des432 - diaphragm design...2020/06/11 · wood diaphragm design 37 wood diaphragm deflection...

Copyright © 2020 American Wood Council.All rights reserved.

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Wood Diaphragm DesignDES432

Michelle Kam-Biron, PE, SE, SECBSenior Director, EducationAmerican Wood Council

W o o d D i a p h r a g m D e s i g n2

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© American Wood Council 2020

COPYRIGHT

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Participants may download the presentation here: http://www.awc.org/education/resources

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 with AIA 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 at the conclusion of this presentation.


This webinar is intended to provide general information only and does not constitute professional or engineering advice. No participant or user should act on the basis of any material contained in the webinar without obtaining proper professional advice specific to their situation. Further, the views expressed by speakers or other third parties are those of the speaker or third-party and not, necessarily, of AWC.

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© American Wood Council 2020

DISCLAIMER (REQUIRED BY OUR LAWYERS)

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COURSE DESCRIPTIONThe 2018 International Building Code (IBC) specifies that structures using wood-framed shear walls and diaphragms to resist wind, seismic and other lateral loads shall be designed and constructed in accordance with AWC’s 2015 Special Design Provisions for Wind and Seismic (SDPWS). Calculation of wood-frame diaphragm deflection should account for bending and shear deflections, fastener deformation, chord splice slip, and other contributing sources of deflections. The 2015 SDPWS incorporates both a 3-term and 4-term deflection equation that accounts for these variables. This course will provide an overview and comparison of the 3-term and 4-term deflection equations. Additionally, an example showing calculation of mid-span deflection of a blocked wood structural panel diaphragm will be presented.


LEARNING OBJECTIVES

Calculate wood-frame diaphragm deflection using the 2015 SDPWS

Wood-Frame Diaphragm Deflection

Compare the difference between the 3-term and 4-term deflection equation in the 2015 SDPWS

3-Term & 4-Term Deflections

Analyze individual components of the deflection equations to determine their magnitude of impact on total deflection.

Components of Deflection Equation

Utilize the example deflection calculation in future design work as a model for their own calculations.

Deflection Examples

Upon completion, participants will be better able to:

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POLLING QUESTION

1. What is your profession?a) Architectb) Engineerc) Code Officiald) Fire Servicee) Builder/Manufacturer/Other


2. If I were to categorize my experience with design or plan review of structural wood construction, I would be:

a) Groot (I have limited exposure)

b) Rocket Raccoon

c) Black Widow

d) Captain America

e) Iron Man (I could teach this course)

POLLING QUESTION

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OUTLINE

• Basic Lateral Load Overview and Code acceptance of 2015 SDPWS

• Diaphragm Deflection Equation• Diaphragm Deflection Example• FAQ• Resources

W o o d D i a p h r a g m D e s i g n1 0

SDPWS (ANSI/AWC SDPWS-15)Special Design Provisions for Wind and Seismic

2015 IBC & 2018 IBC• Mandatory• References 2015 SDPWS in

Section 2305 for lateral design and construction

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SDPWS (ANSI/AWC SDPWS-15)Special Design Provisions for Wind and Seismic

2015 IBC & 2018 IBC• Mandatory• References 2015 SDPWS in

Section 2305 for lateral design and construction

ASCE 7-10 & ASCE 7-16


GENERAL LATERAL LOAD PATH

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w

W

v

L

v

FROM DIAPHRAGM TO SHEAR WALLS


Ties

ChordT T

ChordC C

w

Diaphragm reaction goes to shear walls

Diaphragms supporting Masonry or Concrete Structural Walls -Seismic Design Category C, D, E, & FDiaphragms shall be provided with continuous ties or struts between diaphragm chords to distribute these anchorage forces into the diaphragms (ASCE 7 - 16 sec. 12.11.2.2.1)

