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Structural CLT Floor and Roof Construction
Presenter: [email protected] 1
Structural CLT Floor and Roof Design
Scott Breneman, PhD, PE, SESenior Technical Director – Project Resources and Solutions DivisionWoodWorks – Wood Products Council Photo Ema Peter Photography
“The Wood Products Council” is a Registered Provider with The American Institute of Architects Continuing Education Systems (AIA/CES), Provider #G516.
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.
Structural CLT Floor and Roof Construction
Presenter: [email protected] 2
Course DescriptionThis presentation is intended for designers of building systems seeking to familiarize themselves with the category of products known as mass timber, and specifically cross laminated timber (CLT). Topics will include manufacturing and product performance standards, structural design standards, and recognition of CLT in the International Building Code. Specific attention will be given to the design of CLT in horizontal applications—i.e., as panels of floor and roof systems—and discussion will include how to address important serviceability requirements related to deflection and floor vibration design. Example projects and details will be presented to highlight possible applications of CLT in building structures.
Learning Objectives
1. Discuss product manufacturing and design standards relevant to cross laminated timber (CLT), and identify where these standards are recognized in the International Building Code.
2. Consider the structural design properties of CLT relevant to floor and roof applications.
3. Discover how to design CLT floors to achieve serviceability goals related to deflection and vibration.
4. Examine the use of CLT in example buildings and connection details.
Structural CLT Floor and Roof Construction
Presenter: [email protected] 3
Introduction
Wood Building Systems
Post and Beam Light Frame Mass Timber
Structural CLT Floor and Roof Construction
Presenter: [email protected] 4
Mass Timber Products
Nail Laminated Timber (NLT) Glue Laminated Timber (GLT)
Laminated Veneer Lumber (LVL)Massive Plywood Panels (MPP) Cross Laminated Timber (CLT)
Images Source: Structurecraft
Glulam Beams& Columns
Mass Timber ProductsCross-laminated timber (CLT)
8
Structural CLT Floor and Roof Construction
Presenter: [email protected] 5
Cooley Landing Education CenterEast Palo Alto, CA
Photo: Arbor Building Group Photos: WoodWorks
Cooley Landing Education Center
East Palo Alto, CA
Structural CLT Floor and Roof Construction
Presenter: [email protected] 6
Albina YardPortland, OR
Photo Credit: LEVER Architecture
Albina YardPortland, OR
Photo Credit: WoodWorks
Structural CLT Floor and Roof Construction
Presenter: [email protected] 7
ARCHITECT: Lever ArchitecturePhoto: Scott Breneman
Albina YardPortland, OR
4 stories16,000 sfGreen Roof
13
ARCHITECT: Lever ArchitecturePhoto: Scott Breneman
Albina YardPortland, OR
14
Structural CLT Floor and Roof Construction
Presenter: [email protected] 8
Redstone Arsenal HotelHuntsville, AL
Image Credit: Lend Lease
Photos: Lend Lease, IHG Hotels, & Schaefer
Redstone Arsenal Hotel62,600 sf, 4 story hotel, 92 private roomsCLT used for walls, roof panels, and floor panels
1,557 CLT Panels; Typical floor panel is 8’x50’
Completed Late 2015
Structural CLT Floor and Roof Construction
Presenter: [email protected] 9
ARCHITECT: Acton OstrayENGINEER: Fast & Epp
2 0 1 7TallWood House at Brock Commons
University of British ColumbiaVancouver, Canada
18 Stories (17+1) 174 Feet tallBeamless two-way CLT floor slab
Cross Laminated Timber
Considerations:
• Large light-weight panels
• Dimensionally stable
• Precise CNC machining available
• Recognized by IBC
• Dual Directional span capabilities
• Often architecturally exposed
• Fast on-site construction
Graphic Credit: StructureCraft
Structural CLT Floor and Roof Construction
Presenter: [email protected] 10
CLT History Timeline
1990 2000 2005 2010 2015
Significantly increased
use in Europe
• 2010 – 1st
Production• 2011- PRG320• 2011 -Canadian
Handbook• 2013 – US
Handbookinterest began
.3 million m3 of built
CLT projects
Recognized in 2015 IBC
Austria industry-academia
joint research
.6-1 million m3 of built
CLT projectsE
urop
eN
orth
A
mer
ica
SB31
CLT Product Standardization
Structural CLT Floor and Roof Construction
Presenter: [email protected] 11
Thickness3 to 20 inches*
Max Length24 to 60 feet* Max Width
8 to 10 feet*
3+ layers of laminationsTypically Solid Sawn LaminationsCross-Laminated Layup
What is CLT?
