This document serves as tutorial to show the RAM Elements tool for wind loads generation on load areas.
1.1 Model data
Open the “Simiu Handbook, ASCE 7 - Ex. 5.2.1 (wind parallel to long side).retx” model. The structure is based on Example 5.2.1 of the Handbook for Design of Buildings for Wind by Emil Simiu, and it is a concrete building with a configuration shown in the following figure.
This is a 95 ft high office building with rectangular shape in plan (60 ft x 125 ft), eave height 95 ft and flat roof. It is considered as rigid and enclosed. Exposure B from all directions is selected.
Note that the distribution of bays in the longitudinal direction of the model responds to the criteria of the ASCE 7-16 Chapter 27 to obtain the distances from the windward edge of the building to the zones where there is differenced wind effect on the roof.
Lateral view with bays distribution
Top view with bays distribution
Lateral loads to apply, shown in this example:
- Pressures on all lateral walls due to wind acting towards the global positive X axis direction with positive internal pressure on walls.
- Pressures on roof areas due to wind acting towards the global positive X axis direction with positive internal pressure and load case A (negative values of pressure coefficient).
After the example is finished, it will result very easy to complete the following additional load cases:
- Wind in the X global axis direction with negative internal pressure on walls.
- Wind in the X global axis direction with positive internal pressure and load case B (positive values of pressure coefficient) on roof.
- Wind in the X global axis direction with negative internal pressure and load case A (negative values of pressure coefficient) on roof.
Wind in the X global axis direction with negative internal pressure and load case B (positive values of pressure coefficient) on roof.
1.2 To assign the wind pressures
1. Select the load case for which the wind pressures will be assigned.
2. Select the desired areas to assign wind loads using the tool. For this step, select all the areas in the West side of the building. The tool can assign wind loads at once for the whole selection for one wind direction. Since the assumed wind direction for the first load case is in the direction of the positive X axis, this first selection will serve for the loads on windward.
Note. The tool can assign loads for selected areas of the same type, for example, if the areas in the selection are the whole side wall of the structure, these can be identified as Windward, Leeward or Side walls. As it will be seen in this example, the areas in the roof have more details to consider thus a good result with the assigning tool may be obtained. |
3. Select the Areas > Surface load spreadsheet.
4. On the Spreadsheet ribbon tab, select the Assign wind pressure tool in the Active spreadsheet tools group.
The Wind load generation for areas dialog opens.
5. Select the Pressure type between the four options in the first group. For this first assignment, select Windward.
Note. The options to select the pressure type are: · Windward, to apply the pressure to the face of the structure in front to the wind. · Leeward, to apply the pressure to the rear face to the wind. · Sidewall, to apply the pressure to the lateral faces perpendicular to the wind direction. · Roof, to apply the pressure to the top or roof of the structure. |
6. Enter the structure geometry in the Building geometry group of data, as follows:
- Length, 125 ft.
- Width, 60 ft.
- Meanroof height, 95 ft.
- Ground level, 0 ft.
Note. The building 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. · length: The length value is always the dimension of the structure parallel to the wind direction as it is shown in the image above. · Width: The width value is always the dimension of the structure perpendicular to the wind direction as it is shown in the image above. · Mean roof height: The Mean Roof Height is defined as the average between the roof eave height and the elevation of the highest point on the roof surface. For roof angles of less than or equal to 10°, there is an exception and the mean roof height is permitted to be taken as the roof eave height. · Ground level: Is the level or vertical coordinate (Y) that represents the ground level of the structure |
7. 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, 170 mph.
- Gust factor, 0.85.
- Enclosure category, select Enclosed.
- Elevation above sea level, 0 ft.
- Exposure category, select B.
- Directionality factor, 0.85.
- Internal pressure, select Positive.
