History - · PDF fileallowable stress design (ASD). ASDthrough2001NDSASD through 2001 NDS 1944 1973 ... • ASDvsLRFDASD vs LRFD –adjustedstressesfromreferenceadjusted stresses from

ASD and LRFD ASD and LRFD with the 2005 NDSwith the 2005 NDS®®with the 2005 NDSwith the 2005 NDSPart 1 Part 1 –– Member DesignMember Design

Presented by:Presented by:John “Buddy” Showalter P EJohn “Buddy” Showalter P E

Copyright © 2007-2010 American Wood Council. All rights reserved.

John Buddy Showalter, P.E.John Buddy Showalter, P.E.Vice President, Technology TransferVice President, Technology Transfer

HistoryHistory

The first NDS (1944) was based onCopyright © 2007-2010 American Wood Council. All rights reserved.

The first NDS (1944) was based on allowable stress design (ASD).

ASD through 2001 NDSASD through 2001 NDS

1944 19731944 1973

1962 1977 1991

1968 1982 1997


1971 1986 2001

Load Resistance Factor DesignLoad Resistance Factor Design


ASD and LRFD in 2005 NDSASD and LRFD in 2005 NDS


OutlineOutline• Document organizationg• Overview of LRFD Concept• Chapter-by-chapter description• Changes from previous editions• Examples


NDS® 2005 and SupplementNDS 2005 and Supplement

2001• 16 Chapters

2005• 16 Chapters

• 13 Appendices • 14 Appendices

Wh t’ h d?Copyright © 2007-2010 American Wood Council. All rights reserved.

What’s changed?

NDS 2005 ChaptersNDS 2005 Chapters200520051 General Requirements for Building Design1 General Requirements for Building Design2 Design Values for Structural Members2 Design Values for Structural Members3 Design Provisions and Equations3 Design Provisions and Equations4 Sawn Lumber4 Sawn Lumber4 Sawn Lumber4 Sawn Lumber5 Structural Glued Laminated Timber5 Structural Glued Laminated Timber6 Round Timber Poles and Piles6 Round Timber Poles and Piles7 Prefabricated Wood I7 Prefabricated Wood I--JoistsJoists8 S C8 S C8 Structural Composite Lumber8 Structural Composite Lumber9 Wood Structural Panels9 Wood Structural Panels10 Mechanical Connections10 Mechanical Connections11 Dowel11 Dowel--Type FastenersType Fasteners11 Dowel11 Dowel Type FastenersType Fasteners12 Split Ring and Shear Plate Connectors12 Split Ring and Shear Plate Connectors13 Timber Rivets13 Timber Rivets14 Shear Walls and Diaphragms14 Shear Walls and Diaphragms15 S i l L di C diti15 S i l L di C diti


15 Special Loading Conditions15 Special Loading Conditions16 Fire Design of Wood Members16 Fire Design of Wood Members

NDS 2005 Appendices20052005A Construction and Design PracticesA Construction and Design Practices

NDS 2005 Appendices

ggB Load DurationB Load DurationC Temperature EffectsC Temperature EffectsD Lateral Stability of BeamsD Lateral Stability of BeamsE Local Stresses in Fastener GroupsE Local Stresses in Fastener Groups Important!ppF Design for Creep and Critical Deflection F Design for Creep and Critical Deflection

ApplicationsApplicationsG Effective Column LengthG Effective Column LengthH Lateral Stability of ColumnsH Lateral Stability of Columns

Important!

yyI Yield Limit Equations for ConnectionsI Yield Limit Equations for ConnectionsJ Solution of Hankinson EquationJ Solution of Hankinson EquationK Typical Dimensions for Split Ring and Shear K Typical Dimensions for Split Ring and Shear

Plate ConnectorsPlate ConnectorsL Typical Dimensions for Standard Hex Bolts, Hex L Typical Dimensions for Standard Hex Bolts, Hex

Lag Screws, Wood Screws, Common, Box, Lag Screws, Wood Screws, Common, Box, and Sinker Nailsand Sinker Nails

M Manufacturing Tolerances for Rivets and Steel M Manufacturing Tolerances for Rivets and Steel


ggSide Plates for Timber Rivet Connections Side Plates for Timber Rivet Connections

N Appendix for Load and Resistance Factor N Appendix for Load and Resistance Factor Design (LRFD)Design (LRFD) -- MandatoryMandatory

NDS 2005 SupplementNDS 2005 Supplement

20052005200520051 1 Sawn Lumber Grading AgenciesSawn Lumber Grading Agencies2 2 Species CombinationsSpecies Combinations33 Section PropertiesSection Properties3 3 Section PropertiesSection Properties44 Design Values Design Values

-- Lumber and TimberLumber and Timber-- NonNon--North American Sawn LumberNorth American Sawn Lumber-- Structural Glued Laminated TimberStructural Glued Laminated Timber-- MSR and MELMSR and MEL




Overview of LRFDOverview of LRFDOverview of LRFDOverview of LRFD• Design process• Design concepts• Comparison with ASD


Design ProcessDesign Process

Demand Demand CapacityCapacity


Design ProcessDesign ProcessDesign ProcessDesign Process

LoadSupport Conditions DemandDemandSupport ConditionsGeometryMaterialsMaterials

DemandDemand

C itC itMaterialsMaterialsPerformanceFire

CapacityCapacity

FireEconomicsAesthetics


Aesthetics….

