Novel Test Method for Ultimate Hoop Strain Characterization in FRP Jackets

The use of externally bonded fiber-reinforced polymer (FRP) laminates is an effective solution to increase the strength and deformability of reinforced concrete columns. A critical parameter in predicting the ultimate strength of FRP-confined concrete is the ultimate circumferential (i.e., hoop) strain. This paper presents the development of a novel test method aimed at providing reliable experimental measurements of the ultimate hoop strain in FRP circular jackets with different laminate thickness and diameter. The proposed approach simulates the lateral expansion of concrete columns subjected to axial loads by enlisting the property of water (which expands when it changes state of matter from liquid to solid) as a medium to apply an internal hydrostatic pressure on cylindrical glass FRP (GFRP) jacket specimens. The average ultimate hoop strain results from 54 cylindrical GFRP-jacket specimens with different diameter and laminate thickness clearly indicate a lower level of strain than those found in similar flat coupon specimens. These results indicate that the test method is safe, user-friendly, and generates reliable measurements of the hoop strain in GFRP circular laminates in a more representative fashion than direct tensile tests.