connection solutions for wood- frame structures copyright ... · yield of wood fibers mode ii...

Copyright © 2014 American Wood Council. All rights reserved. 1

Connection Solutions for Wood-frame StructuresMichelle Kam-Biron, PE, SE, SECBDirector of EducationAmerican Wood Council

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© American Wood Council 2014

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Learning Objectives

• On completion of this course, participants will:

• Be familiar with current wood connection design philosophy,Be familiar with current wood connection design philosophy,

behavior, and serviceability issues.

• Be able to identify basic wood material properties and learn how to

avoid splits, notching, and net section issues in connection solutions

• Be able to recommend fastening guidelines for wood to steel, wood

to concrete, and wood to wood connections.

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to concrete, and wood to wood connections.

• Be able to describe effects of moisture on wood connections and

implement proper detailing to mitigate issues that may occur.

Outline

• Wood connection design philosophy

Connection behavior• Connection behavior

• Serviceability challenges

• Connection hardware and fastening systems

• Connection techniques

• Design software

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• Where to get more information


Outline


Connection behavior• Connection behavior

• Serviceability issues



• Design software

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

Basic Concepts

Parallel Perpendicular

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Stronger Less strong


Connecting Wood - Philosophy

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

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


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• Wood likes to take on load spread over its surface

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



• Wood and tension perpendicular to grain

• Not recommended

Initiators:• notches• large diameter fasteners

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• large diameter fasteners• hanging loads

Notching

Problem Solution

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Beam to Concrete

• Notched Beam Bearing

• may cause splitting

Split

may cause splitting

• not recommended

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Beam to Concrete

• Notched Bearing Wall

• alternate to beam notch

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Hanger to Beam

• Load suspended from lower half of beam

• Tension perpendicular to grain

• May cause splits SplitSplit

C

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T

NA

NA

Hanger to Beam

Lower half of beam

• may cause splitsmay cause splits

• not recommended

Exception: light load

• <100 lbs

• >24” o.c.Split

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Split


Hanger to Beam

• Load supported in upper half of beam

Full wrap sling option

• Extended plates puts wood in compression when loaded

C

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compression T

NA

NA

Connecting Wood- Philosophy

• Splitting happens because wood is relatively weak perpendicular to grain

• Nails too close (act like a wedge)

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Framing

Staggered Nailing


Wood Structural

Panel

Nail

1/8" GapBetween Panels

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Nailing not staggered Nailing staggeredNailing not staggered Nailing staggered

Splitting occurs parallel to grain

Connecting Wood- Philosophy

Splitting will not occur

Staggering

Staggering a line of

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perpendicular to grain, no matter how close

nails are

gg gnails parallel to wood

grain minimizes splitting



• Wood, like other hygroscopic materials, moves in varying environments

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• Fastener selection is key to connection ductility, strength, performance

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• Mechanical fasteners

• keep them small

• use lots of them

• Issue is scale of fastener relative to wood member size

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Next...


• Connection behavior




• Design software


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Connection Behavior

• Balance• Strength – L d high strength poor ductilityStrength • Ductility-

Load high strength, poor ductility

good strength, good ductility

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Displacement

low strength, good ductility

Connection Behavior

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Connection Behavior

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Connection Behavior

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Connection Behavior

Load high strength, poor ductility• Balance• Strength –

Si d b fgood strength, good ductility

low strength, good ductility

• Size and number of fasteners

• Ductility-• Fastener slenderness• Spacing• End distance

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Displacement

Next...






• Design software


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Connection Serviceability

Bristlecone Pine

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Giant Sequoia Western Juniper


• Issue: direct water ingress

• Water is absorbed most quickly through wood end grain

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No end caps or flashing




• Re-direct the water flow around the connection

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end caps and flashing



• Or, let water out if it gets in...

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Moisture trap -No weep holes


Moisture Changes In Wood

Causes dimensional changes perpendicular to graingrain

Growing tree is filled with water

As wood dries, it shrinksperp. to grain

ntia

lly

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Tang

e

Radially

Wood Shrinks

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Woodmagazine.com



• Moisture Effects

1% change in dimension for

every 4%

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every 4% change MC

Wet Service Factor, CM

• Dowel-type connectors• bolts

Saturated • drift pins• drift bolts• lag screws• wood screws• nails

Saturated

19% MC

Dry

fabrication MCin-service MC

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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

Dry


Wet Service Factor, CM

CCMM = 1.0 if:= 1.0 if:Saturated CCMM 1.0 if: 1.0 if:

