Subjects Covered:

• Refined Analysis
• 2D Frame
• Sub Model Planes
• Drawing 2D Members
• Splitting Members
• Importing Sections
• Copying Properties
• Filtering
• Rotating Local Axes
• Copying 2D Sub Models
• Renumbering Joints
• Support Conditions
• Member Release of Degrees of Freedom
• User Notes
• Data Reports

Outline

It is required to form a two storey, single bay, building frame analysis model as shown below. Each storey is 8m high and the column spacing is 10m. All joints have fully fixed connections except at the ends of the first floor beams, where there is full shear and axial continuity, but no moment connection. All frame members are constructed with grade 355 structural steel.

To model the beam column joint accurately we will place a model node at the face of the column as well as the column centre. The short member between these nodes will have stiff properties (say 103 times greater than the actual beam). This will ensure that the moment releases applied to the ends of the actual beam are in the correct location.

Each beam and column is split into 10 segments which will define the results output locations.

The beam and column sections have been defined in the section module and are loaded from external files.

Once the frame is defined, produce a full data summary report in PDF format and save the data file for use in another example.

Procedure

1. Start the program and select the New drop down button item Create From Template and pick the “EU Project” template.

   

Setup & Geometry

2. Using the File | Titles menu option set the Project title to “2 Storey Single Bay Frame” with a sub title of “Example 6.2”.

3. Also set the Job Number: to “6.2” and put your initials in the Calculations by: field.

4. Close the form with ✓ OK.

5. Click on Add Model | Refined Model in the toolbar at the top of the Structure Definition pane.

6. With the "Refined Model" node selected in the Structure Definition navigation window, click on the add button and select 2D Sub Model from the selection list. This will create an entry in the navigation tree and open the 2D Sub Model Plane form.

   

7. We wish to define this frame in the XZ plane, so click on the button and you will notice the axes change in the graphics.

8. Close the Sub Model Plane form with the ✓ OK button.

   

9. To create the structural members open the Define Sub Model Members form by clicking on the "sub Model Members" node in the Structure Definition tree.

10. To create a member we simply draw it in the graphics window making use of an appropriate snap mode. Initially click on the icon in the graphics toolbar.

11. Then click on the origin of the graphics screen followed by another click 8m in the vertical direction (Count the grid points as the Snap: mode should be set to grid).

    

12. If the member is drawn wrongly, simply click on the Edit Members item in the Member Tasks list and change the coordinates in the displayed form before closing this form with the ✓ OK button.

13. To draw the second column use the Copy Member(s) item in the Member Task list and enter a translation vector of (10,0) before clicking on the Apply button and then the ✓ OK button.

    

14. Now draw the transverse beam between the top two nodes of the column by following the same procedure as in 8 above, but setting the Snap: mode on the graphics toolbar to “Node in Plane”.

15. The next task is to split the two columns into 10 segments each. This is done by using Split Beam Element... in the Member task list.

16. In the Split Beam Element form set Split specified beam element /by specified division by clicking on the appropriate radio button controls.

17. Set the Number of new elements to “10”.

18. Click on the leftmost column in the graphics (turns red) and then click on the Apply button to see the 10 segments generated in the graphics window.

19. Repeat step 18 for the rightmost column.

20. Now click on the beam, but set Number of new elements to “3” (hit enter to update the table) and change the segment Lengths in the table to “0.15m”, “9.7m” and “0.15m”.

21. Click on the Apply button to split the beam.

    

22. Now click on the middle segment of the beam and split this into 8 equal length segments using the Apply button.

23. Close the Split Beam Element form with the ✓ OK button.

24. Use the Fit View icon on the graphics toolbar to fill the graphics screen with the structure.

    

Section Properties

It is now necessary to define some section properties for the beams and columns. Two design section files are supplied, one for the beam section and one for the column, which will be imported into the project and embedded.

25. Close the Define Sub Model Members form with the ✓ OK button and change the Navigation window to Design Sections.

26. Click the button in the navigation toolbar and choose Existing Design Section... from the list of options which will display the Open Existing file form.

27. Select the file called “EU Example 6_2 Beam Section.sam” in the file browser and “Open” this file.

28. Repeat this for the file “EU Example 6_2 Column Section.sam”. This will create two linked section entries in the navigation window.

29. Click on the Embed All Linked Sections task to break the link with the external files and embed the section data into the project.