Design ConceptsDesign Concepts

Two Limit State concerns:

• safety against failure or collapse

• Serviceability (performance in service)


ServiceabilityServiceability

• Unfactored loads• Mean (avg) material

strength values


LRFD SafetyLRFD - Safety

• Factored loads• Material strength

values - modified


Property Variability

x

Property Variability

x

x = standard deviation

xxx = mean

SCL

COVx =x

x I-Joist

SC

eque

ncy

MSR Lumber

GlulamLoad

elat

ive

Fre

Visually Graded Visually Graded LumberLumber

Re

Copyright © 2007-2010 American Wood Council. All rights reserved.Material Property Values

Statistical ModelStatistical ModelNormal Distribution Curve for Load or Resistance


Based on actual physical measurements - data sets

Statistical ModelStatistical Model

Normal Distribution Curves for Load S and Resistance RNormal Distribution Curves for Load, S , and Resistance, R

failure


failure

Statistical ModelStatistical Model

Normal Distribution Curves for Safety Function, Z

f = f ffZ = fR - fS

mZ = mR - mS

22SRz

z

zm


LRFD Probability of FailureLRFD - Probability of Failure

Pf = one failure expected for x number of t t d i d

Pf

5.2 1 : 10,000,0004 7 1 : 1 000 000structures designed

and built with a given 4.7 1 : 1,000,0004.2 1 : 100,0003.7 1 : 10,0003.2 1 : 1,0002.7 1 : 1002.2 1 : 10


LRFD Range on LRFD - Range on

Range for Wood Strength

Low Typical High 2.4 2.6 2.9P 1 25 1 63 1 251Pf 1 : 25 1 : 63 1 : 251


LRFD Safety Design EquationLRFD Safety Design Equation

DemandDemand CapacityCapacityDemand Demand CapacityCapacity Q Q RRnnn

i=1


What stays the same as ASD?What stays the same as ASD?


Allowable Stress Designo ab e S ess es g

• Same basic equationSame basic equation format

• Same adjustmentSame adjustment factors

• Same behavioralSame behavioral equations

• Formatted forFormatted for compatibility


What changes from ASD?What changes from ASD?gg


LRFD vs ASDLRFD vs. ASD

• Three new notations - , , and KF• Design loads (factored) for safety are

bigger• Design loads (unfactored) for serviceability

are the same• Material resistance values are bigger• Load Duration factor changes to Time

Effect Factor



Theoretical safety margin applied to

ASDapplied stress allowable stress

margin applied to material stresses

Tested material strength

Estimated loads

Design Load

Adjusted Resistance


Design values


Member performance factor

LRFDfactored load factored resistanceLoad factors to account for variations in loads

Tested member resistance

Estimated loads

Factored Design Load

Factored Design Resistance


Design values

2005 NDS LRFD Standard2005 NDS LRFD Standard

Factored Load Combinations ASCE 7-02

F = flood H = hydrostatic


y

NDS 2005 LRFD SpecificationNDS 2005 LRFD Specification


NDS 2005 LRFD SpecificationNDS 2005 LRFD Specification tied to ASCE 7-02 Factored Load Equations:


NDS 2005 LRFD SpecificationFormat Conversion Factor KF:

NDS 2005 LRFD SpecificationF

RN = RASDRN RASDASD

RN = KF RASD

LRFD


RN KF RASD RASD reference strengths

NDS 2005 LRFD Specification

Format Conversion Factor KF:

NDS 2005 LRFD Specification

Format Conversion Factor KF:


RN = KF RASD

2005 NDS LRFD Specification2005 NDS LRFD Specification• Why use LRFD for wood?

f d i i ith lti l– ease of designing with multiple materials that use an LRFD basis (steel or concrete)

– more rational treatment of loads rather than penalizing material strength for unknowns on loads g

– realize efficiencies with:• multiple transient live loads• extreme event loadsextreme event loads

– ASD load combinations have not been maintained in deference to LRFD load combinations


LRFD load combinations



Chapter 1 TerminologyChapter 1 - TerminologyBasic requirements for checking strength are revised to use terminology applicable to both ASD and LRFDto use terminology applicable to both ASD and LRFD

Example:“3.3.1 The actual bending stress or moment shall not exceed

the adjusted allowable bending design value.”j g g

In equation format, this takes the standard form fb ≤ Fb'“ ll bl ” (t i ll i t d ith ASD) l d b– “allowable” (typically associated with ASD) replaced by adjusted

• more generally applicable to either ASD or LRFD• better describe applying adjustment factors to referencebetter describe applying adjustment factors to reference

design values– Reference design values (Fb, Ft, Fv, Fc, Fc, E, Emin) are

multiplied by adjustment factors to determine adjusted


design values (Fb', Ft', Fv', Fc', Fc', E', Emin')

