Cyclic Loading Test for Two-Story RC Moment Frames Retrofitted with Internal Steel Frames

Abstract

An internal steel frame–retrofitting method without diagonal braces was studied to strengthen existing reinforced-concrete (RC) moment frames with nonseismic details. For better constructability and structural capacity, a novel shear connection method was developed and verified by cyclic shear testing. To evaluate the seismic performance of retrofitted frames, three two-story moment frames with and without strengthening were tested under cyclic lateral loading. The test results showed that, despite partial composite action between RC and steel members, the proposed retrofit method significantly increased the stiffness and strength of the RC moment frame, achieving a satisfactory deformation capacity greater than 2% drift ratio. On the basis of the test results, the failure mechanism of the retrofitted frame was discussed, considering the shear connection behavior. The test strengths of the frame specimens were compared with the predictions based on a simple plastic mechanism. Further, the degree of partial composite action between the RC and steel members developed by shear connections was addressed to improve the strength predictions.