DowelleD connections - Metsä Wood...2 kerTo manual dowelled connecTions aPril 2013 thi nstructio ropert Mets wood. th nstructio a ee repare n cooperatio it Vtt exper service ltd

DowelleD connections

Table of conTenTs

1 General .......................................................................................................22 Material properties ...................................................................................23 Loading .......................................................................................................44 Laterally loaded dowels ...........................................................................4 4.1 Timber-to-timber connections .......................................................5 4.2 Panel-to-timber connections .........................................................5 4.3 Steel-to-timber connections ..........................................................6 4.4 Effective number of fasteners ........................................................65 Multiple shear plane connections ..........................................................76 Block shear failure ....................................................................................8 6.1 Timber failure capacity of joint area ..............................................8 6.1.1 Capacity of inner part lamellas ............................................8 6.1.2 Capacity of the edge part of lamellas.................................9 6.2 Connection forces at an angle to the grain ................................10 6.3 Alternative dimensioning method ................................................117 Steel plates...............................................................................................12 7.1 Tension strength ..............................................................................12 7.2 Embedment strength .....................................................................12 7.3 Block tearing ....................................................................................128 Fastener spacings and edge and end distances ...............................139 Allowed tolerances of dowelled connections .................................... 1710 Bibliography ............................................................................................. 17Endnotes .............................................................................................................. 17

2 Kerto manual DowelleD connectionsaPril 2013

This instruction is property of Metsä Wood.The instruction has been prepared in cooperation with VTT Expert Services Ltd.

DowelleD connections

2. Material properties

The calculation method for steel dowels presented in this guide is valid only for dowels with diameter d ≤ 24 mm and ultimate tensile strength fu,k ≤ 800 N/mm2 (class 8.8). In addition, the timber thick-ness of side members t1 and t2 should be at least 4d ja and in dual or multi shear plane connections the timber thickness of inner members ts should be at least 5d.

In this guide timber means solid timber, glued laminated timber, Kerto-S and Kerto-T. Due to its cross-veneers, Kerto-Q has better splitting resistance when compared to other timber when used in flatwise connections.

Wood-based panels should be CE-marked in accordance with EN 13986 (plywood, particleboard, OSB-board, medium fibreboard and hard fibreboard) or they should have a local type approval or statement/certificate from an institution approved by local building authorities that covers their use as load-bearing structures.

1. General

The dowel diameter should be greater than 6 mm and less than 30 mm.1 Dowel holes D in timber members should have a diameter of 0.95d ≤ D ≤ d. If the end of the dowel is left inside the timber and the holes are not drilled through then the drill depth tolerance is -0 / +5 mm. The end of the dowel can be bevelled to make installation easier. The bevel is usually 2 mm. Allowed tolerances are shown in Table 6.

Dowel holes in steel plates should have a diameter no more than 1 mm or 1.1d (whichever is greater). Steel plates can be drilled with 2 mm bigger holes than the dowel if:

t1 and t2

where: the connection uses the thin steel plate (tt ≤ 0.5d) equations

t1 and t2 are the thicknesses of outer timber members

ts is the thickness of the inner member in double shear connection

My is the characteristic fastener yield moment, equation (5)

d is the fastener diameter, in mm

fh,k is the characteristic embedment strength in the timber member, equation (4)

Tie bolts should be used in dowelled connections. The amount of tie bolts should be at least one tenth of the amount of dowels in the connection. At least one tie bolt should be installed in the closest row to the end of the side member. Tie bolts may be used for lateral loads if they are unthreaded within the connection area and they have the same diameter and grade as the dowels.

After assembly the timber in the connection should not dry by over 5 % of it’s weight.

In practice we recommend using 2 mm shorter dowels than the total thickness of the members in the connection. This shortening should be taken into account in the design.

Parts that are according to the Finnish national annex are marked with green text or they are given in the endnote. these rules may not apply outside Finland. the equations by Ril 205-1-2009 are generalized from the eurocode and are on the safe side. Additional general information about connections is also collected from several sources.

dfM

h

y

⋅⋅≥ 2

dfM

th

ys ⋅

⋅≥ 4



table 1: strength modification factors for service classes and load-duration classes kmod and partial factors γM for material properties and resistances.2

sTrengTh modificaTion facTors for service classes and load-duraTion classes kmod

load-duraTion class

maTerial service class PermanenT acTion long Term acTion medium Term acTion

shorT Term acTion insTanTaneous acTion

Solid timber, round timber, glued laminated timber, Kerto lVl, plywood

123

0.600.600.50

0.700.700.55

0.800.800.65

0.900.900.70

1.101.100.90

Particleboard EN 312-4* and -5, OSB/2*, Hard fibreboard

12

0.300.20

0.450.30

0.650.45

0.850.60

1.100.80

Particleboard EN 312-6* and -7, OSB/3, OSB/4

12

0.400.30

0.500.40

0.700.22

0.900.70

1.100.90

Medium fibreboard: MBH.LA*, MBH.HLS, MDF.LA* and MDF.HLS

12

0.20-

0.40-

0.60-

0.800.45

1.100.80

Partial factors γM (EN 1995 recommended values and the Finnish NA values)

