American Wood Council
www.awc.org
2015 NDS® Changes
John “Buddy” Showalter, PE
Vice President, Technology Transfer
American Wood Council
Michelle Kam-Biron, PE, SE, SECB
Director of Education
American Wood Council
Copyright Materials
This presentation is protected by US and International
Copyright laws. Reproduction, distribution, display and use
of the presentation without written permission of AWC is
prohibited.
© American Wood Council 2015
2
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Course Description
AWC's National Design Specification (NDS) for Wood Construction 2015 is
the dual format Allowable Stress Design (ASD) and Load and Resistance
g (LRFD)
(
) document referenced in US building
g codes and used
Factor Design
to design wood structures worldwide. Participants will learn about
changes in the 2015 NDS and Supplement relative to previous editions
and gain an overview of the standard.
4
Objectives
Upon completion, participants will be:
1. Able to understand the load and material resistance design process
and how it applies to wood structural design.
2. Familiar with the significant changes between the 2012 and 2015 NDS
and supplement.
3. Able to identify the similarities and differences with respect to ASD,
design values, and behavioral equations.
4. Able to analyze
y format and content within the 2015 NDS.
5
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Outline
• Overview
• Design Process Overview
• NDS
•
Chapter-by-chapter discussion
•
Changes from previous editions
•
Summary
•
More Info
6
NDS History
1944
1977
2001
1962
1982
2005
1968
1986
2012
1971
1991
2015
1973
1997
7
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Governing Codes for Wood Design
2015 NDS referenced in 2015 IBC
8
ANSI Accreditation
• AWC –ANSI-accredited standards developer
• Consensus Body
y
•
Wood Design Standards Committee
9
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2015 NDS – Primary Change
New Provisions to Address CLT
• Charging Language
• Design Values
• Design Equations
• Product Chapter
g
• Connection Design
• Fire Design
10
2015 NDS Chapter Reorganization
2012 NDS
2015 NDS
• 1-3 General
• 1-3 General
• 4-9 Products
• 4-10 Products +CLT
• 10-13 Connections
• 11-14 Connections
• 14 Shear Walls & Diaphragms
• Shear Walls & Diaphragms
• 15 Special Loading
• 15 Special Loading
• 16 Fire
Fi
• 16 Fire
Fi
11
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Outline
• Overview
• Design Process Overview
• NDS
•
Chapter-by-chapter discussion
•
Changes from previous editions
•
Summary
•
M
IInfo
f
More
12
Design Process
Demand  Capacity
13
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Design Process
Load
Support Conditions
Geometry
Materials
Performance
Fire
Economics
Aesthetics
….
Demand
Capacity
14
Design Concepts
Two Limit State concerns
• Serviceability (performance
in-service)
• Safety against failure or
collapse
15
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Serviceability
• ASD and LRFD
•
Unfactored loads
•
Mean (avg) material
strength values
16
Safety
• ASD
• Unfactored
U acto ed loads
oads
• Material strength
values - modified
• LRFD
• Factored loads
• Material strength
values – modified less
17
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Structural Property Variability
Normal Distribution Curves
x = mean
x = standard deviation
x
x
x
R
Relative Frequency
SCL
x
COVx =
I-Joist
x
Coefficient of variation
Load
Glulam
MSR Lumber
Vi
ll Graded
G d d
Visually
Lumber
Material Property Values
18
Engineered Wood Design
S>R
Failure
19
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LRFD vs ASD
ASD
•applied stress  allowable stress
Theoretical safety
margin applied to
material stresses
Estimated
Loads
Design
Load

Adjusted
Resistance
Tested
material
strength
Design values
26
LRFD vs ASD
LRFD
•factored load  factored resistance
Member performance
factor
Load factors to
account for
variations in loads

Estimated
loads
Factored
Design
Load
Factored
Design
Resistanc
e
Design values
Copyright © American Wood Council. All rights reserved. Tested
member
resistance
27
10
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2015 NDS
LRFD Basic Load Combinations ASCE 7-10
28
2015 NDS
ASD Basic Load Combinations ASCE 7-10
29
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2005 NDS & ASCE 7-02
LRFD vs. ASD Load Combinations
http://www.awc.org/publications/Papers/WDF
15-4-LRFDvASD.pdf
30
2015 NDS
Format Conversion Factor KF
ASD
RN = CDRASD
LRFD
RN = KF RASD
RASD reference strengths
31
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2015 NDS
Reliability indices or data confidence factors
32
2015 NDS
 tied to ASCE 7 Factored Loads
•Baseline 10 min (ASD uses 10 yrs)
Permanent
Long term
Short term
33
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2015 NDS
RN = KF RASD
KF converts reference design values (ASD normal load duration) to
LRFD reference resistance
34
Outline
• Overview
• Design Process Overview
• NDS
•
•
Chapter-by-chapter discussion
•
Changes from previous editions
•
Summary
More Info
36
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NDS 2015 Chapters
1.
