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Презентация на тему Consequences of EC 5 for Danish best practise

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Introduction 1Danish Timber Code has approached Eurocode 5 – except for fastenersEurocodes replaces Danish Codes from 1 Jan 2009
Consequences of EC 5 for Danish best practiseJørgen Munch-AndersenDanish Timber Information Introduction 1Danish Timber Code has approached Eurocode 5 – except for fastenersEurocodes Introduction 1Danish Timber Code has approached Eurocode 5 – except for fastenersEurocodes Introduction 1Danish Timber Code has approached Eurocode 5 – except for fastenersEurocodes Introduction 2Numerous problems using Eurocode 5 found when writing the chapter on Introduction 2Numerous problems using Eurocode 5 found when writing the chapter on Introduction 2Numerous problems using Eurocode 5 found when writing the chapter on Strength parametersDowel (FJohansen): combination ofEmbedment strength of timber – depends on densityYield Strength parametersDowel (FJohansen): combination ofEmbedment strength of timber – depends on densityYield Strength parametersDowel (FJohansen): combination ofEmbedment strength of timber – depends on densityYield Density 1Well established that strength of fasteners depend on timber densityCharacteristic densities Density 1Well established that strength of fasteners depend on timber densityCharacteristic densities Density 2Strength class for Nordic timber is usually governed by knot sizes Axially loaded fastenersHead pull-throughWithdrawal Head pull-throughEurocode value formally given only for smooth nailsVery low strength given Head pull-throughEurocode value formally given only for smooth nailsVery low strength givenShould Head pull-throughEurocode value formally given only for smooth nailsVery low strength givenShould Correction of measured strength for densityExample: Head pull through, threaded nail, dhead Correction of measured strength for densityExample: Head pull through, threaded nail, dhead Withdrawal – smooth nailsStrength parameters given are NOT conservative! – especially not Withdrawal – smooth nailsStrength parameters given are NOT conservative! – especially not Withdrawal – smooth nailsStrength parameters given are NOT conservative! – especially not Roof of steel plates300 m2 blew offWind speed far from characteristicOther part CauseBattens fastened with smooth nails (square and rusty) Withdrawal – threaded nailsStrength parameter must be declared individuallyTests show no significant Withdrawal – threaded nailsStrength parameter must be declared individuallyTests show no significant Withdrawal – screws 1Very complicated formula given and only for “old Withdrawal – screws 2No significant dependency on diameter for d = 4-6 Laterally loaded fastenersNails, timber to timberScrews, timber to timberSteel to timber Laterally loaded nails – timber to timberEurocode:Dowel load capacity from Johansen-theory with Laterally loaded screws Eurocode still focus on screws with smooth shank Laterally loaded screws Eurocode still focus on screws with smooth shank Laterally loaded screws Eurocode still focus on screws with smooth shank Measured embedment strength for screwsdroot / d ~ 0.6 => deff = Laterally loaded nails - steel to timberEurocode:Separate formulas for thick and thin Higher values will appear in an ETA-agreement for most commonly used connector Spacing parallel to grainIf fasteners not staggered 1d Eurocode 5 requires Spacing parallel to grainIf fasteners not staggered 1d Eurocode 5 requires Common connection not allowed by EC545 mm member with connecter-plates on Conclusions 1Initial Type Testing (ITT) is necessary for most types of fasteners Conclusions 1Initial Type Testing (ITT) is necessary for most types of fasteners Conclusions 2Minimum penetration lengths appears very conservativeCorrection for changing moisture content might Conclusions 2Minimum penetration lengths appears very conservativeCorrection for changing moisture content might Conclusions 2Minimum penetration lengths appears very conservativeCorrection for changing moisture content might
Слайды презентации

Слайд 2 Introduction 1
Danish Timber Code has approached Eurocode 5

Introduction 1Danish Timber Code has approached Eurocode 5 – except for

– except for fasteners
Eurocodes replaces Danish Codes from 1

Jan 2009

Слайд 3 Introduction 1
Danish Timber Code has approached Eurocode 5

Introduction 1Danish Timber Code has approached Eurocode 5 – except for

– except for fasteners
Eurocodes replaces Danish Codes from 1

Jan 2009
Most strength parameters should be declared in the CE-mark in accordance with prEN14592
Eurocode 5 equations can be used where applicable, but Initial Type Testing (ITT) is needed for many types of fasteners

Слайд 4 Introduction 1
Danish Timber Code has approached Eurocode 5

Introduction 1Danish Timber Code has approached Eurocode 5 – except for

– except for fasteners
Eurocodes replaces Danish Codes from 1

Jan 2009
Most strength parameters should be declared in the CE-mark in accordance with prEN14592
Eurocode 5 equations can be used where applicable, but Initial Type Testing (ITT) is needed for many types of fasteners
Eurocode 5 ought to give slightly conservative parameters

