Title:
A Rational Approach toward Strain Efficiency Factor of Fiber-Reinforced Polymer-Wrapped Concrete Columns (with Appendix)
Author(s):
Pedram Sadeghian and Amir Fam
Publication:
Structural Journal
Volume:
111
Issue:
1
Appears on pages(s):
135-144
Keywords:
column; confinement; design guideline; fiber-reinforced polymer; model; strain efficiency factor; wrap
DOI:
10.14359/51686437
Date:
1/1/2014
Abstract:
This paper aims to provide a rational approach to the concept of circumferential strain efficiency factor of circular concrete columns wrapped with fiber-reinforced polymer (FRP) jackets. The variable ke reflects the reduction in the FRP hoop rupture strain observed in experiments, relative to the true rupture strain of the FRP material obtained from standard coupon tests or manufacturer datasheets. Currently, the ACI 440.2R-08 design guide uses a constant empirical ke factor of 0.55 for any column, regardless of geometric or mechanical properties. A rational approach is proposed to calculate ke. It employs a simplified Tsai-Wu interaction failure envelope of FRP laminates and acknowledges the biaxial state of stresses in the jacket. A large database of 454 circular concrete specimens wrapped with unidirectional FRP fabrics has been compiled from literature and subjected to rigorous statistical evaluations. While the proposed model performed quite similarly to the current ACI 440.2R-08 in that it did not lead to significant improvement in prediction, it has the advantage of offering analytical rational bases to the observed phenomenon. It also distinguishes between columns of different geometric and mechanical properties, leading to a variable ke of 0.05 to 0.98 with a 0.65 average, which is consistent with experimental observations and more logical than the constant value of 0.55.