Retrofit and Repair of Reinforced Concrete Columns with Active Confinement

Abstract

There are too many reinforced concrete (RC) columns built before the 1970s without sufficient transverse reinforcement. Past earthquakes have demonstrated the vulnerability of such columns and the need for their retrofit. Popular retrofit techniques such as steel and fibre-reinforced-polymer jackets have been proven to be effective in increasing shear strength and improving drift capacity of RC columns. Nevertheless, those techniques have been also reported as labour-intensive with involved installation procedures. An alternative that is reliable and easy to apply is needed especially for developing countries and mass retrofit of a large inventory of structures. Ease of installation is also key when it comes to emergency repairs after strong ground motion. After a strong earthquake, the repair of a building often needs to be done quickly to ensure rapid restoration of the safety of its occupants and neighbours. An easy-to-design and easy-to-implement retrofit technique involving post-tensioned external clamps fastened around the column is examined here. The post-tensioned clamps consist of four corner brackets, made with pairs of steel angles, and high-strength threaded rods connecting the brackets. The confining lateral pressure provided by the clamps is expected to help delay the spalling and crushing of concrete as well as the formation of inclined shear cracks. Results of tests on full-scale RC columns furnished with the proposed clamps suggest the clamps can be effective in increasing column shear strength and drift capacity.