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EUROCODESBackground and Applications EN1995-1-1: Section 8 - Connections

TIMBER CONNECTIONS

by

Dr. Ad Leijten

TU-EindhovenThe Netherlands

Former PT-member

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EUROCODESBackground and Applications

We can not escape connections

THE WEAKEST LINK

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EUROCODESBackground and Applications EN1995-1-1: Section 8 - Connections

What kind of connections do we use?

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EUROCODESBackground and Applications EN1995-1-1: Section 8 - Connections

Carpenter connections (not in Eurocode 5)

National regulations apply

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EUROCODESBackground and Applications EN1995-1-1: Section 8 - Connections

Carpenter connections compression forces

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EUROCODESBackground and Applications EN1995-1-1: Section 8 - Connections

Glued connections (not in Eurocode 5)

Structural Finger joints Glued in steel rods

National regulations apply

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EUROCODESBackground and Applications

What do we find in Eurocode 5

Section 8: Connections with metal fastenersMechanical connections with

Dowel type fasteners- Nails, staples,- punched metal plates,- screws,- dowels and bolts

Connectors- Shear plates- Split-rings

EN1995-1-1: Section 8 - Connections

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EUROCODESBackground and Applications EN1995-1-1: Section 8 - Connections

Nails < 8 mm (EN14592)definition profiled nails Bolts > 8 mm

Dowels > 6 mm

Screws

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EUROCODESBackground and Applications EN1995-1-1: Section 8 - Connections

Punched metal plate fasteners

Split-ring connectors64- 104 mm diameter

Bolts M12 to M20

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EUROCODESBackground and Applications EN1995-1-1: Section 8 - Connections

Steel to timber

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EUROCODESBackground and Applications EN1995-1-1: Section 8 - Connections

Eurocode 5 allows :

Design by testing:

EN 1075 tests punched metal plates connections

EN 1380 tests nails,screws,dowels,bolted conn.

EN 1381 - tests on stapled connections.

EN 26891 Specimen density selection.

EN 28970 Test procedure for connection tests.

Design by calculation

- Model provided in EN1995-1-1

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EUROCODESBackground and Applications

a 3,t

a 3,c

a 4

, t

a 4

, c

-90 90 90 270 0 180 180 360

(1) (2) (3) (4)

a 2

a 2

a 1a

1

a 1a

1

a 2

a 2

a)

b)

12

Fastener spacing requirementsKey:

(1) Loaded end(2) Unloaded end(3) Loaded edge(4) Unloaded edge

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EUROCODESBackground and Applications

Fastener spacing requirements (bolts)

3 d 180 360 a 4,c (unloaded edge)

max([2 + 2 sin ) d ; 3d )0 180 a 4,t (loaded edge)

max([1 + 6 sin ) d ; 4d )4 d

max([1 + 6 sin ) d ; 4d )

90 < 150

150 < 210

210 270

a 3,c (unloaded end)

max (7 d ; 80 mm)-90 90 a 3,t (loaded end)

4 d 0 360 a2

(perpendicular to grain)

(4 + cos ) d 0 360 a 1 (parallel to grain)

Minimum spacing ordistance

AngleSpacing and end/edgedistances

(see Figure 8.7)

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EUROCODESBackground and Applications EN1995-1-1: Section 8 - Connections

Spacing requirements determine timber dimensionsa1

a2

Decrease memberwidth ?

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EUROCODESBackground and Applications EN1995-1-1: Section 8 - Connections

Spacing requirements determine timber dimensions

a12 2a1 a 2

a 2

0 1( ) ( ) 1 with

0 1

+

k k k

k

k a2a2

k a1a1

k a1

a 1

k a 2

a 2

a2Only for connectorsSplit-rings andshear plates

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EUROCODESBackground and Applications EN1995-1-1: Section 8 - Connections

The strength capacity model for

laterally loaded dowel-type-fasteners

(based on Johansen (1949)

Background:

-Structural Education Timber Program (STEP 1)(1994)

