Wood Connections - AWC

11/10/2017

Copyright © 2017 American Wood Council1

Wood ConnectionsCornucopia of Classic Connection Conundrums (DES340)

Lori Koch, P.E.Manager, Educational OutreachAmerican Wood Council

Michelle Kam-Biron, P.E., S.E. S.E.C.BSenior Director, EducationAmerican Wood Council

Co r nu cop i a o f C l a s s i c Conne c t i o n Conund r ums 2

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.

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Co rnu cop i a o f C l a s s i c Conne c t i o n Conund r ums 3

COURSE DESCRIPTION

The American Wood Council’s (AWC) National Design Specification® (NDS®) for Wood Construction and Special Design Provisions for Wind and Seismic (SDPWS) are documents referenced in US building codes and used to design wood structures worldwide. Based on numerous help desk questions and feedback from design professionals, AWC has identified some of the most commonly overlooked wood connection engineering requirements from the NDS and SDPWS. These requirements will be discussed as well as resources and examples to meet these requirements. Examples include NDS Appendix E Local Stresses in Fastener Groups, NDS 3.4.3.3 shear design of members at connections, resources for power-driven fasteners such as ISANTA ESR 1539, and detailing requirements for high capacity shear walls and diaphragms.

Co r nu cop i a o f C l a s s i c Conne c t i o n Conund r ums 4

LEARNING OBJECTIVESUpon completion, participants will be better able to identify:

Be able to understand overlooked wood connection engineering issues.

Wood Connections

Obtain resources for complying with wood connection engineering issues.

Resources

Identify and design for local stresses in fastener groups.

Local Stresses

Identify and detail high capacity shear walls and diaphragms.

Detailing

1 3

2 4

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POLLING QUESTION

1. What is your profession?

a) Architect

b) Engineer

c) Code Official

d) Builder/Product Manufacturer

e) Other


CONNECTION BEHAVIOR

• Balance• Strength • Ductility

Load

Displacement

high strength, poor ductility

good strength, good ductility

low strength, good ductility

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CONNECTION BEHAVIOR


CONNECTION BEHAVIOR

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CONNECTION BEHAVIOR

Co rnu cop i a o f C l a s s i c Conne c t i o n Conund r ums 1 0

CONNECTION BEHAVIOR

• Balance• Strength –

• Size and number of fasteners

• Ductility-• Fastener

slenderness• Spacing• End distance

Load

Displacement

high strength, poor ductility

good strength, good ductility

low strength, good ductility

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CONNECTING WOOD - PHILOSOPHY

Fastener selection is key to connection ductility, strength, performance

Cornu cop i a o f C l a s s i c Conne c t i o n Conund r ums 1 2

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

BASIC CONCEPTS

Stronger Less strong

Parallel Perpendicular

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




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

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Mechanical fasteners

• keep them small

• use lots of them

Issue is scale of fastener relative to wood member size



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


PRE-ENGINEERED CONNECTORS

Column Cap & Base hardware

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Hanger hardware



Truss hardware

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LOCAL STRESSES IN FASTENER GROUPS

2015 NDS - 11.1.2 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

Wood failure mechanisms need to be considered in design

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•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''

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•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 AFZZ

Z '

'''

22


EXAMPLE: BOLTED SPLICE – LOCAL STRESSES•Assume 1” diameter x 5” long bolts

•2x12 No. 2 Southern Pine main and side members

Net Section Tension Check

ZNT’ = Ft’ Anet

Ft’ = 450(1.25) = 562.5 psi

Anet = 13.7 in2

ZNT’ = 7,706 lbs

Note: hole size for net area includes 1/16” oversizing per NDS 12.1.3.2

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EXAMPLE: BOLTED SPLICE – LOCAL STRESSESRow Tear-Out Check

ZRTi’ = ni Fv’ t scritical

ni = 3

Fv’ = 175(1.25) = 219 psi

t = 1.5”

scritical = 4”

ZRTi’ = 3,938 lbs for one row

ZRT’ = 7,875 lbs for two rows

Note: scritical is the minimum of the end distance and the in-row bolt spacing = 4”


EXAMPLE: BOLTED SPLICE – LOCAL STRESSESGroup Tear-Out Check

ZGT’ = ZRT1’/2 + ZRT2’/2 + Ft’ Agroup-net

ZRT1’ = ZRT2’ = 3,938 lbs

Ft’ = 450(1.25) = 562.5 psi

Agroup-net = 4.41 in2

ZGT’ = 6,418 lbs

Note: hole size for net area includes 1/16” oversizing per NDS 12.1.3.2

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EXAMPLE: BOLTED SPLICE – LOCAL STRESSES

