Generation of wind loads on members
This document serves as tutorial to show the RAM Elements tool for wind loads generation on members (open structure).
1.1 Model data
Open the “45.00m-height electrical tower.retx” model. The structure is formed by A36 steel equal leg angles for all segments and elements in the tower. The configuration is typical for electrical transmission towers.
3D model Lateral view
All support bases are assumed to be pinned for the four-legged tower.
Gravitational loads are assumed as follows:
- Self-weight
- Cable weight
Imposed load considered as dead loads:
- Cable tension
Live load:
- Cable assembly load
The referenced model has been created with the previous loads. This example is focused on assigning the wind loads using the wind loads generation tool for members.
Lateral loads to apply:
- Wind in the X global axis direction
- Wind in the Z global axis direction
The model already has several design and service load combinations based upon ASCE 7-16 code.
1.2 To create the wind definitions
- The wind loads definition manager can be accessed from the Home tab, and Definitions > Wind.
- A dialog window opens. In this dialog, press +New in the top left toolbar to create a new wind definition. Note that once a new item is created, it may be deleted and saved after modifying the values in the fields at the right part where wind load data is shown.
- Create a new definition for wind load with the +X axis direction and setting the direction to 0 degrees in the dialog region for Members. Edit the rest of the information in the manager fields using the following data:
- Enter the structure geometry in the Building geometry group of data, as follows:
- Length, 8.00 m.
- Width, 8.00 m.
- Meanroof height, 45.00 m.
- Ground level, 0.00 m.
Note. The tower dimensions are used to fill the geometry of the building. These field are defined in ASCE/SEI 7-16, Minimum Design Loads and Associated Criteria for Buildings and Other Structures, chapter 26 and chapter 27, Directional Procedure, Part 1.
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- Enter the wind parameters in the Parameters group, as follows (refer to notes at the end of this section for an explanation of each field):
- Basic wind speed, 120 km/h.
- Gust factor, 0.85.
- Enclosure category, Open.
- Elevation above sea level, 0.00 m.
- Exposure category, C.
- Directionality factor, 0.85.
- Wind direction, 0 degrees. This will coincide with the positive global X axis direction.
Note. The previous data is defined in ASCE/SEI 7-16, Minimum Design Loads and Associated Criteria for Buildings and Other Structures, chapter 26 and chapter 27, Directional Procedure, Part 1.
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- Enter the topographic parameters in the Topographic factor, Kzt group, as follows (refer to notes at the end of this section for an explanation of each field):
- Select User defined and enter Kzt equal to 1.0.
Note. The previous data is defined in ASCE/SEI 7-16, Minimum Design Loads and Associated Criteria for Buildings and Other Structures, chapter 26 and chapter 27, Directional Procedure, Part 1.
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- Enter data in the Aerodynamic shape factor group, as follows (refer to notes at the end of this section for an explanation of each field):
- Leave unchecked the User defined checkbox to let the program calculate the factor automatically.
Note. The data used in this group is defined in the Australian Standard AS/NZS 1170.2-2011, Structural design actions, Part 2: Wind actions, section 5 and Appendix E for exposed structural members.
The wind load is calculated using the following expression: Load = qz * G * Cfig * Width Where, qz is the velocity pressure evaluated using ASCE/SEI 7-16, Chapter 26. G is the gust-effect factor determined from ASCE/SEI 7-16. Cfig is the aerodynamic shape factor evaluated using the AS/NZS 1170.2-2011 criteria. Width is the member face width against the wind. |
1.3 To assign the wind loads
- Select the load case for which the wind loads will be assigned.
2. Select the desired members to assign wind loads using the tool. For this example, select all the members in the tower model since the tool can assign wind loads at once for the whole selection for one wind direction.
3. Select the Members > Loadson members spreadsheet.
4. On the Spreadsheet ribbon tab, select the Assign wind loads tool in the Active spreadsheet tools group.
The dialog to assign Wind load on members opens.
- Select the “+X (0 deg)” load definition and press OK.
- To see a report of calculated wind loads for selected members before confirming the assigned values in the dialog press the Preview report button and a report window will be displayed.
- Once the dialog is closed, the wind loads are added for the current load case for all the selected members.
Wind loads on horizontal members
Wind loads on vertical members
Wind loads on diagonal members
Wind loads on all tower loads
- After the wind loads are assigned, it is possible to access a wind loads report for the selected members, by looking for the Output tab, in the Reports group, the Data button and search for ..
Then select the Wind loads option for a desired load condition:
