Creating loadcases for the All Heights 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 (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 the loadcase will be created for and set default values for all the zone loads generated in the loadcase.
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 so that the number of load combinations that need to be considered can be minimized.
Adding wind loadcases
By clicking the Add button 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:
- AISC 7-16: Table 26.13-1, p271
- AISC 7-10: Figure 26.11-1, p201
- AISC 7-05: Figure 6-5, p47
You are able to flag if it is a Torsional Loadcase or not: when flagged, reduced pressure loads are applied to parts of the standard zones (by applying a net pressure factor of 25%).
For torsional loadcases, you are able to flag if positive or negative eccentricity is applied.
You are able to flag if loads are to be created for roof zones or not.Note: This option is provided to allow for the following note, (depending on the wind code you have selected):
- AISC 7-16: Figure 27.3-1, Note 7, p276
- AISC 7-10: Figure 27.4-1, Note 9, p207
- AISC 7-05: Figure 6-6, Note 9, p49
If loads are created for roof zones, you are able to flag if positive or negative pressure coefficients are to be used for roof zones.
Auto generating wind loadcases
By clicking the Auto button you are able to control the total number of loadcases generated.
Up to 8 loadcases can be generated for each direction. You may choose positive and/or negative GCpi derived from the Enclosure Classification, (see Figure 26.11-1, p201). If you include a direction, but have not checked either +ve GCpi or -ve GCpi, then that is interpreted as a loadcase with GCpi of zero. Similarly you may choose positive and/or negative Cp values for roof zones - checking neither indicates Roof Loads to be ignored for this direction. Torsional loadcases will not be included by default, but can be added with positive or negative eccentricity.
By clicking OK the loadcases are generated, but you can then make any changes required before clicking OK once more to close the Wind Loadcases dialog.