*All dimensions are approximate.Consult with manufacturers
First Tech Credit Union, Hillsboro, Oregon Photo Credit: Structurlam Products
Structural CLT Floor and Roof Construction
Presenter: [email protected] 12
North American CLT Product Standard
ANSI/APA PRG 320 Standard for Performance-Rated Cross-Laminated Timber
The Standard Covers:- U.S. and Canada Use- Panel Dimensions and Tolerances- Component Requirements- Structural Performance
Requirements- Panel and Manufacturing
Qualification- Marking (Stamping)- Quality Assurance
CLT Stress Grades
Stress Grade Major StrengthDirection
Minor Strength Direction
E1 1950f-1.7E MSR SPF #3 Spruce Pine FirE2 1650f-1.5E MSR DFL #3 Doug Fir LarchE3 1200f-1.2E MSR Misc #3 MiscE4 1950f-1.7E MSR SP #3 Southern PineV1 #2 Doug Fir Larch #3 Doug Fir LarchV2 #1/#2 Spruce Pine Fir #3 Spruce Pine FirV3 #2 Southern Pine #3 Southern Pine
Standard (Non-mandatory) CLT stress grade in PRG 320-2012.Other custom stress grades including structural composite lumber (SCL) permitted
Structural CLT Floor and Roof Construction
Presenter: [email protected] 13
Common CLT Layups
3-ply 3-layer
9-ply 9-layer
5-ply 5-layer
7-ply 7-layer 7-ply 5-layer
9-ply 7-layer
PRG 320 Defined Layups
Structural CLT Floor and Roof Construction
Presenter: [email protected] 14
3rd Party Product Certification of CLT
CLT Product ReportsStress Grade
(standard or custom)Layup
(standard or custom)Panel Properties
Structural CLT Floor and Roof Construction
Presenter: [email protected] 15
Structural Design Standardization
National Design Specification for Wood Construction2015 Edition
Model Building Code Acceptance
2015 International Building Code
Structural CLT Floor and Roof Construction
Presenter: [email protected] 16
CLT is Defined – 2015 IBCSB9
Highlights of CLT Provisions in IBC 2015
• CLT is generally available for use in Type III, IV and V construction.
