american wood council connection solutions for wood-frame · pdf filerecommend fastening...

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Connection Solutions for Wood-frame Structures

Presented by:Michelle Kam-Biron, PE, SEDirector, Education

American Wood Council

The American Wood Council (AWC)provides wood design and construction information to assist building industry professionals, develops structural and fire performance data on a wide range of traditional and engineered wood products, and engages in long-term research.

American Wood Council

www.awc.org

American Wood CouncilDesign Professional Membership:• Optional listing in AF&PA Design Professional Services Directory with

description of professional services.• Member discounts on Technical Publications.• AWC IMPACT newsletter.• Wood Design Focus, the Forest Products Society quarterly journal of

contemporary wood engineering. • Wood Design & Building, a quarterly North American magazine on

design and construction of modern wood buildings.• Use of the AWC Design Professional Member logo.• Frequent updates on wood industry developments, association activity,

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“The Wood Products Council” is a Registered Provider with The American Institute of Architects Continuing Education Systems (AIA/CES). Credit(s) earned on completion of this program 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 program 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.

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.

© American Wood Council 2013

Learning Objectives

At the end of this program, participants will be knowledgeable of:

1. Identify basic wood material properties and learn how to avoid splits, notching, and checking in connection solutions.

2. Recommend fastening guidelines for wood-to-steel, wood-to-concrete, and wood-to-wood connections.

3. Describe effects of moisture on wood connections and implement proper flashing to avoid problems.

4. Identify proper fastener selection in size, scope, and pattern.

Outline• wood connection design

philosophy• connection behavior• serviceability challenges• connection hardware and

fastening systems• connection techniques • design software• where to get more information



Outline• wood connection design

philosophy• connection behavior• serviceability issues• connection hardware and

fastening systems• connection techniques • design software• where to get more information

Stronger Less strong

Parallel Perpendicular

Model wood cells as a bundle of strawsBundle is very strong parallel to axis of the straws

Basic Concepts

Connecting Wood - Philosophy• wood likes compression parallel to grain

– makes connecting wood very easy

Wood likes compression parallel to grain – makes connecting wood very easy

Connecting Wood - Philosophy




• wood likes to take on load spread over its surface

Concentrated at a single fastener –wood is more prone to split and crush

Connecting Wood - Philosophy• wood and tension perpendicular to grain

– Not recommended

initiators:• notches• large diameter fasteners• hanging loads

Notching

Problem Solution



Split

Beam to Concrete

Notched Beam Bearing– may cause splitting– not recommended

Beam to Concrete

Notched Bearing Wall– alternate to beam notch

Hanger to Beam

Load suspended from lower half of beam Tension perpendicular

to grain May cause splits

SplitSplit

C

T

NA

NA

Hanger to Beam

Lower half of beam– may cause splits– not recommended

Exception: light load- <100 lbs- >24” o.c.

Split



Hanger to Beam

Load supported in upper half of beamExtended plates puts

wood in compression when loaded

compression

Full wrap sling option

C

T

NA

NA

• Splitting happens because wood is relatively weak perpendicular to grain– Nails too close (act like a

wedge)


Nailing not staggered Nailing staggered

Framing

Wood StructuralPanel

Nail

1/8" GapBetween Panels

Nailing not staggered Nailing staggered

Staggered NailingConnecting Wood - Philosophy

Splitting will not occur perpendicular to grain,

no matter how close nails are

Splitting occurs parallel to grain

Staggering

Staggering a line of nails parallel to wood grain

minimizes splitting




Connecting Wood - Philosophy• wood, like other hygroscopic materials,

moves in varying environments

Connecting Wood - Philosophy• fastener selection is key to connection

ductility, strength, performance


• mechanical fasteners– keep them small– use lots of them

issue is scale of fastener relative to wood member size

Connecting Wood - PhilosophyQuick summary• Wood likes compression parallel to grain• Wood likes to take on load spread over its

surface• Avoid tension perpendicular to grain• Wood, like other materials, moves in varying

environments• Fastener selection is key to connection

ductility, strength, performance



Next...

• wood connection design philosophy• connection behavior• serviceability challenges• connection hardware and fastening systems• connection techniques • design software• where to get more information

Connection Behavior

Load

Displacement

high strength, poor ductility

good strength, good ductility

low strength, good ductility

Balance• Strength –• Ductility-

Connection Behavior Connection Behavior



Connection Behavior Connection Behavior

Load

Displacement

high strength, poor ductility

good strength, good ductility

low strength, good ductility

Balance• Strength –

– Size and number of fasteners

• Ductility-– Fastener

slenderness– Spacing– End distance

Next...