Chapter 1 Design LoadsChapter 1 – Design Loads

• references loads inreferences loads in accordance with minimum load standards, such as ASCE 7 – 02


Chapter 2 Adjustment FactorsChapter 2 – Adjustment Factors• Applicable to ALL defined wood products• Adjusts from reference to site conditions

– CD, time-dependent– CM wet service– Ct temperature


Chapter 2 Adjustment FactorsChapter 2 – Adjustment Factors

• Wet Service Factor, CMWet Service Factor, CM


W t S i C ditiWet Service Conditions

25

30

15

20

d EM

C %

Temp 30 deg FTemp 70 deg F

5

10Woo

d

Temp 130 deg F

00 20 40 60 80 100

R l ti H idit %


Relative Humidity %

Wet Service ConditionsWet Service Conditions

100

110

Con

tent

80

90

% M

oist

ure

Impact StrengthModulus of Elasticity

50

60

70

engt

h at

12% Modulus of Rupture

Crushing Strength

40

50

12 14 16 18 20 22 24 26 28 30

%St

re


Moisture Content of Wood (%)

W t S i F t CWet Service Factor, CM• values found in the NDS Supplement for

l blumber


Chapter 3 Behavioral EquationsChapter 3 – Behavioral Equations

• ASD vs LRFD adjusted stresses from reference• ASD vs LRFD – adjusted stresses from reference

ASD F′ = F C x adjustment factorsASD F′n = Fn CD x adjustment factors

LRFD F′n = Fn KF n x adjustment factors


Chapter 3 Behavioral EquationsChapter 3 – Behavioral Equations• Beams

– CL beam stability


Chapter 3 Behavioral EquationsChapter 3 – Behavioral Equations• Beams

F equivalence– FbE equivalence

'bE

'min EKE20.1F 2

b

bE2b

minbE RR

F

2005 NDS

2001 NDSNDS NDS

– Emin adjusted for safety for both ASD and LRFD processes


Chapter 3 Behavioral EquationsTR14 - Designing for

Chapter 3 – Behavioral Equations

Lateral-Torsional Stability in Wood MembersB i f t NDS ff ti•Basis of current NDS effective

length approach•Summarizes equivalent uniform moment factor approach•Provides comparison


Application LRFD vs ASDApplication - LRFD vs. ASD

QBeam Example - UDL Simply Supported

LA, S, I

LRFD ASDDEMAND LOADSO S

Safety wf = Q w = Q

Q Q


Serviceability wL= QL wL= QL


Safety Limit State 1

Beam Example - UDL Simply Supported

LRFD ASDSHEAR

L 2 K F′ A Cwf L 2 v KF F′v A2 3 w L 2 F′v CD A

2 3

demand capacitydemand capacity


Prime denotes inclusion of applicable C factors except CD


Safety Limit State 2


w L2 K F′ S

FLEXURE

w L2 F′ C S

LRFD ASD

wf L2 b KF F b S8

w L2 F b CD S8



Prime denotes inclusion of applicable C factors except CD


Serviceability Limit State


DISPLACEMENT LRFD ASD

L 5 wL L4

360 384 E I L 5 wL L4

360 384 E I

demandcapacity demandcapacity


Chapter 3 Behavioral EquationsChapter 3 – Behavioral Equations• Columns

– CP column stability


Chapter 3 Behavioral EquationsChapter 3 – Behavioral Equations• Columns

– FcE equivalence

2

'cE

2

'min

cEEKE822.0F 2

e2

ecE

dl

dl

2005 20012005 NDS

2001 NDS


– Emin adjusted for safety for both ASD and LRFD processes

Chapter 3 Behavioral EquationsChapter 3 – Behavioral Equations• Emin

– FcE equivalence

661/))COV(64511(E031E 66.1/))COV(645.11(E03.1E Emin

E = reference MOEE = reference MOE1.03 = adjustment factor to convert E to a pure bending

basis (shear-free) (use 1.05 for glulam)1.66 = factor of safetyCO ff f O ( S )COVE = coefficient of variation in MOE (NDS Appendix F)


Chapter 3 Column EquationsChapter 3 – Column Equations

Safety Limit State

Column Example – Axial Load only

LRFD ASD

P P′ P P′(Q) A Fc KF c CP CM Ct (Q) A Fc CD CP CM Ct




Column Example

PDead Load = 5500 lbs PDead Load 5500 lbs

Live Load = 31500 lbs

Normal Time Duration

A, S, IL = 16 ft (each direction)