Fundamental combinations:Solid and Round timber in generalSoftwood structural timber, strength class ≥ C35Kerto lVlGlued laminated timberPlywood, OSBParticle- and fibreboardsConnections

Accidental combination

1.301.301.201.251.201.301.301.00

1.401.251.201.201.251.25according to timber material1.00

* Can only be used in service class 1

table 2: in en 1993-1-1, en 1993-1-2 and en 1993-1-8 the following partial factors are used according to en 1993 recommended values and fi na for structural members, cross sections and connections

marking value (en 1993) value fi: na

γM0 1.00 1.00

γM1 1.00 1.00

γM2 1.25 1.25

γM3 1.25 1.25

γM3,ser 1.10 1.10

γM4 1.00 1.00

γM5 1.00 1.00

γM6,ser 1.00 1.00

γM7 1.10 1.10

γM,fi 1.00 1.00

service class

fasTener 1 2 3

Dowels None None Fe/Zn 25c, Z350

Steel plates up to 3 mm thickness Fe/Zn 12c, Z275 Fe/Zn 12c, Z275 Stainless steel

Steel plates from 3 mm up to 5 mm in thickness None Fe/Zn 12c, Z275 Fe/Zn 25c, Z350

Steel plates over 5 mm thickness None None Fe/Zn 25c, Z350

table 3: The minimum specifications for material protection against corrosion for fasteners. electroplated zinc coating fe/Zn classes are according to iso 2081 and hot-dip coating Z classes according to en 10346.3 stainless steel according to en 10088-1 (grades 1.4401, 1.4301 and 1.4310).4

Steel plates need to be predrilled structural steel.

Dowelled connections can be done by through drilling the holes to timber members and pre-set steel plates. The design of this kind of connection is not covered in this guide.

Dowels and steel plates should, where necessary, either be inherently corrosion-resistant or be protected against corrosion.



3. loadinG

Dowels can be loaded only laterally. Reductions in cross section should be taken into account when analysing capacity of timber members.

In compressed Kerto-to-Kerto joints, 2/3 of the perpendicular compression force can be transferred directly through contact from member to member. If the contact surfaces have been CNC-machined, 3/4 of the perpendicular compression force can be trans-ferred directly through contact from member to member. Splitting of the compressed side in sloped connections, such as ridge connections, should be prevented by shaping the end of the member or installing a hard fibreboard or steel plate with a height of about 3/4 of the total height of the connection.

4. laterally loaded dowels

Figure 1: laterally loaded connection

When calculating the lateral load-capacity of the connection, the capacity of fasteners and block shear in the timber member should be checked. See Figure 1.

The design capacity of connection:

M

kd

RkR

γ

⋅= mod (1)5

where: kmod is the modification factor for duration of load and moisture content

γM is the partial factor for connection resistance

When connecting two different materials the smallest value of kmod / γM should be used.



⎪⎪⎩

⎪⎪⎨

⎧

+

+

+

+

=

hardwoodsfor 015.090.0softwoodfor 015.035.1

Q-Kertofor 015.015.1T-Kerto and S-Kertofor 015.030.1

90

dddd

k

⎪⎩

⎪⎨⎧

≤−= sconnection edgewisefor 87.02

1sconnection flatwisefor 1

dkQ

⎩⎨⎧

−⋅⋅

⋅−⋅=

Q-Kertofor )01.01(37generalIn )01.01(082.0

,0, dkd

fQ

kkh

ρ

kpanelhpanel f

dt

,,

80 ⋅≥

(5)9

(6)10

(9)13

(10)15

fh,k = min ( fh.1,k ; fh,2,k ; fh,s,k )

t1 and t2 are the timber thicknesses or penetration depths of outer member

fh.1,k ja fh,2,k are the characteristic embedment strengths of

outer timber members

fh,s,k is the characteristic embedment strength of inner

timber member in a two shear plane connection

d is the fastener diameter

The characteristic value for the yield moment:

My = 0.3 . fu,k . d 2.6 [Nmm]

where: fu,k is the characteristic tensile strength, in N/mm2 d is the fastener diameter, in mm

The characteristic embedment strength, at an angle α to the grain:

(3)7

(4)8

where:

[N/mm2]

for Kerto-Q fh,a,k = fh,45 ,k when 45° ≤ α ≤ 90° 14 ρk is the characteristic timber density, in kg/m3d is the fastener diameter, in mmα is the angle of the load to the grain

4.2 Panel-To-Timber connecTions

When the thickness of a wood based panel is larger than the limit set out in equation (10), then the characteristic loading capacity of panel-to-timber connections should be calculated with the equations for timber-to-timber connections.

