and short, flexible columns that were susceptible to shear failure under lateral loads. The strengthening technique used a steel X-bracing system attached to the exterior of the frame using epoxy-grouted dowels. A two-thirds-scale frame model consisting of two bays and three levels was subjected to statically applied cyclic lateral load. Test results indicated substantial increases in both lateral stiffness and strength. The lateral capacity of the strengthened frame was governed by brace buckling and eventual connection failures and column shear failures. Measured brace buckling loads agreed well with predicted capacities assuming fixed (K = 0.5) connections, and dowel performance was excellent. Bracing-system elements attached to the side faces of the concrete columns also substantially increased column shear capacities.