L

Ends pinned



Column Example

LRFD ASDLOADSLOADS

Safety P = Q= 1.2 D + 1.6 L

P = Q= D + L

= 1.2 (5500) + 1.6 (31500)= 57000 lbs

= 5500 + 31500= 37000 lbs



Column Example Try 6-3/4″ x 9″ Glulam visually graded western species, 16F-1.3E

GEOMETRYGEOMETRYSectiond = 9 inb = 6 75 in

X-XPinned endK = 1 0

Y-YPinned endK 1 0b = 6.75 in

A = 61 in2Ked = 1.0Ld = 16 ftLed = Ked Ld

Keb = 1.0Lb = 16 ftLeb = Keb Lb

X-X Slenderness = max

= 28

dL,

bL edeb


Y-Y

= 28


Column Example Try 6 3/4″ x 9″ Glulam visually graded western species, 16F-1.3E

SERVICE CONDITIONS

Adjustment Factors

LRFD ASD

Time-dependent (normal)Wet-service (dry) CMTemperature (normal) Ct

λ = 0.81.01.0

CD = 1.01.01 0Temperature (normal) Ct 1.0 1.0



MATERIALS

Column Example

LRFD ASD

Try 6 3/4” x 9” Glulam visually graded western species, 16F-1.3E

MATERIALS

FcE

1,550 psi1,500,000 psi

1,550 psi1 500 000 psi

LRFD ASD

EEminc (Glulam)

1,500,000 psi780,000 psi0.9

1,500,000 psi780,000 psi0.9

φc (compression)φs (stability)KF compression

0.900.852.16 / c = 2.40


pKF stability

c1.5 / s = 1.76


Column Example

LRFD ASDCAPACITYCAPACITY

Crushing Fc* = Fc KF c CM Ct= (1,550)(2.40)(0.8)(0.9)(1.0 all)

Fc* = Fc CD CM Ct= (1,550)(1.0)(1.0 all)( , )( )( )( )( )

= 2,678 psi

P0 = A Fc*

( , )( )( )= 1,550 psi

P0 = A Fc*= (61)(2,678)= 163,382 lbs

= (61)(1,550)= 94,550 lbs



Column Example

LRFD ASDCAPACITYCAPACITYBuckling E′min = Emin KF s CM Ct E′min = Emin CM Ct

= 780,000 psi= (780,000)(1.76)(0.85)(1.0)

2

'min

cE s)Slendernes(0.822EF 2

'min

cE s)Slendernes(0.822EF

p= 1,166,880 psi

s)Slendernes(

2(28))(780000)822.0(

s)Slendernes(

2(28))(1166880)822.0(


= 818 psi= 1,223 psi


Column ExampleLRFD ASDCAPACITY

c Ratios1550818

FF

*c

cE 26781223

FF

*c

cE

= 0.46 = 0.53

c



Column ExampleColumn Example

LRFD ASDCAPACITY

Cpc2c

12c

1C

*c

cE*c

cE*c

cEFF2

FF

FF

p

= 0.43 = 0.48

P′ = A Fc* Cp

= (61)(2,678)(0.43)= (61) (1,146)

P′ = A Fc* Cp= (61)(1,550)(0.48)= (61)(744)


(61) (1,146)= 69,914 lbs

( )( )= 45,384 lbs


Safety Limit State

Column Example – Axial Load only

LRFD ASDCOMPRESSIONP P’ P P’P P P P

57,000 lbs 69,914 lbs 37,000 lbs 45,384 lbs



0.82 0.82Load / Capacity Ratio

Chapter 3 Behavioral EquationsChapter 3 – Behavioral Equations• Tension members (tension parallel to grain)( p g )

ASD F′t = Ft CD x adjustment factorsS t t CD adjus e ac o s

LRFD F′t = Ft KF t x adjustment factors


Chapter 3 Behavioral EquationsChapter 3 – Behavioral Equations• wood and tension perpendicular to grain

– Not recommended per NDS 3.8.2

initiators:• notches• moment connections• hanging loads


Chapter 3 Behavioral EquationsChapter 3 – Behavioral Equations• Combined bi-axial bending and axial g

compression


Chapter 3 Behavioral EquationsChapter 3 – Behavioral Equations• Combined bending and axial - compression


Chapter 3 Behavioral EquationsChapter 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)

– Cb bearing area factor


same as NDS 2001

Chapter 4 LumberChapter 4 – Lumber• Design values

– Visually graded lumber– MSR / MEL

Ti b– Timber– Decking


Chapter 4 LumberChapter 4 – Lumber• Lumber adjustment factors

– CF - size factor– Cfu - flat use

C i i i– Ci - incising– CT - buckling stiffness– C - repetitive memberCr - repetitive member



– CF - size factor– Cfu - flat use



– Ci - incising– CT - buckling stiffness



– Cr – repetitive member


Chapter 4 LumberChapter 4 – Lumber• Adjustment factors

C f f t d– Cf form factor removed

Why?Why?– derived from plastic deformation in

small clear specimens that may not be applicable to full size membersbe applicable to full-size members

– applicability to standard wood products was limited (not allowed in

l & il it’ b ilt i t thpoles & piles – it’s built into the reference design value)


Chapter 4 LumberChapter 4 – Lumber• Example

– F′t = Ft CD CF (ASD)– F′t = Ft CF KF t (LRFD)– Unincised, axially loaded y

tension member in normal environment


Chapter 4 Finger Jointed LumberChapter 4 – Finger-Jointed Lumber

• Widely accepted for• Widely accepted for use by IBC and IRC

• Interchangeable withInterchangeable with solid sawn lumber with certain limitations:– HRA/NON-HRA– Moisture– Load conditions