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. · Basic wind speed: The basic wind speed, is used to determine design wind loads on the structures. · Gust factor: Gust-effect factor, which is a design value that represent or is defined as the ratio between a peak wind gust and mean wind speed over a period of time. · Enclosure category: · Enclosed. Building that has the total area of openings in each wall, that receives positive external pressure, less than or equal to 4 sq. ft (0.37 m2) or 1% of the area of that wall, whichever is smaller. · Partially enclosed. Building that complies with the following conditions: o The total area of openings in a wall that receives positive external pressure exceeds the sum of the areas of openings in the balance of the building envelope (walls and roof) by more than 10%. o The total area of openings in a wall that receives positive external pressure exceeds 4 ft2 (0.37 m2) or 1% of the area of that wall, whichever is smaller, and the percentage of openings in the balance of the building envelope does not exceed 20%. · Partially open. Building that does not comply with the requirements for open, partially enclosed, or enclosed buildings. · Open. Building that has each wall at least 80% open. This condition is expressed for each wall by the equation A0 >= 0.80 x Ag. o A0 = Total area of openings in a wall that receives positive external pressure. o Ag = Gross area of the wall in which A0 is identified. · Elevation above sea level: Design value to define the elevation or altitude above the sea level used by the application to calculate the ground elevation factor to adjust for air density. · Exposure category: For each wind direction considered, the upwind exposure shall be based on ground surface roughness that is determined from natural topography, vegetation, and constructed facilities. · B. Urban and suburban areas, wooded areas, or other terrain with numerous, closely spaced obstructions that have the size of small family houses. · C. Open terrain with scattered obstructions that have heights generally less than 30 ft (9.1 m). · D. Flat, unobstructed areas and water surfaces. This category includes smooth mud flats, salt flats, and unbroken ice. · Directionality factor: Design factor determined from Table 26.6-1 of the ASCE 7-16 code. · Internal pressure: Gives the user the capability to choose between the positive or negative values of internal pressure coefficient (GCpi). |
8. Enter the Interior point coordinates data, which helps determining the external and internal faces of the load areas to apply the push or suction pressures. For this case, enter the coordinates of any interior point, for instance, the following:
- X: 60 ft
- Y: 5 ft
- Z: 30 ft
9. 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. · User defined. This option allows to use a topographic factor (Kzt) value chosen by the user. If site conditions and locations of buildings and other structures do not meet all the conditions specified in the code, then Kzt may be set to 1.0. · Use calculated. If the user desires the application to calculate the topographic factor it is necessary to enter the multipliers K1, K2 and K3 properly as it is recommended in the code. · K1. Factor to account for shape of topographic feature and maximum speed-up effect. · K2. Factor to account for reduction with distance upwind or downwind of crest. · K3. Factor to account for reduction speed-up with height above local terrain. |
10. Enter data in the Roof parameters group, for this first assignment, all fields are disabled since the Pressure type was set to Windward.
11. Enter data in the Pressure coefficient group.
- Leave unchecked the User defined checkbox to let the program calculate the coefficient automatically.
12. To see a report of calculated wind loads for selected areas before confirming the assigned values in the dialog press the View report button and a report window will be displayed.
13. Click OK to close the dialog. The wind loads are added for the current load case for all the selected areas.
Windward pressures on all West walls
Note that once the dialog is closed the pressure values and the global direction for the wind load are printed in the Surface load spreadsheet.
Now, it is time to use the tool for the rest of the load areas in the model.
14. Select all the areas in the East side of the building, this selection will serve for the loads on leeward.
15. Select the Areas > Surface load spreadsheet.
16. On the Spreadsheet ribbon tab, select the Assign wind pressure tool in the Active spreadsheet tools group.
The Wind load generation for areas dialog opens.
17. Set the Pressure type to Leeward.
18. Enter the structure geometry in the Building geometry group of data, as those were before:
- Length, 125 ft.
- Width, 60 ft.
- Meanroof height, 95 ft.
- Ground level, 0 ft.
