Resolving Wood Shear Wall Design Puzzles with Force ...€¦ · Resolving Wood Shear Wall Design...
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Resolving Wood Shear Wall Design Puzzles with Force Transfer Around Openings
Resolving Wood Shear Wall Design Puzzles with Force Transfer Around Openings
Presented by: Jared S. Hensley, P.E.Disclaimer: This presentation was developed by a third party and is not funded by
American Wood Council or the Softwood Lumber Board.
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“The American Wood Council” is a Registered Provider with The American Institute of Architects Continuing Education Systems (AIA/CES), Provider #50111237.
Credit(s) earned on completion of this course will be reported to AIA CES for AIA members. Certificates of Completion for both AIA members and non‐AIA members are available upon request.
This course is registered withAIA CES for continuing professional education. As such, it does not include content that may be deemed or construed to be an approval or endorsement by the AIA of any material of construction or any method or manner of handling, using, distributing, or dealing in any material or product.
______________________________Questions related to specific materials, methods, and services will be addressed atthe conclusion of this presentation.
Resolving Wood Shear Wall Design Puzzles with Force Transfer Around Openings
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Course Description
This presentation provides an overview of the Force Transfer Around Openings (FTAO) shear wall design approach, recent research in this area, and a side-by-side comparison of design results between segmented, perforated, and FTAO design methods. This methodology is based on a joint research project of APA – The Engineered Wood Association, University of British Columbia (UBC), and USDA Forest Products Laboratory that examined variations of shear walls with code-allowable openings. The study evaluated internal forces generated during testing and assessed the effects of opening sizes, full-height pier sizes, and different construction techniques, including the segmented, perforated, and FTAO methods. Asymmetric piers, multiple openings, and C-shaped sheathing were investigated and rational design methodologies in accordance with the International Building Code have been created.
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Learning Objectives
1. Participants will investigate past and current methods for determining force transfer around openings for wood shear walls through discussion of the joint research project of APA – The Engineered Wood Association, the University of British Columbia (UBC), and the USDA Forest Products Laboratory (FPL).
2. Participants will compare the effects of different opening sizes, full-height pier sizes, and their relationships to the three industry shear wall approaches by illustrating use of the segmented, perforated, and FTAO methods.
3. Participants will observe how the study examined internal forces generated during loading by reviewing full-scale wall test data as well as analytical modeling performed in determining statistical accuracy.
4. Participants will conclude that research results obtained from this study can be used to support different design methodologies in estimating forces around openings accurately.
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Audience Poll
1. What is your profession?A. Architect
B. Engineer
C. Builder
D. Building Official
E. Other
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Audience Poll
2. How would you describe your knowledge of Force Transfer Around Openings?A. Expert
B. Intermediate
C. Novice
D. What am I doing here?
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Agenda
1. Shear Wall Design Challenges
2. History of FTAO Research at APA
3. Advancements in FTAO Asymmetric Pier Widths
Multiple Openings
C-shaped Panels
Deflection Calculations
Conceptual Keys
4. Benefits of FTAO with Continuous Wood Structural Panels
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Shear Wall Design Challenges
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Shear Wall Design Challenges
Segmented1. Aspect Ratio of
2:12. Aspect ratio up to
3.5:1, if allowable shear is reduced by 2b/h
Force Transfer1. Code does not
provide guidance for this method
2. Different approaches using rational analysis could be used
Perforated1. Code provides
specific requirements
2. The capacity is determined based on empirical equations and tables
15 SDPWS 4.3.5
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H H H Hvv
Vbs
Only full height segmentsare consideredHold-downs at each
wall segmentMax aspect ratio 2:1 – without
adjustment 3.5:1 – with
adjustment New to SDPWS-15
Aspect ratio h:bs as shown in figure
h
15 SDPWS Section 4.3.5.1
Shear Wall Design Challenges
Segmented Wood Shear Walls
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Openings accounted for by empirical adjustment factorHold-downs only at
endsUplift between hold
downs, t, at full height segments is also required Limited to 870 plf H H
V
Aspect ratio h:bs as shown in figure
t t
15 SDPWS 4.3.5.3
Shear Wall Design Challenges
Perforated Shear Walls
vmax vmax
h
bs
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Openings accounted for by strapping or framing “based on a
rational analysis”