• IBC 2015 Chapter 6 Defines Dimensions of CLT to qualify as Heavy Timber (Type IV Construction)
• 6” Walls• 4” Floors• 3” Roofs• Non Fire-Retardant Treated CLT allowed in Exterior Walls of Type
IV construction in many conditions. (IBC 2015 602.4)
The Heavy Timber construction size requirements only apply to Type IV Construction
SB16SB17
Structural CLT Floor and Roof Construction
Presenter: [email protected] 17
CLT Manufactures for use in the US to PRG-320
• DR Johnson Lumber, Oregon• KLH USA, Subsidiary of KLH Massivholz, Austria.• Nordic Structures, Quebec, Canada• SmartLam, Columbia Fall, Montana• Structurlam, British Columbia, Canada
Working with CLT: Know Your Supply Chain
• CLT Manufactures different CLT grades and maximum panel sizes• CLT Manufacturers have specific CNC capabilities• 3rd Party Fabricators can have additional CNC capabilities
Photo: DR Johnson Photo: Sauter Timber
Structural CLT Floor and Roof Construction
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Working with CLT: Communicate Your Requirements
Define the deliverables you need from the supplier:- Shop drawings- Shop drawings with Engineering Stamp- Engineered Drawings and Calculations (e.g. as a deferred submittal)
Structural Properties
Structural CLT Floor and Roof Construction
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Non-homogenous, anisotropic material
Structural Section Properties
FLATWISE Panel Loading
Span in MAJOR Strength Direction“Parallel” Direction
Span in MINOR Strength Direction“Perpendicular” Direction
Reference & Source: ANSI/APA PRG 320-2017
Structural CLT Floor and Roof Construction
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EDGEWISE Panel Loading
Span in MAJOR Strength Direction Span in MINOR Strength Direction
Reference & Source: ANSI/APA PRG 320-2017
Design properties based on an Extreme Fiber Model:
Flexural Capacity Check:
Mb ≤ (FbSeff)′
Mb = applied bending moment
(FbSeff)′ = adjusted bending capacity
Seff = effective section modulus
Fb = reference bending design stress of outer lamination
Flatwise Flexural Strength
Mb
Bending Stress
Reference: NDS 2015
Structural CLT Floor and Roof Construction
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Flexural Capacity Check (ASD)
(FbSeff)′ = CD CM Ct CL (FbSeff)
Flatwise Flexural Strength
Mb
Bending Stress
Commonly1.0
Provided as combined value
Mb ≤ CD (1.0) (FbSeff)
perNDS
Reference: NDS 2015
Select acceptable CLT section
Given:
16 foot span floor
40 psf live load, 40 psf total dead load.
Assume:
one-way spanning action in major axis of CLT
Analysis of a 1 ft strip of panel as beam
Calculate ASD Dead + Live Applied Moment
Mb = w L2 / 8 = (40+40psf) (16ft)2 / 8 = 2560 lb-ft/ft
Flatwise Flexural Strength Design Example
16 foot span
40 psf DL, 40 psf LL
Structural CLT Floor and Roof Construction
Presenter: [email protected] 22
Look for Acceptable CLT Grade from PRG 320: FbSeff,0 > 2560 lb-ft/ft
Flatwise Flexural Strength Design Example
Reference: ANSI/APA PRG 320-2012
4,800
Select 5-Ply 6 7/8” Thick V1 Panel with FbSeff,0 = 4800 lb-ft/ft
ASD Flexural Capacity:Dead + Live load, CD = 1.0
(FbSeff)′ = CD (1.0) (FbSeff)
= 1.0 (1.0) (4800 lb-ft/ft)= 4800 lb-ft/ft
Mb = 2560 lb-ft/ft ≤ (FbSeff)’ = 4800 lb-ft/ft
Flexural Strength OK
Flatwise Flexural Strength Design Example
16 foot span
40 psf DL, 40 psf LL
Structural CLT Floor and Roof Construction
Presenter: [email protected] 23
Design Properties based on Extreme Fiber Model:
Shear Capacity Check:
Va ≤ Fs(Ib/Q)eff′Va = applied shear
Fs(IbQeff)′ = adjusted shear strength
Flatwise Shear Strength
Va
Shear Stress
Reference: NDS 2015
Jargon Alert! AKA “Planar Shear”, “Out-of-Plane Shear”, or “Rolling Shear” Strength
Wood Structural Panel Term
Structural Engineering Term
CLT Term
Design Properties based on Extreme Fiber Model:
Shear Capacity Check (ASD):
Fs(IbQ)eff′ = CM Ct (Fs(IbQ)eff) = CM Ct Vs
Vplanar ≤ (1.0) Vs
Flatwise Shear Strength
Vplanar
Shear Stress
Commonly1.0 From Manufacturer
Reference: NDS 2015 & Product Reports
Note: Duration of Load Effects (Cd and λ) NOT applicable to Flatwise Shear Strength in the NDS
Structural CLT Floor and Roof Construction
Presenter: [email protected] 24
Shear Force Terminology
Planar ShearRolling Shear
Shear-In-the-Plane?Out-of-plane forces?
