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Load Cases, Distribution Methods, and Directions
Internally, the program runs separate shear design for wind loads, for seismic loads, and for the rigid diaphragm and flexible diaphragm analysis and for each direction along a shear line. These combinations make a total of eight design cases, however for the vast majority of designs, there are only four, because forces are identical in opposing directions. In the case of wind, this might not be the case for monoslope roofs or eccentric ridge lines. For seismic, it might happen in the unusual circumstance that different hold-downs are on different ends of wall segments. This can also occur if vertically non-aligned openings create different Jhd factors in opposing directions, which can only happen if anchorages are used rather than hold-downs
Wind Load Generation Cases
There may be as many as four low-rise wind load generation cases for each wind direction corresponding to two windward corners and Case A and Case B wind directions. However, the strongest of these forces per shear line is taken before the design process starts, and the program does not design separate shear walls for these loading scenarios.
Component and Cladding Wind Loads
There is only one load case for component and cladding loads used for out-of-plane sheathing bending and shear design and nail withdrawal. This load case is applied during shear wall design, and for each main wind force load case, a wall is selected that satisfies both the MWFRS case and component and cladding design.
Worst-Case Design
Once the walls are designed in initial design iterations, the program then determines the stronger of the wall materials designed for wind and seismic for each wall, and selects that wall for final design. If you have chosen to implement worst-case rigid and flexible diaphragm design in the Design Settings, then the program also determines the stronger of the wall materials designed for each of these distribution methods and selects that wall for final design. (Some designers like to conservatively address the semi-rigid condition by taking the worst of rigid and flexible design in an envelope approach.)
Alternatively, you can reduce the number of designed walls for each physical wall to just one if you know whether your building has rigid diaphragms or flexible diaphragms, and are thus able to turn off one of these methods in the Structure dialog.
If some wall material values are left as unknown, and you have not selected worst-case rigid and flexible design, and you are designing for both methods, the program may design different wall materials for the same physical wall because the two distribution methods have different shear line forces.
Output
The four cases that appear as separate sections in the Design Results are seismic rigid, seismic flexible, wind rigid, and wind flexible. Within the Shear Results table of these sections, the separate design cases for opposing directions, if they exist, appear on separate lines.
Note that the walls shown in these tables may appear to be over-designed, in that a weaker wall would have withstood the load shown. This is because the table is showing a wall designed for a more severe condition, e.g. a wall designed for seismic loads in the wind load table, or a wall designed for rigid diaphragms in the flexible diaphragm table. The tables are meant to show the performance of the wall that was selected by the design process with respect to the various design cases.
All eight possible design cases can be viewed separately in Plan view or Elevation view. The separate low-rise wind load cases can also be viewed in Plan view, but in Elevation view, the worst of the low rise cases is always shown.