Hold-downs only at endsH/w ratio defined
by wall pier
15 SDPWS 4.3.5.2
Shear Wall Design Challenges
FTAO Shear Walls
H H
V
Aspect ratio h:bs as shown in figure
v
h
bs
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Audience Poll
3. How often do you use FTAO when designing a building utilizing wood shear walls?A. > 50% (Frequently)
B. 0-25% (At least once per job)
C. 0% (I only use segmented or perforated)
D. N/A (I don’t design wood buildings.)
1414h:b ratio Perforated
Excerpt Fig 4Ch:b ratio Segmented
Excerpt Fig 4D
Shear Wall Design Challenges
Shear Wall Aspect Ratio AdjustmentsDefinitions of h and b are the same as in previous codes
ALL shear walls with 2:1 < aspect ratios <= 3.5:1 shall apply reduction factor known as the aspect ratio factor
Aspect Ratio Factor (WSP) = 1.25-0.125h/bs Formerly applied only to high seismic
15 SDPWS 4.3.4
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Shear Distribution to Shear Walls in Line Individual shear walls in line shall provide the same
calculated deflection. Exception: Nominal shear capacities of shear walls having 2:1<aspect
ratio<=3.5:1 are multiplied by 2bs/h for design. Aspect ratio factor (4.3.4.2) need not be applied.
15 SDPWS 4.3.3.4.1
Shear Wall Design Challenges
h:b ratio PerforatedExcerpt Fig 4C
h:b ratio SegmentedExcerpt Fig 4D
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Perforated Shear Wall Aspect Ratios Full Height wall segments 2:1 < aspect ratio <= 3.5:1 Multiply those segments by 2bs/h to calculate Li and ΣLi
Sections 4.3.4.2 and 4.3.3.4.1 do not apply
L1 L2 L3 L4
L
Shear Wall Design Challenges
15 SDPWS 4.3.4.3
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4. When designing shear walls with the NEW aspect ratio factor of 1.25-0.125h/bs, the deflection of each individual shear wall must be…A. < 1 inch
B. equal.
C. dependent on the wall material.
D. a parabola.
Audience Poll
4. When designing shear walls with the NEW aspect ratio factor of 1.25-0.125h/bs, the deflection of each individual shear wall must be…A. < 1 inch
B. equal.
C. dependent on the wall material.
D. a parabola.
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Shear Wall Design Challenges
Typical FTAO Application Residential, Multifamily Single Opening Design assumes equal pier width
Commercial Strap continuous wall line above
and below openings Fully sheath wall
Field Survey 18+ sites fall 2010 (LA, Orange and San Diego Counties) Multi-Family 40-90% of all shear applications utilized FTAO
Single-Family 80% Minimum 1-application on front or back elevation 70% Multiple applications on front, back or both 25% Side wall application in addition to front or back application
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History of FTAO Research at APA
Joint Research Project APA - The Engineered Wood Association (Skaggs & Yeh)
University of British Columbia (Lam & Li),
USDA Forest Products Laboratory (Rammer & Wacker)
Study was initiated in 2009 to: Examine the variations of walls with code-allowable openings
Examines the internal forces generated during full-scale testing
Evaluate the effects of size of openings, size of full-height piers, and different construction techniques
Create analytical modeling to mimic testing data
2020
Study results will be used to:Support design methodologies in estimating the forces
around the openings Develop rational design methodologies for adoption in
the building codes and supporting standardsCreate new tools/methodology for designers to
facilitate use of FTAO
History of FTAO Research at APA
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L1 Lo L2
h
V
vp
v v
vp
v v
1
2
History of FTAO Research at APA
Prominent FTAO Techniques
Drag Strut Analogy Forces are collected
and concentrated into the areas above and below openings
Strap forces are a function of opening and pier widths
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ho/2F1
V1
L1
h1
ho/2F2
V2
L2
hU
1
2
History of FTAO Research at APA
Prominent FTAO Techniques
Cantilever Beam Analogy Forces are treated as moment
couples
Segmented panels are piers at sides of openings
Strap forces are a function of height above and below opening and pier widths
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Diekmann Assumes wall behaves as
