Lateral Post-Tensioned Metal Strips for Strength and Ductility Enhancement of Concrete Columns: Investigation of Size and Shape Effects

Abstract eng:
Recent earthquakes in urban areas have repeatedly demonstrated the vulnerability of inadequately designed or constructed reinforced concrete structures, with deficient shear strength, low flexural ductility, insufficient lap splice length of longitudinal bars and poor seismic detailing. This paper presents the results of a study on the application of strapping technique for seismic upgrade of existing concrete columns. In this method, high strength metal strips are applied to externally confine concrete by means of standard strapping machines. The axial behavior of confined small-scale columns is investigated experimentally and analytically. Experimental program included axial compressive tests on some cylindrical and prismatic small-scale columns which were confined by metal strips. The effects of various parameters on strength and ductility of confined concrete were studied including compressive strength of concrete core, mechanical volumetric ratio of confining strips, number of strip layers wrapped around the specimens and details of strip joint. The effects of strength and ductility of confining strips on behavior of columns were also studied. Longitudinal and lateral 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 by metal strips. It was also observed that ductility of confining material plays the most important role in ductility enhancement of concrete. The active and passive confinements were compared by studying the influence of amount of active lateral pressure on the strength and ultimate strain of specimens. Nonlinear finite element models of tested columns were also made and analyzed by using various failure surfaces. The axial stress-strain behaviors of columns were obtained from these NLFEA and are compared to the experimental results.

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