Mass Timber Structural Design: Engineering Modern Timber Structures - DVASE
Please add relevant logo here Mass Timber Structural Design: Engineering Modern Timber Structures Terry Pattillo, AIA Mid-Atlantic Regional Director WoodWorks – Wood Products Council terryp@woodworks.org (919) 995-6672 Photo: Alex Schreyer
“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.
Course Description This presentation will provide a detailed look at the structural design processes associated with a variety of mass timber products, including glued-laminated timber (glulam), crosslaminated timber (CLT), and nail-laminated timber (NLT). Applications for the use of these products in gravity force-resisting systems under modern building codes will be discussed. Other technical topics will include and an introduction to lateral systems common in mass timber buildings, mass timber floor vibration criteria, and connection options. Mass timber framing components are often left exposed to act as a finish while taking advantage of their aesthetics. As such, they are often required to provide a fire-resistance rating demonstrating their ability to maintain structural integrity in the event of a fire. This session will also discuss structural design of mass timber elements under fire conditions.
Learning Objectives 1. Compare properties and performance characteristics of mass timber products and review their unique design considerations. 2. Review structural design steps for members and connections in common mass timber framing systems. 3. Highlight common connection systems in modern timber structures and resources for associated design values. 4. Demonstrate design steps for calculated fire resistance of exposed structural timber elements.
MASS TIMBER OVERVIEW
CURRENT STATE OF MASS TIMBER PROJECTS As of July 2019, 599 multi-family, commercial, or institutional projects have been constructed out of mass timber across the U.S., or they’re currently in design. Stage Construction Started / Built In Design ng-trends-mass-timber/
Mass timber is a category of framing styles often using small wood members formed into large panelized solid wood construction including CLT, NLT or glulam panels for floor, roof and wall framing Mass Timber What is it?
OVERVIEW TIMBER METHODOLOGIES Heavy Timber Photo: Benjamin Benschneider Mass Timber Photo: John Stamets
Glue Laminated Timber (GLT) Cross-Laminated Timber (CLT) Nail-Laminated Timber (NLT) Photo: Think Wood Photo: StructureCraft Photo: LendLease Photo: Ema Peter
Dowel-Laminated Timber (DLT) Photo: StructureCraft Photo: StructureCraft Mass plywood panels (MPP) Decking Photo: Freres Lumber Photo: LEVER Architecture Photo: Bernard André
OVERVIEW MANUFACT URING
Mass Timber Framing Systems
Mass Timber Framing Systems Gravity Framing Styles Post & Beam Mass Timber Walls “Honeycomb” Hybrid LightFrame & Mass Timber Two-Way Deck
Mass Timber Framing Systems Gravity Framing Styles Post & Beam Mass Timber Walls “Honeycomb” Hybrid LightFrame & Mass Timber Two-Way Deck
OVERVIEW STRUCTURAL SOLUTIONS Photo: Ema Peter S T R U C T U R A L S O L U T I O N S P O S T, B E A M P L AT E
Mass Timber Framing Systems Gravity Framing Styles Post & Beam Mass Timber Walls “Honeycomb” Hybrid LightFrame & Mass Timber Two-Way Deck
Candlewood Suites Redstone Arsenal, AL 62,600 SF, 4 story hotel, 92 private rooms CLT utilized for walls, roof panels, and floor panels Image Credit: Lend Lease
Mass Timber Framing Systems Gravity Framing Styles Post & Beam Mass Timber Walls “Honeycomb” Hybrid LightFrame & Mass Timber Two-Way Deck
