DETERMINATION OF CABLE FACTOR FOR EXTERNALLY DEVIATED POLYETHYLENE RECTANGULAR TENDON BUNDLES

Abstract

In recent years, a number of new technologies have been developed and applied to the design and construction of Pre-stressed Concrete Bridges, in order to improve not only the structural properties but also the long-term durability, which has become one of the most important problems in bridge structures. One of such innovative methods is external post-tensioning technology. The present study deals with external post-tensioning of polyethylene deviated tendon bundles, including its background. Polyethylene ducts serve as corrosion protection hulls for tendons and is necessary to ensure durability of the tendon and tensioned structure. The aim of the present study is to develop a simplified approach to determine the maximum cable factors, in quick time, for polyethylene rectangular deviated tendon bundles. Previously simplified methods/approaches were developed to estimate the maximum cable factor for circular tendon bundles. Cable factor of tendon bundles is a parameter that quantifies the pressure of the pre-stressing steel on polyethylene ducts. The knowledge of the maximum pressure between strands to the duct is important to estimate the imprints of pre-stressing steel in polyethylene ducts of bondless tendons. The higher the pressure the higher is the imprints in polyethylene ducts or the higher is the danger of fatigue fracture due to fretting corrosion. It is important to know the maximum cable factors for different duct shapes in order to predict their durability. The duct shape with low cable factor value is more durable with fewer imprints in it. In a rectangular duct, the maximum cable factors are determined exactly by using two dimensional truss analysis for several stable configurations of prestressing steel with the help of software package called `Stab2d'. Microsoft Excel is used as tool to know the stable configuration of prestressing steel. The final equation is expressed as an empirical formula in terms of the number of prestressing steel elements, dimensional properties of the prestressing steel elements and the duct. The simplified approach is developed by using trial and error method.