-Timber Engineering; Thelandersson & Larsen (2003) ISBN 0-470-84469-8

Laterally loaded axially loaded

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EUROCODESBackground and Applications EN1995-1-1: Section 8 - Connections

single shear

fasteners

multiple shear

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EUROCODESBackground and Applications EN1995-1-1: Section 8 - Connections

Double shear

Embedmentstresses

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EUROCODESBackground and Applications EN1995-1-1: Section 8 - Connections

Embedment = f emb f f embemb

displacementdisplacement

Starting point for strength model - Embedment strength

Idealised f emb= f v

embedment

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EUROCODESBackground and Applications EN1995-1-1: Section 8 - Connections

Determination of embedment strength EN 383

Eurocode 5 Design clause embedment strength

Nails (not pre-drilled)

Nails pre-drilled

Bolts/dowels

2-0,3h,k k 0,082 N/mm f d =

2h,k k 0,082 (1- 0,01 ) N/mm d f =

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EUROCODESBackground and Applications EN1995-1-1: Section 8 - Connections

Taken from Sawata and Yasumura (2002).

Background: Whale L. and Smith, I. The derivation of design clauses for nailed and bolted joint in Eurocode5, In Proceedings of paper CIB-W18 paper 19-7-6/ Florenze 1986

Yasumura, M. and Sawata, K., Determination of embedment strength of wood for dowel-type-fasteners. In:Journal of Wood Science, nr. 48, 2002, Japan Wood Research Society, Inst. Of Wood Techn, Akita, Japan

Parallel Perpendicular

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EUROCODESBackground and Applications EN1995-1-1: Section 8 - Connections

Dowels Parallel All wood species

0,0

20,0

40,0

60,0

80,0

100,0

120,0

200 400 600 800 1000 1200

Density

E m

b e

d m

e n

t

5mm data

7mm data

8mm data

12mm data

16mm data

20mm data

30mm data

Embedment test - parallel to grain

Background: Leijten, A.J.M. & Khler, J.& A Jorissen, Review of Probability Data for Timber Connections

with Dowel-Type Fasteners; In Proceedings of CIB-W18, paper 37-7-12, Edinburgh, UK, September 2004

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EUROCODESBackground and Applications

Re-evaluation parallel to grain embedment results

for future consideration in EC5?

Nails (pre-drilled)

Coniferous

Bolts and dowels

Coniferous

Decideous

EN1995-1-1: Section 8 - Connections

1,07 0,25;0

;90

0,097

?

h

h

f d

f

=

=

1,35 0,27;0

1,48 0,42;90

0,0104

0,046

h

h

f d

f d

=

=

1,09 0,25;0

1,13 0,46

;90

0,087

0,106

h

h

f d

f d

=

=

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EUROCODESBackground and Applications EN1995-1-1: Section 8 - Connections

Embedment - perpendicular to grain

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EUROCODESBackground and Applications EN1995-1-1: Section 8 - Connections

Embedment at angle to grain

h,0,k h, ,k

90 sin cos 2 2 f

= f +k

h,0,k k 0,082 (1- 0,01 ) = d f Bolts/dowel:

901,35 0,015 for softwoods

0,90 0,015 for hardwoods

d k

d

+=

+

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EUROCODESBackground and Applications EN1995-1-1: Section 8 - Connections

Coniferous: Embedment test - perpendicular to grainEmbedding strength, based on average values embedding tests

(European Whitewood (EW), European Redwood (ER), Canadian Spruce Pine Fir (CS))

0

5

10

15

20

25

30

35

40

0 5 10 15 20

Nail or Bolt diameter [mm]

f h ; 9 0

( E m

b e

d d i n g s

t r e n g

t h ) [ N / m m

2 ]

Nails ERNails EWNails CSBolts ERBolts EWBolts CSEurocode 5Power (All)Power (Eurocode 5)

BoltsNails

Eurocode 5

Needs adjustment in future EC5

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EUROCODESBackground and Applications EN1995-1-1: Section 8 - Connections