Connection Serviceability



Connection ServiceabilityIssue: direct water ingress• water is absorbed most quickly through wood

end grain

No end caps or flashing


Issue: direct water ingress

• re-direct the water flow around the connection

end caps and flashing


Issue: direct water ingress• or, let water out if it gets in...

Moisture trap -No weep holes

Moisture Changes In Wood

• Causes dimensional changes perpendicular to grain

Growing tree is filled with water

As wood dries, it shrinksperp. to grain



Wood Shrinks

Woodmagazine.com


Moisture Effects

Wet Service Factor, CM

CM 1.0 0.7 0.4* Lateral load (*CM=0.7 for D<1/4″)1.0 0.7 1.0 Withdrawal load - lag & wood screws only1.0 0.25 0.25 Withdrawal load - nails & spikes

• Dowel-type connectors• bolts• drift pins• drift bolts• lag screws• wood screws• nails

Saturated

19% MC

Dryfabrication MCin-service MC

CM 0.4 Lateral load (D>1/4″)

CM = 1.0 if:

1 fastener

2+ fasteners

split splice plates

Wet Service Factor, CM

Saturated

19% MC

Dry

fabrication MCin-service MC

Table 10.3.3 footnote 2



Beam to Column

Full-depth side plates– may cause splitting– wood shrinkage

Beam to Column

Smaller side plates– transmit force– allow wood

movement

Beam to Column

Problem– shrinkage– tension perp

Beam to Wall

Solution– bolts near bottom– minimizes effect of

shrinkage

Slotted hardware



Beam on Shelf– prevent contact with

concrete– provide lateral

resistance and uplift

Avoid contact with cementitious materials

Connection Serviceability Beam to Concrete

Beam on Wall– prevent contact with

concrete– provide lateral

resistance and uplift– slotted to allow

longitudinal movement– typical for sloped beam

Beam to Masonry

Application

Need 1/2” air gap between wood and masonry

Column to Base

Problem– no weep holes in closed

shoe– moisture entrapped– decay can result



Column to Base

Angle brackets– anchor bolts in brackets

Column to Base

Where’s the plate?

Hidden Column Base

Floor slab poured over connection– will cause decay– not recommended

Column to Base

Floor slab poured below connection



Next...


Mechanical Connectors

Traditional Connectors

All-wood solution• time tested• practical• extreme

efficiencies available with computer numeric control (CNC) machiningwww.tfguild.org

www.timberframe.org

Long History > 100 years Uses automated

Computer numerical Control (CNC) milling technology machine joints pre-drill holes Timber Framer’s

Guild -www.tfguild.org





Wood dowel connection design technology now available

Schmidt, R.J. (2006): Timber Pegs – Considerations for Mortise and Tenon Joint Design, Structure Magazine, March 2006, NCSEA, 13(3):44-47.

Common Fasteners• Nails • Staples • Wood Screws• Metal plate connectors• Lag screws • Bolts

Mechanical Connectors

Fastener Values

Included in U.S. design literatureFastener Type Reference Bolts NDS or NER Lag Screws NDS or NER Wood Screws NDS or NER Nails & Spikes NDS or NER Split Ring Connectors NDS Shear Plate Connectors NDS Drift Bolts & Drift Pins NDS Metal Plate Connectors NER Hangers & Framing Anchors NER Staples NER

National Evaluation Reports (NER) are developed for proprietary products

NDS Chapter 11 – Dowel-type FastenersASD and LRFD accommodated through Table 10.3.1– Bolts– Lag screws– Wood screws– Nails & spikes



Fastener Bending Yield Test

Center-Point Bending Test

Load

Dowel Bearing Strength

Yield Limit Equations

•4 Modes of failure•6 Yield equations•Single & double shear

MODE I– bearing-dominated yield of wood fibersMODE II– pivoting of fastener with localized crushing of wood fibers

Yield Modes



MODE III– fastener yield in bending at one plastic hinge and bearing –dominated yield of wood fibersMODE IV– fastener yield in bending at two plastic hinges and bearing –dominated yield of wood fibers

Yield Modes Yield Limit Equations

•4 Modes of failure•6 Yield equations•Single & double shear•Wood-to-wood•Wood-to-Steel•Wood-to-Concrete

Spacing, End, & Edge Distance 2005 NDS Spacing, End, & Edge Distance 2005 NDS



Spacing, End, & Edge Distance 2012 NDS

Unless special detailing is provided to accommodate cross-grain shrinkage of the wood member.


