Connection Design Solutions For Wood -Frame Structures...the use of steel connectors in wood -frame...

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Presented by: Jared S. Hensley, P.E.

Connection Design SolutionsFor Wood-Frame Structures

Disclaimer: This presentation was developed by a third party and is not funded by WoodWorks or the Softwood Lumber Board.

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Course DescriptionThis session will feature a discussion of wood connection design and specification, including

common fastener types and where design values can be found for each. Other topics will include the

orthotropic nature of wood and its role in connection design, commodity and specialty connectors, and

the use of steel connectors in wood-frame construction. Discussion will also include

techniques for designing efficient, durable and code-compliant connections, examples of best practice

connection details, and additional resources.


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Learning Objectives1. Discuss code-compliant connection design in the

context of wood and fastener properties.2. Review design processes for dowel bearing

connections in wood structures.3. Demonstrate effective wood connection design,

considering the effects of expansion and shrinkage.

4. Highlight proper specification and detailing of steel connectors used in wood-frame construction.


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Agenda

Key to Connections1. Wood Basics & Connection Philosophy2. Serviceability3. Connection Types

§ Direct Bearing Connections§ Multi-Ply Beam Connections§ Pre-Engineered Connectors

4. Dowel Bearing Connections5. Wood Structural Panel Connections6. Corrosion Resistant Connections

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Agenda




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Wood Basics & Connection Philosophy

Loads Parallel to Grain vs. Loads Perpendicular to Grain

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Compression Parallel To Grain

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Tension Perpendicular to Grain § Weakest connection in wood

Initiators:§ Notches§ Large diameter

fasteners§ Hanging loads


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§ Concentrated loads vs. Group loading§ Large diameter bolts vs. Multiple small fasteners§ Keep scale of fastener small relative to wood

member


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Agenda




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Serviceability

USDAFPL-GTR-190

Referenced Publications

APA Publication T300

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Serviceability

Moisture Changes in Wood § Start as soon as a tree is cut§ Wood shrinks perpendicular to grain

Figure 4-3 :FPL-GTR-190

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Serviceability

Wood Moves in Varying Environments § Temperature§ Humidity and Moisture

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Serviceability

§Ambient conditions and Wood Equilibrium Moisture Content (EMC)

§Relative Humidity ≠ EMCEMC of Wood

Figure 4-1 & Table 4-2: FPL-GTR-190

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Serviceability

§ Ambient conditions and wood EMC

Figure 10-5 & Table 13-1: FPL-GTR-190

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Serviceability

§Wood EMC at installation is important

Table 13-2: FPL-GTR-190

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Serviceability

Column Connections to Concrete§ Prevent contact with concrete§ Allow drainage

Figures 15 & 16: APA T300

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Serviceability

Detailing Considerations: § End grain moisture uptake§ Potential for decay

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Serviceability

Detailing Considerations: § Avoid tension

perpendicular to grain§ Provide drainage

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Serviceability

Detailing Considerations: § Allows water collection§ Saturated wood decays

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Serviceability

Detailing Considerations: § Elevated plates§ Hidden connectors

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Serviceability

Beam Connections to Concrete

Figures 2A & 2B: APA T300

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Detailing Considerations:§ Masonry and Grout also contain moisture§ Need 1/2” air gap between wood and masonry

Serviceability

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Agenda




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Direct Bearing Connections

Its ALL in the Details

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Do Not Bear Directly On Concrete

Most Popular ConnectionsBeam HangerBeam Pocket

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§ Unnecessary Notching§ Creates shear load

concentrations

Detailing Errors to Avoid

§ Exposed End Grain§ Reduces shear strength

Figures 1A & 1B: APA T300

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§ Notch should not exceed 1/10 of beam depth or 3 inches§ Reduced capacity of a 14” beam is 28%

Bottom Notches and Over-Cuts Create Cross Grained Tension Stresses

Figure 1C: APA T300

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Heavy Concentrated Loads§Attach above neutral access§Engages more

Figure 6: APA T300

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Beam to Wall ConnectionsWhat’s easier than setting the beam on something?

