Nội dung text 39 Prestressed Concrete.pdf
PSAD 39: Prestressed Concrete This module shows the basic concepts of pre-stressed concrete applied to the board exam. Figure 1. From WikiPedia As shown from the figure, concrete is introduced to a pre-stressing force. This is a compressive force that allows the concrete to deflect in a way that when the expected loads are applied, the total deflection in the beam becomes 0. Pre-stressing forces are usually placed at a certain eccentricity from the centroid. This induces a bending moment which allows the concrete to have an initial axial and bending stress. Usually, this is done in a direction that counteracts the direction of the expected loads. The prestress loss is an amount of reduction in the effective value of the prestress force. This is typically applied during performance of the structure (when the external forces are applied). To apply the prestress loss, simply change P to P ′ = P(1 − L) where L is the prestress loss, in percent. Shown below are the stress diagrams at different conditions.
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