2.
3.
General Requirements for Building Design
Design Values for Structural Members
Design Provisions and Equations
4.
4
5.
6.
7.
8.
9.
10.
Sawn Lumber
S
L b
Structural Glued Laminated Timber
Round Timber Poles and Piles
Prefabricated Wood I-Joists
Structural Composite Lumber
Wood Structural Panels
Cross-Laminated Timber
11.
12.
13.
14.
Mechanical Connections
Dowel-Type Fasteners
Split Ring and Shear Plate Connectors
Timber Rivets
15. Special Loading Conditions
16. Fire Design of Wood Members
37
NDS 2015 Supplement
1.
2.
3.
4.
Sawn Lumber Grading Agencies
Species Combinations
Section Properties
Reference Design Values
•
Sawn Lumber and Timber
•
MSR and MEL
•
Decking
•
Non-North American Sawn Lumber
•
Structural Glued Laminated Timber
•
Timber Poles and Piles
38
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NDS 2015 Appendices
A.
B.
C.
D.
E
E.
F.
G.
H.
I.
J.
K.
L
L.
M.
N.
Construction and Design Practices
Load Duration (ASD Only)
Temperature Effects
Lateral Stability of Beams
L
Local
l Stresses
St
iin F
Fastener
t
G
Groups
Design for Creep and Critical Deflection
Applications
Effective Column Length
Lateral Stability of Columns
Yield Limit Equations for Connections
Solution of Hankinson Equation
Typical Dimensions for Split Ring and Shear
Plate Connectors
Typical Dimensions for Standard Hex Bolts
Bolts,
Hex Lag Screws, Wood Screws, Common,
Box, and Sinker Nails
Manufacturing Tolerances for Rivets and Steel
Side Plates for Timber Rivet Connections
Appendix for Load and Resistance Factor
Design (LRFD) – Mandatory
39
NDS – Chapter 1
40
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Chapter 1 - Terminology
fb ≤ Fb'
Reference design values (Fb, Ft, Fv, Fc, Fc, E, Emin)
Adjusted design values (Fb', Ft', Fv', Fc', Fc', E', Emin')
41
Chapter 1 – Design Loads
• Reference loads
• Minimum load standards
• ASCE 7 – 10
42
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Chapter 1 – CLT Charging Language
43
NDS – Chapter 2
44
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Chapter 2 – Adjustment Factors
Reliability indices or data confidence factors
45
Chapter 2 – Adjustment Factors
RN = KF RASD
KF converts reference design values (ASD normal
load duration) to LRFD reference resistance
46
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Appendix N – Adjustment Factors
 tied to ASCE 7 Factored Loads: Baseline 10 minutes (ASD uses 10 years)
Permanent
Long term
Sh t term
Short
t
47
Chapter 2 – Adjustment Factors
Adjusts from reference to site conditions
•
CD ttime-dependent
e depe de t
Baseline 10 years
48
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Chapter 2 – Adjustment Factors
Adjusts from reference to site conditions
•
Ct te
temperature
pe atu e
Exposed for “sustained” period
49
Chapter 2 – Adjustment Factors
Adjusts from reference to site conditions
•
CM wet service factor
50
