Improving Predictions for Camber in Precast, Prestressed Concrete Bridge Girders

Abstract

Most of the modern medium-span bridges in the United States are constructed with precast, prestressed concrete girders. An accurate estimate of girder camber is important for all parties involved in the precast concrete industry for several reasons. The most important reason is that achieving vertical alignment, and casting the deck, becomes much more difficult if the cambers of two adjacent girders in the bridge are not the same, since the girders are generally too large to make the correction by brute force. In addition, any uncertainty of the estimated camber in the precast, prestressed concrete girders can lead to construction delays and can increase material and labor costs. However, the prediction and control of camber over time is difficult, because camber varies with many parameters, such as the concrete properties, curing methods, and temperature variations. The goal of this research is to improve the methods to predict camber in precast, prestressed concrete girders, with an emphasis on determining the effect of temperature on camber both during curing and in service. The research focused on monitoring and collecting fabrication camber to calibrate the current models for predicting camber. Temperature histories at release and service were also recorded to examine the effect of fabrication temperatures on initial camber and the effect of daily temperature variations on service camber. Two models were developed to predict daily camber changes under solar radiation based on ambient temperature data. The predictions of the models correlate well with the data collected during the research.