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Beam to Wall Connections§Slotted Hardware§Allows for wood shrinkage


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Beam to Beam Connections§ Avoid angles§ Keep bolts low

Figures 3A & 1C: APA T300

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Hybrid Bearing Connections


Figure 3E: APA T300

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Concealed Connections§ Kerf must accommodate steel and weld§ Dowel hole plugged


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Lateral Stability for Deep Beams§ Allows for wood shrinkage§ Restricts lateral movement


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Beam to Column Connections§Side Plates and Caps

§ Allow for shrinkage


Figure 10A: APA T300

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Smaller side plates§ Slotted holes§ Allow wood movement


Figure 10B: APA T300

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Embedded or “Shoed” Column Base


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Bearing plate§ Anchor bolts in bearing plate§ Slotted column end

Angle brackets§ Anchor bolts in brackets

Simple steel dowel§ Bearing plate§ Shear transfer


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Where’s the plate?§ Contractor substituted

grout§ Moisture will wick into

wood§ Potential for decay


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Agenda




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Connection TechniquesMulti-ply Connections

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Figure 1: APA TT-011C

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Agenda




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Pre-Engineered Connectors

Joist and Beam Hangers§ Top-Flange and

Face-Mount§ Product specific§ Use correct fastener

(nails or screws)§ Fill all holes§ Ensure proper fastener

penetration

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53Figure 1h: APA Z725


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Figure 1p: APA Z725

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Agenda




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Dowel Bearing Connections

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Power Driven FastenersFour important considerations:§ Nail nomenclature§ Contact§ Thin galvanizing§ Overdriving


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Nail Nomenclature:§ There is no control over nail nomenclature!

Manufacturers can and will call fasteners anything that they want.

§ 10d does not equal 10d!! § 10d common = .148” diameter§ 10d box = 0.128” diameter§ 10d sinker = .120” diameter


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Nail Nomenclature:§ Common § Box§ Bring Shank§ Smooth Shank

Nail Specification§ Include pennyweight,

type, diameter and length§ Ex: 10d common

(0.148” shank dia. x 3” shank length)


Figures 5.2 & 5.3: CWC Wood Reference Handbook

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Power Driven Fastener Considerations§ Contact:

§ Power driven fasteners rely on velocity to drive fasteners and not mass. They do not have the “clamping” action that the last swing of a hammer provides.

§ Thin Galvanizing:§ Power driven fasteners that are “galvanized” are thinly coated to

prevent rusting in the box. The protection is scraped off of the fastener during driving.

§ Overdriving:§ If the “gun” is improperly adjusted, overdriven fasteners can be

expected. Adjusting air pressure is NOT the correct way to prevent over-driven fasteners.


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Fastener Interchangeability§ International Staple, Nail and Tool Assoc. - ESR-

1539§ Has values for engineered designs for staples and a variety

of other power-driven fasteners§ Available from international staple, nail and tool association

(ISANTA) www.isanta.org708-482-8138


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Design approach:§Engineered“do the calculations”All variables are accounted for in calculations


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4 Yield Limit Modes For Wood DesignI - Bearing, II – Pivoting,

III – Fastener Yield, IV – Fastener Yield at two hinge points.


Table 12.3.1A: 2015 NDS

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§Six Yield Limit equations for single shear

§Four Yield Limit equations for double shear


Figure 11: 2015 NDS

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2015 NDS Equations

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Reduction Factors, Rd


Table 12.3.1B: 2015 NDS

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Yield Limit Equations: Im (12.3-1) and Is (12.3-2)Assuming: DF-G=0.50, D=1.0”, lm=3.5”, ls=1.5”

Table 12.3.32015 NDS


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Im = 4900 lbs

Is = 2100 lbs

II = 1827 – Governs Design

IIIm = 2664 lbs

IIIs = 2016 lbs

IV = 2846 lbs

Dowel Bearing ConnectionsYield Limit Equations: Im (12.3-1) and Is (12.3-2)

Assuming: DF-G=0.50, D=1.0”, lm=3.5”, ls=1.5”

Values table 12.3.3: 2015 NDS

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Angle to Grain Adjustment

Hankinson Formula§ Used to resolve wood bearing

strength at any angle to grain§ Assume in previous example that the side member was at

a 45 degree angle. The allowable stress Fes would be calculated using the Hankinson formula to 3210 psi, as opposed to the 5600 psi used in the example.