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Wet Service Conditions
30
Wood EMC %
25
20
Temp
Temp
15
Temp
10
5
0
0
20
40
60
80
100
51
%Strength at 12% Moisture
%
e Content
Wet Service Conditions
110
100
90
Impact Strength
80
Modulus of Elasticity
70
Modulus of Rupture
Crushing Strength
60
50
40
12
14
16
18
20
22
24
26
28
30
Moisture Content of Wood (%)
52
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Wet Service Factor, CM
• Sawn lumber MC < 19% considered dry
• Otherwise, NDS Supplement for lumber
53
Chapter 2 – CLT Design Values
54
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NDS – Chapter 3
55
Chapter 3 – Behavioral Equations
ASD vs LRFD – adjusted stresses from reference
• ASD
F′n = Fn CD
x adjustment factors
• LRFD F′n = Fn KF n  x adjustment factors
56
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Chapter 3 – Behavioral Equations
Beams
•
CL beam stability
Critical Buckling Design Value
for bending members
57
Chapter 3 – Behavioral Equations
Columns
•
CP column stability
Critical Buckling Design Value
for compression members
58
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Chapter 3 – Behavioral Equations
E min  1.03 E (1  1.645 (COV E )) / 1.66
E
1.03
1.66
COVE
= reference MOE
= adjustment factor to convert E to a pure bending
basis (shear-free) (use 1.05 for glulam)
= factor of safety
= coefficient of variation in MOE (NDS Appendix F)
OR
Emin values published in NDS Supplement
59
Chapter 3 – Behavioral Equations
Tension members (tension parallel to grain)
• ASD
F′t = Ft CD
x adjustment factors
• LRFD
F′t = Ft KF t  x adjustment factors
60
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Chapter 3 – Behavioral Equations
Tension perpendicular to grain
•
Not recommended per NDS 3
3.8.2
82
initiators:
• notches
• moment connections
• hanging loads
61
Chapter 3 – Behavioral Equations
Combined bi-axial bending and axial
compression
62
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Chapter 3 – Behavioral Equations
Combined bi-axial bending and axial
compression
63
Chapter 3 – Behavioral Equations
Bearing perpendicular to grain
•
F′c = Fc CM Ct Ci Cb (ASD)
•
F′c = Fc CM Ct Ci Cb Kf c  (LRFD)
64
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Chapter 3 – CLT Design Equations
New
65
Chapter 3 – CLT Design Equations
New
NDS Commentary – guidance on CP
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NDS – Chapter 4
67
Chapter 4 – Lumber
Design values
• Visually graded lumber
• MSR / MEL
• Timber
• Decking
68
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Chapter 4 – Lumber
Lumber
adjustment
factors
69
Chapter 4 – Lumber
Lumber adjustment factors
• CF - size factor
70
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Chapter 4 – Lumber
Lumber adjustment factors
71
Chapter 4 – Lumber
Lumber adjustment factors
• Repetitive member
• Cr = 1.15
• 2” – 4” lumber
• < 24” o.c.