Some failure modes ofsingle shear fasteners

Some failure modes ofdouble shear fasteners

Mode I Mode II Mode III

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EUROCODESBackground and Applications EN1995-1-1: Section 8 - Connections

Equations for every failure mode

Fasteners in single shear

h,1,k 1

h,2,k 2

2 2

h,1,k 1 2 32 2 2 2

1 1 1 1

y,Rk h,1,k 1 ax,Rk v,Rk

2h,1,k 1

h,1,k 2

(a)

(b)

2 1 1 (c)1

4 (2 )min 1, 05 2 (1 ) (d)2 4

1, 051 2

+ + + + + +

+ = + + + +

+

f t d

f t d

f t d t t t t

t t t t

M f t d F F f d t

f t d y,Rk ax,Rk 22

h,1,k 2

ax,Rk y,Rk h,1,k

4 (1 2 )2 (1 ) (e)

4

21,15 2 (f)

1 4

+ + + +

+

+

M F

f d t

F M f d

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EUROCODESBackground and Applications EN1995-1-1: Section 8 - Connections

Equations for every failure mode

Fasteners in double shear

h,1,k 1

h,2,k 2

y,Rk h,1,k 1 ax,Rk v,Rk 2

h,1,k 1

ax,Rk y,Rk h,1,k

(g)

0,5 (h)

4 (2 )min 1,05 2 (1 ) (j)2 4

21,15 2 (k)

1 4

+= + + + +

+ +

f t d

f t d

M f t d F F f d t

F M f d

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EUROCODESBackground and Applications EN1995-1-1: Section 8 - Connections

Some failure modes ofsingle shear fastenerssteel to woodconnections

thick steel plate t > d = fastener diameter

thin steel plate t < 0,5d

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EUROCODESBackground and Applications

Test results still higher than Johansen equations

Cord effect:Only valid forMode II and III

Requires knowledge about withdrawalTheory for nails 15% extra

Background: Kuipers, J. Van der Put, T.A.C.M., Betrachtungen zum Bruchmechanismus von Nagel verbindungen,In: Ingenieuholzbau in Forschung und Praxis, J. Ehlebeck and G. Steck, editors, Bruderverlag Karlsruhe 1982

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EUROCODESBackground and Applications

Test results still higher than Johansen equations

Cord effect:Fax /4 = withdrawal capacity/4 = estimated effect

% are estimates

MaximumNails 15%Grooved nails 50%Screws 100%Bolts 25%Dowels 0%

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EUROCODESBackground and Applications EN1995-1-1: Section 8 - Connections

Fasteners in double shear

h,1,k 1

h,2,k 2

y,Rk h,1,k 1 ax,Rk v,Rk 2

h,1,k 1

ax,Rk y,Rk h,1,k

(g)

0,5 (h)

4 (2 )min 1,05 2 (1 ) (j)

2 4

21,15 2 (k)

1 4

+= + + +

+

+ +

f t d

f t d

M f t d F F

f d t

F M f d

Test results still higher than Johansen equations

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EUROCODESBackground and Applications EN1995-1-1: Section 8 - Connections

theory

k k m

k d F F yk

F F === 69,03,19,0modDesign value

M s = yield bending moment steel fastener

Partial material factor of timber mapplied to M s !!

Better seperate:

Mode III

schroef ,hs d f M F +

= 1212

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EUROCODESBackground and Applications EN1995-1-1: Section 8 - Connections

Fasteners in double shear

h,1,k 1

h,2,k 2

y,Rk h,1,k 1 ax,Rk v,Rk 2

h,1,k 1

ax,Rk y,Rk h,1,k

(g)

0,5 (h)

4 (2 )min 1,05 2 (1 ) (j)

2 4

21,15 2 (k)

1 4

+= + + +

+

+ +

f t d

f t d

M f t d F F

f d t

F M f d

Eurocode 5 equations

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EUROCODESBackground and Applications EN1995-1-1: Section 8 - Connections

Failure of multiple of fasteners in a row

Splitting

Shear

Tensile

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EUROCODESBackground and Applications EN1995-1-1: Section 8 - Connections

