Direct Method for Strengthening Continuous RC Beams with External Tendons

Abstract

A simple direct method to determine the external tendon configuration required for a desired increase in load-carrying capacity of continuous beams is presented in this paper. The tendon layout is selected based on the concept of equivalent loads, but need not be concordant. By considering the collapse mechanism of the beam, the increase in load-carrying capacity can be related directly to the tendon force. The paper shows that the increase in load-carrying capacity is partly due to an increase in the force in the compression zone that arises from the horizontal component of the prestressing force, and partly due to the upward components of the prestressing force. The method was verified with a test program on six two-span continuous beams, in which the tendon profile and loading pattern were varied. Comparison of the test results and those available in the literature showed that the proposed method gives a reasonably conservative design. A simplified method based on the direct balancing of increased loads is also proposed in the paper.