Photo: John Klein STRUCTURAL SOLUTIONS HYBRID LIGHT-FRAME MASS TIMBER
Virtuoso, Vancouver, BC Image: Adera Image: Seagate Structures
CrossFit Center Spokane, WA Photo Credit: WoodWorks Photo Credit: Mike Bradley, Beacon Builders
Mass Timber Framing Systems Gravity Framing Styles Post & Beam Mass Timber Walls “Honeycomb” Hybrid LightFrame & Mass Timber Two-Way Deck
OVERVIEW STRUCTURAL SOLUTIONS Photo: Seagate Structures S T R U C T U R AL S O L U T I O N S P O S T P L AT E
Mass Timber Framing Systems Gravity Framing Styles Post & Beam Mass Timber Walls “Honeycomb” Hybrid LightFrame & Mass Timber Alternative Systems Two-Way Deck
Photo: SOM STRUCTURAL SOLUTIONS HYBRID STEEL MASS TIMBER
Photo: Structurlam STRUCTURAL SOLUTIONS HYBRID CONCRETE MASS TIMBER
Mass Timber Framing Systems Post & Beam Structural Frame Horizontal Deck
Post & Beam T3 Minneapolis Minneapolis, MN Image Credit: Blaine Brownell
Glulam Framing Photo Credits: WoodWorks
Glulam Framing Photo Credits: WoodWorks
Glulam Framing Photo Credits: WoodWorks
Glulam Framing Photo Credits: WoodWorks
Mass Timber Framing Systems Post & Beam Structural Frame Horizontal Deck
Mass Timber Products Nail-Laminated Timber (NLT) Tongue & groove decking (T&G) Cross-Laminated Timber (CLT) Timber concrete composite Image source: StructureCraft Horizontal Framing Glue-Laminated Timber (GLT) Structural Composite Lumber
Building Code Acceptance of CLT 2015 International Building Code
Mass Timber Lateral Systems Lateral Force Resisting Systems (LFRS) Vertical LFRS Code Recognized Horizontal LFRS (Diaphragms) Non-Code Recognized
Vertical LRFS Code Recognized Concrete shear walls at core Photo Credit: structurecraft
Vertical LFRS Code Recognized Light-frame wood shearwalls Photo Credit: woodworks
Code Recognized Vertical Seismic System Photos: WoodWorks
Vertical LFRS Code Recognized Steel moment frame at exterior wall Photo Credit: woodworks
Vertical LFRS Code Recognized Steel Braced Frame
Mass Timber Lateral Systems Lateral Force Resisting Systems (LFRS) Vertical LFRS Code Recognized Horizontal LFRS (Diaphragms) Non-Code Recognized
Vertical LFRS Not Code Recognized Mass Timber Shearwalls Photo Credit: alex schreyer
Vertical LFRS Not Code Recognized Timber braced frame Photo Credit: alex schreyer
Vertical LFRS Timber Braced Frame
Mass Timber Lateral Systems Lateral Force Resisting Systems (LFRS) Vertical LFRS Horizontal LFRS (Diaphragms)
NLT Diaphragm Design Pre-fabricated panels often pre-sheathed Once installed, add splice strips, tape joint if applicable Photo Credit: structurecraft
CLT Diaphragms Strength of CLT rarely controls Strength of connections controls diaphragm strength
Connection Details
Connection Details Photo Credit: Alex Schreyer Long self tapping screws used extensively throughout mass timber construction 50
Panel to Beam Connection Styles
Panel to Panel Connection Styles Half-Lap Source: Simpson Strong-Tie
Panel to Panel Connection Styles Single Surface Spline Source: Simpson Strong-Tie
Panel to Panel Connection Styles Surface Spline Half Lap Butt Joint Load Sharing not load bearing
Proprietary Products Source: MTC Solutions Variety of Self Tapping Screws
An Efficient Panel to Panel Connection Self-Tapping Screws as “erection bolts” @ 18” – 24” o.c 5 ½” to 6” plywood strip ¾” or 1” Thick Nails at spacing required for shear transfer Graphics: ASPECT Structural Engineers
Proprietary Products Source: Simpson Strong-Tie Source: rothoblaas
Component Design (Panels)
