Geometrical Nonlinearity and Length of External Tendons

External prestressing is achieving widespread success. However, some practical rules are not yet well established. An important question deals with the maximum distance between anchorages and deviators. Due to the absence of contact between the tendons and the concrete beam (other than at the anchorages and deviators), the change in the deformed shape of the concrete beam involves changes in the position of the tendons with respect to the center of gravity of the concrete beam (second-order effects), so that their influence on the equilibrium conditions of the beam near collapse can be significant. This paper suggests a simple equation that determines the maximum clear length of the tendons small enough not to take into account the second-order effects in common practice. A parametric analysis (made by means of a numerical method previously verified by comparisons with experimental test results) verifies the reliability of the simple equation suggested.