Fiber-Reinforced Polymer Jacketed and Shape-Modified Compression Members: I-Experimental Behavior

Fiber-reinforced polymer (FRP) composites are effective for strengthening circular concrete columns. In the case of square and rectangular columns, FRP confinement for axial strength is less effective due to the shape of the section; however, axial strain capacity can still be increased. Shape modification can eliminate column corners and flat sides, thereby improving the axial strength capacity of FRP-confined square and rectangular concrete columns. In this paper, shape modification of square and rectangular concrete compression members confined using post-tensioned FRP composite shells with expansive cement concrete is investigated; confinement effectiveness is compared with square and rectangular compression members confined with bonded FRP jackets. The experimental results demonstrate the effectiveness of shape modification with expansive cement concrete using chemical post-tensioning of the FRP shell. Compared with specimens confined with bonded FRP jackets without shape modification, shape-modified square compression members with post-tensioned FRP shells achieved a significant increase in axial strength, axial compressive strain, and energy absorption; shape-modified rectangular compression members with aspect ratios of 2:1 and 3:1 achieved moderate increases in axial strength. In addition, confinement concepts for different FRP confinement types, including bonded FRP composite jackets and post-tensioned FRP composite shells are introduced for developing an analytical stress-strain confinement model. [PUBLICATION ABSTRACT]