1. Modeling Base Plate Attachments with Partial Welds
Rob Abernathy
CASE Center
GTSUG
June, Seattle, WA

2. What is a “Partially Welded Attachment”?
Attachments are assumed to be welded to the base plate along all attachment lines. However, in some situations, only part of the attachment is welded to the base plate. In versions 31 and earlier of the Base Plate Wizard, this situation could only be modeled by creating a custom attachment which included the welded parts of the attachment and omitted the unwelded parts. Version 32 adds new tools to allow modeling the unwelded parts of attachments.
GTSUG June, 2012

3. Custom Attachment Omitting Unwelded Lines
A wide flange welded on the flanges but not the web could be modeled as 2 lines, leaving out the line representing the web. You would need to create the two line version since the standard profiles are assumed to be welded all around.
Custom W8x10 -
Flanges
only
Standard W8x10
GTSUG June, 2012

4. Custom Attachment .gtbp Files
From Appendix A1 The GTBP File Format
100 ID type Profile_ID OffsetX OffsetY RotX RotY RotZ Extension
110 Profile_ID Shape Mirrowed Name Table values[6]
int Profile_ID: Matches with Profile_ID in Attachment (100)
int Shape: : I, 2: tube, 3: channel, 4: T, 5: 2L, 6: L, 100: Arbitrary
120 Profile_ID type X1 Y1 X2 Y2 CX CY THICK
$ ---- Attachments: Standard W8X
W8X10 WSHAPES
$ ---- Attachments: Custom W8X
W8x10-Flanges Custom
GTSUG June, 2012

5. Issues with Omitted Lines
Omitting attachment lines that are not welded introduces two concerns. They may or may not affect your results – engineering judgment must be exercised.
Issue 1: If an unwelded and therefore un-modeled part of the attachment were to translate in the –Z direction (into the base plate) or the base plate were to deflect in +Z direction in an area where an omitted line was would cause an inconsistency between the physical structure and the mathematical model.
Issue 2: An “extension” model could not be created for the un-modeled part of the attachment, effectively precluding using this method for unwelded portions of the attachment.
GTSUG June, 2012

6. How to Model Unwelded Attachment Sections?
The edge of a plate butted against but not welded to a base plate should transfer compressive force to the base plate, but not tension or shear (ignoring friction) forces and no moments. This condition will be referred to as “Contact Only”.
Two components in GTSTRUDL can model this type of action: Nonlinear Spring (NLS) elements and TYPE SPACE TRUSS members declared as COMPRESSION ONLY with the NONLINEAR EFFECTS command.
GTSUG June, 2012

7. Modeling Contact Only with NLS
Nonlinear springs are already used to model the compression-only bearing surface, in much the same way as is needed for Contact Only, exerting only +Z force without shear. However, NLS elements add more complexity, requiring curve data and element stiffness assignments like the bearing surface NLS:
NONLINEAR SPRING PROPERTIES
CURVE 'BearSurf' FORCE
END OF NONLINEAR SPRING PROPERTIES
NONLINEAR SPRING ELEMENTS
INCIDENCES
'S1‘ ATTACHED TO JOINT 1
STIFFNESS
'S1' Z CURVE 'BearSurf' FACTOR
END OF SPRING DATA
GTSUG June, 2012

8. Modeling Contact Only with Compression Only
TYPE SPACE TRUSS members designated as COMPRESSION ONLY with the NONLINEAR EFFECTS command will also transfer only +Z resistance without shear or moments. For several reasons, compression only members was decided as the modeling method:
Simple, easy to understand commands
2. Able to be viewed in GTMenu
3. Less complicated internal nonlinear processing
GTSUG June, 2012

9. Stiffness Connection between Contact Only Attachment and Base Plate
Both the compression-only and NLS methods need a spring constant to represent the resistance to compression between the Contact Only attachment and the base plate. This resistance can be viewed as the transverse compression of the base plate due to the –Z force applied by the Contact Only attachment. A spring constant equal to a short, stubby steel member was chosen to model the transverse stiffness of the base plate.
GTSUG June, 2012