FLATWISE Shear in PRG 320 2017
Source: ANSI/APA PRG 320-2017
NDS 2015: Fs(Ib/Q)effPRG 320 Product Reports: Vs,0 & Vs,90
Source: NDS 2015 Manual
Flatwise Shear Strength
Rolling Shear
Source: CSA O86-14, 2016 Supplement
Structural CLT Floor and Roof Construction
Presenter: [email protected] 25
Shear Force Terminology & Jargon
Through-the-Thickness ShearIn-plane Shear Forces
EDGEWISE Shear in PRG 320-2017
Source: ANSI/APA PRG 320-2017
NDS 2015: Fv(tv)PRG 320-2017: Fv,e,0 tp & Fv,e,90 tp
Source: NDS 2015 Manual
Flatwise Flexural Stiffness
Bending Stress
EIeff
Shear Analogy Method
Reference: US CLT Handbook Chapter 3
Structural CLT Floor and Roof Construction
Presenter: [email protected] 26
Flatwise Flexural Stiffness
EIeff
GAeff
Flatwise Flexural Stiffness
EIeff
GAeff
Important to develop properties of new CLT Sections.
Not to use standard CLT Sections
Structural CLT Floor and Roof Construction
Presenter: [email protected] 27
Flatwise Flexural Stiffness
EIeff
GAeff
Advanced Use: Calculating Structural Capacities under Fire
Conditions usingNDS 2015 Chapter 16
Flatwise CLT Panel Section Properties
Values in RED provided by CLT manufacturer
Flexural Strength: FbSeff,0
Flexural Stiffness: EIeff,0
Shear Strength: Vs,0
Shear Stiffness: GAeff,0
FbSeff,90
EIeff,90
Vs,90
GAeff,90
Reference: PRG 320 and CLT Product Reports
Structural CLT Floor and Roof Construction
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Using PRG 320 Standard Grades for Design?
PRG 320 includes pre-defined Stress Grades, Layups and related
Design Properties
Is doesn’t tell you what CLT grades and layups are available.
Coordinate your design with manufactures availability and
information
General Purpose: 1 Way, Beam ActionNeeded Stiffness: EIeff,0 GAeff,0
Deflection Calculations
Can model multiple spans, cantilevers, etc.
Structural CLT Floor and Roof Construction
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Example Calculation:Uniform loading on one way slab:
Beam Analysis using
Flexural Stiffness: EIeff,0
Shear Stiffness: 5/6 GAeff,0
Maximum Deflection @ Mid-Span
Example Deflection Calculations
16 foot span
5/6 GAeff
Design Example:
= 0.284 in + 0.034 in = 0.318 in
= L / 604
w = 80 psf
Deformation to Long Term Loads
Deflection Creep Factor
Δ" = $%&Δ(" + Δ*" NDS Eq 3.5-1
Δ*"Δ("$%&
Deflection due to short-term loading
Immediate deflection due to long term loading
2.0 for CLT in dry service conditions
Reference: NDS 2015
Design Example:
∆ST from 40psf = 0.159 in
∆LT from 40psf = 0.159 in
∆T = 2.0 (0.159) + 0.159 = 0.477 in
= L / 40316 foot span
w = 40 + 40 psf
Structural CLT Floor and Roof Construction
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Simplified Beam Deflections:Given load pattern and support conditions:
Deflection Calculations
Span, L5/6 GAeff
Uniform load, w
Find Apparent Flexural Stiffness, EIapp, such that
EIapp
+,-.. =+,/00
1 +11.5+,/0045/0067Reference: US CLT Handbook