where: f h,panel,k is the characteristic embedment strength of

panel, in N/mm2


For plywood the following embedment strength should be used for all angles to face grain:

f h,panel,k = 0.11 . (1–0.01d) . ρk [N/mm2]

where: ρk is the characteristic density of plywood, in kg/m3


For particleboard and OSB the following embedment strength should be used for all loading directions:

f h,k = 50 . d -0.6 . t 0.2 [N/mm2]

where: d is the fastener diameter, in mm

t is the panel thickness, in mm

(11)16

[mm]

where:

⎪⎪

⎩

⎪⎪

⎨

⎧

⋅

⋅

=

kh

kh

kh

kh

u

fft

fft

t

,

,2,2

,

,1,1

min

4.1 Timber-To-Timber connecTions

The characteristic load-carrying capacity for a fastener per shear plane:

⎪⎪⎩

⎪⎪⎨

⎧

⋅⋅⋅

⋅⋅

⋅+⋅⋅⋅⋅

=

dfM

tdf

Mdtf

R

khy

ukh

yukh

k

,

2,

,

6.1

3132.0

min (2)6

ααα 2290

,0,,, cossin +⋅=k

ff kh

kh [N/mm2]

(7)11

(8)12

(12)17

[–]

[–]



4.3 sTeel-To-Timber connecTions

The capacity of steel plate should be checked according to EN 1993.

In compressed steel plate connections the buckling length of 0.8La can generally be used for outside plates, where La is the distance between the first fasteners at opposite sides of the connection. The buckling does not need to be taken into account for steel plates instal-led inside a timber member if the expansion of timber members is prevented, for example, by using tie bolts and limiting the size of the slot for the steel plate to maximum of 1.25tt.

The drying shrinkage perpendicular to the grain direction should be taken into account with steel-to-timber connections.

It should also be taken into account that the load-carrying capacity of steel-to-timber connections with a loaded end may be reduced by failure along the perimeter of the fastener group. There are two types of loaded end failures: block shear and plug shear failure.

The characteristic load-carrying capacity for a thin steel plate, with tt ≤ 0.5d, in single shear:

The characteristic load-carrying capacity for a thick steel plate, with tt ≥ d, in single shear:

where: fh,k is the characteristic embedment strength of the timber member, equation (4) t is the thickness of the timber member d is the fastener diameter My is the characteristic fastener yield moment, equation (5)

The characteristic load-carrying capacity of connections with steel plate thickness between a thin and thick plate, where 0.5d < tt < d, should be calculated by linear interpolation between equations (13) and (14).

The characteristic load-carrying capacity for a steel plate of any thickness as the central member of a double shear connection should be calculated with equation (14) where t is the smaller thickness of the timber side member.

(13)18

(14)19

The characteristic load-carrying capacity for steel plates as the outer member of double shear connection:

(15)20

4.4 effecTive number of fasTeners

For one row of n fasteners parallel to the grain direction, the load-carrying capacity parallel to the grain should be calculated using the effective number of fasteners nef :

where: ni is the number of fasteners in the row i d is the fastener diameter

a1 is the spacing of fasteners in the direction of the grain a3 is the end distance of fasteners

t1 and t2 are the thicknesses of outer timber members, these should be discarded if the outer member is not timber

ts is the thickness of the inner member of double shear connection or the smallest thickness of an inner member of a multiple shear connection

(16)21

(17)22

(18)23

⎪⎩

⎪⎨⎧

⋅⋅⋅

⋅⋅⋅=

dfM

dtfR

khy

khk

,

,

6.1

32.0min

⎪⎪⎪

⎩

⎪⎪⎪

⎨

⎧

⋅⋅⋅

⎥⎥

⎦

⎤

⎢⎢

⎣

⎡−

⋅⋅

⋅+⋅⋅⋅⋅

⋅⋅⋅

=

dfM

tdf

Mdtf

dtf

R

khy

kh

ykh

kh

k

,

2,

,

,

4.2

14

204.1

8.0

min

⎪⎪⎪

⎩

⎪⎪⎪

⎨

⎧

<<⋅⋅⋅⎟⎠

⎞⎜⎝

⎛+⋅

≥⋅⋅⋅

≤⋅⋅⋅

⋅⋅⋅

=

dtddfMdt

dtdfMdtdfM

dtf

R

tkhyt

tkhy

tkhy

kh

k

5.0for 15.0

8.0

for 4.2

5.0for 6.14.0

min

,

,

,

,

⎪⎩

⎪⎨

⎧

⋅

⋅=4

29.0

50

min

dta

n

nn

i

i

ef

⎩⎨⎧

=

≥=

1 when ,2 when ,);min(

3

31

i

i

nanaa

a

connectionshear multiple and other twomembersouter in only er with timbconnection

);2;2min();min(

21

21

⎩⎨⎧

=sttt

ttt



5. Multiple shear plane connections

In multiple shear plane connections the resistance of each shear plane should be determined by assuming that each shear plane is part of a series of three-member connections. The total capacity of multiple shear connections is obtained by multiplying the smallest per shear capacity by the number of shear planes, see Figure 2.

