Experimental Determination of Transfer Length in Pre-stressed Concrete Using 3D-DIC

Abstract

Since pre-stressed concrete structures have much higher tensile load carrying capacity, they are being used more often in the construction of highway bridges and railroad ties. Increased load-carrying capacity is achieved through transfer of the tensile loading in the reinforcement tendons into compressive stress in the concrete. The distance over which the pre-stress in the tendons is fully transferred to compressive stress in the concrete is known as the ‘transfer length’. Since local tensile stresses in concrete are problematic, the transfer length is an important parameter in the design of pre-stressed concrete components to ensure that the concrete remains in compression when subjected to in-service loads. In this work, the authors developed a stereo-vision digital image correlation system for both laboratory and industrial environments to measure the relatively small surface strains that are imposed on the concrete during release of pre-tensioned reinforcement tendons. In comparison to the current approach that requires physically embedding of Whittemore gages in the concrete beam during the curing process, results for these studies show that the non-contacting optical measurement method is much less time-consuming, more accurate and more consistent, while requiring no physical placement of gages.