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Shearwalls checks the compressive resistance of the wall bottom plate beneath the shear wall end chord stud pack.
Compressive Resistance
The factored compressive resistance perpendicular to the grain is
Rr’ = A Fc⊥',
where
Fc⊥’ = CM Ct Cb Fc
where
Cross-sectional Area A
A is the cross-sectional area of the end studs, the same A as is used in the bending term of the deflection equation, so it can be found in the Deflection table in the Design Results output. .
In-service Moisture Factor CM
NDS 4.3.3 refers to Tables 4A-F of the NDS Supplement, which defines the factor separately for MSR, MEL,and visually graded lumber. Wet service conditions are defined by NDS 4.1.4 as greater than 19% in-service moisture.
Moisture content is input in the Service Conditions Design Settings in Shearwalls.
If it is other than 1.0 it is shown in the notes to the Framing Materials table.
Temperature Factor Ct
The determination of Ct in NDS 2.3.3 depends on temperature range and wet service conditions (see above.) For elevated temperatures the factors are:
Range |
Dry |
Wet |
100 – 125 F |
0.8 |
0.7 |
125 – 150 F |
0.7 |
0.5 |
Temperature range is also input in the Service Conditions Design Settings.
If it is other than 1.0 it is shown in the notes to the Framing Materials table.
Bearing Area Factor
The bearing area factor Cb is defined as
Cb = (lb + 0.375) / lb
where lb is the width of the stud pack. Cb is 1.0 for lb ≥ 6.0", so stud packs with 4 members or more are unfactored.
Cb applies only to those force locations that are under openings, and the openings do not extend to the bottom of the wall.
The notes to the framing material table indicate the possibility of the of the Cb factor but to not provide the value, as it can be different for each compression force location in the structure.
Design Results Output
Refer to Design Results Output for a description of the output tables showing compression force design.
Non-wood or Proprietary Walls
There are no assumptions made as to the composition of end chords for Non-wood/Proprietary walls and no compression force design for these walls.