Improving Camber Predictions for Precast, Prestressed Concrete Bridge Girders
Type of DegreeDissertation
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In precast, prestressed concrete construction, the eccentricity of the prestressing force typically results in a net upward girder deflection known as camber. Camber is first observed at the time of prestress transfer and tends to increase thereafter as a function of time-dependent material properties. While accurately predicted levels of camber are desirable to concrete bridge construction, inaccuracies in design camber estimates can result in construction difficulties and the need to modify bridge designs to ensure proper girder fit. In order to mitigate such troublesome issues, the Alabama Department of Transportation (ALDOT) sponsored this investigation to develop a suggested procedure for use during girder design to more accurately predict pre-erection camber in precast, prestressed concrete bridge girders. In support of this objective, various laboratory and field studies were conducted exploring relevant regionally-variable concrete material properties (e.g. concrete compressive strength, concrete unit stiffness, and creep and shrinkage behavior) as well as the effect of transient environmental conditions on girder camber. Relying on the conclusions of these laboratory and field studies, a revised camber prediction procedure was developed, implemented in a user-friendly computer software, and validated by comparison to multiple design and production cycles of ALDOT precast, prestressed concrete bridge girders.