FROM DIAPHRAGM LOAD PATH

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OUTLINE

Stella Apartments, Marina Del Rey, CAPhoto courtesy: GLJ Partners


• Diaphragm Deflection Equation

• Diaphragm Deflection Example• FAQ• Resources


3-TERM DIAPHRAGM DEFLECTION EQUATION

• Applies to flat and folded (roof) diaphragms.• SDPWS provides tables for a variety of sheathing

material• SDPWS extends to unblocked diaphragms

SDPWS Chapter 4 - Wood Diaphragms

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SDPWS Commentary Chapter 4 - Wood Diaphragm



SDPWS Commentary Chapter 4 - Wood Diaphragm


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COMPARISON: 3-TERM VS. 4-TERM

Shear panel deformation and nail slip

4-term 3-term


COMPARISON: 3-TERM VS. 4-TERMApparent Shear Stiffness

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4-TERM DEFLECTION

Diaphragms

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4-TERM DEFLECTION


4-TERM DEFLECTION

Use to calculate en

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3-TERM DEFLECTION


3-TERM DEFLECTION

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COMPARISON: 3-TERM VS. 4-TERMEXAMPLE C4.2.2-1 Derive Ga in SDPWS Table 4.2ADerive Ga in SDPWS Table 4.2A for a blocked wood structural panel diaphragm constructed as follows:

Sheathing grade = Structural I (OSB)Sheathing layup = Case 1Nail size = 6d common

(0.113″ diameter, 2″ length)Minimum nominal panel thickness = 5/16 in.Boundary and panel edge nail spacing = 6 in.Minimum width of nailed face = 2x nominalNominal unit shear

capacity for seismic, s = 370 plf SDPWS Table 4.2AAllowable unit shear capacity for seismic: s(ASD) = 370 plf/2 = 185 plf


COMPARISON: 3-TERM VS. 4-TERMEXAMPLE C4.2.2-1 Derive Ga in SDPWS Table 4.2A (cont.)

Panel shear stiffness:Gv tv = 77,500 lb/in. of panel depth Table C4.2.2A

Nail load/slip at 1.4 vs(ASD):Vn = fastener load (lb/nail)

= 1.4 vs(ASD) (6 in.)/ (12 in.) = 129.5 lb/nailen = (Vn/456)3.144 Table C4.2.2D

= (129.5/456)3.144 = 0.0191 in.Calculate Ga:

(C4.2.2-3)

Ga = 14,6600 lb/in. 15 kips/in. SDPWS Table 4.2A

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Determine allowable unit shear capacity for seismic:

EXAMPLE C4.2.2-1 Derive Ga in SDPWS Table 4.2A (cont.)



Determine panel shear stiffness:EXAMPLE C4.2.2-1 Derive Ga in SDPWS Table 4.2A (cont.)

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Nail load/slip at 1.4 s(ASD):Vn = fastener load (lb/nail)

= 1.4 vs(ASD) (6 in.)/ (12 in.) = 129.5 lb/nail (Based on EN)

SDPWS Table 4.2A Footnotes




Determine fastener slip:


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Calculate Ga:

(C4.2.2-3)

Ga = 14,6600 lb/in. 15 kips/in. SDPWS Table 4.2A




Calculated deflections at 1.4 x vs(ASD) closely match test data for blocked and unblocked diaphragms


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POLLING QUESTION

3. SDPWS includes which of the following sheathing materials for diaphragms?a) WSP b) Lumberc) Gypsum boardd) All of the abovee) a. and b.


OUTLINE

Genesis, Los Angeles, CAPhoto courtesy: KC Kim GB Construction


• Prescriptive Diaphragm Example• Diaphragm Deflection Equation• Diaphragm Deflection

Example• FAQ• Resources

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WOOD DIAPHRAGM DEFLECTION EXAMPLE2015 SDPWS Commentary

EXAMPLE C4.2.2-3 Calculate Mid-Span Diaphragm Deflection

L=48’16’ 16’

Diaphragm chord joint

W=

24’

Case 1 blocked diaphragm, 7/16” OSB sheathing, 8d common nails at 6”o.c. at all panel edges

A B

Allowable stress design load, =255 plf


WOOD DIAPHRAGM DEFLECTION EXAMPLE2015 SDPWS CommentaryCalculate mid-span deflection for the blocked wood structural panel diaphragm shown in Figure C4.2.2-2. The diaphragm chord splice is sized using allowable stress design loads from seismic while deflection due to seismic is based on strength design loads in accordance with ASCE 7.