1 fastener

2+ fasteners

19% MC

Dry

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CM 0.4 Lateral load (D>1/4″) split splice plates

y

fabrication MCin-service MC Table 10.3.3 footnote 2

Beam to Column

• Full-depth side plates

• may cause splitting

• wood shrinkage

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Beam to Column

• Smaller side plates

• transmit force

• allow wood movement

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Beam to Column

• Problem

• shrinkage

• tension perp

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Beam to Wall

• Solution

b l b• bolts near bottom

• minimizes effect of shrinkage

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Slotted hardware

• Avoid contact with cementitious materials


• Beam on Shelf

• prevent contact with concrete

• provide lateral resistance and uplift

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Beam to Concrete

• Beam on Wall

• prevent contact with concrete

• provide lateral resistance and uplift

• slotted to allow longitudinal movement

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• typical for sloped beam

Beam to Masonry

• Application

• Application

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Need 1/2” air gap between wood and masonry


Column to Base

• Problem

• no weep holes in closed shoe

• moisture entrapped

• decay can result

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Column to Base

• Angle brackets

• anchor bolts in brackets

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Column to Base

Where’s the plate?

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Hidden Column Base

• Floor slab poured over connection

• will cause decay

• not recommended

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Column to Base

• Floor slab poured below connection

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Next...






• Design software


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Mechanical Connectors

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Traditional Connectors

• All-wood solution

• time tested

• practical

• extreme efficiencies available with computer numeric control (CNC) machining

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www.tfguild.orgwww.timberframe.org


• Long History > 100 years

• Uses automated


• Uses automated Computer numerical Control (CNC) milling technology • machine joints• pre-drill holes

• Timber Framer’s Guild -www.tfguild.org

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http://www.tfguild.org/downloads/TFEC-1-2010-with-Commentary.pdf


• Wood dowel connection design technology now available

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Schmidt, R.J. (2006): Timber Pegs – Considerations for Mortise and Tenon Joint Design, Structure Magazine, March 2006, NCSEA, 13(3):44-47. http://www.structuremag.org/wp-content/uploads/2014/09/SF-Timber-Pegs-March-061.pdf


Mechanical Connectors

•Common Fasteners• Nails • Staples

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p• Wood Screws• Metal plate

connectors• Lag screws • Bolts

• Included in U.S. design literature

Fastener Values

Fastener Type Reference

B l NDS ER

Evaluation Reports (ER) are developed for proprietary products

Bolts NDS or ER

Lag Screws NDS or ER

Wood Screws NDS or ER

Nails & Spikes NDS or ER

Split Ring Connectors NDS

Shear Plate Connectors NDS

Drift Bolts & Drift Pins NDS

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Metal Plate Connectors ER

Hangers & Framing Anchors

ER

Staples ER


NDS Chapter 11 – Dowel-type Fasteners

• ASD and LRFD accommodated through Table 10.3.1

• Bolts

L• Lag screws

• Wood screws

• Nails & spikes

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Fastener Bending Yield Test

Center-Point Bending Test

Load

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Dowel Bearing Strength

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Yield Limit Equations

•4 Modes of failure•4 Modes of failure

•6 Yield equations

•Single & double shear

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Yield Modes

MODE Ib i d i d•bearing-dominated

yield of wood fibers

MODE II•pivoting of fastener with localized crushing of wood fibers

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Yield Modes

MODE III•fastener yield in b di tbending at one plastic hinge and bearing –dominated yield of wood fibersMODE IV•fastener yield in bending at two

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gplastic hinges and bearing –dominated yield of wood fibers



•4 Modes of failure•6 Yield equationsSi l & d bl h•Single & double shear

•Wood-to-wood•Wood-to-Steel•Wood-to-Concrete

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Chapter 11- Dowels

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Updated TR 12

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http://www.awc.org/publications/TR/index.php

TR 12

• Background and derivation of the mechanics-based approach for calculating lateral connection capacity used in the NDS

• Provides additional flexibility and broader applicability to the NDS provisions. • Simplified Equations

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TR 12

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TR 12

Allows for evaluation of ti ithconnections with gaps

between connected members

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TR 12

• 2014 Edition - New information on design of• wood members attached to hollow members• design of driven-fasteners with tapered tips• optimizing connections based on location of thre

ads relative to the connection shear plane.

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Chapter 11- Dowels

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Chapter 11-Dowels

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Chapter 11-Dowels

Threaded length < lm/4 lm

Dia. Fastener = D

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Dia. Fastener = D

Threaded length < lm/4 lm


Chapter 11-Dowels

lm

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Dia. Fastener = Dr

Spacing, End, & Edge Distance 2012 NDS

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• 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 e ceed 5" (see Fig e 11H) nless special detailing isexceed 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. For

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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.



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• 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 multipleLocal 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.”

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• Closely spaced fasteners

• brittle failure

• lower capacity

• wood failure mechanisms need

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to be considered in design


• Properly spaced fasteners

• increased ductility

• higher capacity

• spread out the fasteners!