Tip. The information in the dialog will remain from the first time it was open, thus the building information and all the data that was previously entered will be already set for the next time. This is useful for a building like this example in which there are portions of the structure where to assign different pressure types. |
19. Enter the wind parameters in the Parameters group. Note that these will be the same for the whole model and thus the information remains since the last time the dialog was open.
20. Enter the Interior point coordinates data. The same data is used. No changes for the current assignment.
21. Enter the topographic parameters in the Topographic factor. The same data is used. No changes for the current assignment.
22. Enter data in the Roof parameters group, for this assignment, all fields are disabled since the Pressure type was set to Leeward.
23. Enter data in the Pressure coefficient group.
- Leave unchecked the User defined checkbox to let the program calculate the coefficient automatically.
24. To see a report of calculated wind loads for selected areas before confirming the assigned values in the dialog press the View report button and a report window will be displayed.
25. Click OK to close the dialog. The wind loads are added for the current load case for all the selected areas.
Leeward pressures on all East walls
26. Select all the areas in the North side of the building.
27. Select the Areas > Surface load spreadsheet.
28. On the Spreadsheet ribbon tab, select the Assign wind pressure tool in the Active spreadsheet tools group.
The Wind load generation for areas dialog opens.
29. Set the Pressure type to Sidewall.
30. Leave the Building geometry, Parameters, Interior point coordinate, Topographic factor and Pressure coefficient groups without changes.
31. Click OK to close the dialog. The wind loads are added for the current load case for all the selected areas.
32. Repeat the steps 26 to 31 but selecting the South walls in the model.
33. After that, the wind pressures in the North and South walls are shown like the following:
Sidewall pressures on all North and South walls
34. To assign wind loads to the roof areas, select the two first rows of areas close to the West side (windward for this load case).
Note. The first two rows of areas are between X=0 ft and X=47.5 ft (half the mean roof height, h/2), which is the first zone to consider for wind pressure on roof per ASCE/SEI 7-16, Chapter 27, Directional Procedure, Part 1. |
35. Switch the load condition to:
36. Select the Areas > Surface load spreadsheet.
37. On the Spreadsheet ribbon tab, select the Assign wind pressure tool in the Active spreadsheet tools group.
The Wind load generation for areas dialog opens.
38. Set the Pressure type to Roof. Note that some fields in the Roof parameters group are now enabled.
Note. Flow type, Free roof type and Pressure direction are fields in the Roof parameters group that are enabled only when the Enclosure category is set to Open to handle wind loads for roofs of open structures. |
39. Leave the Building geometry, Parameters, Interior point coordinate, Topographic factor and Pressure coefficient groups without changes.
40. Enter the following information in the Roof parameters group of data, as follows (refer to notes at the end of this section for an explanation of each field):
- Load case, select A.
- Wind direction, select 90 (degrees).
- Area, 2850 ft2. This area is calculated multiplying 60 ft x 47.5 ft (area of the first roof zone).
- Distance from windward edge, 47.5 ft.
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.
· 0 (degrees). · 90 (degrees) – wind parallel to roof ridge. · 180 (degrees).
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41. Click OK to close the dialog. The wind loads are added for the current load case for all the selected areas.
Roof pressures on the first zone from windward edge
42. Select the next two rows of areas in the roof for the next zone, for a distance from the windward edge between h/2 to h.
43. Repeat the operation from step 35 to 41, changing in the tool dialog only the Area and Distance from windward edge fields as follows:
44. Click OK to close the dialog. The wind loads are added for the current load case for all the selected areas.
45. Select the last row of areas in the roof for the next zone, for a distance from the windward edge between h and 2*h:
46. Repeat the operation from step 35 to 41, changing in the tool dialog only the Area and Distance from windward edge fields as follows:
47. Click OK to close the dialog. The wind loads are added for the current load case for all the selected areas.
48. To complete the additional load cases the user may vary some of the parameters in the tool dialog, switching the Internal pressure to Negative in some cases, or changing the Load case parameter for roofs from A to B option.