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Important Note – These are descriptions to changes implemented in WoodWorks Shearwalls for version 10.0 and may not reflect current behavior
The program has implemented the change in intensity for minimum wind pressures in ASCE 7-10, minimum wind loads from ASCE 27.1.5 and 28.4.4 as a separate, simultaneous load case, and over-rides of the intensity of minimum pressures for local design codes.
For ASCE 2005, a minimum wind load of 10 psf was applied to the walls and the projected roof area. For ASCE 7-10, this has been changed to 16 psf for walls and 8 psf for roofs. Because of the new 0.6 ASD load factor for winds, this amounts to virtually the same wall loads, but a reduction in roof loads by ½.
Note that gable ends are treated as walls, not roofs, despite the fact they are modelled as part of the roof creation procedure.
Certain local design codes require a different minimum load, for example New York City requires 20 psf. Therefore, the program now allows you to adjust the intensity of the minimum load for walls and for roofs, with the defaults being 16 psf and 8 psf. These are input in the Site Information dialog box, and are recorded in the Site Information output table.
As Commentary C27.4.7 states that minimum loads are to be applied “as a separate load case in addition to the normal load cases..”, the program now generates minimum loads simultaneously with either Directional (All Heights) or Envelope (Low-rise) loads and calculates shearline forces separately for those loads.
Previously, a checkbox in the Load Generation input allowed you to generate minimum loads. The operation was different for All Heights vs. Low-rise loads; for All Heights, the program would selectively apply the minimum load to building elements that it determined were not loaded to the minimum for the all-heights procedure; for Low-rise, the program would generate minimum loads on the structure but not generate low-rise loads. You had to make separate runs and compare your results manually.
The input in the Load Generation box has been eliminated, along with associated message box warnings.
The program always creates loads due to the minimum pressure on walls and the projected roof area. It then distributes loads to the shearlines using each set of loads, and determines the heaviest loading to use for shearwall design. That is, the program compares the shearline forces derived from minimum loads to all four low-rise cases in a particular direction, or two the Case 1 and Case 2 all heights loads, and chooses the critical force for design.
A choice “Minimum” has been added to the Show… menu under “Wind Load Case”, enabling you to see the loads and shearline forces created using Minimum loads. An equivalent checkbox has been added to the Loads and Forces settings.
In the Load Input View, the word Min appears in the load list for generated minimum loads. It is not possible to designate a force that you enter manually as minimum.
In all the tables that currently have a column for load case word, the word Min has been added for minimum loads, with an explanation in the legend below:
Wind Shear Loads
Hold-down Design
Drag Strut Forces
The note regarding the previous minimum load procedure has been removed from the Wind Shear Loads table.
The note that previously appeared saying that you must run minimum loads separately from normal load cases and compare has been removed.
Minimum loads do not appear in the load generation section of the log file, as the log file output shows intermediate data used to arrive at the pressures used to generate loads, and minimum loads specify the pressure without the intermediate data.
In the torsional analysis section of the log file for rigid diaphragms, the case showing the calculations for minimum loads is shown by e.g. E->W and N->S WIND DESIGN (MINIMUM LOADS)
The program detects whether a project from a previous version of the program includes minimum loads, and then prompts you with a recommendation to delete the loads and regenerate.