Слайд 5 Introduction 2
Numerous problems using Eurocode 5 found when

Introduction 2Numerous problems using Eurocode 5 found when writing the chapter

writing the chapter on timber structures in the handbook

used by Danish Engineers (Ståbi)

Слайд 6 Introduction 2
Numerous problems using Eurocode 5 found when

Introduction 2Numerous problems using Eurocode 5 found when writing the chapter

writing the chapter on timber structures in the handbook

used by Danish Engineers

ITT not yet carried out for relevant fastener types
Embedment strength not a declared parameter


Слайд 7 Introduction 2
Numerous problems using Eurocode 5 found when

Introduction 2Numerous problems using Eurocode 5 found when writing the chapter

writing the chapter on timber structures in the handbook

used by Danish Engineers

ITT not yet carried out for relevant fastener types
Embedment strength not a declared parameter

Load capacity for fasteners generally decreases
Some common Danish connection types can no longer be used

Слайд 8 Strength parameters
Dowel (FJohansen): combination of
Embedment strength of timber

Strength parametersDowel (FJohansen): combination ofEmbedment strength of timber – depends on

– depends on density
Yield moment of dowel – depends

on steel strength




Слайд 9 Strength parameters
Dowel (FJohansen): combination of
Embedment strength of timber

Strength parametersDowel (FJohansen): combination ofEmbedment strength of timber – depends on

– depends on density
Yield moment of dowel – depends

on steel strength




Tension (Fax): minimum of
Withdrawal – depends on shape of tread and density
Pull-through – depends on shape of head and density

Слайд 10 Strength parameters
Dowel (FJohansen): combination of
Embedment strength of timber

Strength parametersDowel (FJohansen): combination ofEmbedment strength of timber – depends on

– depends on density
Yield moment of dowel – depends

on steel strength




Tension (Fax): minimum of
Withdrawal – depends on shape of tread and density
Pull-through – depends on shape of head and density
Lateral load
Combination of dowel and tension
Eurocode: Fv = FJohansen + Fax/4

Слайд 11 Density 1
Well established that strength of fasteners depend

Density 1Well established that strength of fasteners depend on timber densityCharacteristic

on timber density
Characteristic densities in EN 338 decrease rapidly

with decreasing strength class:




Слайд 12 Density 1
Well established that strength of fasteners depend

Density 1Well established that strength of fasteners depend on timber densityCharacteristic

on timber density
Characteristic densities ensities in EN 338 decrease

rapidly with decreasing strength class:



Densities below 350 kg/m3 very hard to find
Up to now 350 kg/m3 has been presupposed for all strength classes in Denmark
C18 is most widely uses in Denmark – looses 10 % of density

Слайд 13 Density 2
Strength class for Nordic timber is usually

Density 2Strength class for Nordic timber is usually governed by knot

governed by knot sizes – not the clear wood

properties
This might explain why the experience using 350 kg/m3 is good
If different grow conditions causes other relations for timber grown in other places EN 338 ought to take account of regional differences

Слайд 14 Axially loaded fasteners
Head pull-through
Withdrawal

Axially loaded fastenersHead pull-throughWithdrawal

Слайд 15 Head pull-through
Eurocode value formally given only for smooth nails
Very

Head pull-throughEurocode value formally given only for smooth nailsVery low strength given

low strength given

Слайд 16 Head pull-through
Eurocode value formally given only for smooth nails
Very

Head pull-throughEurocode value formally given only for smooth nailsVery low strength

low strength given
Should be similar for threaded nails and

screws
Nails: Depends on ρ2 !
Screws: Depends on ρ0.8 ?
A linear relationship appears reasonable for test values

Слайд 17 Head pull-through
Eurocode value formally given only for smooth nails
Very

Head pull-throughEurocode value formally given only for smooth nailsVery low strength

low strength given
Should be similar for threaded nails and

screws
Nails: Depends on ρ2 !
Screws: Depends on ρ0.8 ?
A linear relationship appears reasonable for test values
Correction from ρ = 350 to ρ = 410 with ρ0.8 makes only 3% difference form linear correction !