NLT Structural Design NLT Design Guide includes: Architecture Fire Structure Enclosure Supply and Fabrication Construction and Installation Erection engineering Free download from www.thinkwood.com
NLT Structural Design NLT shrinkage/expansion design: Rule of thumb: leave gap between ½” and one ply wide per 8’-10’ wide panel
North American CLT Product Standard 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 ANSI/APA PRG 320 Standard for Performance-Rated Cross-Laminated Timber
FLATWISE Panel Loading Span in MAJOR Strength Direction “Parallel” Direction Span in MINOR Strength Direction “Perpendicular” Direction Use subscript ‘0’ in Notation Use subscript ‘90’ in Notation Reference & Source: ANSI/APA PRG 320
PRG 320 Defined Layups CLT Grade (basic) Layup Panel Properties
CLT Basic Stress Grades CLT Grade Major Strength Direction Minor Strength Direction E1 1950f-1.7E MSR SPF #3 Spruce Pine Fir E2 1650f-1.5E MSR DFL #3 Doug Fir Larch E3 1200f-1.2E MSR Misc #3 Misc E4 1950f-1.7E MSR SP #3 Southern Pine E5 1650f-1.5E MSR Hem-Fir #3 Hem-Fir V1 #2 Doug Fir Larch #3 Doug Fir Larch V1(N) #2 Doug-Fir Larch (North) #3 Doug-Fir Larch (North) V2 #1/#2 Spruce Pine Fir #3 Spruce Pine Fir V3 #2 Southern Pine #3 Southern Pine V4 #2 Spruce Pine Fir (South) #3 Spruce Pine Fir (South) V5 #2 Hem-Fir #3 Hem-Fir Basic solid sawn CLT stress grade in PRG 320-2019. Other custom stress grades including structural composite lumber (SCL) permitted
Common CLT Layups 3-ply 3-layer Most Designs Least /sf 5-ply 5-layer 7-ply 7-layer 9-ply 9-layer 7-ply 5-layer 9-ply 7-layer
3rd Party Product Qualification of CLT
CLT Product Reports CLT Grade (basic or custom) Layup Panel Properties
Structural Design Standardization National Design Specification for Wood Construction 2015 & 2018 Edition
Scope of PRG 320 CLT Panels shall be used in dry service conditions, such as in most covered structures, where the average equilibrium content of solid wood is less than 16 percent CLT panels qualified in accordance with the provisions of this standard are intended to resist the effects of moisture on structural performance as may occur due to construction delays or other conditions of similar severity.
International Community Health Services Shoreline, WA Photo Credit: Andrew Pogue Photography
Flatwise Flexural Strength Design properties based on an Extreme Fiber Model: Flexural Capacity Check: Mb Mb (FbSeff )′ Mb (FbSeff )′ Seff Fb applied bending moment Bending Stress adjusted bending capacity effective section modulus reference bending design stress of outer lamination Reference: NDS Separate values for most components
Flatwise Flexural Strength Flexural Capacity Check (ASD) Mb Bending Stress (FbSeff )′ CD CM Ct CL (FbSeff ) per NDS Commonly Provided as 1.0 combined value Mb CD (1.0) (FbSeff) Reference: NDS Here and in the following, items in RED are provided CLT properties
Flatwise Shear Strength Design Properties based on Extreme Fiber Model: Shear Capacity Check (ASD): Va Shear Stress Fs(IbQ)eff′ CM Ct (Fs(IbQ)eff ) CM Ct Vs Commonly 1.0 Va (1.0) Vs Reference: NDS & Product Reports From Manufacturer Note: Duration of Load Effects (Cd and λ) NOT applicable to Flatwise Shear Strength in the NDS
Flatwise CLT Panel Section Properties Flexural Strength: Flexural Stiffness: Shear Strength: Shear Stiffness: FbSeff,0 EIeff,0 Vs,0 GAeff,0 FbSeff,90 EIeff,90 Vs,90 GAeff,90 Values in RED provided by CLT manufacturer Reference: PRG 320 and CLT Product Reports
Deflection Calculations General Purpose: 1 Way, Beam Action Needed Stiffness: EIeff,0 GAeff,0 Analyze as beam representing a strip (e.g 1. ft) of CLT Can model multiple spans, cantilevers, etc.