!"#$ = '())*+,×..')*+,('())*+,)+,1. 2' 3(..')*+,)45+.(2') = 3210:$;

2015 NDSTable 12.3.3

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NDS Tables 12A to 12T provide a reference for Lateral Design Values in both Single and Double Shear with Wood or Steel Side Plates.


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Table 12A2015 NDS


Same Assumptions: DF-G=0.50, D=1.0”, lm=3.5”, ls=1.5”

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Dowel Connection Adjustment Factors

Table 11.3.1: 2015 NDS

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CD – Load Duration FactorWood capacity is greater for short term loading

Table 2.3.2: 2015 NDS

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CM - Wet Service Factor for connection Z values

Saturated

19% MC

DryCM 1.0 0.7 0.4 Lateral LoadCM 1.0 0.7 1.0 Withdrawal Load (screws)

§ Bolts§ Lag screws§ Wood screws

fabrication MCin-service MC


Table 11.3.3: 2015 NDS

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Ct - Temperature FactorUsed for Structural Members that will be exposed to

sustained temperatures up to 150°F


Table 2.3.3: 2015 NDS

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Cg - Group Action Factor§ Accounts for load distribution within the connection§ Tabulated values in NDS Section 11.3.6§ Can calculate your own group factor if outside the

tabulated table range


Sect. 11.3.6: 2015 NDS

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Rows are established in direction of load§ 2 or more bolts of same diameter § 2 or more lag screws of same type and size§ 2 or more aligned split ring/shear plate connectors


Figure 11B: 2015 NDS

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Group Action Factor Equation Method

Where:


EQ 11.3-1: 2015 NDS

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CD- Geometry Factor


Tables 12.5.1A & 12.5.1B: 2015 NDS

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CD- Geometry Factor


Tables 12.5.1C & 12.5.1D: 2015 NDS

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Local Fastener Stresses

Net tension:

Row tear-out:

Group tear-out:

nettNT AFZ '' =

∑=

=

=

row

i

i

n

iRTRT

viRT

ZZ

tsFnZ

1

''

min''

netgrouptGT AFZZ

ZnRTRT

−++=−− ''

2'

2' 1

2015 NDS Appendix E


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End Grain Factor

Diaphragm Factor


Sections 12.5.2 & 12.5.3: 2015 NDS

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Ctn – Toe-Nail Factor§ Installation per Figure 12A§ 0.83 adjustment for lateral§ 0.67 adjustment for

withdrawal


Figure 12A & Section 12.5.4: 2015 NDS

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Agenda




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Wood Structural Panel Connections

Nail installation§Overdriving reduces performance

APA TT-012

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Staggered Nailing§ Code nailing is typically 6” o.c. for edges and 12” o.c. in the

field§ Shear Walls can require tighter nail spacing so staggered

nailing is critical


Figure F: APA M310

88Nailing not staggered Nailing staggered

Framing

Wood StructuralPanel

Nail

1/8" GapBetween Panels

Nailing not staggered Nailing staggered

Framing

Wood Structural Panel

Nail

1/8″ Gap Between Panels


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


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Shear wall or diaphragm applications with panels applied parallel to supports and/or edge nailed 4" o.c. or closer…

…high risk because the conditions may reduce the standard panel edge gap’s effectiveness in absorbing the panel expansion.


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F

B C

G

Shearwall Overturning


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Large plate washers (3”x3”x0.229”) prevent splitting of sill plate –

Required for SDC D, E or F (IBC 2305.3.11)

Plate washer

Sill plate

Wood structural panel


PLAN VIEW

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Glued Floor System§ Decrease vibration§ Minimize squeaks§ Increase stiffness


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Gluing is Not Recommended for bonding wall or roof sheathing to framing


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Agenda




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Corrosion Resistant Connections

2015 IBC Requirements

Chapter2304.10

2015 IBC


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What Causes Corrosion?§ Dissimilar Metals§ Environment

§ Ocean Salt Air§ Pollution§ Humidity§ De-icing Salts

§ Preservative Treatments§ ACQ-D, Copper Azole type C,

Micronized Copper Azole, CCA-C

Corrosion Resistant Connections

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Questions?

Jared S. Hensley, P.E.APA – The Engineered Wood Association

[email protected] concludes The American Institute of Architects

Continuing Education Systems Course

Can you crack the code?

Connection Design Solutions For Wood -Frame Structures...the use of steel connectors in wood -frame...

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