Tensile and Nondestructive Testing of FRP Bars

An exploratory study was carried out to support the development of standard test methods for fiber reinforced plastic (FRP) bars for use as concrete reinforcement. The principal objectives were to develop a simple, economical, and effective system to permit tensile loading of the bars in a universal test machine; to evaluate the influence of the free-length-to-bar-diameter ratio on the measured tensile strength; and to explore the potential of measuring the elastic modulus using available nondestructive test methods. A successful system for applying tensile load was developed. The ends of a bar were embedded in steel tubes using a high-strength gypsum cement mortar. The bars were loaded by gripping the tubes in the conventional wedge friction grips of a tensile testing machine. No statistically significant influence of the free-length-to-diameter ratio was observed for ratios varying between 40 and 70. However, large within-test variability of tensile strength was observed. Dynamic modulus of elasticity was determined using two stress-wave propagation methods: ultrasonic pulse velocity and resonant frequency. The dynamic values compared favorably with static values obtained from tensile stress-strain curves. Recommendations are provided for additional studies to support the development of standard test methods.