Stress Calculation

When calculating stresses for a given longitudinal location, each vertex in the cross-section’s polygon is checked. This guarantees that the controlling stresses are found and accounts for all asymmetries in the cross-section, the prestressing force, and any lateral loading that may exist.

Symmetric Sections

For symmetric sections, the stress at a given location is as follows:

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Where:

Prestress Force

The prestressing force generates both axial force and internal moments on the member. The prestressing moments generated can be about either the horizontal axis or the vertical axis depending on magnitude and location of the strand eccentricities. Lateral strand eccentricity, which generates moments about the vertical axis, can often be ignored.

Principal Stresses

Stresses due to asymmetric sections are accounted for by modifying the stress equation above. The general form of the stress equation above is as follows:

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Where:

Note that in the equation for asymmetric cross-sections, if the product of inertia is zero the equation simplifies to the same equation used for symmetric cross-sections.