Chapter 4 Finger Jointed LumberChapter 4 – Finger-Jointed Lumber• HRA

H t R i t t Adh i– Heat Resistant Adhesive– Designated on grade

stampp– Used where fire rated

assemblies are required by codeby code

• Exterior walls• Dwelling unit separations• Commercial tenant• Commercial tenant

separations


Chapter 4 Finger Jointed LumberChapter 4 – Finger-Jointed Lumber• NON-HRA

– Adhesive not rated for heat resistanceDesignated on grade– Designated on grade stamp


Chapter 4 Finger Jointed LumberChapter 4 – Finger-Jointed Lumber• HRA marks absent?

– Treat same as NON-HRA

????


Chapter 4 Finger Jointed LumberChapter 4 – Finger-Jointed Lumber• Other Stamp Designations

– Exterior Use allowed– Structural applications are not

limitedlimited– Must meet HRA criteria in

rated assemblies


Chapter 4 Finger Jointed LumberChapter 4 – Finger-Jointed Lumber• Other Stamp Designations

– STUD USE ONLY or – VERT USE ONLY

– Limited to use where bending or tension stresses gare of short duration


Chapter 4 Finger Jointed LumberChapter 4 – Finger-Jointed Lumber• Older Stamps

– Old grade marks• Obliterated

New finger jointed– New finger-jointed grade stamps apply


Chapter 5 Glued Laminated TimberChapter 5 – Glued Laminated Timber• Design values added to NDS Supplement• Reformatted glulam radial tension values• Shear values increased 10%


Chapter 5 GlulamChapter 5 – Glulam• Design values

– Frt radial tension


Chapter 5 GlulamChapter 5 – Glulam• Adjustment factors

– CV volume– Not cumulative with CL


Chapter 5 GlulamChapter 5 – Glulam• Adjustment factors

– Cc curvature– Applies to Fb

C d ti f– Curved portion of bending member

– Not applied to straight pp gportion of member


Chapter 5 GlulamChapter 5 – Glulam• Example

– F′c = Fc CD CP (ASD)– F′c = Fc CP KF c (LRFD)– Axially loaded compression y p

member in normal environment


Chapter 6 Poles & PilesChapter 6 – Poles & Piles• Poles - post-frame• Piles - foundations


Chapter 6 Poles & PilesChapter 6 – Poles & Piles• Design values

– No changes from 2001 NDS


Chapter 6 Poles & PilesChapter 6 – Poles & Piles• Adjustment factors

– LRFD provisions


Chapter 6 Poles & PilesChapter 6 – Poles & Piles• Adjustment factors

– Cu - untreated– Ccs - critical section

C i l il– Csp - single pile


Chapter 6 Poles & PilesChapter 6 – Poles & Piles• Example

– F′c = Fc CD Csp (ASD)– F′c = Fc Csp KF c (LRFD)– Single, axial load, treated, g

full lateral support, normal environment


Chapter 7 I joistsChapter 7 – I-joists• Design values

– M, V, EI, K – no changes• Evaluation Reports

– Contain proprietary design


Chapter 7 I joistsChapter 7 – I-joists• Adjustment factors

– LRFD provisions


Chapter 7 I JoistsChapter 7 – I-Joists• Adjustment factors

– Cr = 1.0 • revised to agree with

ASTM D5055-02

• factor of 1.0 maintained for clarity transitioning y gfrom 2001 NDS


Chapter 7 I joistsChapter 7 – I-joists• Example

– M′r = Mr CD (ASD)– M′r = Mr KF b (LRFD)

F ll l t l t– Full lateral support, bending member, normal environment


Chapter 8 – Structural Composite Lumber (SCL)Composite Lumber (SCL)• Design values in evaluation reports

– Note less variability (low COV)– No changes from 2001 NDS

E l ti R t• Evaluation Reports– Contain proprietary design

x

x = mean

COVx = GlulamI-JoistSCL

requ

ency

COVxxx

Visually Graded Visually Graded LumberLumber

MSR LumberLoad

Rel

ativ

e Fr


Material Property Values

Chapter 8 – Structural Composite Lumber (SCL)Composite Lumber (SCL)• Adjustment factors

– CV – volume• Not cumulative with

lateral stability factor, CLy , L


Chapter 8 – Structural Composite Lumber (SCL)Composite Lumber (SCL)• Adjustment factors

– Cr = 1.04• Cr is different than lumber (Cr lumber = 1.15) r ( r lumber )• Applied to Fb


Chapter 8 – Structural Composite Lumber (SCL)Composite Lumber (SCL)• Example

– F′b = Fb CD CV (ASD)– F′b = Fb CV KF b (LRFD)– Full lateral support, bending pp g

member, normal environment


Chapter 9 – Wood Structural Panels (WSP)Structural Panels (WSP)• Design values – obtain from an approved source