    

30. Now move to the Structure Properties navigation window. All the defined Design Sections (and beams, if there were any defined) can be inserted as Structure Properties by clicking on the Create Section and Beam Groups task.

31. Select the Beam section property which will open the Structure Properties: Section form.

32. In the structure graphics, use the toolbar button to obtain a view on the xz plane and use the General side menu button and tick Show Nodes. Then graphically select the associated beam elements by making a window round the horizontal beam elements (using a left mouse click at the top left hand corner, releasing the button and moving the cursor to the bottom right corner and clicking again) taking care not to select any of the column members. The selected members will turn red.

    

33. Before closing the Import File form with the ✓ OK button, change the description to “Beam section 686x254x152” by typing it into the field.

    

34. Repeat this for the “SP2: EU Example 6_2 Column Section.sam” and change the Description: to be “Column section 305x305x158”.

35. In the graphics window, right mouse click and select “Tile Vertically” to show the structure and the applied section in the same frame.

    

36. To select the column members, window round the whole structure and when the Confirm window asks whether the beam elements should be overwritten answer No to All.

37. Close the Structure Properties: Section form in the normal way.

Modify Section Properties

As described in the outline we now need to enhance the stiffness of the short elements at the ends of the beam. To do this we add an Advanced Beam property which increases the elastic modulus and shear modulus and assign it to the two end beam elements.

38. In the navigation window toolbar click on the button and select Advanced Beam Assignment | Modified Elastic/Shear Modulus.

39. Change both elastic modulus and shear modulus to 210000 and 80769 respectively and then change the Description to “1000 times extra Stiff”.

40. To assign this advanced property to the two short beam elements it is necessary to zoom in to each of the top corners to select the elements as they are very short.

    

Local Axes

The section properties defined are related to a certain set of axes and these must be consistent with the local axes of the beam elements. The YY axis of the sections is the horizontal axis parallel to the flanges, so the local y axis of all the beam and column members must be perpendicular to the plane of the frame.

41. To check this we can turn on the local axis display using the General button on the graphics window and tick the Local Axes box.

    

    The red axis is the YY axis so, it can be seen that the column members are orientated in the wrong way. Additionally, if we want the bending moment diagrams to show sagging moments always on the inside of the frame then the local Z axis should always be pointing to the outside of the frame. This means the local axis system of the members should be rotated to correct this.

42. To do this the leftmost column members should be rotated by 90 degrees and the rightmost by -90 degrees. This can be done by changing the navigation window to Structure Definition and using the button to open Advanced beam Set | Local Axes.

43. In the resulting form, Twist: should be set to “90" degrees and then the leftmost column selected graphically (to do this use the following procedure:

    • Select the filter toolbar button on the graphics screen.
    • Click on De-select all in the selection tasks.
    • In the Select By: field select “Structure Property.”
    • Available groups “Column Section ...” sent to selected groups using the”>” button.
    • ✓ OK
    • Window round the leftmost column.
    • Set the Name of the Advanced Beam Set to “Twist 90."
    • ✓ OK

44. Add a second Advanced beam Set | Local Axes but set the Twist: to -90.

45. Change the Name of this property to “Twist -90”. The current filter will allow the windowing around just the right column without selecting any beams.

46. Click the small arrow next to the filter and select Select all to remove the filter. It can be seen that all the y axes (red) are now perpendicular to the plane of the frame and all the z axes are pointing to the outside of the frame.

Copying Members

48. The single storey can now be copied to create the second storey. To do this we open the Define Sub Model Members form by clicking the Sub Model Members item in the navigation window.

49. Select all the members by first getting focus on the table by clicking on the first member in the list and press Ctrl-A. Click on Copy Member(s) in the Members Tasks list to open the Copy Member Selection form and enter a Translation vector of (0m, 8m) before clicking on the Apply button and then the ✓ OK button to close the forms.

    

50. In the Graphics window click on the toolbar icon to fit the structure to the window.

51. Switch off the local axis display and turn on Joint Annotation using the General button.

Renumbering Nodes

Because the structure has been created by splitting and copying members, the node and member numbers do not form a logical pattern. These next steps are not absolutely necessary but make reading of output tables easier. We will now renumber the nodes in a more logical manner.

Required Column Numbering

Required Beam Numbering

52. Open the Joint Details form from the navigation window and change the graphics view to an XZ view by clicking on the toolbar icon.