Simplified Beam DeflectionsFor single span, simple loading patterns, Apparent Flexural Stiffness, EIapp, to determine maximum (mid-span) deflection:
Deflection Calculations
US CLT Handbook&
NDS 2015 Commentary
+,-.. =+,/00
1 +16$9,/005/0067+,-.. =
+,/001 + $9+,/0045/0067
NDS 2015
,/00 =+,/00
+:;
5/00= 45/00 4:⁄4: = +: 16⁄
For Major Axis Spans:
Reference: US CLT Handbook & NDS 2015
Structural CLT Floor and Roof Construction
Presenter: [email protected] 31
Simplified Beam DeflectionsFor single span, simple loading patterns, Apparent Flexural Stiffness, EIapp, to determine maximum (mid-span) deflection:
Deflection Calculations
+,-.. =+,/00
1 +16$9,/005/0067+,-.. =
+,/001 + $9+,/0045/0067
Apparent Flexural Stiffness depends on Span Length
L1 = 20 foot+,-..= ≠ +,-..7
L2 = 16 foot
General Purpose, 2 Way, Plate ActionFlexural Stiffness
EIeff,0 EIeff,90
Shear Stiffness:5/6 GAeff,0 5/6 GAeff,90
5/6 from A′ = 5/6 A shape factor for rectangular sections
Deflection Calculations
Structural CLT Floor and Roof Construction
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Occupant perception of vibration is a highly recommended design consideration.One approach: US CLT Handbook, Chapter 7 (FPI Method)
Calculated natural frequency of simple span of bare CLT:
? = 2.188267
+,-.."5
Where:
EIapp = apparent stiffness for 1 foot strip, pinned supported, uniformly loaded, simple span (Ks = 11.5) (lb-in2)
ρ = specific gravity of the CLT
A = the cross section area (thickness x 12 inches) (in2)
Floor Vibration
Reference: US CLT Handbook, Chapter 7
FPI Method Recommends Limiting CLT Floor Span such that
Floor Vibration
Span L
Reference: US CLT Handbook, Chapter 7
Frequency f > 9.0 Hz
Based on:- Un-topped CLT- Simple span - Bearing wall supports.
Does not account for:- Supporting beam flexibility- Multi-span conditions- Additional floor mass (topping slab, etc)
Recommend for preliminary sizing only
Structural CLT Floor and Roof Construction
Presenter: [email protected] 33
CLT Handbook, Chapter 7 Recommendations
Floor Vibration
Research by Lin Hu, et al. at
Experimental Verification – Results
0.04
0.03
0.02
0.01
0
0.05
0.06
0.07
0 5 10 15
Fundamental Natural Frequency (Hz)20
Stat
ic D
efle
ctio
n(in
ch)
Criterion ( f/d^0.7>125.1) UnacceptableMarginal Acceptable
FPI Method Recommends Limiting CLT Floor Span such that
Floor Vibration
Span L
Reference: US CLT Handbook, Chapter 7
Frequency f > 9.0 Hz Using spreadsheet & iterate:1) Estimate L2) Calculate EIapp3) Calculate L limit4) Repeat until converges
OR Values provided by Manufacturers, et al.Recall:
Structural CLT Floor and Roof Construction
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FPI Method Recommends Limiting CLT Floor Span such that:
Floor Vibration
Span L
Reference: US CLT Handbook, Chapter 7
Frequency f > 9.0 Hz16 Foot Simple Span Design Example:
5-Ply V1 CLT Layup previously selected:EIeff,0 = 415x106 lbf-in2/ft
Converged solution:EIapp,0 = 375.9x106 lbf-in2/ftf = 11.0 Hzmax L = 17.03 ft > 16 ft
Span meets recommended limit. Probably OK performance.