tu ts tu tu tu ts ts tu tu

Rv,d = 2R1,d Rv,d = 4 min{R1,d; R2,d} Rv,d = 6 min{R1,d; R2,d; R3,d} }

Figure 2: calculating the connection capacity of a multiple shear plane steel plate connection. R1,d is the capacity per shear of a two shear plane timber-steel-timber (tu-steel-tu ) connection, R2,d is the capacity per shear of a two shear plane steel-timber-steel (tu-ts-tu ) connection and R3,d represents the capacity per shear of a two shear plane timber-steel-timber (ts-steel-ts ) connection. 24



⎪⎪⎪

⎩

⎪⎪⎪

⎨

⎧

=

timberlaminated gluefor 7.0T-Kerto flatwisefor 7.0Q-Kerto flatwisefor 0.1

Q-Kerto edgewisefor 7.0S-Kertofor 7.0

vk

( ) ( )( ) iefipv taannA ,3112, 112 ⋅+⋅−⋅−⋅=

( ) ( ) iipt tdanA ⋅−⋅−= 22, 1

kvipvvkv fAnkF ,,1.0

1, ⋅⋅⋅= −

timberlaminated gluedfor LVL-Kertofor

0.27.1

,0,,1.0

1

,0,,1.0

1,

⎪⎩

⎪⎨⎧

⋅⋅⋅

⋅⋅⋅= −

−

ktipt

ktiptkt fAn

fAnF

⎪⎪

⎩

⎪⎪

⎨

⎧

>⎟⎟⎠

⎞⎜⎜⎝

⎛⋅−

≤⎟⎟⎠

⎞⎜⎜⎝

⎛⋅−

=

kvktkt

kvkv

kvktkv

ktkt

ktv

FFFF

F

FFFF

F

F

,,,

,,

,,,

,,

,

when,3.01

when,3.01

∑=

=m

iRkiRk FF

1,0,,0where:

where Fi,0,Rk is the timber failure capacity for lamella i of the timber member calculated according to equation (21) and m is the number of joint lamellas in the timber member.

Timber failure capacity for the lamella i should be takes as:

6.1.1 caPaciTy of inner ParT lamellas

The capacity of inner part lamellas:

RkM

RdEd Fk

FF ,0mod

,0,0 γ=≤

6. Block shear failure

6.1 Timber failure caPaciTy of joinT area

The effective number of fasteners is taken into account in the following equations. This method can be used for Kerto-S, Kerto-Q, Kerto-T used flatwise and glued laminated timber.

To take into account the possibility of splitting or shear or tension failure of the joint caused by the force component parallel to grain F0,Ed the following expression should be satisfied:

(19)25

(20)26

khf ,0,

( ) iiph tdnnA ⋅⋅−= 1,

( ) khiefkvkcv ftdnFF ,0,,2,, 1 ⋅⋅⋅−+=

where: is the embedment strength of timber parallel to grain

for Kerto-LVL

for glued lami-nated timber

(21)27

(22)28

(23)29

(24)30

(25)31

(26)32

(27)33

(28)34

n is the number of fastenersn1 is the mean number of fasteners in the rows parallel to grain (n1=n/n2)d is the fastener diameterti is the lamella thickness ≤ penetration of the fastener

n2 is the maximum number of fasteners in the fastener rows perpendicular to grain

fy is the yield strength of the fastener

a1 is the fastener spacing parallel to the grain

a2 is the fastener spacing perpendicular to the grain

a3 is the fastener end distance

(29)35

(30)36

(31)37

RkepRkipRki FFF ,,,0, +=

( )( )⎩

⎨⎧

⋅

⋅=

jointsn compressioin ;minjoints in tension;min

,,0,,

,,0,,,

kcvkhiph

ktvkhiphRkip FfA

FfAF

ft,0,k is the tension strength of the timber member

f v,0,k is the shear strength of the timber member

⎪⎪

⎩

⎪⎪

⎨

⎧

≤⋅⋅

≤⋅⋅

=

lamellas middlefor 63.1

lamellas sidefor 68.0

,0,

,0,,

ikh

y

ikh

y

ief

tff

d

tff

dt

The characteristic timber failure capacity of the joint area:

