Strength and Ductility of Concrete Members Confined by External Post-Tensioned Strips

This paper presents the results of experimental and analytical study on a new technique of seismic retrofitting of concrete columns. In this technique, standard strapping machines, which are used in the packaging industry, are used to posttension metal strips around concrete columns. The two ends of the strip are tightened in sealed clamps to maintain the pre-stress force in the strip. Experimental program included axial compressive tests on 30 cylindrical as well as 30 prismatic small-scale columns which were actively confined by pre-stressed metal strips. Longitudinal strain of concrete and strain in the strips were monitored. Test Results showed significant increase in strength and ductility of columns due to active confinement with metal strips. The effect of various parameters such as pretensioning force in the strip, number of strip layers wrapped around the specimens, details of strip joint and the mechanical volumetric ratio of confining strip on strength of concrete is studied. The observed stress-strain relations of columns with different levels of confinement are compared to those calculated based on Mander’s and Madas’s confinement models.