Shear Behavior of Externally Prestressed Beams with Carbon Fiber-Reinforced Polymer Tendons

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Title: Shear Behavior of Externally Prestressed Beams with Carbon Fiber-Reinforced Polymer Tendons

Author(s): Stanley Tsz Kit Ng and Khaled Soudki

Publication: Structural Journal

Volume: 107

Issue: 4

Appears on pages(s): 443-450

Keywords: external prestressing; fiber-reinforced polymer tendons; posttensioning; rods; shear

Date: 7/1/2010

Abstract:
Shear failure in concrete beams is sudden and catastrophic. Unfortunately, research on the effects of external unbounded prestressing on the shear behavior of concrete beams is scarce, especially for beams prestressed with carbon fiber-reinforced polymer (CFRP) rods. This study attempts to improve the understanding of the shear behavior of externally prestressed concrete beams by testing a total of 15 specimens, including three span-depth ratios (a/d), two shear reinforcement setups, and three external prestressing levels to contrast the shear behavior of concrete beams with the shear behavior of concrete beams prestressed externally with CFRP rods. The test results demonstrated that the development of arch and beam action in prestressed beams does not conform to the traditional a/d of 2.5. Instead, the prestressing force reduced the effective a/d and significantly strengthened the concrete beams in shear. This significant shear enhancement cannot be predicted with the current shear design equations in ACI 318-08. As a result, a better prediction method for the shear capacity of concrete beams externally prestressed with unbounded CFRP rods is needed before this shear strengthening technique can be widely used.