Seismic Strengthening of a Reinforced Concrete Frame Using Structural Steel Bracing

A two-thirds scale model of two bays and two stories of the exterior moment resisting frame of a reinforced concrete building was constructed. The test specimen, which had deep spandrel beams and short narrow columns, was strengthened with an exposed structural steel diagonal bracing scheme in order to increase the lateral capacity of the structure for earthquake loads. Construction and fabrication of the strengthening scheme are discussed.

The model was subjected to reversed, cyclic loads producing maximum interstory drift of 1.3 percent. The behavior of the model is discussed, with special emphasis on the load-drift relationships of the frame. The load carried by the wide flange braces and the forces carried in steel collector members are examined. Slip between the steel elements and the concrete frame was also measured. The importance of quality control in fabricaiton of epoxy-grouted bolts used to attach the steel collectors to the concrete frame and of welded connections is discussed.