monolith
Internal forces resolved via principles of mechanics
History of FTAO Research at APA
Prominent FTAO Techniques
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5. In which FTAO method are the forces determined by calculating moment couples?A. Drag Strut Analogy
B. Cantilever Beam Analogy
C. Diekmann (Thompson)
D. The Unicorn Method
Audience Poll
5. In which FTAO method are the forces determined by calculating moment couples?A. Drag Strut Analogy
B. Cantilever Beam Analogy
C. Diekmann (Thompson)
D. The Unicorn Method
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2.3' 4' 4'
8'4'
2'
2,000 lbf
2'
10.3'
History of FTAO Research at APA
FTAO Design Example Comparison
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Drag Strut Analogy F1 = 284 lbf
F2 = 493 lbf
Cantilever Beam Analogy F1 = 1,460 lbf
F2 = 2,540 lbf
Diekmann Technique F1 = 567 lbf
F2 = 986 lbf
History of FTAO Research at APA
FTAO Design Example Comparison
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Drag Strut Analogy Martin, Z.A. 2005. Design of wood structural panel shear walls with
openings: A comparison of methods. Wood Design Focus 15(1):18-20
Cantilever Beam Analogy Martin, Z.A. (see above)
Diekmann Method Diekmann, E. K. 2005. Discussion and Closure (Martin, above), Wood
Design Focus 15(3): 14-15 Breyer, D.E., K.J. Fridley, K.E. Cobeen and D. G. Pollock. 2014. Design
of Wood Structures ASD/LRFD, 7th ed. McGraw Hill, New York.
SEAOC/Thompson Method SEAOC. 2014. 2015 IBC Structural/Seismic Design Manual, Volume 2:
Examples for Light-frame, Tilt-up and Masonry Buildings. Structural Engineers Association of California, Sacramento, CA
History of FTAO Research at APA
Prominent FTAO Techniques
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Advancements in FTAO
APA Testing w/ CUREE Basic Loading Protocol
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12 wall configurations tested Walls were tested with and without FTAO strapping
Wall nailing; 10d commons (0.148” x 3”) at 2” o.c.
Sheathing; 15/32 Perf Cat oriented strand board (OSB) APA STR I
All walls were 12 feet long and 8 feet tall
Cyclic loading protocol following ASTM E2126, Method C, CUREE Basic Loading Protocol
Advancements in FTAO
Test Plan
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8'-0
"3'-0
"3
'-10
"
Advancements in FTAO
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5'-0
"1
'-10
"
Advancements in FTAO
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4'-0
"
2'-4
"4'
-0"
5'-0
"
7'-0
"
Advancements in FTAO
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Information Obtained Through TestingCyclic hysteretic plots and various cyclic parameters
of the individual walls
Hold down force plots
Anchor bolt force plots
Hysteric plots of the applied load versus the displacement of the walls
Hysteric plots of the applied load versus strap forces
Advancements in FTAO
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Diekmann
Technique
Top Bottom Top Bottom Top Bottom Top/Bottom Top Bottom
Wall 4a 687 1,485 178% 82% 652% 183% 132% 406% 115%
Wall 4b 560 1,477 219% 83% 800% 184% 133% 499% 115%
Wall 4c (3)668 1,316 183% 93% 670% 207% 149% 418% 129%
Wall 4d 1,006 1,665 122% 73% 445% 164% 118% 278% 102%
Wall 5b 1,883 1,809 65% 68% 327% 256% 173% 204% 160%
Wall 5c (3)1,611 1,744 76% 70% 382% 265% 187% 238% 166%
Wall 5d 1,633 2,307 75% 53% 377% 201% 141% 235% 125%
Wall 6a 421 477 291% 256% 1063% 571% 410% 663% 357%
Wall 6b 609 614 201% 199% 735% 444% 319% 458% 277%
Wall 8a 985 1,347 118% 86% 808% 359% 138% 269% 120%
Wall 8b (4)1,493 1,079 78% 108% 533% 449% 124% 177% 150%
Wall 9a 1,675 1,653 69% 70% 475% 383% 185% 217% 166%
Wall 9b 1,671 1,594 69% 73% 476% 397% 185% 218% 172%
Wall 10a 1,580 n.a. (5) 73% n.a. (5) 496% n.a. (5) n.a. (5) n.a. (5) n.a. (5)
Wall 10b 2,002 n.a. (5)58% n.a. (5)
391% n.a. (5) n.a. (5) n.a. (5) n.a. (5)
Wall 11a 2,466 n.a. (5) 47% n.a. (5) 318% n.a. (5) n.a. (5) n.a. (5) n.a. (5)
Wall 11b 3,062 n.a. (5)38% n.a. (5)
256% n.a. (5) n.a. (5) n.a. (5) n.a. (5)
Wall 12a 807 1,163 81% 94% 593% 348% 128% n.a. (5) n.a. (5)
Wall 12b 1,083 1,002 60% 109% 442% 403% 138% n.a. (5) n.a. (5)
Error (2) For Predicted Strap Forces at ASD Capacity (%)
Wall ID
Measured Strap