Final Bolt Capacity

Z’ = 9,562 lbs

ZNT’ = 7,706 lbs

ZRT’ = 7,875 lbs

ZGT’ = 6,418 lbs

4"

7"

38"

P P

PP

3-5/8"

4" 4" 4" 4" 7" 4" 4"

3-5/8"


EXAMPLE: BOLTED SPLICE – LOCAL STRESSES

srow = spacing between bolt rows

Trade‐offs for Bolt Design Values vs. Net Section Capacities (lbs)

Bolt

Diameter

(in.)

Adjusted

Multiple Bolt

Capacity nZ'

Net Section

Tension ZNT'

Row Tear‐

out ZRT' Group Tear‐out ZGT'

srow=4" srow=5"

1 9562 7706 7875 6418 7260

7/8 8368 7910 7875 6521 7365

3/4 7174 8121 7875 6627 7471

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DOWEL DIAMETERS

Threaded length <

lm/4

lm

Dia. Fastener = D

Dia. Fastener = D

Threaded length <

lm/4lm


DOWEL DIAMETERS

Dia. Fastener = Dr

•NDS Chapter 12 Tables use Dr for lateral yield equations for lag screws and wood screws, D for bolts

lm

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POLLING QUESTION

2. Local stresses in connections using multiple fasteners are required to be checked.

or FalseTrue


FASTENER VALUES

• Included in U.S. design literature

Evaluation Reports (ER) are developed

for proprietary products

Fastener Type Reference

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

Metal Plate Connectors ER

Hangers & Framing Anchors

ER

Staples ER

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ALTERNATIVE MATERIALS, DESIGN & METHODS


FASTENERS NOT IN NDS/SDPWS

• Yield Mode Equations can be applied to any dowel-shaped fastener• Fastener dimensions and yield strength come from manufacturer

• ICC-ES (www.icc-es.org) Evaluation Service Reports • Searchable database • ESR 1539 (ISANTA) Power-driven staples

& nails

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ISANTA WEBSITE – TECHNICAL BULLETINS

http://isanta.org/Technical-Resources



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PROPRIETARY FASTENERS

• ICC Evaluation Service Reports• Search by manufacturer or

product

• “Wood screw” search shows 5 manufacturers

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SHEAR DESIGN AT CONNECTIONS

Connections in bending members

Shear Force – within d

May ignore uniform loads

May reduce point load x/d

Reduction also applies to beam design.



NDS 3.4.3.3 allows for adjusted shear values to be used when connection is close to end of member (less than 5 times member depth)

• Where the connection is less than 5d, of from its end, the adjusted design shear, Vr’ calculated using NDS Eq. 3.4-6

• Where the connection is at least 5d, of from its end, the adjusted design shear, Vr’ calculated using NDS Eq. 3.4-7

Split ring or shear plate Split ring or shear plate

Bolt or lag screw

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Wood and tension perpendicular to grain

• Not recommended

Initiators:• notches• large diameter fasteners• hanging loads

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NOTCHING

Problem Solution


Split

BEAM TO CONCRETE

Notched Beam Bearing

• may cause splitting

• not recommended

Split

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BEAM TO CONCRETE

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

NANA

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Split

HANGER TO BEAM

Lower half of beam

may cause splitsnot recommended

Exception: light load

<100 lbs

>24” o.c.


HANGER TO BEAM

Load supported in upper half of beam

• Above the neutral axis

Full wrap sling option

C

T

NANA

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POLLING QUESTION

3. Which of the following can potentially initiate tension perpendicular to grain in wood?a) Notches

b) Small diameter fasteners

c) Hanging loads

d) All of the above

e) a) and c)


CONNECTION SERVICEABILITY

Bristlecone Pine

Giant Sequoia Western Juniper

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Wood, like other hygroscopic materials, moves in varying environments


MOISTURE CHANGES IN WOOD

Causes dimensional changes perpendicular to grain

Growing tree is filled with water

As wood dries, it shrinksperp. to grain

Tang

entia

lly

Radially

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WOOD SHRINKS

Woodmagazine.com



Moisture Effects

1% change in dimension for

every 4% change MC

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WET SERVICE FACTOR, CM

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

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

Saturated

19% MC

Dryfabrication MCin-service MC


WET SERVICE FACTOR, CM

CM 0.4 Lateral load (D>1/4″)

CM = 1.0 if:1 fastener

2+ fasteners

split splice plates

Saturated

19% MC

Dry

fabrication MCin-service MC Table 10.3.3 footnote 2

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Issue: direct water ingress

• Water is absorbed most quickly through wood end grain

No end caps or flashing




• Re-direct the water flow around the connection

end caps and flashing

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Or, let water out if it gets in...

