Shear behavior of dry and epoxied joints in precast concrete segmental box girder bridges under direct shear loading

摘要

Precast segmental concrete bridge construction involves multiple concrete elements joint together by post-tensioning. The joints that represent locations of discontinuity are the prominent factors affecting the overall behavior of segmental bridges. In this study, a series of single cell, box shaped specimens, with a geometry closely resembling the keyed joint of actual segments, were subjected to direct shear test. The joints are flat and keyed, dry and epoxied, having web and flange keys. Tests were carried out to assess the shear capacity, shear behavior, crack propagation and deformations of different kinds of joints. It was found that epoxy can minimize joint imperfections and letting shear stresses to be distributed uniformly. Perfect joint closure and shear transfer was observed for epoxied joint when fully posttensioned immediately. Shear capacity of epoxied joints had consistently higher than dry joints by 25-28%; while, the failure of the epoxied joints was found to be sudden and brittle. The average shear transfer of a single key is higher for specimens with less number of keys. Four flange shear keys are capable to increase shear capacity by 14% and the elastic stiffness of the joints by 73%. It was determined that, the AASHTO design criterion can conservatively predict shear capacity of all kinds of epoxied joints and flat dry joints; however, it is greatly overestimating the shear capacity of multi-key dry joints.