The following explains how these factors are considered, without getting into detailed calculations.
Initial Calculation to Determine Segment Rotation
The program does an initial calculation which concentrates all dead load and wind uplift load at the wall ends and determines whether the total dead force at the tension end counteracts uplift from all sources.
Downward Forces
The dead forces included are:
the force due to all dead loads on the segment distributed via simple span beam mechanics to the member ends. These dead loads come from
dead loads input or generated on the wall. If you specified in the hold-down settings that only a portion of dead load adjacent to the wall will be included, then only that load will be used, unless you specified Include dead load on entire wall if it completely counteracts overturning
dead loads passed through from non-shearwalls or narrow, non-shear-resisting segments on the level above
dead loads passed through to the level below via the process described herein; i.e. they are excess to what is required to resist overturning.
dead loads passed through because you have specified that in the hold-down settings that only a portion of the vertical loads on the upper shear wall is to be passed to the level below. For walls segments that line up, this load will be again passed down to the level below and not used to counteract overturning.
the dead component of the hold-down force on the level above. This represents the weight of upper levels
dead loads and forces transferred from adjacent openings, representing the weight above those openings transferred as point loads to the opening support and the end of the segment
In rare circumstances, a downward-directed shear overturning component at what is ordinarily the tension end could add to these forces. this happens when a shear overturning component on a neighbouring opening that was at the other end of an upper wall segment was transferred to the segment end.
Shear overturning that may be on adjacent openings due to offset openings or jogs in the shear line, transferred to the opening support at the wall segment end
The force due to wind uplift loads on the segment distributed via simple span beam mechanics to the member ends. These loads come from
wind uplift loads input on the wall segment. These are typically on the uppermost level only. If you specified in the hold-down settings that only a portion of wind uplift load adjacent to the wall will be included, then only that load will be used
wind uplift loads passed through from non-shearwalls or narrow, non-shear-resisting segments on the level above
wind uplift loads passed from the wall above because it completely counteracts overturning (see below)
wind uplift loads passed through from levels above because you have specified that in the hold-down settings that only a portion of the vertical loads on the upper shear wall is to be passed to the level below. For walls segments that line up, this load will be again passed down to the level below and not used to contribute to uplift.
wind uplift component of the hold-down force on the level above. This is typically the same on all levels of the structure for shear walls that line up.
wind uplift forces on adjacent openings due to offset openings or jogs in the shear line. These would likely only occur on the second-to-top level.
the vertical earthquake load Ev
Dead Load Does not Completely Counteract Overturning
If the dead load does not completely counteract overturning, then all force components from the sources listed above are concentrated at the wall ends except that at the compression end, the shear overturning force from the wall segment and the vertical earthquake force Ev are ordinarily downwardly directed and combined with the dead load contributions rather than contributing to uplift. There is a net tension force at the tension end and the wind uplift force serves to reduce the compression force at the compression end.
Dead Load Completely Counteracts Overturning
Wind Uplift Loads
If the dead force completely counteracts the overturning force plus the wind uplift force and the vertical earthquake force Ev, then the program transfers the wind uplift load load down to the level below as a line load, as it cannot be assumed to be be concentrated at the end supports for a non-rotating element.
Forces from Levels Above and Adjacent Openings are Sufficient
The program then checks to see if the the dead hold-down force coming in from the levels above or from over adjacent openings, is enough to completely counteract the upwards force from all the sources listed in the Dead Load Does not Completely Counteract Overturning section above minus the wind uplift force that has been transferred down as a line load. If it is, the entire dead load on the wall is transferred as a line load to the level below. The net force at the tension end is in this case a compression force, that is, the excess dead force from the levels above or adjacent openings beyond what is needed to counteract upwards forces.
Dead Load on Wall Required to Completely Resist Overturning
If the dead wall end forces from the levels above or adjacent openings are not sufficient to completely resist overturning and wind uplift, the program calculates how much dead load over the wall is needed. That dead load distributed via simple-span beam mechanics to the wall ends, and the rest is passed through as a line load to the bottom to load the wall on the level below.
In this case the net force at the tension end is zero.
Compression End Force
For both of these scenarios, the compression end is subject to the following forces, all of which are ordinarily directed downwards.
the overturning force component on the wall segment,
overturning forces from offset segments on upper floors that may have been transferred from adjacent openings. This is included in the "C" component shown by the force in Elevation view, so C may be different from T at the other end of the wall segment for this reason.
The proportion of dead load on the wall segment that was needed to counteract overturning at the tension end, distributed to the compression end via simple beam mechanics. For uniform or symmetric dead loads, this will the the same amount of dead load that was applied to the tension end.
The following upward-directed contributions can occur in some circumstances
overturning forces from neighbouring openings
wind uplift loads and forces from neighbouring openings
wind uplift contribution from the hold-down force on the level above. However, if dead load was not sufficient to counteract overturning on the upper level, it would be unlikely to do so on the level below, and the wind uplift forces are concentrated at the member ends only if there is rotation.