F S– FbS– FtA– Fvtv– Fs

– FcA– EIEI– EA– Gvtv

F– Fc


Chapter 9 – Wood St t l P l (WSP)Structural Panels (WSP)• Adjustment factors

– CG - grade & construction– Cs - panel size

C t i– CM - wet service– Ct - temperature



– CG - grade & construction



– Cs - panel size– CM - wet service

C t t– Ct - temperature


Chapter 9 – Wood St t l P l (WSP)Structural Panels (WSP)• Example

– FbS′ = FbS CD (ASD)– FbS′ = FbS KF b (LRFD)

N t t l I >24″– Non-structural I, >24″ width, loaded in bending, normal environment


Chapters 10-13M h i l C tiMechanical Connections• Chapter 10 – mechanical connections• Chapter 11 – dowel-type connectors

(nails, bolts, lag/wood screws)• Chapter 12 – split rings and shear plates• Chapter 13 – timber rivets

• Covered in Part 2• September 30


Chapter 14 – Shear Walls and Di hDiaphragms

• enabling language for shear wall and diaphragm designd i i f ti d• design information and values in:ANSI / AF&PA SDPWS

standard


ANSI / AF&PA SDPWS

• WIND & SEISMIC standard f 2005 NDS– references 2005 NDS

– Special design provisions for wind and seismic loadsV l f id i t f l– Values for a wide variety of panel products

F t W bi• Future Webinar• October 14


Chapter 15 Special LoadingChapter 15 – Special Loading• Built-up columns

– Revised to correct limitation on short built-up columns

15.3.2.2…. Each ratio shall be used to calculate a column stability factor, CP, per section 15.3.2.4 and the smaller CPshall be used in determining the allowable compressionshall be used in determining the allowable compression design value parallel to grain, Fc', for the column. Fc' for built-up columns need not be less than Fc' for the individual laminations designed as individual solid columns per g psection 3.7.


Chapter 16 – Fire Designp g

Applies to ASD onlypp y


Chapter 16 Fire (ASD)Chapter 16 – Fire (ASD)• Fire resistance up to

two hourstwo hours– Columns– Beams – Tension Members– Combined Loading

• Additional special provisions for glulam


Chapter 16 Fire (ASD)

TR10 - Calculating the

Chapter 16 – Fire (ASD)

gFire Resistance of Exposed Wood Membersp•Expands uses for large, exposed wood members

•Expands applicability of current methods to other EWP’s (SCL)

•Expands use of large, exposed wood members to 2 hour fire endurance applications


Chapter 16 FireChapter 16 – Fire

• Superior fire performance of heavy timbers– attributed to the charring effect of wood

• Benefits of charring– an insulating char layer is formedan insulating char layer is formed – protects the core of the section


A l f C S ti l Di iAnalog for Cross-Sectional Dimensions


Estimating Cross-sectional Dimensions due to Charringdue to Charring

• 4-Sided Exposure (i.e. columns) b = B - 2t d = D - 2t

• 3-Sided Exposure (i.e. beams) b = B - 2t d = D - t

S ( )• 2-Sided Exposure (i.e. decking) b = B - t d = D - t

where: is the char rate of the materialt is the fire exposure time


Model for Charring of Wood

N li h d l d i l li h t i t

Model for Charring of Wood

• Nonlinear char model used - nominal linear char rate input.

• To account for rounding at corners and reduction of strength and stiffness of the heated zone, the nominal char rate values, n, are increased 20%., , n,

eff = 1.2 n

t 0.187

where:eff is the effective char rate (in/hr), adjusted for exposure time, tn is the nominal linear char rate (in/hr), based on 1-hr exposuren ( ) pt is the exposure time (hrs)


Effective Char Rates and Char Layer ThicknessEffective Char Rates and Char Layer Thickness

(for = 1 5 inches/hour)

Required Fire Effective Char Effective Char LayerEndurance Rate Thickness

(for n 1.5 inches/hour)

Endurance Rate, eff Thickness, char

(hr) (in/hr) (in)1-Hour 1.80 1.81½ Hour 1 67 2 51½-Hour 1.67 2.52-Hour 1.58 3.2


D i f M b C itDesign for Member Capacity

Dead Load + Live Load K * Allowable Design Capacity

where:K is a factor to adjust from allowable design capacity to

average ultimate capacity


Allowable Design Stress to Average Ultimate Strength Adjustment Factor

Member Capacity KBending Moment Capacity, in-lb. 2.85Tensile Capacity, lb. 2.85Compression Capacity, lb. 2.58Beam Buckling Capacity, lb. 2.03Column Buckling Capacity, lb. 2.03


Fi D i E l (ASD)Fire Design Example (ASD)

• Douglas fir glulam beams– Span L = 18 feet– Spaced at s = 6 feetp

• Design Loadq = 100 psf– qlive = 100 psf

– qdead = 15 psf

• Timber decking nailed to the compression edge of beams provides lateral bracing


Size the beam for required bending strength for 1 hour fire duration


For the structural design of the beam, calculate the induced moment:

