The behavior of short reinforced concrete columns strengthened using new confining technique under uniaxial vertical load is investigated. Steel jacket consists of two u-shape steel parts connected by four angles or plates back to back using high strength bolts of diameter 10 mm. External pretension load was applied using external high strength bolts of diameter 16 mm.
This study considered six parameters affecting the behavior of the strengthened columns as follows; thickness of steel sheets, connections type of steel jacket, value of pre-tension stresses, surface conditions of columns, value of applied vertical load during strengthening and geometry of concrete columns. The experimental program was achieved by testing fifteen short reinforced concrete columns. Eleven of them were square of dimensions 15x15 cm and 150 cm height. In addition, four circular columns of diameter 15 cm and 150 cm height were tested. The columns were strengthened using pre-tensioned steel jacket. These columns were divided into six series to accomplish the research purpose.
The experimental results were analyzed numerically and new design formula to predict the ultimate compressive strength of strengthened concrete columns using this technique was proposed.