Abstract

Deflection control is an important design criterion for the serviceability of pretensioned concrete bridges. Upward cambers due to prestressing forces can be utilized to offset downward deflections due to gravity loads in order to control cracks and/or to produce desired cambers. The traditional hand-calculated approach simplifies the computation of pretensioned concrete girders by: (1) assuming that the prestressing force acting at the midspan of a girder remains constant along the entire span of the girder, (2) neglecting the p-δ effect on the girder due to the axial compression force in the girder, and (3) using the gross concrete section of the girder to compute the moment of inertia of the girder. The purpose of this work is to investigate the accuracy of the hand-calculated approach for the computation of cambers due to prestressing forces. The type of prestressed concrete girder investigated in this work is a pretensioned I-girder with a combination of straight strands and harped strands. The major findings derived from this work are: (1) the variation (non-uniformity) among prestressing forces acting along the tendons has no significant effect on the deflection of the girder, (2) the traditional hand-calculated approach neglecting the P-δ effect may result in considerably smaller girder deflections, and (3) the traditional hand-calculated approach using the moment of inertia of the gross concrete section (neglecting the additional stiffness contributed by tendons) may result in considerably larger girder deflections.

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