• adds the following notes to 11.5.1 The perpendicular to grain distance between the outermost fasteners shall not exceed 5" (see Figure 11H) unless special detailing is provided to accommodate cross-grain shrinkage of the wood member. For structural glued laminated timber members, the perpendicular to grain distance between the outermost fasteners shall not exceed the limits in Table 11.5.1F, unless special detailing is provided to accommodate cross-grain shrinkage of the member.


Unless special detailing is provided to accommodate cross-grain shrinkage of the wood member.




Local Stresses in Fastener Groups

10.1.2 Stresses in Members at Connections “Local stresses in connections using multiple

fasteners shall be checked in accordance with principles of engineering mechanics. One method for determining these stresses is provided in Appendix E.”


• Closely spaced fasteners– brittle failure– lower capacity

wood failure mechanisms need to be considered in design


• Properly spaced fasteners– increased ductility– higher capacity

spread out the fasteners!


• Appendix E NDS Expressions– Net tension:

– Row tear-out:

nettNT AFZ ''

row

i

i

n

iRTRT

viRT

ZZ

tsFnZ

1

''

min''




• Appendix E NDS Expressions– Group tear-out

• Note: spacing between outer rows of fasteners paralleling the member on a single splice plate < 5″

netgrouptbottomRTtopRT

GT AFZZZ

'''

'22

NDS Chapter 12 – Split Rings & Shear Plates• Capacity tables - unchanged

Specialized Connectors• Shear plates

NDS Chapter 12 – Split Rings & Shear Plates

Availability• www.clevelandsteel.com



NDS Chapter 13 – Timber Rivets• Many applications

Canada several decades 2005 NDS Glued Laminated Timber DFL SP

Timber Rivets

Figure 1 – Glulam Surfaces

NDS Chapter 13 – Timber Rivets

NDS - Rivets Hot-Dipped

Galvanized Fixed-shank cross-

section Fixed head

dimension Vary only in length

Rivets• Steel AISI 1035• Rockwell Hardness C32-39• Fu = 145 ksi

Chapter 13 – Timber Rivets

Plates• Steel ASTM A36• Hot-dipped galvanized if in

wet service

Perforated Steel Plates Fixed-hole

pattern geometry Holes sizes lock

and hold rivet to prevent rotation



• Ductility with rivet capacity as governing mode

• Or move ductile zone out of the rivets into the steel plate– Steel plates design as

“weak link”– Control capacity prior to

the rivet connection in wood

– Steel plates – more predictable behavior

Timber Rivets – Seismic Connections Timber Rivets - Design• Four strength limit states:

– Rivet yielding• Pr – parallel to grain• Qr – perpendicular to grain

– Wood failure• Pw – parallel to grain• Qw – perpendicular to grain

– Plate yielding• Enhanced ductility

Lowest value governs design

Timber Rivets – Design 2005 NDS Timber Rivets – Design 2012 NDS



Timber Rivets - Design

• 2005 NDS– Reiterative process– Parallel to grain timber rivet capacity

• Pr = 280 p0.32 nR nC (13.2-1)

– Perpendicular to grain timber rivet capacity• Qr = 160 p0.32 nR nC

– Section 13.3.1: ”The maxiumum distance perpendicular to grain between outermost rows of rivets shall be 12”

188 2012 NDS

108 2012 NDS

Where to Find Design Examples

Timber Rivet Connections –Design Process for a Hanger Connection

http://www.awc.org/pdf/WDF17-4-rivet-pw.pdf

Timber Rivets - Design

• Flow chart per the 2005 NDS– Reiterative process

Design Example – 2005 NDS



Design Example

Dead Load + Snow Load

Design Example – 2005 NDS

Design Example – 2005 NDS Design Example – 2005 NDS



Design Example – 2005 NDS Next...


