Create wind loadcases for the Low Rise Buildings method
It is not practical to automatically determine critical combinations and thus required wind loadcases, therefore you control the generation of appropriate Wind Loadcases manually. This is achieved via the Wind Loadcases dialog box (accessed from the Load tab).
The Auto button on the dialog provides various options to control the number of loadcases before they are generated (its intention being to prevent generation of very large numbers of loadcases). Alternatively you can create loadcases manually using the Add button.
You then specify which direction each loadcase will be created for and set default values for all the zone loads generated in the loadcase.
If you want to consider minimum design wind loadcases these can also be created at the same time.
Once generated these loadcases are standard loadcases so you can include them in combinations in the normal manner.
Try to use engineering judgement to identify the critical loadcases for design. This ensures that the number of load combinations to be considered are minimized. Use the Delete button to remove wind loadcases you do not wish to consider.
Add wind loadcases
By clicking Add you are able to generate loadcases one at a time.
-
The loadcase Name is auto generated from the other input parameters, but it can be edited if required.
-
The Direction the loadcase will be created for is selected from the droplist.
- The internal pressure coefficient is entered directly.
Note: Depending on the wind code you have selected, the default is the negative value depending on the Enclosure Classification from:
- ASCE 7-16: Table 26.13-1, p271
- ASCE 7-10: Figure 26.11-1, p201
- ASCE 7-05: Figure 6-5, p47
-
You are able to select if it is a Torsion Loadcase or not. When selected, "Tors." cases are created in which:
- Reduced pressure loads are applied to parts of the standard zones (by applying a net pressure factor of 25%).
- A system of lateral, radial “push-pull” loads are applied to points in the structure to produce the overall torsion.
-
Because the "Tors." cases also include the lateral wind loads, the “push-pull” loads can be hard to distinguish in the graphical display. An example is illustrated below, showing how the displayed loads are the combined resultants of the lateral wind point loads and the radial "push-pull" torsion loads.
The change in the direction and values of the decomposed wind point loads can best be discerned by comparing to a similar case in which torsion has not been applied.
-
You are able to select if Roof Loads are to be generated for the loadcase or not.
Note: If you selected the Create Minimum Design Wind Loadcases option when running the wind wizard, you are also provided with a Min Design Load option. This can be selected to add a minimum design wind load instead of a standard wind loadcase.
Auto generate wind loadcases
By clicking Auto you are able to control the total number of loadcases generated.
Up to 4 wind loadcases can be generated for each direction, using positive and negative GCpi derived from the Enclosure Classification, (see Figure 26.11-1, p201). If a direction is included, but neither +ve GCpi or -ve GCpi have been checked, then that is interpreted as a loadcase with GCpi of zero. You are also given the option to include the torsional loadcases or not, (default not), but it is assumed that Roof loads are required.
Note: If you selected the Create Minimum Design Wind Loadcases option when running the wind wizard, you are also provided with a Min Design Load option. This can be selected to generate minimum design wind loads in addition to, or instead of, the included standard wind loadcases.
When you click OK the included loadcases are generated. Their names are automatically generated from the other input parameters but can be edited if required (by unchecking the Auto checkbox).
Review wind loadcases
Once wind loadcases have been created they can be reviewed graphically by opening a wind view for the required direction and then selecting the desired wind loadcase from the Loading list.