Diaphragm apparent shear stiffness, Ga:Ga = 14 kips/in. (SDPWS Table 4.2A)

Diaphragm allowable unit shear capacity for seismic, vs (ASD):vs (ASD) = 255 plf (SDPWS Table 4.2A)

Diaphragm chord: (2) 2x6 No. 2 Douglas Fir-Larch, E = 1,600,000 psi, and G = 0.50

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DIAPHRAGM CAPACITY

SDPWS Table 4.2A

Ga = 14 kips/inNominal/2.0 (ASD)vs = 510 plf/2 vs = 255 plf (ASD)


WOOD DIAPHRAGM DEFLECTION EXAMPLE2015 SDPWS Commentary

EXAMPLE C4.2.2-3 Calculate Mid-Span Diaphragm Deflection

vs = 255 plf (ASD)

For this design example:vs = v = 255 plf (ASD)

L=48’16’ 16’


W=

24’


A B

Allowable stress design load, =255 plfvmax=255 plf

Vx= (L/2-x)

x’M = 65,280 ft-lb

Mmax = 73,440 ft-lbM = 65,280 ft-lb

Mx= x(L-x)/2

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CHORD SPLICEPart 1Calculate number of 16d common nails in the chord spliceDiaphragm chord:

Two 2x6 No. 2 DFLE = 1,600,000 psiG = 0.50

Z’ASD (NDS Table 12N)= 141 lb. x 1.6 = 226 lb.

16' 16'

Upper plate designed as continuous chord

Splice plates

Joint A Joint B

48'

Wide face of upper top plate. Twelve nails on each side of each joint.


CHORD SPLICEPart 1Calculate number of 16d common nails in the chord spliceThe axial force (T or C) at each joint:

The number of 16d common nails, n, is:

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CHORD SPLICEPart 1Calculate number of 16d common nails in the chord spliceMight need to consider Mmax if joint location unknown:

x’M = 65,280 ft-lb Mmax = 73,440 ft-lb

M = 65,280 ft-lb

Mx= x(L-x)/2


MID-SPAN DEFLECTIONPart 2 – Calculate mid-span deflection

Use 3-term equation

4.2-1

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MID-SPAN DEFLECTION

Term 1. Deflection due to bending and chord deformation (excluding chord splice slip):

L=48’16’ 16’


W=

24’


A B


𝛿 ,5𝑣𝐿

8𝐸𝐴𝑊

=.

, , . .

0.078𝑖𝑛.

Strength level design loads

ASCE 7 requires that seismic story drift be determined using strength level design loads


MID-SPAN DEFLECTION


L=48’16’ 16’


W=

24’

Case 1 blocked diaphragm, 7/16” OSB sheathing, 8d common nails at 6”o.c. at all panel edgesA B


𝛿 ,5𝑣𝐿

8𝐸𝐴𝑊

=.

, , . .

0.078𝑖𝑛.

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MID-SPAN DEFLECTION


L=48’16’ 16’


W=

24’

Case 1 blocked diaphragm, 7/16” OSB sheathing, 8d common nails at 6”o.c. at all panel edgesA B


𝛿 ,5𝑣𝐿

8𝐸𝐴𝑊

=.

, , . .

0.078𝑖𝑛.

Single chord assumption

One top plate designed to resist induced axial force – second as splice plate. Engineering judgment. Doubling area yields 0.04”.


