Experimental Study of 2-Span Continuous Beams with 2400 MPa Unbonded Tendons

Abstract

Recently, strands with strengths of 2160 MPa and 2400 MPa were developed in Korea in 2008 and 2011, respectively, and newly recognized in Korean Standard (KS) D 7002. In spite of the potential benefits of using 2400 MPa strands in prestressed concrete structures, there have been very limited researches and verifications that assure the feasibility and application of the newly developed very high-strength strands. Accordingly, experiments on the flexural behavior of seven 2-span unbonded post-tensioned beams were conducted under 4-point static loading condition to verify the feasibility of using 2400 MPa strands in a manner consistent with the application of 1860 MPa strands in post-tensioned beam members. The variables considered in the test included the strand type, the height of tendon profile, and the amount of prestress. Ordinary high-strength strands were applied to three of the specimens and very high-strength strands were applied to the other four specimens. The specimens with the very high-strength strands exhibited satisfactory performance developing the equivalent prestress increment, member strength, and ductility while having a bit earlier and wider plastic hinge length at ultimate. Test results also demonstrated that secondary moment increased greatly from the beginning of the loading stage while the internal moment at interior support became constant soon after the first hinge occurred at negative moment region. According to the derived results, the conventional methodology of calculating secondary moment tended to quite underestimate the value at the nonlinear and ultimate behavioral range.