Add and Modify Simple Bracing

This section describes how to insert simple diagonal bracing and then use a short-cut facility to modify the spacing between the ends of the bracing members and some reference plines.

The Mirror Copying facility is used to create the other two bracing members. The facility creates a copy of an existing element and repositions the copy automatically by reflecting it about an axis in a specified plane (so that the original and copy elements are mirror images of one another).

For the profile for the bracing members:

1. From the main tool bar, select Default Profile Specification.

2. Reset the default specification to British Standard, Rect (Rectangular) Hollow Sections, 200.0x100.0x10.0 with Justification, Member Line and Joint Line all set to NA.

3. From the main menu bar select Create > Sections > Straight.

4. From the Positioning Control tool bar select Pick Type: Element and Pick Method: Intersect.

5. When you pick the sections to define each intersection point, the first pick defines the section to which the connection is made. In this case, therefore, you must pick the column before the beam when each end is defined otherwise the bracing gap trimming facility does not work correctly.

6. Click Accept, then click Dismiss to discard any information and close the Section window.

7. In the Design Explorer check that the bracing member is the current element.

8. If the vertical alignment of the bracing member ends looks wrong at this stage, from the main menu bar select Modify > Bracing Gap.

   The Brace Gaps window lists the different ways the required gap can be specified.

9. Ignore the Default Gap setting and select Distance on picked Pline from a fixed point.

   The graphical representation of the Bracing is updated to show the relevant dimensions and picking sequence.

   Note: You can modify bracing gap sections, which have been created between GENSEC elements.

   

10. Click Apply.

11. In the Brace Gap(s) window, select the Confirm checkbox, but do not enter the Gap A data yet.

    You are now in event-driven graphics mode, ready to pick the plines from which the bracing gap is to be calculated.

12. First position the lower end of the bracing member. Use the graphical representation from the Brace Gaps window as a guide, pick plines in this order:

    1. A pline on the lower face of the bracing member, such as BOS. Pick close to the connection, so that the gap is calculated for the correct end.

    2. A pline on Column A along which the gap is to be defined, such as NAL or NAR.

    3. A pline on the upper face of Beam 1, such as TOS.

    Note: Switch the graphics to a wireline view (Press F8) to make it easier to pick the plines.

    

    Once you have picked the third pline, the calculated distance for the current position is shown in the graphical view and is also inserted into the Gap A text-box on the Brace Gap(s) window, Accept/Reject are now active.

13. Click Dismiss to discard any information and close the Brace Gaps window.

To check whether or not the ends of a section are connected:

14. Select the bracing member as the current element.

15. From the main menu bar select Utilities > Beams and Columns.

16. From the menu bar of the small window which results, pick Tag > All ends.

    The ends of the current section should both be tagged as Connected.

17. From the main menu bar select Create > Copy > Mirror.

    The Mirror window allows you to specify what to copy (Object), where the copies are to be stored in the database hierarchy, and the plane in which the copy position is to reflected.

    

    

    

18. With the bracing member as current element, set the Object to be copied to CE and set the to option to Rel.

19. Set the Type of mirror option to Mirror Copy (since you must create a new element rather than simply reposition the original one).

    The plane in which you want to reflect the copied section is represented by the shaded area in the diagram:

    

    The plane is specified in terms of its direction (that is the direction of the normal to the plane) and of the position of any point within it. The Mirror window provides several methods by which these can be specified by picking items in the model that already exists. Column B is used to define the position and the direction entered explicitly.

20. Select Cursor > Element from the Mirror window’s menu and, when prompted, pick any part of Column B.

    The position identified snaps to the start or end of this column (depending on where you picked) and its coordinates are entered into the XEast/YNorth/ZUp text boxes automatically. A symbolic representation of the plane’s position and orientation is shown in the graphical view.

    Note: The Plane Direction text box now shows the cutplane direction of the column’s start or end (namely Up or Down). Change this to XEast. Select the Lock checkbox to prevent its setting being updated when another position is picked.

    

    

21. Click Apply to create the mirrored copy and, when prompted, confirm that you want to retain the copy.

22. Use the same procedure to copy and reflect a second member to create a third bracing member.

    The two copies just created should be positioned correctly, but not connected yet. To check this, instead of the Tag utility for each new bracing member, from the main menu bar select Query > End Connections. The Highlight Connections window shows the connectivity status of all relevant members of the current element.

    

23. Navigate to the SubFrame TESTSBFR and click CE in the Highlight Connections window to update the displayed data.

    The numbers on the coloured bar show the number of sections in each category.

24. Select the corresponding Highlight checkboxes to colour the sections in the graphical view.

25. To change the highlight colour click on a colour.

    Note: It would be assumed that the upper ends of the columns should be shown as connected. However, the beams at those points are connected (via Secondary Joints) to Secondary Nodes positioned along the columns, rather than to Primary Nodes at the column extremities. Therefore, even though the Secondary Nodes in this case happen to be coincident with the tops of the columns, the diagnoses are correct.

26. To connect the ends of the two bracing sections to the appropriate columns, from the main menu bar, select Connect > Connect and follow the status bar prompts carefully. (Escape terminates each stage of the process in the usual way.) Use the Highlight Connections window again to confirm the results.