Behaviour Of RC Columns Of Different Shapes Confined With GFRP Composite Wrap

Abstract

In recent years, the use of externally bonded ber-reinforced polymers (FRP) has become increasingly popular for civil infrastructure applications, including wrapping of Reinforced Concrete(RC) columns. The Glass ber reinforced polymer has signif- icantly enhanced the strength and ductility of concrete by forming perfect adhesive bond between concrete and the wrap as reported in literature. Most of the available studies on the behavior of FRP con ned RC columns have concentrated on circular shaped columns, while relatively few studies have addressed rectangular and square columns. This is partly because the rectangular and square sections are not uniformly con ned and the compressive pressure is unevenly distributed. Present experimental investigation mainly emphasis on e ectiveness of external GFRP strengthening for di erent shape RC Columns having same cross sectional area. Ex- perimental investigation has covered a wide range of cross-sectional dimension ratios for RC columns. Four aspect ratios a/b, where a and b are, respectively, the longer and shorter sides of the cross-section have been studied. a/b equals to 1.0, 1.5, 2.0, 2.5 and circular columns. Experimental work has been conducted on total 25 RC columns.15 columns are control and the rest 10 columns with one layer of GFRP wrap. Axial load has been applied with hydraulic jack. All columns are 1 meter in length and GFRP wrapped specimens have 20mm of corner radius. Columns are designed using IS:456:2000 provisions. Design of GFRP wrapping is evaluated using ACI 440.2R.08 provisions. All the test specimens are loaded to fail in axial com- pression and strain of the specimens in the axial and transverse directions have been investigated. Testing of columns are made to investigates its axial compressive strength, axial strain and lateral strain in order to understand the e ect of di erent parameters on the be- havior of RC columns. Failure modes for all control and GFRP wrapped columns have been observed and discussed in detail. Based on above parameters comparison has been made amongst GRFP wrapped and control columns, cross sectional e ect for GFRP wrapped and control columns has been studied. The test results clearly demonstrate that for rectangular columns the axial load car- rying capacity increases with decrease in aspect ratio. In case of square and circular columns axial load carrying capacity increases further because of geometric stabil- ity.For Control columns the cross sectional variation do not create large impact on strength and ductility whereas for GFRP wrapped columns the cross sectional vari- ation has major impact on strength and ductility.GFRP wrapped circular column undergoes higher axial deformation as compared to that of square and rectangular columns. Based on stress strain behavior it has been observed that strength gains from FRP con nement is superior for circular section. Square and rectangular-section columns are found to experience lesser increase in strength and ductility as compare to that of circular section. This is because of the distribution of lateral con fining pressure in rectangular sections varies from a maximum at the corners to a minimum in between, in contrast for circular section which provides even con fining pressure in order to achieve full con finement.