Verification Example - Wood Shear Wall Design - Perforated - Wind (ASD)
Description
This verification example utilizes Tekla Tedds to check a perforated wood shear wall for in-plane load due to wind. This example is based on Design Example E3.3 of 2015/2018 Structural Wood Design Examples by American Wood Council (AWC) (pages 116 to 118). Comparisons and contrasts are tabularized and discussed regarding the results from Tedds and the AWC Design Example. The Tedds file used in this example is provided in the Tedds “Select Calculation” window, under Verification Examples.
Problem statement
Design the first-floor wall shown in Figure 1 as a perforated shear wall for a two-story house using Allowable Stress Design (ASD) provisions. Check design with and without interior gypsum and neglect deflection.
References
2015/2018 Structural Wood Design Examples by American Wood Council
2018 National Design Specification for Wood Construction
2021 and 2015 Special Design Provisions for Wind and Seismic (SDPWS)
ASCE 7-10 Minimum Design Loads for Buildings and Other Structures
Example information
Design wind speed = 160 mph (700-year wind speed, 3-second gust)
Exposure Category B
Building Dimensions:
L = 40’
W = 32’
Roof pitch = 7:12
Top plate to ridge height = 9.3’
Wall height = 9’
Door height = 7’-6”
Window height = 4’-6”
Stud spacing = 16” o.c.
Studs: Southern Pine (G=0.55)
Applied shear load due to wind force, Vw = 5,520 lbs (factored) (provided in AWC design example). Wind load = 5,520 / 0.6 = 9,200 lbs is used in Tedds to account for the 0.6W factor in the ASCE 7-10 load combination.
Exterior wood sheathing: 15/32” thick Wood Structural Panel (WSP) Sheathing, 8d nails @ 4”o.c. edge spacing.
Interior sheathing: ½” thick Gypsum Wallboard (GWB) Sheathing, 5d cooler nail @ 7” o.c. edge spacing, 16” o.c. studs, blocked.
Notes / Assumptions
-
Deflection is not checked.
-
Chords are not designed in the AWS design example, but (3) 2x4 chords are provided within the shear wall.
-
It is assumed that the shear wall will occur in Dry conditions with a temperature of 100℉ or less.
-
A vertical anchor stiffness of 37,739 lb/in is used which correlates with a Simpson Strong-Tie HDU5-SDS2.5 holdown with an allowable tension load of 5,645 lbs.
-
Self-weight of the panel is not included in the AWC design example. A value of 1 psf was used in Tedds for the self-weight of the panel, since Tedds does not allow a wall self-weight equal to 0 psf.
-
Holdown would need to be combined with 2nd floor holdown requirements, not included in the AWC design example or Tedds example.
-
The AWS design example calculates the design of a wood shear wall with WSP exterior sheathing and interior GWB sheathing. However, according to SDPWS 2015 Table 4.3.4, the maximum aspect ratio for gypsum wallboard is 2:1. The aspect ratio for the 3’ long segments is 3:1, exceeding the maximum 2:1 aspect ratio. However, in SDPWS 2021 Table 4.3.3 Note 2 was added which states “For wind design of blocked wood structural panel shear walls or structural fiberboard shear walls, with gypsum wallboard on the opposite side, maximum h/b for gypsum wallboard shall be permitted to be 3.5:1”. Since this note only occurs in SDPWS 2021, the Tedds calculation will utilize SDPWS 2021 to allow shear walls with an aspect ratio of up to 3.5:1.
-
Only the Tedds calculation design with interior gypsum will utilize SDPWS 2021. The Tedds calculation design without interior gypsum will utilize SDPWS 2015, which matches the Design Example.
Figure 1: Wood shear wall configuration
| Comparison of Results between Tedds and AWC Design Example E3.3 | |||
|---|---|---|---|
| Component | Tedds Result | AWC Design Example E3.3 | % Difference |
| Design with interior Gypsum Wallboard (using SDPWS 2021 in Tedds) | |||
| Maximum aspect ratio (based on WPS, per SDPWS 4.3.3) | 3.5:1 | 3.5:1 | 0.0% |
| Largest aspect ratio in shear wall | 3:1 | 3:1 | 0.0% |
| WSP nominal capacity (Wind) | 1315 lb/ft | 1315 lb/ft | 0.0% |
| ASD shear wall capacity (Wind) | 657.5 lb/ft | 657.5 lb/ft | 0.0% |
| Sum of perforated shear wall lengths (Li) | 18’ | 18’ | 0.0% |
| Shear capacity adjustment factor (Co) | 0.727 | 0.78 | 7.3%a |
| Shear capacity (Wind) | 8,607 lbs |
9231 lbs (532.5 lb/ft * 0.78 * 18’) |
7.3%a |
| Required holdown capacity, T | 3,795 lbs |
3,538 lbs (5,520 lb * 9’ / (0.78 * 18’)) |
7.3%a |
| Design without interior Gypsum Wallboard (using SDPWS 2015 in Tedds) | |||
| Maximum aspect ratio (based on WPS, per SDPWS 4.3.3) | 3.5:1 | 3.5:1 | 0.0% |
| Largest aspect ratio in shear wall | 3:1 | 3:1 | 0.0% |
| WSP nominal capacity (Wind) | 1065 lb/ft | 1065 lb/ft | 0.0% |
| ASD shear wall capacity (Wind) | 532.5 lb/ft | 532.5 lb/ft | 0.0% |
| Sum of perforated shear wall lengths (Li) | 18’ | 18’ | 0.0% |
| Shear capacity adjustment factor (Co) | 0.784 | 0.78 | 0.0% |
| Shear capacity (Wind) | 7,518 lbs |
7,476 lbs (532.5 lb/ft * 0.78 * 18’) |
0.6% |
| Required holdown capacity, T | 3,519 lbs |
3,538 lbs (5,520 lb * 9’ / (0.78 * 18’)) |
0.5% |
Comparison Notes:
aDifferences in shear capacity and required holdown capacity can be attributed to the revised method of calculating the shear capacity adjustment factor (Co) which was revised in SDPWS 2021. The AWC Design Example calculates the adjustment factor per SDPWS 2015. As can be seen in the Tedds calculation without interior gypsum wallboard which utilizes SDPWS 2015, the shear capacity adjustment factor is in agreement with the AWC Design Example.
Conclusion:
Upon reviewing the results above, the determination of shear wall capacity and holdown force for a perforated wood shear wall for wind shear forces using Tekla Tedds is consistent with AWC Design Example 3.3, which references SDPWS. Differences between Tedds and the example can be attributed to rounding and the revised method of calculating the shear capacity adjustment factor in SDPWS 2021. Users should feel confident that results determined in the Tedds Wood Shear Wall Design module are in agreement with NDS and SDPWS.