35 N/mm2 for Kerto-S

19 N/mm2 for Kerto-Q (thickness 21-24 mm)

26 N/mm2 for Kerto-Q (thickness 27-69 mm)

24 N/mm2 for Kerto-T

fv,0,edge,k 4.1 N/mm2 for flatwise Kerto-S connections

fv,0,flat,k 2.3 N/mm2 for edgewise Kerto-S connections

fv,0,edge,k 4.5 N/mm2 for flatwise Kerto-Q connections

fv,0,flat,k 1.3 N/mm2 for edgewise Kerto-Q connections

fv,0,edge,k 2.4 N/mm2 for flatwise Kerto-T connections



⎪⎩

⎪⎨

⎧

=

4

365.0

1max

aashole

⎟⎟⎠

⎞⎜⎜⎝

⎛−

=

4.1cosh

7.2

4

3

aa

send

( ) ktiefend

kse fdatsn

F ,90,3,

9.01

, 5.014

⋅−⋅⋅=

( ) ktiefhole

ks fdatsn

F ,90,3,

9.01

, 5.014

⋅−⋅⋅=

( )( ) iefepv taanA ,311, 12 ⋅+⋅−⋅=

⎪⎪

⎩

⎪⎪

⎨

⎧

≤⎟⎟⎠

⎞⎜⎜⎝

⎛−⋅

≤⎟⎟⎠

⎞⎜⎜⎝

⎛−⋅

=

kskvks

kvkv

kvkskv

ksks

ksv

FFFF

F

FFFF

FF

,,,

,,

,,,

,,

,

when 3.01

when 3.01

Figure 3: definition of symbols for the inner parts of lamellas38

The capacity of the edge part of lamellas:

where:

( )( )⎪⎩

⎪⎨⎧

⋅

⋅=

aliitoksiss ssapuristetui ,;min

aliitoksiss ä vedetyiss,;;;min

,,0,,

,,,,0,,,

kcvkheph

kseksvktvkhephRkep FfA

FFFfAF (32)39

ieph tdnA ⋅⋅= 1,

khiefkvkcv ftdFF ,0,,,, ⋅⋅+=

and Ftv,k is calculated according to equations (25) - (27) with substitutions from equation (36):

(33)40

(34)41

(35)42

(36)43

(37)44

(38)45

epteptipt AkA ,,, ⋅= epvipv AA ,, =

( ) iept tdaA ⋅−= 4, 2

epv

eptept

AAk

,

,,

1

1

+=

a4 is the fastener edge distance

(39)46

(40)47

The splitting capacities:

in tension joints

(41)48

(42)49

(43)50

in compression joints

and

where:

6.1.2 caPaciTy of The edge ParT of lamellas

where: ft,90,k is the tension strength of timber member

0.8 N/mm2 for flatwise Kerto-S connections

0.4 N/mm2 for edgewise Kerto-S connections

6.0 N/mm2 for flatwise Kerto-Q connections

0.4 N/mm2 for edgewise Kerto-Q connections

0.5 N/mm2 for flatwise Kerto-T connections



(44)52

where: F90,d is the design splitting capacity

(45)53

Figure 4: definition of symbols for the edge parts of lamellas51

6.2 connecTion forces aT an angle To The grain

When a force in a connection acts at an angle to the grain, see Figure 5, the possibility of splitting caused by the tension force component, (FEd . sin α), perpendicular to grain, shall be taken into account.

For solid timber, glued laminated timber, Kerto-S, Kerto-T and Kerto-Q edgewise, the following expressions shall be satisfied:

are the design shear forces on either side of the connection caused by the connection force component (FEd . sin α) perpendicular to the grain

Figure 5: connection forces at the angle of grain 54

dEdv FF ,90, ≤

( )2,1,, ;max EdvEdvEdv FFF =

1,EdvF 2,EdvF and

For softwood, the characteristic splitting capacity:

where: he is the loaded edge distance to the centre of the most distant fastener, in mm, see Figure 5 h is the timber member height, in mm b is the member thickness, but not more than the penetration depth, in mm

The equation (46) does not need to be checked for flatwise Kerto-Q connections since Kerto-Q when used flatwise is not sensitive to splitting caused by connection forces at an angle to the grain due to the cross-veneers.

(46)55

⎟⎠

⎞⎜⎝

⎛−

⋅⋅=

hhhbF

e

ek

114,90 [N]



(47)57

where ft,0,k is the tension strength of timber member without the size effect

(53)63

(54)64

6.3 alTernaTive dimensioning meThod

Timber failure capacity of the joint area can be calculated by the met-hod shown in RIL 205-1-2009 in section 8.2.4S Lohkeamismurto. When using this method, the connection area for splitting and row shear is taken into account by using the effective number of fastener nef , see equation (16). This method cannot be used for edgewise Kerto connections.

When connection force components are parallel to the grain, the tim-ber failure should be checked at tension loaded member ends. There are two types of timber failure modes: block shear and plug shear.The block and plug shear capacities do not require checking for connections where all the fasteners are in a single row parallel to the grain (n2 = 1).

For Steel-to-timber connections with Kerto-Q both block shear and plug shear capacity should be checked.

For dowelled connections, where the amount of fasteners in a row parallel to grain is not more than four and the dowel spacing perpendicular to the grain a2 ≥ 4d, the block shear capacity does not need to be checked.