Слайд 18 Correction of measured strength for density
Example:
Head pull

Correction of measured strength for densityExample: Head pull through, threaded nail,

through, threaded nail, dhead = 5.5 mm
Fmean = 1500

N, CoV = 12.5%, ρ = 475 kg/m3
fk,475 ~ 0.75 ∙1500/5.52 = 36,4 MPa
Approved institute corrects to ρ = 350 kg/m3 assuming linear relationship: fk,350 = 26.8 MPa (~ 3 x EC5 for smooth nail)
Using EC5’s ρ2-dependency unsafe for high ρ
Correction must be done with ρ2: fk,350 = 19.8 MPa (~ 2.3 x EC5 for smooth nail)

Слайд 19 Correction of measured strength for density
Example:
Head pull

Correction of measured strength for densityExample: Head pull through, threaded nail,

through, threaded nail, dhead = 5.5 mm
Fmean = 1500

N, CoV = 12.5%, ρ = 475 kg/m3
fk,475 ~ 0.75 ∙1500/5.52 = 36,4 MPa
Approved institute corrects to ρ = 350 kg/m3 assuming linear relationship: fk,350 = 26.8 MPa (~ 3 x EC5 for smooth nail)
Using EC5’s ρ2-dependency unsafe for high ρ
Correction must be done with ρ2: fk,350 = 19.8 MPa (~ 2.3 x EC5 for smooth nail)
Preferable to use timber with smaller density for tests – or a range of densities including low densities

Слайд 20 Withdrawal – smooth nails
Strength parameters given are NOT

Withdrawal – smooth nailsStrength parameters given are NOT conservative! – especially

conservative! – especially not for round nails
No difference in

EC5 between round and square nails
Reduction factor 2/3 for timber near to saturation not enough according to old Danish tests, might be 1/3

Слайд 21 Withdrawal – smooth nails
Strength parameters given are NOT

Withdrawal – smooth nailsStrength parameters given are NOT conservative! – especially

conservative! – especially not for round nails
No difference in

EC5 between round and square nails
Reduction factor 2/3 for timber near to saturation not enough according to old Danish tests, might be 1/3
Minimum penetration length for full strength is 12d and severe reduction for smaller length - nil for 8d
Danish code has 8 d + point

Слайд 22 Withdrawal – smooth nails
Strength parameters given are NOT

Withdrawal – smooth nailsStrength parameters given are NOT conservative! – especially

conservative! – especially not for round nails
No difference in

EC5 between round and square nails
Reduction factor 2/3 for timber near to saturation not enough according to old Danish tests, might be 1/3
Minimum penetration length for full strength is 12d and severe reduction for smaller length - nil for 8d
Danish code has 8 d + point
High withdrawal strength for smooth nail encourage the use of smooth nails for fastening of eg. roof battens – which might cause wind storm damage

Слайд 23 Roof of steel plates
300 m2 blew off
Wind speed

Roof of steel plates300 m2 blew offWind speed far from characteristicOther

far from characteristic
Other part of the roof blew off

3 years ago
No strengthening considered!

Слайд 24 Cause
Battens fastened with smooth nails (square and rusty)

CauseBattens fastened with smooth nails (square and rusty)

Слайд 25 Withdrawal – threaded nails
Strength parameter must be declared

Withdrawal – threaded nailsStrength parameter must be declared individuallyTests show no

individually
Tests show no significant influence of changing moisture so

the reduction factor 2/3 for timber near to saturation should not be applied for threaded nails (and pull-through)



Слайд 26 Withdrawal – threaded nails
Strength parameter must be declared

Withdrawal – threaded nailsStrength parameter must be declared individuallyTests show no

individually
Tests show no significant influence of changing moisture so

the reduction factor 2/3 for timber near to saturation should not be applied for threaded nails (and pull-through)
Minimum penetration length for full strength is 8d and severe reduction for smaller length - nil for 6d
Danish code has 5 d + point


Слайд 27 Withdrawal – screws 1
Very complicated formula given and

Withdrawal – screws 1Very complicated formula given and only for “old

only for “old fashioned” screws with d = 6-12

mm
The simple formula 0.035 d ℓpen ρ can replace within 10% for d = 6-10 mm
ITT will give a single strength parameter, independent on e.g. length. A possible diameter dependency will be included in declared parameter
Separate spacing requirements for withdrawal and only for timber thickness 12d (which members thickness?)

Слайд 28 Withdrawal – screws 2
No significant dependency on diameter

Withdrawal – screws 2No significant dependency on diameter for d =

for d = 4-6 mm
Connector screws and modern wood

screws similar
Fits well with (simplified) Eurocode formula

Слайд 29 Laterally loaded fasteners
Nails, timber to timber
Screws, timber to

Laterally loaded fastenersNails, timber to timberScrews, timber to timberSteel to timber

timber
Steel to timber

Слайд 30 Laterally loaded nails – timber to timber
Eurocode:
Dowel load

Laterally loaded nails – timber to timberEurocode:Dowel load capacity from Johansen-theory

capacity from Johansen-theory with embedment strength and yield moment

of fastener
Rope-effect from friction and inclination
Danish code:
Presupposes failure-mode f
mode e not possible due to required penetration length
mode d somewhat prevented by the head
Rope-effect included by reduced penetration length for threaded nails

