Determination of tensile strength of GFRP bars using flexure tests

Abstract

This paper presents an experimental and theoretical study on finding tensile strength of glass fibre reinforced polymer (GFRP) reinforcing bars using flexure testing. The tensile strength of these bars is their primary property which must be determined before placing them in concrete members. Direct tensile testing of the bars is tedious and often not practical. In the presented work, the three-point flexure test is proposed as an alternative for direct tensile testing of GFRP bars. The flexure test is quick and easy to setup. The tensile strength in a flexure test is referred to as the modulus of rupture which for brittle materials, is generally higher than tensile strength determined in direct tensile tests. Research presented in this paper shows the correlation of the modulus of rupture to the tensile strength of the GFRP bars. The detail procedures for testing, determination of the cracking load in flexure test, and the subsequent procedures for calculations of tensile strength using the Weibull’s weakest link model are presented and discussed. The experimental part includes flexure tests on bars with diameters ranging from 8 mm to 32 mm, followed by calculations of rupture moduli and correlated tensile strengths. Bars with 8 mm, 13 mm and 16 mm diameters were also tested in direct tensile test and the results were used for comparisons with the correlated tensile strengths from flexure test. The results of this work confirm that flexure testing can provide easy and reliable method for obtaining tensile strength of GFRP reinforcing bars.