• 3 or more members
• Load distributing element
72
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NDS – Chapter 5
73
Chapter 5 – Glulam
Adjustment factors
74
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Chapter 5 – Glulam
• Adjustment factors
•
CV Volume Factor
•
CL Beam
Stability
B
St
bilit Factor
F t
•
Not cumulative with CL
•
Min (Cv, CL)
75
NDS – Chapter 6
76
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Chapter 6 – Poles & Piles
• Poles - post-frame
• Piles
Pil - foundations
f
d ti
77
Chapter 6 – Timber Piles
Design values
• NDS Supplement
78
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Chapter 6 – Poles & Piles
Adjustment factors
79
NDS – Chapter 7
80
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Chapter 7 – I-joists
• Design values
•
M, V, EI, K – no changes
• Evaluation
l
i
Reports
•
Contain proprietary design
81
Chapter 7 – I-Joists
Adjustment factors
82
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NDS – Chapter 8
83
Chapter 8 – Structural Composite Lumber
• Design Values
• Evaluation Reports
•
Contain proprietary design
Relative Frequency
x = mean

COVxx=

x
SCL
I-Joist
Glulam
x
MSR Lumber
Load
Visually Graded
Lumber
Material Property Values
84
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Chapter 8 – Structural Composite Lumber
• New products
• Laminated Strand Lumber (LSL)
• Oriented Strand Lumber (OSL)
• ASTM D5456
85
Chapter 8 – Structural Composite Lumber
• Adjustment factors
• CV – volume
Cv < 1.0
1 0 Not cumulative with lateral stability factor,
factor CL, then min
min. (Cv, CL)
Cv > 1.0 Cumulative with lateral stability factor, CL
86
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Chapter 8 – Structural Composite Lumber
• Adjustment factors
•
Cr Repetitive Member Factor = 1.04
•
Cr is different than lumber (Cr lumber = 1.15)
•
Applies to Fb only
87
NDS – Chapter 9
88
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Chapter 9 – Wood Structural Panels
Design values – obtain from an approved source
•
FbS
•
FtA
•
Fvtv
•
Fs
•
FcA
•
EI
•
EA
•
Gvtv
•
Fc
89
Chapter 9 – Wood Structural Panels
Adjustment factors
90
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Chapter 9 – Wood Structural Panels
Adjustment factors
• CM - wet service
• Ct - temperature
91
NDS – Chapter 10
New
92
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Chapter 10 – Cross-Laminated Timber
New
93
Chapter 10 – Cross-Laminated Timber
New
94
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NDS – Chapter 11
Ch 10
Ch 11
95
Chapter 11 – Mechanical Connections
• Design issues
• Reference design values
•
Ch t 12 – dowel-type
Chapter
d
lt
connectors
t
((nails,
il bolts,
b lt lag/wood
l /
d screws))
•
Chapter 13 – split rings and shear plates
•
Chapter 14 – timber rivets
• Adjustment factors
• No significant changes
• Connections session
96
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NDS – Chapter 12
Ch 11
Ch 12
97
Yield Limit Equations
• 4 Yield Modes
• 6 Yield Equations
• Single & Double Shear
• Wood-to-Wood
• Wood-to-Steel
• Wood-to-Concrete
98
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Yield Modes
MODE I
•bearing-dominated
b i d i
d
yield of wood fibers
MODE II
•pivoting of fastener
with localized crushing
of wood fibers
99
Yield Modes
MODE III
•fastener yield in
b di att one
bending
plastic hinge and
bearing –
dominated yield
of wood fibers
MODE IV
•fastener yield in
bending at two
plastic hinges and
bearing –
dominated yield
of wood fibers
100
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Dowel Bearing Strength
101
Fastener Bending Yield Strength
Load
102
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Fastener Bending Yield Strength
103
Chapter 12 – Dowel-type Fasteners
New
104
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Chapter 12 – Dowel-type Fasteners
New
105
Chapter 12 – Dowel-type Fasteners
New
106
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Chapter 12 – Dowel-type Fasteners
New
Non-uniform
for CLT
107
Chapter 12 – Dowel-type Fasteners
• Adjust lm or ls to compensate for orthogonal
grain orientations in adjacent layers
• Parallel to grain: Fe/Feǁǁ
Example: ½” bolt in southern pine 3-ply CLT
with 1-½” laminations
lm = t1ǁ + t2 + t3ǁ = 3(1.5) = 4.5”
lm-adj = t1ǁ + t2(Fe/Feǁ) + t3ǁ
=1.5 +1.5(3650/6150) +1.5 = 3.9”
108
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Chapter 12 – Dowel-type Fasteners
New
109