For dowelled timber-to-timber connection the plug shear capacity does not require checking

The characteristic block shear capacity of timber member:

ktbttnetkbt fktLF ,0,1,, ⋅⋅⋅=

⎩⎨⎧

=LVL ,25,1

liimapuu ja Sahatavara ,5,1btk

( ) ( )DanL tnet −⋅−= 22, 1

n2 is the number of rows perpendicular to the graina2 is the fastener spacing perpendicular to the grainD is the hole diametert1 is the thickness of the timber member (t1 ≤ 2tef)

The characteristic block shear capacity of Kerto-Q member:

where: fv,k is the edgewise shear strength (fv,0.edge,k = 4,5 N/mm2)

Lnet,v =

a3 is the fasteners end distance

a1 is the fastener spacing parallel to the grain

n1 is the amount of rows parallel to the grain

The characteristic plug shear capacity of a Kerto member:

Rk is the characteristic load-carrying capacity per shear plane per fastener

fh,0,k is the characteristic embedment strength

Figure 6: a) block shear b) Plug shear 56

(48)58

(49)59

(50)60

(51)61

(52)62

( ) ( )( )DanaL vnet −⋅−+⋅= 113, 12

where:

1.50. for solid wood and glued laminated timber1.25, for Kerto-LVL

⎪⎩

⎪⎨⎧

⋅⋅⋅

⋅⋅⋅+⋅⋅=

ktbttnet

kvvnetkttnetkbt fktL

ftLftLF

,0,1,

,1,,0,1,,

7.0max

( )( )( )kvkteftnetkps fanaftLF ,0,113,0,,, 1 ⋅⋅−++⋅⋅=

( ) ( )DanL tnet −⋅−= 22, 1

kh

kef fd

Rt

,0,⋅=

fv,0,k is the shear strength of the timber member

fv,0,flat,k 2.3 N/mm2 for flatwise Kerto-S connections

fv,0,flat,k 1.3 N/mm2 for flatwise Kerto-Q connections

fv,0,flat,k 1.3 N/mm2 for flatwise Kerto-T connections



⎟⎟⎠

⎞⎜⎜⎝

⎛= 0.1;;min

u

ubdb ff

a α

where: Ant is the tension stressed net area of cross-section

Anv is the shear stressed net area of cross-section

fu is the ultimate tensile strength

fy is the yield tensile strength

γM0 and γM2 are the partial factors

(55)

the design tension capacity for gross area:

7. steel plates

7.1 Tension sTrengTh

where: NEd is the tension force design value

0,1,

≤Rdt

Ed

NN

⎪⎩

⎪⎨⎧

=Rdu

RdplRdt N

NN

,

,, min (56)

0,

M

yRdpl

fAN

γ

⋅=

the design tension capacity for net area

(57)

(58)

A is the gross area of cross-section

Anet is the net are of cross-section

fu is the ultimate tensile strength

fy is the yield tensile strength

γM0 and γM2 are the partial factors

7.2 embedmenT sTrengTh

The design embedment strength for a single fastener:

2

1,

M

ubRdb

tdfakFγ

⋅⋅⋅⋅= (59)

(60)

perpendicular to force:

- for plate’s end fasteners

- others

7.3 block Tearing

The block tearing design capacity of a steel plate when a symmetrical fastener group has a centric force:

(61)

parallel to force:

- for plate’s end fasteners

- others

;3 0

1

de

d =α

41

3 0

1 −=dp

dα

where:

2,

9.0

M

unetRdu

fAN

γ⋅⋅

=

⎟⎟⎠

⎞⎜⎜⎝

⎛−= 5.2;7.18.2min

0

21 d

ek

⎟⎟⎠

⎞⎜⎜⎝

⎛−= 5.2;7.14.1min

0

21 d

pk

fu is the ultimate tensile strength of the steel plate

fub is the ultimate tensile strength of the fastener

d is the fastener diameter

d0 is the hole diameter in steel plate

e1 is the end distance of the fastener

e2 is the edge distance of the fastener

p1 is the fastener spacing parallel to load

p2 is the fastener spacing perpendicular to load

tt is the thickness of the steel plate

γM2 is the partial factor of the steel plate (see Table 2)



8. fastener spacinGs and edGe and end distances



Figure 7: minimum spacings and end and edge distances



Figure 8: fastener spacings and edge and end distances.65

The fastener spacing parallel to the grain a1 and perpendicular to the grain a2 :

loaded end unloaded end loaded edge unloaded edge

α is the angle between a force and the grain direction



table 5: for dowelled moment resisting multi shear kerto-to-kerto flatwise connections with circular patterns of fasteners, the following minimum values of distances and spacings may be used67

Figure 9: for dowelled moment resisting multi shear kerto-to-kerto flatwise connections with circular patterns of fasteners

sPacing and edge/

end disTance, see figure 8

angle solid Timber and glued

laminaTed Timber

kerTo-s, kerTo-T and

edgewise kerTo-Q

flaTwise kerTo-Q

a1 0°≤ α ≤ 360° (3+2|cosα|) d (4+3|cosα|) d d) (3+|cosα|) d

a2 0°≤ α ≤ 360° 3 d a) 3 d a) 3 d a)

a3t -90°≤ α ≤ 90° max(7 d; 80 mm) max(7 d; 105 mm) b) max(4 d; 60 mm) c)

a3c 90°≤ α ≤ 150° a3t · |sin α| a3t · |sin α| (3+|sinα|) d

150°≤ α ≤ 210° 3 d 3 d (3+|sinα|) d

210°≤ α ≤ 270° a3t · |sin α| a3t · |sin α| (3+|sinα|) d

a4t 0°≤ α ≤ 180° max((2+2 sin α)d; 3 d) max((2+2 sin α)d; 3 d) max((2+2 sinα)d; 3 d)

a4c 180°≤ α ≤ 360° 3 d 3 d 3 d

a) Block shear should also be checked in timber connections if a2 < 4d.