Forces (lbf) (1)
Drag Strut Technique Cantilever Beam TechniqueSEAOC/Thompson
Technique
Advancements in FTAO
Measured vs Predicted Strap Forces
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Wall 13
Click to Play
Advancements in FTAO
Testing Observations
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12 assemblies tested, examining the three approaches to designing and detailing walls with openings Segmented
Perforated Shear Wall
Force Transfer Around Openings
Walls detailed for FTAO resulted in better global response
Advancements in FTAO
Testing Results
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Comparison of analytical methods with tested values for walls detailed as FTAO The drag strut technique was consistently un-conservative
The cantilever beam technique was consistently ultra-conservative
SEAOC/Thompson provides similar results as Diekmann
SEAOC/Thompson & Diekmann techniques provided reasonable agreement with measured strap forces
Better guidance to engineers will be developed by APA for FTAO Summary of findings for validation of techniques
New tools for IRC wall bracing
Advancements in FTAO
Conclusions of Tests
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6. Which FTAO method tested was found to be consistently un-conservative?A. Drag Strut Analogy
B. Cantilever Beam Analogy
C. Diekmann (Thompson)
D. The Unicorn Method
6. Which FTAO method tested was found to be consistently un-conservative?A. Drag Strut Analogy
B. Cantilever Beam Analogy
C. Diekmann (Thompson)
D. The Unicorn Method
Audience Poll
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www.apawood.org/publications
Report is 149 pages, 28.5 MB
Enter: “Force Transfer”
or “M410”
Advancements in FTAO
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Advancements in FTAO
SEAOC Convention 2015 Proceedings
Basis of APA FTAO Design Methodology
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Asymmetric Pier WidthsMartin, Diekmann (Wood Design Focus, 2005)
Advancements in FTAO
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Multiple OpeningsAPA FTAO Testing Wall 12 Two openings
Asymmetric pier widths
Diekmann Rational Analysis
Advancements in FTAO
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Conceptual Keys
The method assumes the following: The unit shear above and below the openings is equivalent.
The corner forces are based on the shear above and below the openings and only the piers adjacent to that unique opening.
The tributary length of the opening is the basis for calculating the shear to each pier. This tributary length is the ratio of the length of the pier multiplied by the length of the opening it is adjacent to, then divided by the sum of the length of the pier and the length of the pier on the other side of the opening.
For example, T1 = (L1*Lo1)/(L1+L2)
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Conceptual Keys
The method assumes the following: The shear of each pier is the total shear divided by the L of
the wall, multiplied by the sum of the length of the pier and its tributary length, divided by the length of the pier: v1 = (V/L)(L1+T1)/L1
The unit shear of the corner zones is equal to subtracting the corner forces from the panel resistance, (R). R is equal to the shear of the pier multiplied by the pier length: Va1 = (v1L1 – F1)/L1
L1 Lo1 L2 L3Lo2V
L
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Conceptual Keys
The method assumes the following:Once the entire segment shears have been calculated,
then the design is checked by summing the shears vertically along each line. The first and last line equal the hold-down force, and the rest should sum to zero.
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Audience Poll
7. Which lateral design method do you believe is the most economical?A. Segmented
B. Perforated
C. FTAO
D. Duct Tape
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Shear Wall Design Examples
Segmented Shear Wall Approach
Perforated Shear Wall Approach
Force Transfer Around Opening Approach
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Shear Wall Design Examples
3’-6” 3’-0” 4’-0” 6’-0” 4’-0” 3’-6”2’-0”
6’-8”
2’-8” 2’-8”
8’-0
”
V
V = 3,750 lb
26’-0”
Standard Example Wall with 3 openings.