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• Appendix E NDS Expressions

– Net tension:

– Row tear-out:

nettNT AFZ ''

85

row

i

i

n

iRTRT

viRT

ZZ

tsFnZ

1

''

min''


• Appendix E NDS Expressions

– Group tear-out

• Note: spacing between outer rows of fasteners

netgrouptbottomRTtopRT

GT AFZZ

Z '

'''

22

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


Chapter 12 – Split Rings and Shear Plates

• Geometry factor, CD

• Side GrainSide Grain

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Chapter 12 – Split Rings and Shear Plates

• Geometry factor, CD

• End GrainEnd Grain

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NDS Chapter 13 – Timber Rivets

• Many applications

• Canada several decades2005 NDS• 2005 NDS• Glued Laminated Timber

• DFL• SP

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• Plates• Steel ASTM A36

H t di d l i d if

Chapter 13- Timber Rivets

• Hot-dipped galvanized if in wet service

• Perforated Steel Plates• Fixed-hole

pattern geometry• Holes sizes lock

and hold rivet to

90

and hold rivet to prevent rotation


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

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• Plate yielding

• Enhanced ductility

• Lowest value governs design

Timber Rivets – Design 2005 NDS

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Timber Rivets – Design 2012 NDS

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Timber Rivets - Design• 2005 NDS

• Reiterative process

Parallel to grain timber rivet capacity• 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

188 2012 NDS

108 2012 NDS

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

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

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Timber Rivets - Design

• Flow chart per the 2005 NDS

• Reiterative process

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Design Example – 2005 NDS

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Next...






• Design software


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Connection Techniques

• Must evaluate:

• forces present

• environmental effects

• material effects

• aesthetics

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• Wood bolts in all-wood structure

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Pre-engineered Connectors

• Post to Beam

• Beam to Beam

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• Joist to Beam (Hanger)

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• Column Cap & Base hardware

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• Hanger hardware

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• Truss hardware

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Custom Hardware

• Difficult situations made easy

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• Bolts in heavy trusses

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• Connecting other frame materials :

• Steel

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• Connecting other frame materials :

• Concrete

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• Steel bolts in columns

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Hidden kerf plates



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Operations CentreGulf Islands National Park Reserve• Larry McFarland

Architect, V BC


Vancouver, BC• CWMM

Consulting Engineers, Inc., Vancouver, BC

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•Regional District of Nanaimo Administration Building Expansion


•Architect: Neale Staniszkis Doll Adams Architects Vancouver, BC

•Owner; Regional District of Nanaimo Nanaimo, BC

•General Contractor: WindleyC t ti Ltd N i BC

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Contracting Ltd Nanaimo, BC

•Structural Engineer: HeroldEngineering Ltd. Nanaimo, BC


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Custom Hardware

• A blend of art and technology

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Concealed Connectors

• Proprietary Systems

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• Hollow steel connection tubetube

• Expanding cross pins

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• Self-tapping dowel s-w-s

• Threaded screw w-w

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•Kwantlen Polytechnic University•Cloverdale Campus


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• Bunting Coady Architects, Vancouver, BC• Bush Bohlman & Partners, Inc., Vancouver, BC


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• Shaped steel shaft

• Steel pins or dowels

• Non-shrink grout

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•Raleigh-Durham International Airport


• Fentress ArchitectsD CO• Denver, CO

• Washington, DC

• Stewart Engineering, Inc.•Raleigh, NC

• Archer Western Contractors

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•Raleigh, NC


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• Steel pipe

• Stitch bolts

• Tie-Bolt

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•Arena Stage at the Mead Center for American Theater


• Bing Thom Architects• Fast + Epp Structural

Engineers• Clark Construction

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•Arena Stage at the Mead Center for American Theater


American Theater

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•Richmond Olympic Oval


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

•Richmond Olympic Oval


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


•Myrick Hixon EcoPark Building - WI


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Whole Trees Architecture, Stoddard, WI

Next...






• Design software


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•WWPA Lumber Design Suite

B d J i t

Software Solutions Exist

• Beams and Joists• Post and Studs• Wood to Wood

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

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

screws)

Connection Calculator

AWC.org

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Next...






• Design software


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More info…

2012 NDS

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More info…

M4 4 Special Design ConsideratiM4.4 Special Design Considerations• Mechanical Connections• Dowel-Type Fasteners• Split Ring and Shear Plates

Connectors• Timber Rivets

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http://www.awc.org/pdf/2012ASD-LRFD_Manual_WEB.pdf

More info???

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2015


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

More info???

• 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

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Se s c e o a ce o eted Co ect o s ea y beConstruction

• 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

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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

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Avoid eccentricity in joint details

• Minimize exposure of end grain

Connections

and you…and you thought connecting wood was complicated!

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Questions?

www.awc.org

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[email protected]

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