Chapter 12 – Dowel-type Fasteners
• Lateral – any end grain
• D<1/4”Ceg=0.67
• Lateral – any CLT edge
New
•
D>1/4” Ceg=0.67
110
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Chapter 12-Dowels
111
Chapter 12-Dowels
112
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Chapter 12-Dowels
Threaded
length < lm/4
lm
Dia. Fastener = D
lm
Threaded
length < lm/4
Dia. Fastener = D
113
Chapter 12-Dowels
lm
Dia. Fastener = Dr
114
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Chapter 12 - Dowels
Provide tools for the analysis of
• gaps between members
• various fastener bending moment
configurations
• fasteners through hollow members
• fasteners with tapered tips
http://www.awc.org/publications/TR/index.php
115
NDS – Chapter 13
Ch 12
Ch 13
116
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Chapter 13 – Split Rings and Shear Plates
Design Values
117
NDS – Chapter 14
Ch 13
Ch 14
118
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Chapter 14 – Timber Rivets
Many applications
119
Chapter 14 – Timber Rivets
Design Values
Capacities > 100 kips
Ch 13
Ch 14
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NDS – Chapter 15
121
Chapter 15 – Special Loading
122
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NDS – Chapter 16
123
Chapter 16 – Fire (ASD)
•
Fire resistance up to two hours
• Columns
• Beams
• Tension Members
• ASD only
•
Products
•
•
•
•
•
Lumber
Glulam
SCL
Decking
g
CLT - NEW
…
124
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Chapter 16 – Calculated Resistance
• Fire resistance of
exposed wood members
may be calculated using
the provisions of NDS
Chapter 16
125
Fire Resistance
Glulam
Steel
126
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Performance of Wood vs. Steel
127
Chapter 16 – Fire Design - CLT
New
128
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Chapter 16 – Fire (ASD)
Technical Report No. 10
• Background
ac g ou d on
o NDS
S provisions
p o so s
• Design examples
• Floor assembly lumber joist
provisions
129
Chapter 16 – Fire (ASD)
Code Updates Design of Fire
FireResistive Exposed
Wood Members
http://www.awc.org/publications
/download.php
p p
130
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NDS – Appendices
131
NDS 2015 Appendices
A
B
C
D
E
F
Construction and Design Practices
Load Duration
Temperature Effects
Lateral Stability of Beams
Local
oca St
Stresses
esses in Fastener
aste e Groups
G oups
Design for Creep and Critical Deflection
Applications
G Effective Column Length
H Lateral Stability of Columns
I Yield Limit Equations for Connections
J Solution of Hankinson Equation
K Typical Dimensions for Split Ring and
Shear Plate Connectors
L Typical Dimensions for Standard Hex
Bolts,
l
Hex Lag Screws, Wood
d Screws,
Common, Box, and Sinker Nails
M Manufacturing Tolerances for Rivets and
Steel Side Plates for Timber Rivet
Connections
N Appendix for Load and Resistance Factor
Design (LRFD)
132
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2015 NDS – Summary
New Provisions to Address CLT
• Charging Language
• Design Values
• Design Equations
• Product Chapter
• Connection Design
• Fire Design
133
What’s Missing for CLT?
Seismic Design!
•
ASCE 7 Minimum Design Loads for
g and Other Structures
Buildings
•
Response Modification Coefficient, R
•
CLT not recognized system in ASCE 7
Table 12.2-1
•
Options
•
Performance-based design procedure
per ASCE 7
•
Demonstrating equivalence to an
existing ASCE 7 system
•
ASCE 7-10, FEMA P695, and FEMA P795
Quantification of Building Seismic
Performance Factors; Component
Equivalency Methodology
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Outline
• Overview
• Design Process Overview
• NDS
•
Chapter-by-chapter discussion
•
Changes from previous editions
•
Summary
•
More Info
135
2015 NDS Supplement
• New Southern Pine Design Values
•
ALSC approves design values
•
•
AWC compiles them
•
•
June 1, 2013
NDS Supplement
More information
•
www.spib.org
•
www southernpine com
www.southernpine.com
136
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Availability
• www.awc.org
PDF versions
•
•
Free view-only
•
Buy a printable PDF
Spring 2015
•
•
C
Commentary
t
•
Printed version
137
Technical Articles
•
Structure Magazine
2015 NDS
•
•
January 2015
2015 SDPWS
•
•
July 2015
• www.awc.org
138
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Questions?
info@awc.org
www.awc.org
140
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