Moisture trap -No weep holes


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


BEAM TO COLUMN

Problem

• shrinkage

• tension perp

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BEAM TO COLUMN

Problem

• shrinkage

• tension perp


BEAM TO WALL

Solution

• bolts near bottom

• minimizes effect of shrinkage

Slotted hardware

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Beam on Shelf

• prevent contact with concrete

• provide lateral resistance and uplift

Avoid contact with cementitious materials


BEAM TO CONCRETE

Beam on Wall

• prevent contact with concrete

• provide lateral resistance and uplift

• slotted to allow longitudinal movement

• typical for sloped beam

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BEAM TO MASONRY

Need 1/2” air gap between wood and masonry

• Application


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


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


POLLING QUESTION

4. Good design practice of connections for wood should consider which of the following:a) Use small diameter fasteners

b) Stagger closely spaced fasteners

c) Avoid direct contact with concrete or masonry

d) Avoid tension perpendicular to grain

e) All of the above

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CH 4 –CONCRETE OR MASONRY WALL ANCHORAGE

• 4.1.5.1 Anchorage of Concrete or Masonry Walls to Diaphragm• SDC C, D, E, or F

New



Source: APA

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IRREGULARITY

Reentrant Corner

Collector

Colle

ctor

C o r nu cop i a o f C l a s s i c Conne c t i o n Conund r ums 7 8

IRREGULARITY

Collector forces likely comply with exception per ASCE Sec. 12.10.2.1

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CHAPTER 4 - LATERAL FORCE-RESISTING SYSTEMS

• Wood Diaphragms

Anchor bolting of ledger: Design for 25% more shear



Wood Diaphragms

Collector beam

Boundary nail (B.N.) diaphragm NOT subject to 25% increase

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IRREGULARITY


EXCEPTION TO OVERSTRENGTH

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EXCEPTION TO OVERSTRENGTH


POLLING QUESTION

5. Increase in forces due to Irregularities for SDC D‐F structures apply to the diaphragm nailing.

FalseTrue or

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SHEAR WALL - PARTS

Five parts of a shear wall

wood frame

wood structural

panels wood frame

nails

plate anchors

hold downs

2

13

5

4


SHEAR WALL TEST

8 ft x 8 ft wood structural panel shear wall cyclic test

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SHEAR WALL TEST

Typical failure of sheathing nailing

a) Nail yielding at ad-joining panel edge b) Nail yielding and head pull through

at panel to bottom plate location


SHEAR WALL 3X REQUIREMENTS

88

At adjoining panel edges

Sill plate

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CONNECTING WOOD- PHILOSOPHY

Splitting happens because wood is relatively weak perpendicular to grain

Nails too close (act like a wedge)

Cornu cop i a o f C l a s s i c Conne c t i o n Conund r ums 9 0Nailing not staggered Nailing staggered

Framing

Wood Structural

Panel

Nail

1/8" GapBetween Panels

Nailing not staggered Nailing staggered

STAGGERED NAILING

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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


CH. 4 - SHEAR WALLS SHEATHED ON 2 SIDES

Provisions for shear walls sheathed on two sides •Table 4.3A Footnote 6

6. Where panels are applied on both faces of a shear wall and nail spacing is less than 6" on center on either side, panel joints shall be offset to fall on different framing members. Alternatively, the width of the nailed face of framing members shall be 3" nominal or greater at adjoining panel edges and nails at all panel edges shall be staggered.

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CH. 4 - SHEAR WALLS SHEATHED ON 2 SIDESAdjoining Panel Edge Details


CHAPTER 4 – CONSTRUCTION REQUIREMENTS

NEW

4.3.6.1.1 Common Framing Members• 2-2x permitted to replace 3x

• Fastened together per NDS• Spacing <4” o.c. shall be

staggered• Applies broadly to all framing

4.3.7 Shear Wall Systems• 2-2x permitted to replace 3x

• Wood Structural Panels (4.3.7.1(5))• Particleboard (4.3.7.3(5))

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(2) 2X AT ADJOINING PANEL EDGES

95


(2) 2X AT ADJOINING PANEL EDGES

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3X AT ADJOINING PANEL EDGE

Section 4.3.7.1(4). 3x framing also required at adjoining panel edges where:

• Nail spacing of 2 in. o.c.