Failure of multiple of fasteners in a rowCaused by group effect

Only for load component in grain direction

13d

Cumulatieve

stress

Stress

EUROCODES

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EUROCODESBackground and Applications EN1995-1-1: Section 8 - Connections

Failure of multiple of fasteners in one row

Caused by group effect effective number

Nails:Empirical (Gehri)

Bolts & dowels:Fracture mechanics

Background:Double shear timber connections with dowel type fasteners, A.J.M. Jorissen, ISBN 90-407-1783-4, DUP Delft,1998

4 090

13d a

nn ,

ef =

ef

ef

k

nn =

a For intermediate spacings, linear

interpolation of k ef is permitted

0,5- a 1 = 4 d

0,70,7 a 1 = 7 d

0,850,85 a 1 = 10 d

1,01,0 a 1 14 d

PredrilledNotpredrilled

kef Spacing

a

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EUROCODES EN1995 1 1 S ti 8 C ti

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EUROCODESBackground and Applications EN1995-1-1: Section 8 - Connections

Failure at fastener perimeter (Prof.Racher, Fr.)

Block shear:Full penetration

Plug shearPartial penetration

Tensile or shear failure, which happens first?Literature: Johnson, H, Stehn, L, A Linear Fracture Mecanics Evaluation of Plug Shear Failure,In Proc of 8th

world conf on Timber Engineering WCTE 2004, Finland

EUROCODES EN1995 1 1: Section 8 Connections

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EUROCODESBackground and Applications EN1995-1-1: Section 8 - Connections

t,1

t,2

v,1

v,2

v,3

v,4

v,5

v,6

v,7

v,8

1

2

net,t t,o,k bs,Rk

net,v v,k

1,5max

0,7=

A f F

A f

t e f

Fasteners keepstraight

Not correct inEC5

see previoussheet

Tensile failure

Shear fracture

Correlationparameters

EUROCODES EN1995 1 1: Section 8 Connections

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EUROCODESBackground and Applications EN1995-1-1: Section 8 - Connections

Amendment A1:Contains:

New design rules for:

compressive strength perpendiculer to grainPresent rules unsafe1

3l

lef

EUROCODES EN1995 1 1: Section 8 Connections

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Background and Applications EN1995-1-1: Section 8 - Connections

Amendment A1

AdditionAxially loaded screws

Traditional screws

Diameter thread=smooth shankNot very effective

not hardenedlow bending moment>8mm requires predrilled holes

EUROCODES EN1995-1-1: Section 8 - Connections

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Background and Applications EN1995-1-1: Section 8 - Connections

Amendment A1

AdditionAxially loaded screws

Very effectivehardenedself tappinghigh axial stiffness

Background:Bla, HJ; Bejtka, I: Self-tapping screws as reinforcements in connections with dowel-type fasteners. In:Proceedings. CIB-W18 Meeting, Karlsruhe, Germany 2005. Paper 38-7-4Blass H.J. Joints with dowel-type-fasteners, In: Timber Engineering Thelanderson and Larsen, editors, Wiley &Sons (2003):

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EUROCODESBackground and Applications EN1995-1-1: Section 8 - Connections

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Background and Applications EN1995 1 1: Section 8 Connections

Some examples

Leg or coach screw

EUROCODESBackground and Applications EN1995-1-1: Section 8 - Connections

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Background and Applications EN1995 1 1: Section 8 Connections

Some examples

Spax-S

Heco Topix/Fix

Rapid Komprex

EUROCODESBackground and Applications EN1995-1-1: Section 8 - Connections

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g pp

Tecfi Woodpecker

BMF Torx

SFS WT

EUROCODESBackground and Applications EN1995-1-1: Section 8 - Connections

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Check:- Withdrawal failure

- Tear-off failure of the head

- Pull through of the head

- Tensile failure of the screw

- Torsional capacity

- Group effect (n eff number of effective fasteners )

EUROCODESBackground and Applications EN1995-1-1: Section 8 - Connections

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-Withdrawal: Code proposals in EU countries