Deflection Creep Factor Deformation to Long Term Loads Δ 𝑇 𝐾𝑐𝑟 Δ𝐿𝑇 Δ𝑆𝑇 NDS Eq 3.5-1 Δ𝑆𝑇 Deflection due to short-term loading Δ𝐿𝑇 Immediate deflection due to long term loading 𝐾𝑐𝑟 2.0 for CLT in dry service conditions Reference: NDS 2015
Deflection Calculations Simplified Beam Deflections: For single span, simply supported uniform load Uniform load, w 5 𝑤𝐿4 1 𝑤𝐿2 𝑚𝑎𝑥 384 𝐸𝐼𝑒𝑓𝑓 8 5Τ6 𝐺𝐴𝑒𝑓𝑓 What is Apparent Flexural Stiffness, EIapp, such that Span, L EIapp Set equal to each other and solve for EIapp Reference: US CLT Handbook & NDS 𝐸𝐼𝑒𝑓𝑓 𝐸𝐼𝑎𝑝𝑝 11.5𝐸𝐼𝑒𝑓𝑓 1 𝐺𝐴𝑒𝑓𝑓𝐿2
Deflection Calculations General Purpose, 2 Way, Plate Action Flexural Stiffness EIeff,0 EIeff,90 Shear Stiffness: GAeff,0 GAeff,90 Analyze as plate in bending using FEM analysis software Note, CLT is not a symmetric isotropic plate
Floor Vibration One approach: US CLT Handbook, Chapter 7 (FPI Method) Limit CLT Floor Span such that Span L Where: EIapp apparent stiffness for 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) Reference: US CLT Handbook, Chapter 7
Component Design (LFRS)
CLT Seismic Design CLT Seismic Force Resisting Systems Not addressed In ASCE/SEI 7-10 or 7-16 SDPWS 2015
Platform Framed CLT Shear Walls 2021 SDPWS Update In Process* - Platform Frame CLT Shear Walls - Prescribed nailed metal plate connectors - Panel aspect ratio, h:bp from 2:1 to 4:1 2022 ASCE 7 Update In Process* - Include Platform Frame CLT Shear Walls - R 3 - 65 ft height limit – all Seismic Design Categories *Final contents subject to ongoing balloting
CLT Diaphragms Strength of CLT rarely governs. Strength of Connections covered by NDS and Proprietary Fastener Evaluation Reports
CLT Diaphragm Design Basic Design Provisions CLT diaphragms shall be designed in accordance with the principles of mechanics using fastener and member strength in accordance with the provisions of the NDS. (or proprietary connectors using 3rd party verified equivalence) Calculations per NDS, not capacity tables in SDPWS
CLT Diaphragm Design Suggestions Basic Design Provisions Diaphragm shear connections at CLT panel edges and diaphragm boundary connections shall be designed to ensure that the connection capacity is limited by fastener yielding in accordance with Mode IIIs or Mode IV per NDS 12.3.1. Design capacity of connection (ductile mode governing) 𝑍′𝐶 Eℎ Applied Seismic Forces
Connection Yield Modes Per the NDS
An Efficient Panel to Panel Connection Self-Tapping Screws as “erection bolts” @ 18” – 24” o.c 5 ½” to 6” plywood strip ¾” or 1” Thick Nails at spacing required for shear transfer Graphics: ASPECT Structural Engineers
NLT Diaphragm Design Source: NLT Design & Construction Guide
2021 Code
Type IV-A Credit: Susan Jones, atelierjones Photos: Structurlam, naturally:wood, Fast Epp, Urban One
Type IV-B Credit: Susan Jones, atelierjones Credit: LEVER Architecture
Type IV-C Credit: Susan Jones, atelierjones Photos: Baumberger Studio/PATH Architecture/Marcus Kauffman
Fire Resistance
Fire Resistance - Charring For Exposed Wood Members: IBC 722.1 References AWC’s NDS Chapter 16 (AWC’s TR 10 is a design aid to NDS Chapter 16)
Fire Resistance- Glulams Glulam beam fire design: For unbalanced beams, Substitute 1 core lam for 1 tension lam for 1 hour rating, 2 core lams for 2 tension lams for 1.5 & 2 hour rating For balanced beams, match on compression side
Mass timber design Fire resistance Similar to heavy timber, mass timber products have inherent fire resistance properties Source: AWC’s TR 10
Fire Resistance - CLT CLT fire design: Lam thickness affects char depth Partially charred cross layers are typically neglected for structural checks
