Title:
Influence of Concrete Strength on Confinement Effectiveness of Fiber-Reinforced Polymer Circular Jackets
Author(s):
Siddhwartha Mandal, Andrew Hoskin, and Amir Fam
Publication:
Structural Journal
Volume:
102
Issue:
3
Appears on pages(s):
383-392
Keywords:
concrete; confinement; fibers; high-strength concrete; polymer; strain; stress
DOI:
10.14359/14409
Date:
5/1/2005
Abstract:
Confinement effectiveness of circular fiber-reinforced polymer (FRP) jackets was studied for axial members with unconfined concrete strength fc¢ ranging from 26 to 81 MPa. The study included two large-scale concrete-filled FRP tubes and 59 plain and FRP-wrapped concrete cylinders. The cylinders were wrapped with one layer of glass FRP (GFRP) sheet, two layers of GFRP sheet, or one layer of carbon FRP (CFRP) sheet. Specimens were tested to failure under axial compression. The study showed that FRP tubes and wraps provide a substantial increase in strength and ductility for low- to medium-strength concrete, which shows a bilinear stress-strain response with strain hardening. For high-strength concrete, however, enhancement in strength is very limited, with hardly any improvement in ductility. The response in this case shows a steep postpeak strain softening. Several confinement models were examined and successfully captured a trend of reduction in confinement effectiveness with the increase of fc¢. All of the models, however, failed to capture the stress-strain behavior of confined high-strength concrete and grossly overestimated its ultimate axial strain. A model is presented to account for the effect of fc¢on ultimate strength and strain of FRP-confined concrete. It is recommended to use lower-strength concrete in filling FRP tubes used as axial members.