New Buckling-Restrained Brace for Seismically Deficient Reinforced Concrete Frames

Abstract

An experimental investigation was conducted to assess the performance of a new buckling-restrained brace (BRB) system for retrofitting seismically deficient reinforced concrete frames. The BRB consists of a ductile inner steel core bar designed to yield in tension and compression without buckling while controlling the response to seismic forces. The core bar is contained within a tubular steel section, which in turn is housed in a larger tubular steel section infilled with mortar, providing lateral restraint against buckling. Self-consolidating mortar is used as filler material between the two tubular sections to increase the buckling resistance. The inner core bar is connected to innovative end units that allow extension and contraction during tension-compression cycles while providing lateral restraint against buckling. The new BRB system has been verified experimentally using two large-scale reinforced concrete frames, one of which was tested as a reference nonretrofitted frame and then repaired and retested three more times after BRB retrofits, while the other was retrofitted and tested, forming the fourth retrofitted frame test. Tests demonstrated substantial increases in the lateral load and energy dissipation capacities of retrofitted frames with satisfactory drift control. Three different types of steel bars with different strength and elongation characteristics were considered. Among the three, stainless steel provided the best strength, stiffness, and ductility enhancements.