Seismic Strengthening of a Reinforced Concrete Frame Using Reinforced Concrete Piers

A two-third scale model of two bays and two stories of an exterior moment resisting frame of a reinforced concrete building was constructed. The prototype exterior frame had been deep spandrel beams which resulted in short clear spans in the slender columns. The existing frame was deficient in seismic resistance in terms of ductility and strength. The column shear capacity was relatively low. The frame was retrofitted with reinforced concrete piers around each of the columns to increase the column capacities and shift the mode of failure of the frame from shear in the columns to flexural hinging in the beams. Construction of the frame and reinforced concrete piers is discussed.

The strengthened frame was subjected to reversed, cyclic loads, with a maximum interstory drift of 0.5%, until flexural hinging of the beams occurred. Behavior of the strengthened frame is discussed; with special emphasis on the ductility, lateral strength, and lateral stiffness of the frame. Pier behavior and interaction with the original frame are also discussed. A discussion of nominal capacities calculated using ACI 318-83 is included.