b) For dowels with diameter d < 15 mm, the minimum end distance may be further reduced to 7d, if the embedment strength fh,0,k is reduced by factor a3 / (105 mm).

c) For dowels with diameter d < 15 mm, the minimum end distance may be further reduced to 4d, if the embedment strength fh,0,k is reduced by factor a3,t / (60 mm).

d) The minimum spacing may be further reduced to 5d if the embedment strength fh,0,k is reduced by factor

table 4: dowel minimum spacings and edge and end minimum distances 66

sPacing and edge/end disTances kerTo-s To kerTo-Q a) kerTo-s To kerTo-s kerTo-Q To kerTo-Q

End distance6 d in Kerto-S4 d in Kerto-Q

7 d 4 d

Edge distance4 d in Kerto-S3 d in Kerto-Q

4 d 3 d

Spacing on a circular 5 d 6 d 4 d

Spacing between circulars b) 5 d 5 d 4 d

a) When Kerto-Q is used as outer memberb) Between radius of the circulars



table 6: allowed tolerances of dowel connections - allowed deviations from designed position, unless structural design otherwise states 68

9. allowed tolerances of dowelled connections

a) Drilling through all the parts without stopping or using a predrilled part as a template.b) Prerequisite that the metal plates have 1 mm bigger holes than the dowel diameter.c) t is the design length of the smooth part of the fastener in the lamella.d) Gap between the timber and steel plate surface in steel-to-timber connections where tt is the thickness of the steel plate.e) In each shear plane of the connection in every member.

10. BiBlioGraphy

1 EN 1995-1-1:2004. Eurocode 5: Design of timber structures - Part 1-1: General - Common rules and rules for buildings. 2004.

2 EN 1995-1-1:2004/A1:2008. Eurocode 5: Design of timber structures - Part 1-1: General - Common rules and rules for buildings. 2008.

3 VTT CERTIFICATE NO 184/03. Revised 24 March, 2009. 2009.

4 RIL 205-1-2009. Puurakenteiden suunnitteluohja, eurokoodi EN 1995-1-1. Suomen Rakennusinsinöörien Liitto RIL, 2009.

5 EN 1993-1-8:2005. Eurocode 3: Design of steel structures. Part 1-8: Design of joints. 2005.

6 EN 1993-1-1:2005. Eurocode 3: Design of steel structures. Part 1-1: General rules and rules for buildings. 2005.

7 VTT-S-07046-09. Design method for timber failure capacity of dowelled and bolted glulam connections. 2009.

8 EN 14592:2008+A1:2012. Timber structures - Dowel-type fasteners - Requirements. 2012.

Dowel diameter d -0 / +0.1 mm

length L ± 2 mm

end bevel 30° bevel length 0.15d ± 0.05 d

Dowel connection dowel location e) simultaneous drilling a) ± 3 mm

hole location e) separate drilling ± 1 mm b)

smooth length of dowel in wood lamella t - max(2 mm; 0.05 t) c)

gap in joint grooved or battened members ≤ min(3 mm; 0.25 tt) d)

