In this Demo example a simple-supported beam with three different prestressing is considered for comparison:
- Variant 1 - PExt: External Tendons Only
- Variant 2 - DEFAULT: External and Internal Tendon
- Variant 3 - PInt: Internal Tendons Only
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The purpose is to explain the differences between internal and external prestressing, how to model the external pressing tendons, and account for deviations. External tendons are unbounded from and placed outside of the concrete Cross-Section over the length between diaphragms where anchor blocks or deviators are used. To justify the applied techniques for reinforcement design some comments on the beam theory and the ULS - Ultimate Limit State are made.
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External Pressing requires the creation of a zone called Deviator, this must coincide with the respective elements' beginning and end. As shown in the images below, there are two possible definitions:
- Minimum: simple with 3 points;
- Complete: with Tangent points to be determined automatically.
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The geometry definition of the external tendons on the Saddles is defined by Three points:
- the Begin,
- the End and,
- the Intersection,
- Or with the additional Tangent points, that can be calculated due to the Radius of the circular saddle.
At these special zones, the external tendons are treated like internal tendons and require the Radius definition. Outside deviators and anchors block the external tendon is considered a separated structural element from the Cross-section, it can elongate, and the strain at any given point of the tendon is different from the associated Cross-section. Moreover, the eccentricity of the tendon changes due to the loading, and the large-deflection theory is required (IIIrd. Order).