1. 2005 NDS:
LRFD Provisions
Paul W. McMullin, P.E., Ph.D.
Sr. Project Engineer
Dunn Associates, Inc.

2. Philosophy
“decisions not to utilize specific practices
require the same background
knowledge as those which lead to the
utilization of fracture-safe design
practices” (Pellini 1969, p. 1)

3. Outline
Development of Beam and Column
Wood Design Codes Provisions
Why LRFD Lateral Supplement
What is LRFD Wood Mechanical
Design Connectors
General Terminology Proprietary
and Requirements Connectors
Resources

4. Last Decade of Wood
Design
1991 NDS
1996 LRFD- New state of the art
1997 NDS- Based on 1991
2001 NDS (ASD)- Updated to
technology of 1996 LRFD
2005 NDS (ASD/LRFD)

5. 2005 NDS

6. 2005 NDS
Combined ASD/ LRFD provisions
LRFD in same format as ASD,
except:
Behavioral equations same
3 LRFD based adjustment
factors
KF—Format Conversion
Factor
φ—Strength Reduction
Factor
λ—Time Effect Factor
No CD—Load Duration Factor
Consistent with ASCE 7-02
and 7-05

7. NDS 2005:
Chapter Layout
1) General Requirements for
Structural Design
2) Design Values for Structural
Members
3) Design Provisions and
Equations
4) Sawn Lumber
5) Structural Glue Laminated
Timber
6) Round Timber Poles and Piles
7) Prefabricated Wood I- Joists
8) Structural Composite Lumber

8. NDS 2005:
Chapter Layout (cont.)
9) Wood Structural Panels
10)Mechanical Connections
11)Dowel-Type Fasteners
12)Split Ring and Shear Plate
Connectors
13)Timber Rivets
14)Shear Walls and
Diaphragms
15)Special Loading Conditions
16)Fire Design of Wood
Members

9. NDS 2005: Appendix
Layout
a) Construction and Design
Practices
b) Load Duration (ASD)
c) Temperature Effects
d) Lateral Stability of Beams
e) Local Stresses in Fastener
Groups (New 2001 NDS)
f) Design for Creep and Critical
Deflection Applications
g) Effective Column Length
h) Lateral Stability of Columns

10. NDS 2005: Appendix
Layout
i) Yield Limit Equations for
Connections
j) Solution of Hankinson
Formula
k) Typical Dimensions for Split
Ring and Shear Plate
Connectors
l) Typical Dimensions for
Dowel-Type Fasteners
m) MFG Tolerances for Rivets
and Steel Side Plates for
Timber Rivet Conn.
n) Load and Resistance
Factor Design (LRFD)

11. Design Value Supplement:
Chapter Layout
1) Sawn Lumber Grading
Agencies
2) Species Combinations
3) Section Properties
4) Reference Design
Values

12. Why Use LRFD?
State-of-the-art
More rational treatment of loads
ASD—Deterministic (inconsistent safety
factors)
LRFD—Reliability based
ASD load combinations not maintained
Ease of designing with multiple materials that
use LRFD
Size benefits with multiple transient loads
Consistent with FEMA 356 (performance based
design codes)

13. LRFD Design Concepts
Safety Limit State Serviceability Limit
Factored Loads State
(Demand)—Larger Unfactored
Reduced Nominal Loads—same
Strength– φRn Mean material
(Capacity)—Larger strength and
stiffness—same

14. LRFD Statistical
Methodology
AF & PA, 2005 NDS e-course

15. LRFD Nuts and Bolts
Basic Relationship αQ ≤ φλRn
Specific f ≤ F 'n
f—demand stress (e.g. Pu/A)
F’n—LRFD level adjusted stress
(capacity)
Example (Sawn Lumber in Bending)
F’b=FbCMCtCLCFCfuCiCrKFφbλ