• 10d common nails having penetration of more than 1-1/2 in. at 3 in. o.c. or less

• Nominal unit shear capacity on either side exceeds 700 plf in SDC D, E, or F

Exception: (2) 2x framing permitted in lieu of (1) 3x where fastened in accordance with the NDS to transfer the induced shear between members.


(2) 2X AT ADJOINING PANEL EDGE

Fastener spacing – 2x stud to 2x stud connection

3”

Approximate stud to stud connection spacing for wood structural panel (WSP) walls sheathed on one side.

* Spacing based on 8’ wall and assuming only 87.5” of stud height available for stud-to-stud fastening.

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FOUNDATION BOTTOM PLATE

Plate washer:

Must extend to within ½ in. of sheathed edge of bottom plate

Exceptions:

Lower capacity sheathing materials (nominal unit shear is 400 plf or less)

Hold-downs are sized for full overturning – neglecting dead load

Co rnu cop i a o f C l a s s i c Conne c t i o n Conund r ums 1 0 0

FOUNDATION BOTTOM PLATE –TESTING

Failure Mode?

Small scale test specimen to induce cross grain bending

Mode A

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FOUNDATION BOTTOM PLATE – TESTING

Mode A and Mode B observed in small specimen testing

Cornu cop i a o f C l a s s i c Conne c t i o n Conund r ums 1 0 2

FOUNDATION BOTTOM PLATE –TESTING

Failure Mode?

Small scale test specimen to induce cross grain bending

Mode BMode A

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View of bottom plate after test.

Co r nu cop i a o f C l a s s i c Conne c t i o n Conund r ums 1 0 4


View of bottom plate after test.Shear wall assembly in test fixture

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CHAPTER 4 - SHEAR WALL ANCHORAGE – 3”X3” DEFAULT

Shear wall anchorage provisions at foundation – Section 4.3.6.4.3

3" x 3" x 0.229" steel

slotted hole permitted

placed within ½" of sheathing material

automatically satisfied for 2x4 plate


Shear wall anchorage provisions at foundation – Section 4.3.6.4.3

• Exception: Standard cut washers permitted• Anchor bolts designed to resist shear only

• Hold downs designed for uplift neglecting DL

• Aspect ratio < 2:1

• Limited nominal shear wall capacities• < 980 plf seismic

• < 1370 plf wind

CHAPTER 4 - SHEAR WALL ANCHORAGE – 3”X3” DEFAULT

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2018 NDS

• References ASCE 7-16• Wind Uplift Loads Increase• Change in Out-of-plane wind loads on roof• New equation for withdrawal design values for

smooth shank stainless steel nails• New provisions for Roof Sheathing Ring Shank

nails in accordance with ASTM F 1667• New design provisions for fastener head pull-thr

ough of fasteners with round heads• Revision to method for calculating of lateral desi

gn values for threaded nails in accordance with ASTM F 1575

• Revised timber rivet design value tables• Revised terminology for Fire Design of Wood

Members• Changes to the NDS Supplement


RAILING DETAIL

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RAILING DETAIL


COLUMN TO BASE

Column on pedestal

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COLUMN TO BASE


COLUMN TO BASE

Column on pedestal

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POLLING QUESTION

6. Square plate washers may be omitted when:

a) Anchor bolts are designed to resist uplift

b) Hold downs designed for uplift neglecting DL

c) Aspect ratio is greater than 2:1

d) The shear capacity is > 1400plf

e) All of the above


MORE INFO???

NDShttp://awc.org/codes-standards/publications/nds-2015

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MORE INFO???

https://www.apawood.org/publication-search?q=connection+details&tid=1

Form EWS T300J


MORE INFO???

AWC Calculators http://awc.org/codes-standards/calculators-software

TR 12 - General Dowel Equations for Calculating Lateral Connection Values (2014) http://awc.org/codes-standards/publications/tr12

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MORE INFO. - LEDGER CONNECTION

DCA 6 Prescriptive Residential Deck Construction Guide http://awc.org/codes-standards/publications/dca6

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 7

in [email protected] | www.awc.org

This concludes the American Institute of Architects Continuing Education Systems Course

Wood Connections - AWC

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