Effect of Prestressing Level on the Time-Dependent Behavior of GFRP Prestressed Concrete Beams

Abstract

The use of fiber-reinforced polymers (FRPs) has become common in many civil engineering applications, including prestressing applications. Glass FRP (GFRP) bars are less expensive than carbon FRP (CFRP) bars, but they have high relaxation properties and are susceptible to creep rupture, which has limited their use in prestressed applications. A new generation of GFRP bars has been recently manufactured with improved mechanical properties that make them suitable for prestressed applications. Much research has been conducted on the short-term behavior of concrete members prestressed/reinforced with GFRP tendons, but relatively little is known about the long-term behavior of these members. This paper presents the results of testing 12 beams as part of an ongoing program to investigate the long-term behavior of GFRP prestressed concrete beams. Three beams were tested to failure in a monotonic four-point loading test, and nine beams were subjected to sustained loading for 300 days. The results showed that the sustained loading for 300 days did not affect the beams’ ultimate capacity, which suggests that creep or relaxation of the GFRP bars was not significant and did not affect the strength of the beams. It was concluded that the prestressing decreased the total and long-term midspan deflection and the total and the long-term concrete strains, mainly at the lower sustained load levels.