Study On Stress Increments Calculating Technique Of External Tendons Based On Energy Method

It is necessary and urgent to improve the bearing capacity of bridges by reinforcement or repairing because of their damage and aging by damnification, load-gain and speed-increase after their service. The external prestressing strengthening method has become the first-selected method in the bridges upper structure strengthen because of its numerous advantages. Thus the stress increment of the external tendons under the action of various loads type and size and its location has become an important research project. In this paper, the analysis and derivation of the stress increment of the external tendons under the action of live loads in various reinforced systems by energy method is advanced, and simple computing expressions of simply supported or continuous beam bridges are established. The results are compared with other theory turn-outs to ensure the reliability. The following are main points of research and conclusions: First, the computing expressions of external tendons with the frictional influence of deviators based on energy method of the following instance are established: linear, single deviator, double deviators of simply supported beams under the action of uniform load, one focus load, three point load, and linear, several deviators of continuous beams under the action of uniform load, one focus load on the whole span, and every span with a focus load. Second, the stress increment of external tendons in the first instance is also derived by force method with the consideration of frictional influence. Third, a stress increment computing program based on Maple9.5 and Java is programmed with the consideration of all above, and it's very friendly and easy to use. Fourth, the program is compared with force method by an example, and the energy method has been testified to be reliable to computing the stress increment of external tendons by the analysis of error and its source and disperse of the relative error, and the precision satisfy well with the demand of engineering design. Five,the frictional influence of deviators is determined by the nature of deviators themselves is promoted after the analysis of the frictional influence and its changes. The reasonable span-depth ratio of simply supported beam bridges neglect the second-order effect is 10, and the way to decline it and some advice to the strengthing design of external prestressing is also given after the analysis of the influence of external tendons efficient eccentricity changes to the stress increment.