Assessment and Validation of Prestress Loss Prediction Models Using Real-Time Prestress Loss Prediction Measurements

This study investigates prestress loss measured on precast, prestressed concrete bridge beams for a bridge in Oklahoma. The research examines the effects of including mild reinforcing steel in the bottom flange of precast concrete girder and the alternative prestressing pattern on the prestressing losses of pretensioned bridge girders. Using solar powered batteries, a structural moni¬toring system has been providing an ongoing stream of data since beam fabrication and will continue through the service life of the bridge. In addition to the measured data, the prestress losses were predicted at the girder midspan using five different methods for computing prestress loss. Data show that current equations overesti¬mate the concrete elastic modulus at early ages, leading to an underprediction of elastic shortening losses. Re¬sults show that prestress losses are reduced by incorpo¬rating a combination of fully tensioned top strand plus mild steel in the bottom flanges of the bridge girder.