Axial strengthening of RC columns by steel encasement with direct fastening connections

Abstract

Reinforced concrete (RC) columns are crucial structural members that sustain vertical loads. Their strength may deteriorate due to fire, corrosion of the reinforcements or design errors. In response, a new strengthening method that uses a steel encasement to increase the axial capacity and ductility of RC columns is proposed in this paper. This method is quick and convenient because direct fastening is used to assemble the system. Four columns including one control column and three strengthened columns have been tested to examine the reliability and effectiveness of the proposed method. Although direct fastening plays a crucial role in the structural performance of the proposed method, current design guidelines have not incorporated this new connection technique. Hence, extensive connection tests have been conducted to evaluate the key factors (e.g. fastener type, fastener spacing, protuberance, etc.) that affect the strength of the connections. New design equations are subsequently proposed based on the test results for shear connections that use direct fastening.