10. Implementing Contact Only in the Base Plate Wizard
A Contact Only designation has been added to attachment lines, along with a line’s start and end location and its thickness. Because any part of an attachment may be Contact Only, any attachment with Contact Only will make that attachment ‘Arbitrary’, instead of wide flange, channel, etc. More on Arbitrary vs. standard profiles later.
GTSUG June, 2012

11. Contact Only Modeling Rules #1 and #2
#1 - If a joint is part of both welded and unwelded lines, it is considered to be welded. Note: this should only occur at line ends.
#2 - Base plate joints along a Contact Only line have new joints created ½ plate thickness above (+Z) them, corresponding to the top of the plate.
$ ---- Base Plate Wizard user defined data
$ Plate: in X in x in  Thickness = 0.5
$ ---- CONTACT ONLY joints and connecting members ----
JOINT COORDINATES
; ;
GTSUG June, 2012

12. Contact Only Modeling Rules #3 and #4
#3 - Compression-only members (TYPE SPACE TRUSS) are added between the plate joints and the new Contact Only joints.
#4 - AX equal to MeshSize*MeshSize is assigned to the new members.
TYPE SPACE TRUSS
MEMBER INCIDENCES
; ;
MEMBER PROPERTIES AX
25 TO 27
NONLINEAR EFFECTS
COMPRESSION ONLY MEMBERS 25 TO 27
GTSUG June, 2012

13. Contact Only Modeling Rules #5 and #6
#5 - If the attachment is modeled as a Rigid Footprint, then the RIGID SOLID includes the new Contact Only joints, but not the plate joints.
#6 - If the attachment is modeled as 2D finite elements (extension), then the first row of the extension elements are incident to the new Contact Only joints, not the plate joints.
GTSUG June, 2012

14. Simple Example
Create an 8” x 10” plate with a W8X10 centered, with a 1” mesh.
Generate a .gtbp file and an input file and run it.
View in GTMenu, noting the RIGID BODY display.
Edit the attachment and set the web as Contact Only (unwelded).
Compare the two .gtbp files.
GTSUG June, 2012

15. Simple Example: Generate files
Save the fully welded standard profile into Simple.gtbp and then create an input file Simple.gti. Check the “Process Input File” box to be able to view the model in GTMenu.
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16. Simple Example: View in GTMenu
GTSUG June, 2012

17. Simple Example: Set Web as Contact Only
On the Attachment page, edit the attachment by double-clicking the column, then click the ‘Edit Weld Status’ button.
GTSUG June, 2012

18. Simple Example: Select Web and Change Status
Note that the web is marked as line 1. Click the “1” in the Line # column. Line 1 becomes dashed, indicating it’s selected.
In the Tools menu, select “Set selected lines as Contact Only. Line 1 returns to a solid line, but is now rose colored, indicating that the web is now considered Contact Only.
Click the OK button to accept the new weld status.
GTSUG June, 2012

19. Simple Example: Accept Contact Only Change
When you return to the Edit Attachment dialog, the web line will still be blue. Click the OK button at the bottom of the dialog to commit the new weld status.
GTSUG June, 2012

20. Simple Example: Generate Contact Only Files
When a standard profile has Contact Only lines, it must be stored as an Arbitrary profile. This dialog informs you of that and also offers two renaming options. Click the NO button (reject the suggested new name) to bring up the New Attachment Name dialog.
You can select from the existing tables or type in a new name. Type in a new profile name. 39 character limit for both names.
GTSUG June, 2012

21. Simple Example: View Contact Only in GTMenu
Note the web is now modeled as a row of joints above the mid-plate joints. These new joints are ½ plate thickness in the +Z direction and the RIGID SOLID includes the new joints and not the plate joints.
GTSUG June, 2012