• Beam load:wtotal = s (qdead + qlive) = (6’)(15+100) = 690 plf

• Induced demand moment:• Induced demand moment:Mmax = wtotal L2 / 8 = (690)(18)2 / 8 = 27,945 ft-lb



Select a 6-3/4” x 12” 24F-V4 Douglas-fir glulam beamTabulated bending stress, Fb, equal to 2400 psi

Calculate the beam section modulus:Ss = BD2/6 = (6.75)(12)2 / 6 = 162.0 in3

Calculate the adjusted allowable bending stress:Assuming: CD = 1.0, CM = 1.0, Ct = 1.0, CL = 1.0, CV = 0.99F’b = Fb CD CM Ct (lesser of CL or CV)

= 2400(1.0)(1.0)(1.0)(0.99) = 2371 psi


p


Calculate the design resisting moment:M’ = F’b Ss = (2371)(162) / 12= 32,009 ft-lb

Structural Capacity Check: M’ > Mmax

32 009 ft lb > 27 945 ft lb32,009 ft-lb > 27,945 ft-lb



For the fire design of the wood beam:• the loading is unchanged,• therefore the maximum moment is unchanged• therefore, the maximum moment is unchanged,• the fire resistance must be calculated

From NDS Table 16.2.1, find charring depth char for 1 hour duration:

Required Fire Effective Char Effective Char LayerRequired Fire Effective Char Effective Char LayerEndurance Rate, eff Thickness, char

(hr) (in/hr) (in) 1-Hour 1.80 1.8

1½-Hour 1.67 2.5


½ 2-Hour 1.58 3.2


Substitute in residual cross-section dimensions for 3-sided beam into the section modulus relation, i.e.:

• 3-Sided Exposure (i.e. beams) b = B - 2t d = D - t= B - 2char = D - char

Calculate charred beam section modulus exposed on 3-sides:Sf = (B-2char)(D- char)2 / 6 = (6.75 - 2(1.8))(12-1.8)2 / 6

54 6 i 3= 54.6 in3



Calculate the adjusted allowable bending stress (some adjustment factors don’t apply and may have been other than 1.0 before):F’b = Fb(lesser of CL or CV) = 2400 (0.99) = 2371 psi

Calculate strength resisting moment using charred cross-section:M’ = K F’b Sf = (2.85)(2371)(54.6) / 12 = 30,758 ft-lbM K F b Sf (2.85)(2371)(54.6) / 12 30,758 ft lb

Fire Capacity Check: M’ > Mmax

30,758 ft-lb > 27,945 ft-lb


NDS 2005Appendices Layout

20052005A Construction and Design PracticesA Construction and Design Practices

Appendices Layoutgg

B Load DurationB Load DurationC Temperature EffectsC Temperature EffectsD Lateral Stability of BeamsD Lateral Stability of BeamsE Local Stresses in Fastener GroupsE Local Stresses in Fastener Groups Important!ppF Design for Creep and Critical Deflection F Design for Creep and Critical Deflection

ApplicationsApplicationsG Effective Column LengthG Effective Column LengthH Lateral Stability of ColumnsH Lateral Stability of Columns

Important!

yyI Yield Limit Equations for ConnectionsI Yield Limit Equations for ConnectionsJ Solution of Hankinson EquationJ Solution of Hankinson EquationK Typical Dimensions for Split Ring and Shear K Typical Dimensions for Split Ring and Shear

Plate ConnectorsPlate ConnectorsL Typical Dimensions for Standard Hex Bolts, Hex L Typical Dimensions for Standard Hex Bolts, Hex

Lag Screws, Wood Screws, Common, Box, Lag Screws, Wood Screws, Common, Box, and Sinker Nailsand Sinker Nails

M Manufacturing Tolerances for Rivets and Steel M Manufacturing Tolerances for Rivets and Steel


ggSide Plates for Timber Rivet Connections Side Plates for Timber Rivet Connections

N Appendix for Load and Resistance Factor N Appendix for Load and Resistance Factor Design (LRFD)Design (LRFD) -- MandatoryMandatory

Appendix N new!Appendix N new!• Load and Resistance Factor Design

source for new variables– source for new variablesASTM D5457 – Standard Specification for Computing the Reference

Resistance of Wood-Based Materials and Structural Connections for Load and Resistance Factor Design

– tabulates KF conversion factors to convert from ASD reference values (see NDS Supplement) to LRFD reference values

– tabulates resistance factors

– tabulates time effect factors for load combinations listed in:ASCE 7-02 – Minimum Design Loads for Buildings and Other Structures• NDS clarified for cases involving hydrostatic loads (H) and for cases

where H is not in combination with L use = 0 6


where H is not in combination with L, use = 0.6

2005 NDS Supplement2005 NDS Supplement

• Updated to include latest reference values for:Updated to include latest reference values for:– visually graded lumber and timber– mechanically graded lumber y g– glued laminated timber


2005 NDS Supplement E2005 NDS Supplement - Emin

• Emin addition for reference MOE for beam andEmin addition for reference MOE for beam and column stability:– visually graded lumber and timber– mechanically graded lumber– glued laminated timber

