The existing commercially available CFRP stirrups with circular section have inherent weakness of premature failure due to fiber kinks and stress concentration at bend. In order to overcome this weakness, a novel stirrup was developed with CFRP chord in the shape of spiral (CSCS). Results from B.5 tests have shown that CSCS were superior to CFRP stirrups with circular section in resisting stresses at bend.

Complete closed-type carbon fiber reinforced polymer stirrups with a rectangular section (CFRPRS) were developed and tested in this research. The CFRPRS was intended to relieve stress concentration and to reduce the number of kinked fibers at the bent portion. A total of 16 B.5 specimens were tested regarding the bend strength of the CFRPRS and CFRP stirrups with circular section. Test results showed that CFRPRS improved the bend strength compared to its counterpart of conventional CFRP stirrups having a circular section, with the larger ratio of width to thickness being more effective for the same sectional area. The best correlation between the test results and predictions on CFRPRS bend strength was observed when the section of CFRPRS was modeled as a collection of transformed individual circular sections.