22. Simple Example: Geometry Close-up
Only Z force (which is FX for the members) is carried by the truss members (81 and 82 in this picture) and only a compressive force. If joints 100 and 23 move away from each other, the member 81 transmits no force.
$ ---- CONTACT ONLY joints and connecting members ----
JOINT COORDINATES
; ;
TYPE SPACE TRUSS
MEMBER INCIDENCES
; ;
MEMBER PROPERTIES AX
81 TO 87
NONLINEAR EFFECTS
COMPRESSION ONLY MEMBERS 81 TO 87
GTSUG June, 2012

23. Simple Example: Compare .gtbp Files
Simple.gtbp
$ ---- Attachments: 1 attachments specified
W8X10 WSHAPES
SimpleContactOnly.gtbp
W8x10-Flanges PartiallyWelded
Attachment type ( 1 = W shape, 100 = Arbitrary)
Profile
Table name
Line type (0 = welded, 4 = Contact Only)
GTSUG June, 2012

24. Example 2: Partially Welded Channel
Compare results from a fully welded channel (C8x11.5) with results from two partially welded channels welded with the patterns shown.
Pattern 1
Pattern 2
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25. Example 2: Plate with Anchors and Loads
Loads are applied at the end of 10” 2D extension, creating MX (loads Down and UP) and MY (loads Left and Right).
GTSUG June, 2012

26. Example 2: Create Custom Attachment
Since the weld patterns do not match the standard profile lines (flanges and web), a custom attachment is required with the line definition matching the weld pattern. The custom attachment below (MyChannels::C8x11.5-Parts2x4) breaks the flanges into 2 parts and the web into 4 parts.
C8x11.5-Parts2x4 MyChannels
GTSUG June, 2012

27. Example 2: View Custom Attachment
This is the view you would see in Edit Weld Status. Create separate .gtbp files for each pattern.
Then write and run the .gti files and compare the ResultsSummary files.
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28. Example 2: Results Comparison
All Welded Pattern 1 Pattern 2
Von Mises S S B B
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29. Attachments in .gtbp and the Attachment File
The .gtbp and Attachment File formats are described in Appendices A1 and A2 of the Base Plate Wizard User Guide. In addition, examples of custom attachments are shown in the file ‘SampleUserDefinedAttachments.txt’ in the <install>\GTStrudl\xx\BasePlate folder (“<install>” = C:\Program Files (x86) or your alternative location, and “xx” = the version number).
Custom attachments built on a standard profile are simple, as we have seen. The next slide shows the standard profile lines – if they match your welds it is simple to create a partially welded attachment file.
GTSUG June, 2012

30. Standard Profile Lines
This the line layout with line numbers for the standard profiles from the GTSTRUDL AISC 9th Edition tables. The Edit Weld Status dialog easily lets you change the status of any individual line to Contact Only. If only part of a line is Contact Only, then you will need to create a custom Attachment File.
GTSUG June, 2012

31. Custom Attachments in the Attachment File
$ In the .gtbp file
C8x11.5-Pattern2 MyChannels
$ In the AttachmentFile
TABLE 'MyChannels'
$ Name NumberOfLines
100 C8x11.5-Pattern2 8
$ X Y X Y2 THICK Type $
GTSUG June, 2012

32. Export Anchor Results for Capacity Anchor Check
The new ANCHOR commands in GTSTRUDL 32 need the anchor geometry and results to check anchor capacity by Appendix D of the ACI code.
The ability to extract this data has been added to the Anchor Results dialog. Click the Write ANCHOR LOADS button to create a file with the geometry (optional) and results in the format required by the ANCHOR CONFIGURATION command.
GTSUG June, 2012

33. Generated ANCHOR CONFIGURATION Commands
ANCHOR 1 X Y TYPE 'Anchor1'
ANCHOR 2 X Y
ANCHOR 3 X Y
ANCHOR 4 X Y
LOAD 'Down'
1 VX VY TENSION
2 VX VY TENSION
3 VX VY TENSION
4 VX VY TENSION
END LOAD DATA
LOAD 'Up'
1 VX VY TENSION
2 VX VY TENSION
3 VX VY TENSION
4 VX VY TENSION
GTSUG June, 2012