Слайд 31

Слайд 32 Laterally loaded screws
Eurocode still focus on screws

Laterally loaded screws Eurocode still focus on screws with smooth shank

with smooth shank penetrating into pointside
Eurocode suggests deff =

1.1 x droot for the treaded part of screws

Слайд 33 Laterally loaded screws
Eurocode still focus on screws

Laterally loaded screws Eurocode still focus on screws with smooth shank

with smooth shank penetrating into pointside
Eurocode suggests deff =

1.1 x droot for the treaded part of screws
deff not likely to be the same for embedment strength fh and yield moment My when measured

Слайд 34 Laterally loaded screws
Eurocode still focus on screws

Laterally loaded screws Eurocode still focus on screws with smooth shank

with smooth shank penetrating into pointside
Eurocode suggests deff =

1.1 x droot for the treaded part of screws
deff not likely to be the same for embedment strength fh and yield moment My when measured
prEN 14592 does not deal with neither deff nor fh
Most straight forward to declare fh (for diameter d) and My

Слайд 35 Measured embedment strength for screws
droot / d ~

Measured embedment strength for screwsdroot / d ~ 0.6 => deff

0.6 => deff = 1.1 x droot = 0.66

d
Measured reduction factor for screws 0.45 – 0.7
Hansen assumes factor to depend on surface roughness
Parallel to grain < Perpendicular to grain

Слайд 36 Laterally loaded nails - steel to timber
Eurocode:
Separate formulas

Laterally loaded nails - steel to timberEurocode:Separate formulas for thick and

for thick and thin steel-plates (head fixed against rotation or

not)
Thick plate t ≥ d, thin plate t ≤ d/2

Danish code:
Head assumed fixed against rotation
Typical d = 4 mm and t = 2 mm
Timber to timber strength increased by 25 % (larger rope-effect when not pull-through)


Слайд 37

Слайд 38 Higher values will appear in an ETA-agreement for

Higher values will appear in an ETA-agreement for most commonly used

most commonly used connector nails and screws (smaller penetration length,

larger rope-effect, fixed head)

Слайд 39 Spacing parallel to grain
If fasteners not staggered 1d

Spacing parallel to grainIf fasteners not staggered 1d Eurocode 5 requires

Eurocode 5 requires increased spacing (14d) - or reduced

load capacity

Слайд 40 Spacing parallel to grain
If fasteners not staggered 1d

Spacing parallel to grainIf fasteners not staggered 1d Eurocode 5 requires

Eurocode 5 requires increased spacing (14d) - or reduced

load capacity
Steel connector plates:
Spacing can be reduced by factor 0.7
Not possible to stagger
Not specified if increased spacing requirement can be reduced by 0.7
Very questionable if staggering is meaningful for small diameters

Слайд 41 Common connection not allowed by EC5
45 mm member

Common connection not allowed by EC545 mm member with connecter-plates on

with connecter-plates on both sides
Eurocode requires 4d from

point to opposite site Minimum member thickens for d = 4 mm: (4 + 8)d = 48 mm
Danish code requires only 3d from point to opposite site

Слайд 42 Conclusions 1
Initial Type Testing (ITT) is necessary for

Conclusions 1Initial Type Testing (ITT) is necessary for most types of

most types of fasteners to establish strength parameters at

all
For types of fasteners covered by Eurocode 5 the strength parameters are mostly - but not always - conservative

Слайд 43 Conclusions 1
Initial Type Testing (ITT) is necessary for

Conclusions 1Initial Type Testing (ITT) is necessary for most types of

most types of fasteners to establish strength parameters at

all
For types of fasteners covered by Eurocode 5 the strength parameters are mostly - but not always - conservative
The dependency on density should in general be similar for nails and screws
Strict rules are needed for correcting measured strength parameters for density
Preferable to carry out tests with a natural span of densities rather than a fixed density

Слайд 44 Conclusions 2
Minimum penetration lengths appears very conservative
Correction for

Conclusions 2Minimum penetration lengths appears very conservativeCorrection for changing moisture content

changing moisture content might be unsafe for withdrawal of

smooth nails but irrelevant for threaded nails and pull-through

Слайд 45 Conclusions 2
Minimum penetration lengths appears very conservative
Correction for

Conclusions 2Minimum penetration lengths appears very conservativeCorrection for changing moisture content

changing moisture content might be unsafe for withdrawal of

smooth nails but irrelevant for threaded nails and pull-through
For screws either embedment strength for diameter of thread or effective diameter should be a declared parameter
Spacing requirement in grain direction unnecessary and unclear for connector plates

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