Grade Layup Thickness FPI Span LimitE1 3ply 4 1/8” 12’ 5”E1 5ply 6 7/8” 17’ 4”E1 7ply 9 5/8” 21’ 8”E2 3ply 4 1/8” 12’ 0”E2 5ply 6 7/8” 16’ 8”E2 7ply 9 5/8” 20’ 10”E3 3ply 4 1/8” 11’ 7”E3 5ply 6 7/8” 16’ 1”E3 7ply 9 5/8” 20’ 1”E4 3ply 4 1/8” 12’ 2”E4 5ply 6 7/8” 17’ 0”E4 7ply 9 5/8” 21’ 3”
FPI Span Limit for Standard Grades / Layups
Grade Layup Thickness FPI Span LimitV1 3ply 4 1/8” 12’ 2”V1 5ply 6 7/8” 17’ 0”V1 7ply 9 5/8” 21’ 3”V2 3ply 4 1/8” 11’ 11”V2 5ply 6 7/8” 16’ 8”V2 7ply 9 5/8” 20’ 10”V3 3ply 4 1/8” 12’ 0”V3 5ply 6 7/8” 16’ 9”V3 7ply 9 5/8” 21’ 0”
Approximate FPI Span Limits:- Not for final design:- Does not account for strength or deflections- Does not account for project specifics- Vibrations can be felt by the client.
Sharpen your pencil!
Approximate FPI Span Limits:3-ply: 11 to 12 ft5-ply: 16 to 17 ft7-ply: 20 to 21 ft
Structural CLT Floor and Roof Construction
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Alternative: Use acceptance criteria which address low frequency floors and alternative support configurations.
Calibration of dynamic modelingwith physical testing valuable
Alternative Vibration Criteria
AISC Design Guide 11, Velocity Criteria (Chapter 6 & 7)
Example Acceptance Criteria: (good performance)
≤ 16,000 µ-in/sec (mips) response to moderate walking in living areas
≤ 8,000 µ-in/sec (mips) response to slow walking pace in sleeping areas.
AISC DG 11 suggests approximate velocity limit of human perception
8,000 µ-in/sec at 8 Hz and above.
AISC Design Guide 11 not for dynamic modeling of CLT floors
Possible Alternative Vibration CriteriaSB10
Structural CLT Floor and Roof Construction
Presenter: [email protected] 36
A common European CLT Floor Design Method:
a) Static deflection to 1 kN point load > 0.25 mm
b) Keep fundamental frequency > 8 Hz
OR
Fundamental frequency > 4.5 Hz
+ additional acceleration investigation and limits
For more information see:
- “Floor Vibrations – New Results” Hamm, Richter & Winter, 2010
- Cross-Laminated Timber Structural Design. Basic design and engineering principles according to Eurocode. proHolz Austria, 2014
Possible Alternative Vibration CriteriaSB23
Edgewise Structural Properties
Structural CLT Floor and Roof Construction
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EDGEWISE Panel Loading
Span in MAJOR Strength Direction Span in MINOR Strength Direction
Reference & Source: ANSI/APA PRG 320-2017
CLT Panels have a significant in-plane shear strength.
CLT in Lateral Force Resisting Systems
Source: ICC-ES ESR 3631
~75 to 195+ PSI Allowable Edgewise Shear
~900 to 2300 PLF per Inch of Thickness.