Tested Fire Resistance Many successful fire tests of mass timber assemblies have been conducted, both with and without gypsum board protection See WoodWorks Inventory of Tested Assemblies
Additional Resources
US CLT Handbook 1. 2. 3. 4. 5. 6. 7. 8. Introduction Manufacturing Structural Lateral Connections DOL and Creep Vibration Fire 9. Sound 10.Enclosure 11.Environmental 12.Lifting
Additional Resources – WoodWorks.org
Additional Resources – WoodWorks.org Inventory of Fire-Resistance Tested Mass Timber Assemblies
Additional Resources – WoodWorks.org Inventory of Mass Timber Acoustic Assemblies
Questions? This concludes The American Institute of Architects Continuing Education Systems Course Terry Pattillo, AIA Mid-Atlantic Regional Director WoodWorks – Wood Products Council terryp@woodworks.org (919) 995-6672
Copyright Materials This presentation is protected by US and International Copyright laws. Reproduction, distribution, display and use of the presentation without written permission of the speaker is prohibited. The Wood Products Council 2020
WoodWorks -Wood Products Council terryp@woodworks.org (919) 995-6672 "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
Timber service life design - Design Guide for Durability 06. Timber-framed Construction - Sacrificial Timber Construction Joint 07. Plywood Box Beam Construction for Detached Housing 08. Stairs, Balustrades and Handrails Class 1 Buildings - Construction 09. Timber Flooring - Design Guide for Installation 10. Timber Windows and Doors 11.
1 EN 14081 -1:2005 A1:2011 Timber structures Strength graded structural timber with rectangular cross section Part 1: General requirements 2 EN 14080:2013 Timber structures - Glued laminated timber and glued solid timber - Requirements 3 EN 14374:2004 Timber structures - Structural laminated veneer lumber - Requirements
N6 Technical Guide Timber Curtain Wall Timber Curtain Wall Technical Guide N7 Timber Curtain Wall Detail Timber Curtain Wall Corner Detail Curtain Wall CL to CL 34 7/8" [887mm] Glass 33 7/8" [861mm] CL to CL 34 7/8" [887mm] Glass 33 7/8" [861mm] F.S. Timber to Timber 103 11/16" [2634mm] Outside Dimension 111 3/8" [2829mm]
The American Institute of Timber Construction, established in 1952, is a non-profit industry association for the structural glued laminated timber industry. Its members design, manufacture, fabricate, assemble, and erect structural timber systems utilizing both sawn and structural glued laminated timber components.
Structural design software produced by timber companies’ i.e. Hyne Design, Carter Holt Harvey Wood Products’ Design IT and FWPA’s Timber Solutions were found to be used by engineering firms for domestic residential applications. 70% of the engineers surveyed said that they were either likely or very likely to specify more timber
STRUCTURAL TIMBER 1 ENGINEERING BULLETIN REV 0 - 11.11.14/EB001 2 Table 1: Historic use of timber and structural forms in buildings Table 2: Characteristic strength, stiffness and density properties for typical softwoods from EN 338 Table 1 Figure 2 Early 20th Century timber post and bea
Design Guide for Durability #06 Timber-framed Construction - Sacrifi cial Timber Construction Joint #07 Plywood Box Beam Construction for Detached Housing #08 Stairs, Balustrades and Handrails Class 1 Buildings - Construction #09 Timber Flooring - Design Guide for Installation #10 Timber Windows and Doors #11 Noise Transport Corridor Design Guide
Glued laminated timber structures. Part 2: construction and connection details www.structuraltimber.co.uk STRUCTURAL TIMBER 9 ENGINEERING BULLETIN. REV 0 - 11.11.14/EB009 www.structuraltimber.co.uk STRUCTURAL TIMBER 9 ENGINEERING BULLETIN 2 Figure 1 Glulam pin-jointed connections