16. LRFD Adjustment
Factors
2005 NDS

17. LRFD Nuts and Bolts
(Cont.)
“Adjusted” strength, rather than “allowable”
Three new adjustment factors
KF—Format Conversion Factor
(ASTM D 5457)
Generally 2.16/φ
Rearranged φKF=2.16
φ—Strength Reduction Factor
λ—Time Effect Factor
Essentially only one additional adjustment
factor

18. LRFD Specific Adjustment
Factors
2005 NDS
2005 NDS

19. LRFD Specific Adjustment
Factors (Cont.)
2005 NDS

20. Beams and Columns
Behavioral equations typically same
Very minor adjustments to FbE and FcE
Shear increase from 2001 NDS maintained
'
FbE = 1.20 Emin
2
RB
'
FcE = 0.822 Emin
(le d )2
E’min—for stability, 5th percentile, App D
Use E’ for deflection

21. Wind and Seismic
Supplement
Design guidance for lateral loads
Chapters
1) Designer Flowchart
2) General Design Requirements
3) Members and Connections
4) Lateral Force-Resisting
Systems
General
Wood Diaphragms
Wood Shear Walls
Appendix A (Plywood tables)

22. Diaphragms
Rigid/Flexible defined
Based on relative deflection
Deflection equations
Limits on diaphragms resisting load
from concrete and masonry walls
3-sided diaphragms discussed
Cantilevered diaphragms permitted

23. Diaphragms (Cont.)
Capacities for structural sheathing
Wind and Seismic values different
Values for lumber diaphragms
Tables contain Ga (shear stiffness)
Ga includes nail slip term
Multiply table values by φD=0.8

24. Diaphragm Table
2005 NDS

25. Diaphragm Table
2005 NDS

26. Shear Walls
Deflection equation
Guidelines for double sheathed walls
Aspect ratio criteria remains same as IBC
2003
Perforated shear wall values
Tables
Structural Panels [Tab 4.3A]
Gypsum and Cement Plaster [Tab 4.3B]
Lumber [Tab 4.3C]
Plywood [Tab A.4.3A]

27. Shear Walls (Cont.)
Shear Wall Framing
2” Nominal—Typical
3” When
Nails 2” O.C. or less
10d @ 3” O.C.
Nominal Capacity (vs)>700 lb/ft
• For seismic design category D, E, F
Requirements irrespective of ASD or LRFD

28. Shear Wall Table
2005 NDS

29. Shear Wall Table
2005 NDS

30. Mechanical Connectors
Same behavioral
equations
Check Local Wood
Stresses
Multiple Fasteners
Based on
Mechanics OR
Appendix E
For both ASD & 2005 NDS
LRFD

31. Mechanical Fastener:
Local Wood Failure Modes
Local Wood Stress
Modes
Net Section
Tension
Row Tear-out
Group Tear-out
2005 NDS

32. Mechanical Fastener
Adjustment Factors
2005 NDS

33. Pre-Engineered
Connectors
Convert using ASTM D5457-93 (1998)
Multiply ASD value by φ and λ (CM, Ct)
KF
1996 LRFD Manual- Pre-Engineered Metal
Connectors, Supplement

34. 2005 NDS Learning
AF&PA e-course
http://www.awc.org/Hel
pOutreach/eCourses/S
TD104/NDS2005.pdf
AWC and AF&PA web
sites—misc. papers
Structural Wood Design
Using ASD and LRFD
(Workbook)
ASD/LRFD Manual for
Engineered Wood
Construction 2005
Edition

35. 2005 NDS Design Aids
2005 NDS
2005 Design Value
Supplement
2005 Wind & Seismic
Supplement
ASD/LRFD Manual
for Engineered Wood
Construction 2005
Edition—Available
December 2005?

36. Summary
2005 NDS—dual format LRFD adds essentially 1
LRFD advantageous adjustment factor
because: Behavioral equations
State-of-the-art same as ASD
Reliability based Design guide not
Consistent with other available
material codes Code currently available
Size benefits Adopted in 2006 IBC
Consistent with FEMA
356