Consult with the Manufacturers for Details
Source: APA Product Report PR-L306
Standard test method defined using ASTM D198
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ICC-ES Acceptance Criteria AC 455
Standardizes In-plane Panel Shear Strength for use in Floor and Roof Decks
Similar Tests in PRG 320 Standard 2017 Update
EDGEWISE Panel Loading
Span in MAJOR Strength Direction
Source: ANSI/APA PRG 320-2017
Preview of PRG 320-2017 Update Nomenclature
Reference Shear CapacityFv,e,0 Wp tp
Shear StiffnessGe,0 Wp tp
Reference Flexural CapacityFb,e,0 Se,0 Se,0 = Wp
2 tp / 6
Flexural StiffnessEe,0 Ie,o Ie,0 = Wp
3 tp / 12
SB32
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Connection Details
Panel to Panel at floors, roofs or walls
Connection Styles
Single Surface Spline Half Lap
SB7
Structural CLT Floor and Roof Construction
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An Efficient Panel to Panel Connection
Graphics: ASPECT Structural Engineers
5 ½” to 6” plywood strip ¾” or 1” Thick
Self-Tapping Screwsas “erection bolts”
~18” – 24” o.c
Nails at spacing required for shear
transfer
Connection Styles
Simple connections with:- Metal angles- Self taping Screws and
Nails
Source: US CLT Handbook
Structural CLT Floor and Roof Construction
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Mass Timber DesignConnections
Photo Credit: Alex Schreyer
Long self tapping screws Long self tapping screws Long self tapping screws Long self tapping screws used extensively used extensively used extensively used extensively throughout mass timber throughout mass timber throughout mass timber throughout mass timber constructionconstructionconstructionconstruction
87
Proprietary Products
Variety of Self Tapping Screws
Structural CLT Floor and Roof Construction
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Proprietary Products
Source: Simpson Strong-Tie Source: rothoblaas
SB24
Connectors for CLT in NDS 2015:
Dowel Type Fasteners, e.g. Lag Screws, Bolts and Nails
CLT in NDS 2015 - ConnectorsSB22
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CLT in Lateral Force Resisting System
CLT in Lateral Force Resisting Systems
Source: A Ceccotti in the US CLT Handbook
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Similar to Wood Structural Panel Shear Walls
Connections Determine Lateral Strength
Light frame shear wallstrength is dependent on perimeter (edge) nailing
Source: SDPWS 2008
Similar to Wood Structural Panel Shear Walls
Connections Determine Lateral Strength
CLT Shear Strength Depends on ConnectionsSource: US CLT Handbook
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CLT Shear Wall Seismic Design Values
What R value can I use?
Photo: KLH Photo: FPI?
CLT Seismic Force Resisting Systems Not addressed In
CLT Seismic Design
ASCE/SEI 7-10 SDPWS 2015
Structural CLT Floor and Roof Construction
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Albina Yard – Portland OregonLEVER Architecture
KPFF Engineering4-story office
CLT floors and RoofGlulam Gravity Frame
Light-Frame Shear Walls
Photo: WoodWorks
The Bullitt CenterSeattle, WA
Architect: Miller Hull PartnershipPhotos © Nick Lehoux for the Bullitt Center
Structural CLT Floor and Roof Construction
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T3 MinneapolisCentral Core – concrete shearwalls
Photo Credit: Structurecraft99
FEMA P-695 Study for CLT Shear Walls
Project Lead: John van de Lindt, Colorado State University
Design Method
Modeling
-6 -4 -2 0 2 4 6
-4
-3
-2
-1
0
1
2
3
4
Displacement (in.)
Forc
e (k
ip)
TestFit
Testing
Non-Linear AnalysesDesign
Peer Review
Report
Structural CLT Floor and Roof Construction
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State of Oregon Statewide Alternative
State of Oregon Statewide Alternative
Y
Y
ASCE 7-10 Table 12.2-1 modified by Oregon Buildings Code Division
Structural CLT Floor and Roof Construction
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Mass timber designLateral framing systems
Central core – mass timber shearwalls
Photo Credit: alex schreyer
103
CLT Diaphragms
Strength of Connections covered by NDS 2015 and
Proprietary Fastener Evaluation Reports
Strength of CLT rarely (never?) governs. Capacity provided by
manufactures via ASTM standard testing. Standard to be included
in PRG 320 Update.
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Panel In-Plane Strength:
• Panel strength generally does not govern diaphragm shear strength.