MID-SPAN DEFLECTIONTerm 2. Deflection due to shear, panel shear, and nail slip

Ga = 14 kips/in., apparent shear stiffness (SDPWS Table 4.2A)

𝛿0.25𝑣𝐿1000𝐺

0.25 1.4𝑥255𝑝𝑙𝑓 48𝑓𝑡

100014𝑘𝑖𝑝𝑠

𝑖𝑛

0.306𝑖𝑛.

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MID-SPAN DEFLECTIONTerm 3. Deflection due to bending chord splice slip

x = 16 ft, distance from the joint to the nearest support. Each joint is located 16 ft from the nearest support



Δc = Joint deformation (in.) due to chord splice slip in each joint.

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• 180,000 D1.5 load/slip modulus for dowel type connections per NDS 10.3.6

• Diameter for 16d common NDS Table L4• 180,000 (0.162)1.5 = 11,737 lb/in./nail

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Constant of 2 used in numerator to account for slip in nailed splices on each side of joint

𝛥2 𝑇 𝑜𝑟 𝐶

𝛾𝑛2 3,808 𝑙𝑏𝑓

11,737 𝑙𝑏𝑓/𝑖𝑛./𝑛𝑎𝑖𝑙 12 𝑛𝑎𝑖𝑙𝑠

0.054𝑖𝑛



Tension chord slip calculation

0.036 𝑖𝑛.

𝛿 ∑ 16 𝑓𝑡 0.054 𝑖𝑛. 16 𝑓𝑡 0.054 𝑖𝑛.

2 24 𝑓𝑡

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MID-SPAN DEFLECTIONTerm 3. Deflection due to bending and chord splice slip

Assume compression chord butt joints have a gap that exceeds the splice slip, so tension chord slip also used for compression chord

Compression chord and total slip calculation

Total deflection due to chord splice slip is:

𝛿 0.036 𝑖𝑛.

𝛿 0.036 𝑖𝑛. 0.036 𝑖𝑛. 0.072 𝑖𝑛.


MID-SPAN DEFLECTION

Total mid-span deflection:

𝛿 0.078𝑖𝑛. 0.306 𝑖𝑛. 0.072 𝑖𝑛. 0.456 𝑖𝑛.

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POLLING QUESTION

4. Which of the following contributed the most to the deflection of the diaphragm?a) Bending and chord deformationb) Shear, panel shear and nail slipc) Chord splice slipd) All of the above


OUTLINE


• Prescriptive Diaphragm Example• Diaphragm Deflection Equation• Diaphragm Deflection Example• FAQ• Resources

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FREQUENTLY ASKED QUESTIONS

Q: What deflection limits are shown in the code for walls?

A: It depends on the sheathing material•Plaster or Stucco Finishes – L/360 – IBC Table 1604.3

•Brittle Finishes – L/240 – IBC Table 1604.3•Flexible Finishes – L/120 – IBC Table 1604.3•Glass –1/175 of glass edge length or 3/4" - IBC Table 2403.3


Q: What diaphragm deflection limits are shown in the code?


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A: ASCE 7-10

DIAPHRAGM 2 x SHEARWALLS

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A: ASCE 7-16



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ASCE 7-10 Sec. 12.12 DRIFT AND DEFORMATION



ASCE 7-10 Sec. 12.12 DRIFT AND DEFORMATION


Etc…..

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Q: Is diaphragm deflection cumulative with shear wall deflection?

A: Yes. Shear walls supporting a horizontal diaphragm would also be evaluated for deflection. Cumulative deflection would then be calculated to determine the maximum anticipated movement to compare with allowables.



Q: Are there provisions to calculate the deflection for a diaphragm that is only partially blocked (i.e. at ends only) or is it proper to base the deflection on the entire diaphragm being unblocked?

A: There are no provisions for a partially blocked diaphragm. Suggest calculating for both a blocked and unblocked diaphragm to determine magnitude of difference and use engineering judgment.