53. From the toolbar open the filter form using the button.

54. In the graphics toolbar change “Select” to “Remove”.

55. Window round the columns but include the very short stiff members at the ends of the beams.

56. Click on the Save in Member Set Tasks and enter a name of “Beams Only” before closing the Save Member Selection form with ✓ OK.

57. Now close the Filter form with ✓ OK.

    

58. Click on Sort in Table Tasks and in the Sort form Sort by “Z” and Then by “X” (both ascending).

59. Close this form with ✓ OK.

60. Now click on Renumber in the Joint Tasks List.

61. In the Renumber form set the Renumber Range to All in Filter and the Start Number to 101 before clicking on the Apply button and then ✓ OK. Scrolling up and down the list of joints using the arrows on the keyboard will illustrate the joint sequence in the graphics window.

    

62. From the toolbar open the filter form using the button.

63. In the graphics toolbar change “Select” to “Create”.

64. Deselect all then Select By “Structure Property”, choosing the Column section from the list and moving it to the Selected Groups with >.

65. Click the Save in Member Set Tasks and enter a name of “Columns Only” before closing the Save Member Selection form with ✓ OK.

66. Now close the Filter form with ✓ OK.

67. Click on Sort in Table Tasks and in the Sort form Sort by “X” and Then by “Z” (both ascending).

68. Close this form with ✓ OK.

69. Renumber the filtered joints from “1” in the same way as in step 9 above and then close the Joint Details form with ✓ OK.

70. To do the same thing for member numbers open the Member Details form by clicking on Member Details in the navigation Window.

71. Filter on Columns Only, using the filter drop down list displayed when the Down Arrow next to the filter icon is clicked, and sort by Lowest Joint Ref.

72. Renumber the filtered members from “1”. (Use Renumber from the Member Task tool bar).

73. Filter on Beams Only and sort by Lowest Joint Ref.

74. Renumber the filtered members from “41”.

75. Filter on stiff elements by first using Select All then change the Select By: field to “Member Selection Set”, moving both beam and column sets to Selected Groups and then moving them back again into Available Groups.

76. Save the selection set as “Stiff Members Only”.

77. There is no need to sort these members but just renumber from “101”.

78. Remove all filters.

Supports

79. We now need to support the structure by fixing certain degrees of freedom of the two joints at the base of the columns.

80. Move to Structure Definition in the navigation tree and then click on the button.

81. Select “Supported Nodes” from the list.

82. In the graphics toolbar change “Along Span End Lines” to “All Joints” and then click on the two base joints in the graphics window. Both joints will have the same fixity, so they will be Uniform.

83. Change all degrees of freedom except Rotation Restraint about Y to Fixed before closing the form with ✓ OK.

    

Release of Member Degrees of Freedom

84. The first floor beam needs to be simply supported at its ends, so it is necessary to release the RY degree of freedom at the beam ends. In the Structure Definition navigation window click on and select Advanced Beam Set | Releases from the displayed list.

85. Change the name of the releases to “Free RY” and change the Moment y: field to “Free”.

86. Set the filter to “Beam Only” and click on the two ends of the first floor beam. A small cyan circle will appear near to the end of the member selected.

87. Close the Specify Beam Releases form with the ✓ OK button.

    

User Notes

It is good practice to make a note of any modelling techniques used in your model so that others can check it more readily.

88. Open up the User Notes form using the menu item File | Notes... Enter the following text into the form:

    “To model the first floor simply supported beam additional nodes have been place along the beam at the location of the column faces. This will enable member releases to be applied at this location and model the eccentricity of the beam reaction into the column. The short beams connecting the beam ends to the columns will have a stiffness 1000 times greater than the standard beam by adjusting the elastic and shear modulus accordingly."

89. Close the User Notes form with ✓ OK.

Data Reports

90. Now create a data summary and save as a PDF file using the menu item File | Data Reports

91. Click on the Include All button and then the View button.

92. In the Results Viewer form click on the PDF View tab to display the results in PDF format.

93. To save this as a file click on the save icon in the floating toolbar and enter a name of “Portal frame data report.PDF” before closing the Results Viewer and the Data Reports form.

    

94. Finally save the data file using the menu item File | Save as using a file name of “My EU Example 6_2.sst”.

95. Close the program.

Summary

This example provides a basic introduction to the Refined Analysis module of Autodesk® Structural Bridge Design and demonstrates the basic principles of creating structural elements in a sub-model, manipulating these elements and assigning properties. Special care is taken when assigning properties with respect to local axis definitions. Member releases and User notes are also introduced as well as node and element renumbering.