Shear Deficiency in Reinforced Concrete Continuous Beams Strengthened with External Tendons

Abstract

External tendons provide a relatively simple means to strengthen 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. In this study, the shear deficiency in continuous beams strengthened with external tendons was investigated. Tests carried out on four two-span continuous beams demonstrated that the strengthened beam could fail in shear, particularly 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 eight variations of tendon profiles. Two practical profiles, straight and draped, were then selected for a parametric study that was carried out to establish design charts for the purpose of checking the shear capacity of the strengthened beams. In general, straight tendon proflies, 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 force, thereby minimizing the risk of shear failure in the strengthened beams.