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3’-6” 3’-0” 4’-0” 6’-0” 4’-0” 3’-6”2’-0”
6’-8”
2’-8” 2’-8”
8’-0
”
V
Does not consider contribution of sheathing above and below openings
26’-0”
Segmented Approach
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4’-0” 6’-0” 4’-0” 3’-6”2’-0”
6’-8”
2’-8” 2’-8”
8’-0
”
V
V = 3,750 lbsHeight/width Ratio = 8:3.5
2w/h = (2)(3.5)/8 = 0.875
vH HCode Limitation
3’-6” 3’-0”
vH H vH H vH H
15 SDPWS 4.3.3.4.1
Segmented Approach
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1. Unit Shear
V = V/∑L = 3,750/15 = 250 lbs/ft
2. Allowable Shear 3’-6” wallsv allowable = 380 (0.875)=332 lbs/ft > 250 lbs/ft
3. Allowable Shear 4’ walls (2:1 h:w)
v allowable = 260lb/ft > 250 lbs/ft
4. Hold-down forcesH = vh = 250 x 8 = 2,000 lbs
15/32” Rated Sheathing 8d @ 4”o.c. at 3.5’ walls
Note: For simplicity Dead Load contributions and various footnote adjustments have been omitted
8 – hold downs @ 2000+ lb capacity
15/32” Rated Sheathing 8d @ 6”o.c. @ 4’ walls
Segmented Approach
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8 – hold downs @ 2000+ lb capacity
4’-0” 6’-0” 4’-0” 3’-6”2’-0”
6’-8”2’-8” 2’-8”
8’-
0”
V
V = 3,750 lbsv = 250 lbs/ftH = 2,000 lbs
v v v vH H H H H H H H
3’-6” 3’-0”
15/32” Rated Sheathing 8d @ 6”o.c.
15/32” Rated Sheathing 8d @ 4”o.c.
Summary
Segmented Approach
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Shear Wall Design Examples
Segmented Shear Wall Approach
Perforated Shear Wall Approach
Force Transfer Around Opening Approach
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3’-6” 3’-0” 4’-0” 6’-0” 4’-0” 3’-6”2’-0”
6’-8”
2’-8” 2’-8”
8’-0
”
V
V = 3,750 lb
v, tH H
26’-0”
Code LimitationHeight/width Ratio = 8:3.52w/h = (2)(3.5)/8 = 0.875
v, t v, tv, t
Perforated Approach
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1. Unit shear in the wall
v = 3,750/15 = 250 lb/ft
2. Percent of Full-Height Sheathed
∑Li/L = 15/26 = 0.57 (57%)
3. Maximum opening heighth = 6’-8”
Perforated Approach
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57% 0.61
15 SDPWS Table 4.3.3.5
Perforated Approach
Shear Capacity Adjustment Factor, Co
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4. Co – Shear Resistance Adjustment Factor
Co = 0.612 say 0.61
5. Adjusted Shear Resistance 4’-0” Walls
v allowable = 490 x 0.61 = 299 lbs/ft > 250 lbs/ft
3’-6” WALLS
v allowable = 490 x 0.875 x 0.61 = 262 lbs/ft > 250 lbs/ft
15/32” Rated Sheathing 8d @ 3”o.c.
15 SDPWS Table 4.3A
Perforated Approach
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6. Uplift at Perforated Shear Wall ends (hold downs)
R = (v*H)/Co = (250*8)/(0.61) = 3,280 lbs
7. In-plane Shear Anchorage
vmax = 250/0.61 = 410plf
8. Uplift anchorage between shear wall ends
t = 250/0.61 = 410 plf (at full segments only)
9. Deflection is calculated using the 4-term deflection
equation from Chapter 23 of the 2015 IBC
using our vmax value for v and the sum of
the full height segment lengths for b.
15 IBC Equation 23-2
Perforated Approach
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3’-6” 3’-0” 4’-0” 6’-0” 4’-0” 3’-6”2’-0”
6’-8”
2’-8” 2’-8”
8’-0
”
V
V = 3,750 lbv = 250 lbs/ftH = 3,280 lbs
v, tH Hv, t v, tv, t
Summary
Vmax = t = 410 lbs/ft
(wall anchorage)
15/32” Rated Sheathing 8d @ 3”o.c.
