Shear Deficiency in Reinforced Concrete Continuous Beams Strengthened with External Tendons

Abstract

External tendons are a relatively simple means of strengthening reinforced concrete beams in flexure. The increase in flexural capacity of the beams, however, is not always accompanied by an equivalent increase in shear capacity. With this in mind, this paper investigates the shear deficiency in continuous beams strengthened with external tendons. Tests conducted on 4 two-span continuous beams showed that the strengthened beam could fail in shear, especially at the high-shear region near the interior support, due to the limited increase in shear capacity. An analytical study is presented to explain and further examine the phenomenon in beams strengthened with 8 variations of tendon profiles. Two practical profiles, straight and draped, were then selected for a parametric study conducted to establish design charts to check the shear capacity of the strengthened beams. In general, straight tendon profiles, although attractive due to their simplicity, lead to relatively high shear forces in the strengthened beams. Adopting a draped or parabolic tendon profile with large eccentricity would reduce shear forces, thereby minimizing the risk of shear failure in the strengthened beams.