Bend Strength of FRP Stirrups: Comparison and Evaluation of Testing Methods

Abstract

This paper provides a comparison and evaluation of the current test methods used to determine the strength of fiber-reinforced polymer (FRP) bent bars/stirrups at the bend location (bend strength). The available methods depend on applying tensile forces through the straight portion of the bent bar/stirrup and keeping the bend zone restrained to generate a stress perpendicular to the bend direction in addition to the stress in the longitudinal direction. This could be achieved through the ACI 440.3R-04 B.12 test method for U-shaped bare FRP bars. Another possible method is the ACI 440.3R-04 B.5 which evaluates the bend strength of FRP stirrups by embedding them in two concrete blocks, which are pushed apart until the rupture of the FRP bent bars. Both methods were employed in testing FRP stirrups and bent bars and the bend strength was compared. The test results showed that the ACI 440.3R-04 B.12 test method consistently underestimates the bend strength of FRP stirrups. On the other hand, B.5 test method is more reliable and representative to the actual state of stresses in real concrete structural elements.