Abstract
A large-scale model of a nonductile concrete frame with columns susceptible to shear failure was retrofitted with two strengthening schemes. In the first scheme, full-height concrete piers were added to the original columns. Tests showed that the strengthened column section behaved monolithically and the failure mode was shifted to hinging of the spandrel beams. Large increases in frame strength and stiffness were also realized. In the second scheme, a steel X-bracing system was attached to the frame's exterior face. Lateral capacity was governed by yielding and buckling of the braces. The system exhibited substantially increased frame stiffness and strength. Both systems were quite constructable and relied extensively on epoxy-grouted dowels. The pier system required a lower level of construction skill but was somewhat more labor intensive. The bracing system required a higher level of construction skill due to local variations in fit-up requirements and the need for field welding.
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