In this guide we will go through all the possibilities using the Strand pattern manager for a hollowcore element (height: 380mm), although any type of element would work, except D-slab.
First we need to create the template for the prestressing strands. This is easily done by reinforcing an element with the maximum amount of reinforcement.
Place the reinforcement by either placing them in the reinforcement matrix or by using Layer of reinforcement for initial placement.
To verify the placement graphically, go to View reinforcement to hover over each prestressing strand. It is possible to zoom and pan in the window.
Back at the main reinforcement matrix, select Save to the right of the matrix.
Save the pattern-file in a good place where it will not be forgotten.
This will be the basis for any possible strand patterns. It is now possible to start new projects and elements and assign this pattern. Either by selecting load and load that specific pattern or by selecting Reinforcement pattern.
The Reinforcement pattern window contains several good buttons, Load pattern... will browse for a valid pattern file (like the one we saved earlier).
Up in the right corner there are possibilities to apply a reinforcement strand/bar to the cross section. Note that by running this script several times it is possible to add different prestressing, different materials and different diameters.
Select the positions for the strands you want to add. Left-click adds, Ctrl+Left-click removes the selection.
If the placement is valid it will show up in blue with the text OK, that means that the strand can be placed along the whole length of the element. For CUSTOM beams a position might end up partly outside for a portion of the length or completely outside.
The red Section center shows the center of gravity (COG) for the cross section and the blue Selection center shows the center of the prestressing force. It is best practice to have the blue cross vertically below the COG. Aplacement like the one in the picture above will cause the element to have an uneven prestressing force causing banana-shape bending sideways. With the blue cross below the COG the element will deflect upwards (camber) depending on the prestressing force and dead load.
Good selection! Grey strands will not be included in the selection.
In the bottom left corner it is possible to adjust the pattern horizontally or vertically, center align or save the pattern as a master pattern.
Add: Add the strands to the reinforcement matrix
Replace: Replace will remove and replace any strands already placed in the matrix with this new selection.
Cancel: Well, this will ignore any input made in this window...
If there are already bars in the reinforcement matrix and bars are tried to be added to it, in the same location, a warning will appear:
To solve this either deselect the strand (Ctrl+Left mouse button) or use replace to remove any reinforcement already in the matrix with this new selection.
The Strand pattern manager is suited for adding a strand in a known pre-defined location. Especially after a design has been made that shows too high or too low capacity, either by removing existing strands quickly or adding more strands until the design fulfills all design criterias.
There are now only need to know what available strand patterns a factory CAN have and the designer can pick the best locations for the strands with regards to the design.
Note that several elements can be cast on the same bed to optimize the material usage, so don't go completely bananas!
More information can be found in the PRE-Stress user manual for the Reinforcement pattern manager.