14. Close the program.
Summary
Sections can be built by combining many different simple components to create more complicated shapes. Special libraries have been built containing the major shapes for steel sections which can be used to build up the section. This covers UK, American, Australian, European and Japanese standard sections.
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2.7. Pre-stressed section
Subjects Covered:Precast concrete beams; Tendon definition and placement; Section outline from text file; Initial Prestress forces; Arcs; Merging; Hook points;
Outline
It is required to generate a section of a precast edge beam comprising of a standard I-Girder Type 2 precast beam (Grade 40 concrete) and an insitu slab and edge detail (Grade 32 concrete) as shown below. The section is created using 3 components, 1) a standard precast section from a built in library, 2) a parametric rectangular section for the slab, 3) a general defined shape with specific coordinates for the edge detail and 4) an infill piece of concrete. These sections will overlap so they must be merged to eliminate the duplicated material.
Two rows of tendons are placed in the bottom of the beam (8 in the bottom row and 6 in the second) together with two tendons in the top. The bottom row is placed 60mm from the bottom face of the beam with the end tendons 50mm from the vertical faces.
The second row is placed 110mm from the bottom face of the beam. The top two tendons are placed 870mm from the bottom face. Each tendon (Grade 1750) is initially stressed to 188kN.
1. Start the program and ensure that the current Project Template: is set to
“Version 6 Examples - AU” using the Options|Projects Templates menu item.
2. Begin a new section using the menu item File|New Section....
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3. Use the menu item Data|Titles... to set the title as “Prestressed Section” with a sub-title of “Example 2.7”. Also add your initials to the Calculated by data item.
Click on “OK” to close the titles form.
4. Open the Define Material Properties data form using the menu item
Data|Define Material Properties... Delete the structural steel by clicking twice in the name field and then using the delete key. Open the data form for the prestress material and ensure that the Tensile Strength is set to 1750MPa.
(This strength could be changed if required, but the default strength is used in this example).
5. Click the “OK” button on both the Define Property Details and the Define Material Properties form to close both forms and ensure that any changes are saved.
6. Open the Define Section data form using the menu item Data| Define Section...
7. In the first row of the Library column select “Concrete Beams” from the dropdown list. This will display a secondary form (with graphic showing a standard bridge beam). Ensure that “Australian Sections” is selected. Use the dropdown list Concrete beam range to select a “I-Girder” and set the Shape no.
to “Type 2 Fig H1(A)”. Click on “OK” to close this secondary form.
8. Assign Grade 40 concrete to this component by using the drop down selection of the Property field.
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9. In the second row of the Define Section form create a second component by picking “Parametric Shape” from the dropdown list. Set the width to “600mm”
and the depth to “160mm”. Assign Grade 32 concrete to this component.
10. Now manipulate the positions of the components so that the origin is at the midpoint of the bottom face of the beam. This is done by setting the hook point of the concrete beam section to “-1” and setting the coordinates to (0,0). The insitu slab can be positioned by also setting the hook point to -1 and the coordinates to (200,870) (allowing 30mm for permanent formwork above the rebate).
11. The two components overlap, so, to cut out the insitu slab around the beam, select the slab in the list of components and, in the graphics window toolbar, click on the Merge button.
12. An insitu infill concrete component is now defined. Create a third component, using the dropdown list in the Library column, as a “parametric shape”. Set the width to “400mm” and the depth to “900mm”. Assign Grade 32 concrete to this component.
13. With the hook point set as “1” for this third component, set the X Coord to
“-350”. Use the Merge button to shape the infill concrete to the profile of the girder.
14. The insitu edge detail now needs to be defined. Create a fourth component, using the dropdown list in the Library column, as a “define shape”. The
coordinates, as defined in the table above, can be entered by either typing the coordinates directly into the shape coordinates table (using the “+” button to add a row), or by entering the coordinates into a text file such as notepad, copying them to the clipboard (Control/C) and then using the right mouse button menu option in the coordinate table, pasting them in. Set the section name to “Edge Detail”.
15. A more accurate shape can be given by fitting arcs where appropriate. Tick the arc box in rows 3 & 5 and click on “OK” to close the Define Element Shape form. A form appears telling you that the sections intersect. Click the “OK”
button on this form.
Merge
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16. Assign Grade 32 concrete to this component.
17. Again the two components overlap, so, to cut out the edge detail around the beam, select the “Edge Detail” in the list of components and, in the graphics window toolbar, click on the Merge button. Click on the “OK” button to close the Define Section form. Click “No” on the Confirm form for this example.