1 en 14592:2008+A1:2012 6.4.32 en 1995-1-1:2004/A1:2008 tAble 3.1 AnD en 1995-1-1:2004/nA tAble 2.3(Fi)3 en1995-1-1:2004 tAble 4.14 en 14592: 2008+A1:2012 tAble A.15 en 1995-1-1:2004 (2.17)6 Ril 205-1-2009 (8.28.1s) AnD section 8.67 Ril 205-1-2009 (8.28.2s)8 Ril 205-1-2009 (8.28.3s)9 en 1995-1-1:2004 (8.30)10 en 1995-1-1:2004 (8.31)11 en 1995-1-1:2004 (8.32) AnD Vtt 184/03 ReV. 24 MARch 2009 pAge 2012 Vtt 184/03 ReV. 24 MARch 2009 pAge 2013 en 1995-1-1:2004 (8.33) AnD Vtt 184/03 ReV. 24 MARch 2009 pAge 2014 Vtt 184/03 ReV. 24 MARch 2009 pAge 2015 Ril 205-1-2009 (8.35.1s)16 en 1995-1-1:2004 (8.36)17 en 1995-1-1:2004 (8.37)18 Ril 205-1-2009 (8.37.1s) AnD section 8.619 Ril 205-1-2009 (8.37.2s) AnD section 8.620 Ril 205-1-2009 (8.37.3s) - (8.37.5s) AnD section 8.621 Ril 205-1-2009 (8.33.3s)22 Ril 205-1-2009 (8.33.4s)23 Ril 205-1-2009 pAge 11624 Ril 205-1-2009 pAge 9625 Vtt 184/03 ReV. 24 MARch 2009 (b.1) AnD Vtt-s-07046-09 (1)26 Vtt 184/03 ReV. 24 MARch 2009 (b.2) AnD Vtt-s-07046-09 (2)27 Vtt 184/03 ReV. 24 MARch 2009 (b.3) AnD Vtt-s-07046-09 (3)28 Vtt 184/03 ReV. 24 MARch 2009 (b.4) AnD Vtt-s-07046-09 (4)29 Vtt 184/03 ReV. 24 MARch 2009 (b.5) AnD Vtt-s-07046-09 (5)30 Vtt 184/03 ReV. 24 MARch 2009 (b.6) AnD Vtt-s-07046-09 (6)31 Vtt 184/03 ReV. 24 MARch 2009 (b.7) AnD Vtt-s-07046-09 (7)32 Vtt 184/03 ReV. 24 MARch 2009 (b.8) AnD Vtt-s-07046-09 (8)33 Vtt 184/03 ReV. 24 MARch 2009 (b.9) AnD Vtt-s-07046-09 (9)34 Vtt 184/03 ReV. 24 MARch 2009 pAge 24

35 Vtt 184/03 ReV. 24 MARch 2009 (b.10) AnD Vtt-s-07046-09 (10)36 Vtt 184/03 ReV. 24 MARch 2009 (b.11) AnD Vtt-s-07046-09 (11)37 Vtt 184/03 ReV. 24 MARch 2009 (b.12) AnD Vtt-s-07046-09 (12)38 Vtt 184/03 ReV. 24 MARch 2009 pAge 2539 Vtt 184/03 ReV. 24 MARch 2009 (b.13) AnD Vtt-s-07046-09 (13)40 Vtt 184/03 ReV. 24 MARch 2009 (b.14) AnD Vtt-s-07046-09 (14)41 Vtt 184/03 ReV. 24 MARch 2009 (b.15) AnD Vtt-s-07046-09 (15)42 Vtt 184/03 ReV. 24 MARch 2009 (b.16) AnD Vtt-s-07046-09 (16)43 Vtt 184/03 ReV. 24 MARch 2009 pAge 2644 Vtt 184/03 ReV. 24 MARch 2009 (b.17) AnD Vtt-s-07046-09 (17)45 Vtt 184/03 ReV. 24 MARch 2009 (b.18) AnD Vtt-s-07046-09 (18)46 Vtt 184/03 ReV. 24 MARch 2009 (b.19) AnD Vtt-s-07046-09 (19)47 Vtt 184/03 ReV. 24 MARch 2009 (b.20) AnD Vtt-s-07046-09 (20)48 Vtt 184/03 ReV. 24 MARch 2009 (b.21) AnD Vtt-s-07046-09 (21)49 Vtt 184/03 ReV. 24 MARch 2009 (b.22) AnD Vtt-s-07046-09 (22)50 Vtt 184/03 ReV. 24 MARch 2009 (b.23) AnD Vtt-s-07046-09 (23)51 Vtt 184/03 ReV. 24 MARch 2009 pAge 2752 en 1995-1-1:2004 (8.2)53 en 1995-1-1:2004 (8.3)54 en 1995-1-1:2004 FiguRe 8.155 en 1995-1-1:2004 (8.4)56 Ril 205-1-2009 pAge 9957 Ril 205-1-2009 (8.4.1s)58 Ril 205-1-2009 (8.4.2s)59 Ril 205-1-2009 (8.4.3s)60 Ril 205-1-2009 (8.4.1s) AnD (8.4.34)61 Ril 205-1-2009 (8.4.5s)62 Ril 205-1-2009 (8.4.6s)63 Ril 205-1-2009 (8.4.3s)64 Ril 205-1-2009 (8.4.7s)65 en 1995-1-1:2004 FiguRe 8.766 en 1995-1-1:2004 tAble 8.5 AnD Vtt 184/03 ReV. 24 MARch 2009 pAges 20-2167 Vtt 184/03 ReV. 24 MARch 2009 pAge 2168 Ril 205-1-2009 tAble 10.2s

endnotes

This document is property of Metsäliitto Cooperative (Metsä Wood) and is only applicable when used along with products produced by Metsä Wood. Use of the document for other manufacturer's product is prohibited. Metsäliitto Cooperative is not responsible for application of documents or possible faults in documents. This clausul must not be removed. Metsä Wood and Kerto are registered trademarks of Metsäliitto Cooperative (Metsä Wood).

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DowelleD connections - Metsä Wood...2 kerTo manual dowelled connecTions aPril 2013 thi nstructio ropert Mets wood. th nstructio a ee repare n cooperatio it Vtt exper service ltd