Verification Example - Wood Shear Wall Design - Segmented - Seismic (ASD)
Description
This verification example utilizes Tekla Tedds to check a segmented wood shear wall for in-plane load due to seismic. This example is based on Design Example E3.2 of 2015/2018 Structural Wood Design Examples by American Wood Council (AWC) (pages 114 to 115). 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 segmented 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
2015 Special Design Provisions for Wind and Seismic (SDPWS)
ASCE 7-10 Minimum Design Loads for Buildings and Other Structures
Example information
Seismic Design Category D1 (Based on 2015 International Residential Code (IRC))
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 seismic force, Vs = 4,733 lbs (factored) (provided in AWC design example). Seismic load = 4,733 / 0.7 = 6,761 lbs is used in Tedds to account for the 0.7E factor in the ASCE 7-10 load combination.
Exterior wood sheathing: 7/16” thick Wood Structural Panel (WSP) Sheathing, 8d nails @ 4”o.c. edge spacing.
Interior sheathing: none
Notes / Assumptions
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Deflection is not checked.
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Chords are not designed in the AWS design example, but (3) 2x4 chords are provided within the shear wall.
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It is assumed that the shear wall will occur in Dry conditions with a temperature of 100℉ or less.
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A vertical anchor stiffness of 25,170 lb/in is used which correlates with a Simpson Strong-Tie HDU2-SDS2.5 holdown with an allowable tension load of 3,075 lbs.
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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.
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Holdown would need to be combined with 2nd floor holdown requirements, not included in the AWC design example or Tedds example.
Figure 1: Wood shear wall configuration
| Comparison of Results between Tedds and AWC Design Example E3.2 | |||
|---|---|---|---|
| Component | Tedds Result | AWC Design Example E3.2 | % Difference |
| Maximum aspect ratio (based on WPS, per SDPWS 4.3.4) | 3.5:1 | 3.5:1 | 0.0% |
| Largest aspect ratio in shear walla | 3:1 | 3:1 | 0.0% |
| WSP nominal capacity (Seismic) | 760 lb/ft | 760 lb/ft | 0.0% |
| ASD shear wall capacity (Seismic) | 380 lb/ft | 380 lb/ft | 0.0% |
| Shear capacity (Seismic) | 6,840 lbs | 5,320 lbs | 28.6%b |
| Required holdown capacity, T | 2,366 lbs | 3,043 lbs | 28.6%b |
Comparison Notes
aMaximum aspect ratio for WSP shear walls to avoid capacity adjustments = 2:1, so 3’ wide segments will require capacity adjustments per SDPWS 4.3.3.4.1., which is performed within Tedds.
bDifference in shear capacity and holdown forces is due to the AWC design example utilizing (2) 5’ wide panels and (2) 3’ wide panels to resist the required shear loads, while Tedds utilizes all of the available panels within the shear walls to resist shear. A separate Tedds calculation with only (2) 5’ wide panels and (2) 3’ wide panels could be created, which would then produce the same results as the AWC design example.
Conclusion
Upon reviewing the results above, the determination of shear wall capacity and holdown force for a segmented wood shear wall for seismic shear forces using Tekla Tedds is consistent with AWC Design Example 3.2, which references SDPWS. Differences between Tedds and the example can be attributed to engineering design differences. Users should feel confident that results determined in the Tedds Wood Shear Wall Design module are in agreement with NDS and SDPWS.