• Reference Design Values
• Not covered by APA PRG 320-12 product standard• Are covered by New ICC AC455 Acceptance Criteria• Ask for design values from the Manufacturers
Connection Strength:
• Commodity connectors (e.g. Nails) per NDS 2015
• Proprietary Connectors (Self-Tapping Screws) per Evaluation Reports, Manufacturer’s Information and Engineering Mechanics.
• For seismic design, select connection details so ductile limit states govern capacities.
CLT Floors as Diaphragms
CLT Diaphragm Design Example PaperSB26
Structural CLT Floor and Roof Construction
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CLT Diaphragm Design Example Paper
Lateral load, w =1 kip/ft
Shear Wall
CLT Panels
SB27
CLT Diaphragms
Is the Diaphragm Rigid or Flexible?.
SB28
Structural CLT Floor and Roof Construction
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Calculated Diaphragm DeflectionsOR
Enveloped Diaphragm Design(check for both flexible and rigid diaphragm behavior)
(check for conservatively flexible and conservatively stiff semi-rigid behavior)
CLT Diaphragms in US Seismic Applications
#$%& ='()*+,-.+ ()
/0(1(+ 2)34 +
∑ 6789.
CLT Diaphragm Design Example Paper
• Detailed design example for simple diaphragm following NDS 2015, US CLT Handbook
• Includes approximate deflection equation:• Modified 4-term wood panel sheathed diaphragm
equation in SDWPS 15
2 = :9
:;)
+ :;.
PL is panel lengthPW is panel widthen is connector slip at diaphragm edge
ChordFlexure
PanelShear
ChordSlip
ConnectorSlip
Structural CLT Floor and Roof Construction
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CLT Diaphragm Design Example Paper
0.283 in + 0.300 in + 0.568 in + 0.199 in = 1.35 in
Seismic Detailing: An European Approach
Yielding Connections
Non Yielding Connections
Designed to Overstrengthfactor of 1.3 to 1.6 of yielding connection strength
Fragiacomo, Vasallo et al.
Typical Assumption of Rigid Diaphragm Behavior for CLT wall
and floor systems
Structural CLT Floor and Roof Construction
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Seismic Detailing: US CLT Handbook Approach
Yielding Connections
Non Yielding ConnectionsChords and Anchorage
• NDS Yield Modes III and IV govern.• Strength of other (non-yielding) limit
states at connection designed to nominal yielding connection capacity. 1/ϕ = 1/0.65 = 1.54 overstrengthfactor
Possible routes for near term seismic project designs under Alternative Means and Methods include:
1) Elastic Design Method• Based on lower-bound strength of components• Following new ASCE 7-16 alternative diaphragm method to determine
elastic seismic diaphragm force demands
2) Capacity-Based Design Method
• Using designated yielding connections with overstrengthdesign of non-desirable limit states.
• Based on yielding connection technologies of proven cyclic behavior! Relatively equivalent to Wood Structural Panel diaphragm
behavior OR! Advanced Engineering with supporting testing to justify design
Routes for Seismic Diaphragms
Structural CLT Floor and Roof Construction
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WoodWorks Solutions Paper on CLT Modeling
http://www.woodworks.org/wp-content/uploads/Approach-to-CLT-Diaphragm-Modeling-for-Seismic-WoodWorks-Jan-2017.pdf
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Additional Resources
Structural CLT Floor and Roof Construction
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June 2016 Structures Magazine Article
http://www.structuremag.org/wp-content/uploads/2016/05/C-StrucDesign-Breneman-Jun161.pdf
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US CLT Handbook
1. Introduction2. Manufacturing3. Structural4. Lateral5. Connections6. DOL and Creep7. Vibration8. Fire
9. Sound 10.Enclosure11.Environmental12.Lifting
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Structural CLT Floor and Roof Construction
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Source of CLT Handbook
www.rethinkwood.com/masstimber
Questions?This concludes The American Institute of Architects Continuing Education Systems Course Scott Breneman
144
Structural CLT Floor and Roof Construction
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