Connection Techniques• must evaluate:

– forces present– environmental effects– material effects– aesthetics

Connection Techniqueswood bolts in all-wood structure



Pre-engineered ConnectorsPost to BeamBeam to Beam

Pre-engineered ConnectorsJoist to Beam (Hanger)

Pre-engineered ConnectorsColumn Cap & Base hardware

Pre-engineered ConnectorsHanger hardware



Pre-engineered ConnectorsTruss hardware

Custom HardwareDifficult situations made easy

Connection Techniquesbolts in heavy trusses

Connection Techniques

• connecting other frame materials : Steel




• connecting other frame materials : Concrete

Connection Techniquessteel bolts in columns

Hidden kerf plates

Bullitt Center, Seattle, WA, USAArchitect: Miller Hill PartnershipPhoto Credit: Miller Hull Partnership

Connection Techniques Connection Techniques



Operations CentreGulf Islands National Park Reserve

Larry McFarland Architect, Vancouver, BCCWMM

Consulting Engineers, Inc., Vancouver, BC


Regional District of Nanaimo Administration Building Expansion

Architect: Neale Staniszkis Doll Adams Architects Vancouver, BC

Owner; Regional District of Nanaimo Nanaimo, BC

General Contractor: WindleyContracting Ltd Nanaimo, BC

Structural Engineer: HeroldEngineering Ltd. Nanaimo, BC




Custom Hardware

A blend of art and technology

Concealed Connectors

Proprietary Systems

Concealed Connectors

Timberlinx• Hollow steel

connection tube

• Expanding cross pins

Concealed ConnectorsSFS Intec• Self-tapping

dowel s-w-s• Threaded

screw w-w



Kwantlen Polytechnic UniversityCloverdale Campus

Bunting CoadyArchitects, Vancouver, BCBush Bohlman

& Partners, Inc., Vancouver, BC


Concealed ConnectorsBS Connector• Shaped steel shaft• Steel pins or dowels• Non-shrink grout

Raleigh-Durham International AirportConnection Techniques

Fentress Architects• Denver, CO• Washington, DC

Stewart Engineering, Inc.•Raleigh, NC

Archer Western Contractors•Raleigh, NC




Concealed ConnectorsStavebolt®• Steel pipe• Stitch bolts• Tie-Bolt

Concealed ConnectorsSherpa



Concealed ConnectorsSherpa Arena Stage at the Mead Center for

American Theater

• Bing Thom Architects

• Fast + EppStructural Engineers

• Clark Construction


Arena Stage at the Mead Center for American Theater


Richmond Olympic Oval

CANNON DesignGerald Epp, Fast + EppRichmond (south of Vancouver)




Richmond Olympic Oval

CANNON DesignGerald Epp, Fast + EppRichmond (south of Vancouver)

Connection TechniquesMyrick Hixon EcoPark Building - WI

Whole Trees Architecture, Stoddard, WI


Next...

• wood connection design philosophy• connection behavior• Serviceability challenges• connection hardware and fastening systems• connection techniques • design software• where to get more information

Software solutions exist




Connectionsdesign software

http://www2.wwpa.org/TECHGUIDEPAGES/DesignSoftware/tabid/859/Default.aspx

WWPA Lumber Design Suite Beams and Joists Post and Studs Wood to Wood Shear

Connections (nails, bolts, wood screws and lag screws)


Connection Calculator

AWC.org

Next...




DES110:Connection Design

•www.awc.org•More comprehensive

More info.???

http://www.apawood.org/level_c.cfm?content=pub_searchresults&pK=t300h&pT=Yes&pD=Yes&pF=Yes&CFID=41187636&CFTOKEN=25311692

Form EWS T300H

• Technica papers on Timber rivets: http://www.awc.org/helpoutreach/faq/faqFiles/Timber_rivets.html

• Timber rivets in structural composite lumber• Simplified analysis of timber rivet connections • Timber rivet connections in U.S. domestic species• Timber Rivets-Structure Magazine• Seismic Behavior of Timber Rivets in Wood

Construction• Seismic Performance of Riveted Connections in

Heavy Timber Construction• Timber rivet suppliers

More info.???• Load-carrying behavior of steel-to-timber

dowel connections: http://timber.ce.wsu.edu/Resources/papers/2-4-1.pdf

• New Concealed Connectors Bring More Options for Timber Structures http://www.structuremag.org/Archives/2007-1/p42-43D-Insights-ConcealedConnectorsJan07.pdf

More info.???



Take home messages...

• transfer loads in compression / bearing whenever possible

• allow for dimensional changes in the wood due to potential in-service moisture cycling

• avoid the use of details which induce tension perp stresses in the wood

• avoid moisture entrapment in connections• separate wood from direct contact with masonry or

concrete• avoid eccentricity in joint details• minimize exposure of end grain

Murphy’s Law

No matter how well it is designed...

?

Connections

…and you thought connecting wood was complicated!



This concludes The American Institute of Architects Continuing

Education Systems Course

www.awc.org

[email protected]

Questions?

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