Perforated Approach
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Shear Wall Design Examples
Segmented Shear Wall Approach
Perforated Shear Wall Approach
Force Transfer Around Opening Approach
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3’-6” 3’-0” 4’-0” 6’-0” 4’-0” 3’-6”2’-0”
2’-8” 2’-8”
8’-
0”
V
V = 3,750 lbs
H H
26’-0”
Height/width Ratio = 2’-8” / 3’-6”
6’-8”
19’-6”6’-6”
FTAO Approach
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FTAO Approach
1. Calculate the hold-down forces:
H = Vh/L = (3750 x 8’)/19.5’ = 1538lbs
2. Solve for the unit shear above and below the openings:
va = vb = H/(ha+hb) = 1538/(1.33’+4’) = 289 plf
CK: The unit shear above and below the openings is equivalent.
L1 Lo1 L2 L3Lo2
2’-8” 2’-8”
V
H H
L
6’-8”
hho
ha
hb
va
vb
va
vb
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FTAO Approach
3. Find the total boundary force above and below the openings
First opening: O1 = va x (Lo1) = 289 plf x 6’ = 1734lbs
Second opening: O2 = va x (Lo2) = 289 plf x 2’ = 578lbs
CK: The corner forces are based on the shear above and below the openings and only the piers adjacent to that unique opening.
L1 Lo1 L2 L3Lo2
2’-8” 2’-8”
V
H H
L
6’-8”
hho
ha
hb
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FTAO Approach
4. Calculate the corner forces:
F1 = O1(L1)/(L1+L2) = 866# F2 = O1(L2)/(L1+L2) = 866#
F3 = O2(L2)/(L2+L3) = 308# F4 = O2(L3)/(L2+L3) = 269#
CK: Strap forces
L1 Lo1 L2 L3Lo2
2’-8” 2’-8”
V
H H
L
6’-8”
hho
ha
hb
F1 F2 F3 F4
F1 F2 F3 F4
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FTAO Approach
5. Tributary length of openings (ft)
T1 = L1(Lo1)/(L1+L2) = 3’ T2 = L2(Lo1)/(L1+L2) = 3’
T3 = L2(Lo2)/(L2+L3) = 1.1’ T4 = L3(Lo2)/(L2+L3) = 0.9’
CK: Ratio of the length of the pier x length of the opening it is adjacent to, then / (length of the pier + length of the pier on the other side of the opening).
L1 Lo1 L2 L3Lo2V
H H
L
6’-8”
hho
ha
hb
T1 T2 T3 T4
6666
FTAO Approach
6. Unit shear beside the openingV1 = (V/L)(L1+T1)/L1 = 337 plf V2 = (V/L)(T2+L2+T3)/L2 = 388 plf
V3 = (V/L)(T4+L3)/L3 = 244 plf Check V1*L1 +V2*L2+V3*L3=V? YES
CK: The shear of each pier = the total shear / the L of the wall x (length of the pier + its tributary length)/ by the length of the pier
L1 Lo1 L2=4’ L3Lo2V
H H
L=19’-6”
6’-8”
hho
ha
hb
T1 T2
3’-0”
T3
1.1’
T4V1 V3V2
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FTAO Approach
7. Resistance to corner forces
R1=V1*L1 = 1346lbs
R2 = V2*L2 = 1551lbs
R3 = V3*L3 = 853lbs
8. Resistance – corner force
R1-F1 = 480lbs
R2-F2-F3 = 377lbs
R3-F4 = 583lbs
L1 Lo1 L2 L3Lo2
2’-8” 2’-8”
V
H H
L
6’-8”
hho
ha
hb
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FTAO Approach
9. Unit shear in the corner zones
va1 = (R1-F1)/L1 = 120 plf
va2 = (R2-F2-F3)/L2 = 94 plf
va3 = (R3-F4)/L3 = 167 plfCK: The unit shear of the corner zones = panel resistance (R) -the corner forces . R = the shear of the pier x the pier length.
L1 Lo1 L2 L3Lo2
2’-8” 2’-8”
V
H H
L
6’-8”
hho
ha
hb
va1 va2
vb1 vb2
va3
vb3
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FTAO Approach
L1 Lo1 L2 L3Lo2
2’-8” 2’-8”
V
H H
6’-8”
hho
ha
hb
10. Check your solution – YES to all
Line 1: va1(ha+hb)+v1(ho)=H?
