SHEAR PERFORMANCE OF POST-TENSIONED BULB-TEE GIRDERS

摘要

AASHTO specifications assume a reduction in the shear strength of a girder if a post-tensioning duct is present in the web. This reduction is accounted for by taking an ‘effective web width’ which is dependent on the duct diameter, the gross web thickness, and if the duct has been grouted. Currently, this reduction in shear strength has been calibrated using small scale compressive tests designed to model the compressive strut in the web. The scarcity of shear tests on post-tensioned girders is of concern because the literature contains one series of panel tests indicating that plastic post-tensioning ducts may cause up to a 30% reduction in compressive strength when compared to galvanized steel ducts of similar size. To better understand the shear behavior of post-tensioned girders, six post-tensioned bulb-tee girders were tested to failure in shear. These girders contained pre-tensioning in the bottom flange and a stressed post-tensioning tendon in the web. This paper examines existing code provisions for the reduction in shear strength due to the presence of a post-tensioning duct, and specifically the usefulness of panel testing to evaluate the shear strength of full scale girders.