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Q: When the nailing pattern in a horizontal diaphragm varies instead of being uniform, how is deflection calculated?A: One approach is to modify the nail-slip constant in the 4-term equation in proportion to the average load on each nail with non-uniform nailing compared to the average load with uniform nailing. APA’s Diaphragm and Shear Wall Design and Construction Guide (L350) provides an example: www.apawood.org.



Q: Is there any benefit if wood structural panels are glued to the assembly?

A: We are not aware of any added benefit with respect to diaphragm deflection.

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Q: Is there a multiplier to use for a long-term consideration due to possible enlargement of nail holes or is that all included in the nail slip deflection calculations?

A: Testing done to verify diaphragm deflection calculations is based on full reverse cyclic loads, so the effects of nail hole enlargement has been addressed.



Q: For large diaphragm, what adjustments to deflection equations need to be made to obtain inelastic diaphragm deflection?

A: ASCE 7 Minimum Design Loads for Buildings and Other Structures, Section 12.8.6 includes an amplification factor Cd which is used for story drift and seismic gaps.

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Q: What resources are available for designing NLT Diaphragms?

A: Thinkwood Nail-Laminated Timber Design & Construction Guide (U.S. & Canada versions) https://www.thinkwood.com/products-and-systems/mass-timber/nail-laminated-timber



Q: What resources are available for designing CLT Diaphragms?

A: Structurlam Cross Laminated Timber Horizontal Diaphragm Design Example (U.S. & Canada versions) https://www.structurlam.com/resources/manufacturing-standards/

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OUTLINE

Photo courtesy: KC Kim GB Construction


• Prescriptive Diaphragm Example• Diaphragm Deflection Equation• Diaphragm Deflection Example• FAQ• Resources


RESOURCES

www.apawood.org

Publication no. L350

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RESOURCES

http://www.amazon.com/Design-Wood-Structures-ASD-LRFD-ebook/dp/B00386MRG8


OTHER MEANS?

4.2.2 Deflection

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RESOURCES

http://www.amazon.com/Analysis-Irregular-Shaped-Structures-Diaphragms/dp/007176383X#_

R. Terry Malone, PE, SE –Senior Technical Director WoodWorks

Slides: https://www.woodworks.org/wp-content/uploads/2017-April-Webinar-diaphragms-with-openings.pdf

Recorded Webinar: https://vimeo.com/woodproductscouncil/review/212986898/17ca94ef6f


RESOURCE

BCD710-1 – Special Inspections for Wood Construction

https://awc.org/education/main/lists/bcd-building-codes/bcd710-1-special-inspections-for-wood-construction

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RESOURCE

BCD236 – Demobilizing Construction Sites Safely Using NFPA241

https://awc.org/education/main/lists/bcd-building-codes/bcd236-demobilizing-construction-sites-safely-using-nfpa241

Ta l l Wo o d S t r u c t u r e s8 4

RESOURCES

www.awc.org• Print versions

• PDF versions

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RESOURCES

https://awc.org/pdf/codes-standards/publications/sdpws/StructureMag-SDPWS2015-Changes-1507.pdf


RESOURCES

https://awc.org/education/main/lists/des-design-considerations/des430-seismic-design-of-large-wood-panelized-roof-diaphragms-in-heavy-wall-buildings

eCourseDES430 – Seismic Design of Large Wood Panelized Roof Diaphragms in Heavy Wall Buildings

John Lawson, SE – Associate Professor, Cal Poly, SLO

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T h i s p r e s e n t a t i o n i s p r o t e c t e d b y U S a n d I n t e r n a t i o n a l C o p y r i g h t l a w s . R e p r o d u c t i o n , d i s t r i b u t i o n , d i s p l a y a n d u s e o f t h e p r e s e n t a t i o n w i t h o u t w r i t t e n p e r m i s s i o n o f A m e r i c a n W o o d C o u n c i l ( A W C ) i s

p r o h i b i t e d . © A m e r i c a n W o o d C o u n c i l 2 0 1 9

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des432 - diaphragm design...2020/06/11 · wood diaphragm design 37 wood diaphragm deflection...

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