Line 2: va(ha+hb)-va1(ha+hb)-V1(ho)=0?
Line 3: va2(ha+hb)+V2(ho)-va(ha+hb)=0?
Line 4 = Line 3
Line 5: va(ha+hb)-va3(ha+hb)-V3(ho)=0?
Line 6: va3(ha+hb)+V3(ho)=H?
1 2 43 5 6
CK: Once all segment shears are calculated, check the design by summing the shears vertically along each line. The 1st and last = hold-down force, and the rest should = zero.
va1 va2 va3
V1 V2 V3
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FTAO Approach
2-Horizontal straps rated at 866lbs
Summary
3’-6” 3’-0” 4’-0” 6’-0” 4’-0” 3’-6”2’-0”
2’-8” 2’-8”
8’-
0”
V
H H
26’-0”
6’-8”
19’-6”6’-6”
V = 3,750 lbv = 388 lbs/ftH = 1,538 lbs 15/32” Rated Sheathing 8d @ 4”o.c.
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15/32” Rated sheathing
8d @ 4”o.c. (3’-6” walls)
8d @ 6” o.c. (4’ walls)
8 – hold downs @ 2000+ lb capacity
Segmented Approach
15/32” Rated Sheathing
8d @ 4”o.c.
2 – hold downs @ 1,538 lb capacity
2 Straps – 866 lb
Force Transfer
v, tH Hv, t v, t
15/32” Rated Sheathing
8d @ 3”o.c.
2 – hold downs @ 3280 lb capacity
extensive plateanchorage
Perforated
v, t
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2’-0” 3’-0” 3’-0” 8’-0” 3’-0” 2’-0”5’-0”
7’-0” 4’-0” 10’-
0”
V
H H
26’-0”
Segmented & Perforated use full height segments 3.5:1 for 10’-0” = 34”
FTAO uses heights adjacent to openings 3.5:1 for 7’-0” = 24” 2:1 for 4’-0” = 24”
6’-8”P2 P3 P4P1
Shear Wall Design Examples
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Deflection Calculations - Concept
V+
H Hh
2+
h1
+
h3
+
1+ 2
+ 3+
V-
H H
h2
-
h1
- h3
-
1- 2
- 3-
= average(1+2
+ 3+
1-2
-3-)
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Deflection Calculations
Wall drift estimation when using FTAO
Historical 4-term deflection equation Average deflection, varying h
‐3,000
‐2,000
‐1,000
0
1,000
2,000
3,000
‐5 ‐4 ‐3 ‐2 ‐1 0 1 2 3 4 5
Applied Load (plf)
Deflection (in.)
Wall 12
12a
12b
4 term
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8. True or False: Wall sheathing can aid in FTAO tension force resistance?A. True
B. False
Audience Poll
8. True or False: Wall sheathing can aid in FTAO tension force resistance?A. True
B. False
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APA FTAO Test Wall 6
Framing status quo
Reduce/eliminate strap force
C-shaped Panels
Benefits of FTAO with ContinuousWood Structural Panels
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Benefits of FTAO with ContinuousWood Structural Panels
For the Structural Engineer…Straightforward rational analysis
Easy to program: Excel, web based application, or other
Design check = confidence in calculations
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Benefits of FTAO with ContinuousWood Structural Panels
Value propositionReduction of more costly components
Continuous nail base + stiffer wall = fewer callbacks due to: Stucco cracking, water intrusion, wall buckling
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Learning Objectives
1. Participants will investigate past and current methods for determining force transfer around openings for wood shear walls through discussion of the joint research project of APA – The Engineered Wood Association, the University of British Columbia (UBC), and the USDA Forest Products Laboratory (FPL).
2. Participants will compare the effects of different opening sizes, full-height pier sizes, and their relationships to the three industry shear wall approaches by illustrating use of the segmented, perforated, and FTAO methods.
3. Participants will observe how the study examined internal forces generated during loading by reviewing full-scale wall test data as well as analytical modeling performed in determining statistical accuracy.
4. Participants will conclude that research results obtained from this study can be used to support different design methodologies in estimating forces around openings accurately.
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Questions/ Comments?
Jared S. Hensley, [email protected] (253) 426-1224 www.apawood.org
This concludes The American Institute of Architects Continuing Education Systems Course