( ) aald Rk

ef k aax 22

5,138,0

,, cos5,1sin106,3

+

=

ef k

k ax ld aa

R +

=

2342

26

;

cossin

1060

( ) ( ) += nomhecnomk ax d ld R 6,05,1,

Eurocode 5 = (1)

( )aa

ld R k ef k ax 223

8,01, cos5,1sin

100,37,1

+

=

(1)

(2)

(3)

(4)

EUROCODESBackground and Applications EN1995-1-1: Section 8 - Connections

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Model uncertainty evaluation of test results

0

5

10

15

20

25

-1 -0,8 -0,6 -0,4 -0,2 0 0,2 0,4 0,6 0,8 1

ln(model/meetpunt)

F r e q u

e n

t i e . .

Eurocode 5

Current EC5 design rule unsafe

(1) (4) (2) (3)

EUROCODESBackground and Applications EN1995-1-1: Section 8 - Connections

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New proposal in Amendment A1:

RequirementScrews as defined in EN 14592

6 mm d 12 mm

All other screws:

Parameters determined by tests EN14592 (EN 1382)

80

22 21

,

a

k ef axef k ,a ,ax

acos ,asin

l.d . f n R

+=

acos ,asin

l.d ,n R

,k

,ef

ef k ,a ,ax 22

8090

21

520

+

=

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EUROCODESBackground and Applications EN1995-1-1: Section 8 - Connections

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Head pull throughEN 14592

Test standard EN 1383

axax f A R =

( ) ( ) k csk k f d d R ,90,2

212

21 0,3- =

Eurocode 5:

20,16 k k d N =Zulassung Germany 9.1-235:

In the absents of information Clause 8.5.2. bolt washers

EUROCODESBackground and Applications EN1995-1-1: Section 8 - Connections

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short elastisch behaviourLarge non-elastic traject

EUROCODESBackground and Applications EN1995-1-1: Section 8 - Connections

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Model uncertainty design rule 9.1-235andn Eurocode 5 for screwswith washers

0

1

2

3

4

5

6

7

8

9

-1 -0,5 0 0,5 1 1,5

ln (model/meetwaarde)

F r e q

u e n

t i e

Eurocode 5Zulassung

EUROCODESBackground and Applications EN1995-1-1: Section 8 - Connections

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- Group (tear out) effect:Due to a lack of background information

Based on test by Gehri (empirical):0,9

ef =n n

EUROCODESBackground and Applications EN1995-1-1: Section 8 - Connections

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Splitting by perpendicular to grain forces

F Ed

F v,Ed,1 F v,Ed,2

h e h

b

b b /2b /2

a) b)

Background: Leijten A.J.M. & Vander Put T.A.C.M, Evaluation of Perpendicular to Grain Failure of Beamscaused by Concentrated Loads of Joints, In: Proceedings of CIB-W18, paper 33-7-7, Delft, 2000.

Design clause 8.1.4 (3) is formulated as a maximumshear force criterion on either side of the connection

EUROCODESBackground and Applications EN1995-1-1: Section 8 - Connections

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Splitting by perpendicular to grain forces

0,35

pl

max for punched metalplate fasteners1001

1 for all other fasteners

w

w

=

e90,Rk

e14

1=

hF b w h

h

Fracture mechanics background

14 is calibration parameter

w = (political factor)

Design clause 8.1.4 (3) isformulated as a maximum shearforce criterion on either side ofthe connection

EUROCODESBackground and Applications EN1995-1-1: Section 8 - Connections

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Splitting by perpendicular to grain forces

Some empirical models considerFastener spacing

=

=

+=

+=

n

i i

r

s

.

hh

nk

ha.

.maxk

f )ht (ha

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Splitting by perpendicular to grain forces

Fracture mechanicalmodel

Consider energybalance after crackappearance

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Splitting by perpendicular to grain forces

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Punched metal plate fasteners

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Comparison between models

Eurocode 5

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Research in progressFuture changes and additions are

expected