Strain efficiency of carbon fibre reinforced polymer confined RC columns

Abstract EN

Fibre reinforced polymer (FRP) composite materials in the form of FRP wraps provide one of the most effective means of confining existing reinforced concrete columns where the strength of these columns must be enhanced.

Such wraps are often formed in a wet layup process with the fibres being mainly in the hoop (lateral) direction.

Numerous studies have found that the nominal properties published by the manufacturer are different from the properties of materials obtained from testing the combination of CFRP and epoxy (i.e.

CFRP coupons) as tensile coupons.

Research studies have also shown that the CFRP wraps when applied to reinforced concrete columns have a lower ultimate hoop strain (and therefore a lower ultimate hoop stress) compared to the failure strain measured from direct tensile tests of the CFRP coupons.

This is the result of differences in the fabrication processes and the in-situ forms.

It was also noted that it is possible to repair or even restore the lost strength of columns damaged by elevated temperature, depending on the performance of the CFRP material.

This paper presents also the results of a study that reports and compares the ultimate tensile strains of CFRP obtained from flat coupon tensile tests and CFRP-confined concrete columns tests using an innovative digital image correlation (DIC) technique.

It was found that the CFRP lateral rupture strains in CFRP-confined RC columns are reduced below the ultimate tensile strains from flat coupon tests.

Based on comparisons of these test results, for all columns wrapped with 1 or 2 CFRP layers, the strain efficiency was found to be in the range of 0.54 to 0.9 or 0.54 to 0.94 respectively.