• Represents 5% lower exclusion shear-free E value so that design value adjustments are not part of the basic design equation for column and beam stabilitydesign equation for column and beam stability


2005 NDS Supplement Lumber2005 NDS Supplement - Lumber

Visually graded dimension lumber (Table 4A)Visually graded dimension lumber (Table 4A)• Four new species added:

– Alaska cedar (Alaska & Western states)( )– Alaska Hemlock (Alaska & Western states)– Alaska Yellow Cedar (Alaska only)– Baldcypress– Baldcypress


2005 NDS Supplement Timber2005 NDS Supplement - Timber

Visually graded timber (Table 4D)Visually graded timber (Table 4D)• Two new species added:

– Alaska cedar (Alaska & Western states)( )– Baldcypress


2005 NDS Supplement Non north American Species– Non-north American Species

Non-north American Species (Table 4F)Non north American Species (Table 4F)• Several new species added:

– Montane pine (South Africa)p ( )– Norway Spruce (Romania and the Ukraine)– Silver fir (Germany, NE France, and Switzerland)– Southern pine (Misiones Argentina)– Southern pine (Misiones Argentina)– Southern pine (Misiones Argentina free of heart center and

medium grain density


2005 NDS SupplementMSR d MEL- MSR and MEL

Mechanically graded dimension lumber (Table 4C)Mechanically graded dimension lumber (Table 4C)• New design values added:

– Table 4C Footnote 2 – new G, Fv, Fc values for MSR and MELTable 4C Footnote 2 new G, Fv, Fc values for MSR and MEL– Table 4C new Emin values for MSR and MEL


2005 NDS Supplement Glulam2005 NDS Supplement - Glulam

Structural glued laminated timber (Table 5A)• New design values added:

– Table 5A new Emin values added– Table 5A 16F stress class – revised Ft, Fc, G

T bl 5A l t h T bl 5A E d d l– Table 5A values now match Table 5A-Expanded values• Species groups for split ring and shear plate connectors removed

(NDS Table 12A values inappropriate) – use G of the wood located on the face receiving the connector with NDS Table 12A assignment of species group.

• Fv values increased for prismatic members (Footnote d revised) –use of test-based shear values removing the 10% reduction used previously (AITC and APA).previously (AITC and APA).

• Fv values increased for non-prismatic members unchanged (AITC and APA).

• Non-prismatic Frt (radial tension) for D.fir-L, and SP glulam increased slightly


increased slightly

2005 NDS Supplement Glulam2005 NDS Supplement - Glulam

Structural glued laminated timber (Table 5B)Structural glued laminated timber (Table 5B)• New combinations added for Southern Pine with more

information on slope of grain differences.• Fbx design values reformatted to include footnoted table

adjustments for special tension laminations.• F columns consolidated and values updated with Table• Fvy columns consolidated and values updated with Table

5A info.


Changes from previous editionsChanges from previous editions

• NDS is one volume!!• NDS is one volume!!

= + +


2005 Wood Design Package2005 Wood Design Package

• ANSI/AF&PA NDS-2005 National Design Specification (NDS) for Wood Construction with Commentary and Supplement

• ANSI/AF&PA SDPWS-2005 – Special Design Provisions for Wind and Seismic - with Commentary- with Commentary

• ASD/LRFD Manual for Engineered Wood ConstructionWood Construction

• Structural Wood Design Solved Example Problems (Workbook)


Example Problems (Workbook)

Manual for Engineered Wood C t tiConstruction

Most non mandatory information• Most non-mandatory information contained in 2001 ASD Manual, Supplements, and Guidelines pp ,bound in one volume

• Manual Chapters correspond to NDS Ch tNDS Chapters


Solved Examples (Workbook)

• ASD solutions in addition• ASD solutions in addition to the 40 examples and solutions in the currentsolutions in the current LRFD Workbook –updated to the 2005 NDS


NDS 2005 SummaryNDS 2005 Summary• format changes to accommodate addition of LRFD:

– Revised terminologyRevised terminology– Expanded applicability of adjustment factor tables– Re-format of radial tension design values– Revised format of beam and column stability provisions y p

(addition of Emin property)– Addition of NDS Appendix N – Load and Resistance Factor

Design• other changes introduced in the 2005 Edition:• other changes introduced in the 2005 Edition:

– Removal of form factor– Revision of repetitive member factor for I-joists– Revision of full-design value terminology– Revision of full-design value terminology– Clarification of built-up column provisions


NDS 2005 Supplement SummaryNDS 2005 Supplement Summary• changes in design value tables :

– Emin values added for all materials– Fv values for prismatic glulam increased

i f tti– minor re-formatting– updated to include latest reference values for:

• visually graded lumber and timbervisually graded lumber and timber• mechanically graded lumber • glued laminated timber


2005 Wood Design Package2005 Wood Design Package


Documents

History - · PDF fileallowable stress design (ASD). ASDthrough2001NDSASD through 2001 NDS 1944 1973 ... • ASDvsLRFDASD vs LRFD –adjustedstressesfromreferenceadjusted stresses from