Field Instrumentation of a Post-Tensioned Segmental Box Girder Bridge

This article presents selected results from a comprehensive field study of a post-tensioned segmental box girder bridge. Three spans of the San Antonio "Y" Project, Phase IIC, were heavily instrumented to study many aspects of bridge behavior during construction, under static live loads and with time. Special instrumentation systems to measure post-tensioning forces and overall span deflections were developed for the project and are described herein. Brief results are presented in three areas: prestress losses in external tendons due to friction across deviators, diffusion of post-tensioning forces from the anchors into the cross-section, and measured vertical thermal gradients and their effects.