Bolted connections - · PDF fileBolted connections Table of conTenT s 1 ... Steel plates up to 3 mm thickness Fe/Zn 12c, Z275 Fe/Zn 12c, Z275 Stainless steel Steel plates from 3 mm

Bolted connections

Table of conTenTs

1 General ...................................................................................................................... 22 Material properties ................................................................................................. 23 Loading ..................................................................................................................... 34 Laterally loaded bolts ............................................................................................. 3 4.1 Timber-to-timber connections ..................................................................... 4 4.2 Panel-to-timber connections ....................................................................... 4 4.3 Steel-to-timber connections ........................................................................ 4 4.4 Effective number of fasteners ...................................................................... 45 Multiple shear plane connections........................................................................ 56 Block shear failure .................................................................................................. 6 6.1 Timber failure capacity of joint area ........................................................... 6 6.1.1 Capacity of inner part lamellas ......................................................... 6 6.1.2 Capacity of the edge part of lamellas ................................................7 6.2 Connection forces at an angle to the grain ................................................ 8 6.3 Alternative dimensioning method ............................................................... 97 Steel plates ............................................................................................................. 10 7.1 Tension strength ........................................................................................... 10 7.2 Embedment strength .................................................................................. 10 7.3 Block tearing .................................................................................................. 108 Axially loaded bolts ............................................................................................... 109 Fastener spacings and edge and end distances .............................................. 1110 Allowed tolerances of bolted connections ........................................................1411 Bibliography ............................................................................................................14

Calculation example: Laterally loaded timber-to-timber bolt connection ...............15Endnotes ...........................................................................................................................17

2 KERTO MANUALBOLTED CONNECTIONSAPRIL 2013

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

1. General

Washers with a side length or an external diameter of at least 3d (where d is the diameter of the bolt) and a thickness of at least 0.3d should be used under the head of bolts and nuts. Washers should have a full bearing area.

Bolts should be tightened so that the members fit closely, and they should be re-tightened if necessary when the timber has reached equilibrium moisture content. If re-tightening cannot be done, and there is a possibility that the timber can dry by over 5 % of its weight after installation of the bolts, only 80 % of the calculated capacity of the bolt connection can be utilised.

Bolt holes in timber should have a diameter no more than 1 mm larger than the bolt. Bolt holes in steel plates should have a diameter no more than 2 mm or 1.1d (whichever is greater). If the connection is designed using thick steel plate (tt ≥ d) equations and bolt diameter d < 20 mm, the maximum allowed hole in the steel plate should not be more than 1.1d.

Bolted connections

2. Material properties

The calculation method for steel bolts presented in this guide is valid only for bolts with a diameter d ≤ 24 mm and ultimate tensile strength fu,k ≤ 800 N/mm2 (class 8.8)1. In addition, the timber thick-ness of side members t1 and t2 should be at least 4d 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.

service class

fasTener 1 2 3

Bolts 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 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

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

table 2: The minimum specification 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

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.


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

⎪⎪⎩

⎪⎪⎨

⎧

⋅⋅⋅

⋅⋅

⋅+⋅⋅⋅⋅

=

dfM

tdf

Mdtf

R

khy

ukh

yukh

k

,

2,

,

2

314.0

min

table 3: in en 1993-1-1, en 1993-1-2 and en 1993-1-8 the following par-tial 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

3. loadinG

Bolts can be loaded laterally or axially. The loading can also be combined lateral and axial load.

Reductions in cross section should be taken into account when analysing the 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.

When a force in a connection acts at an angle to the grain, the bolts of laterally loaded joints should ideally be positioned at the compressed side of the member. In these cases there is generally no need to check the tension capacity perpendicular to the grain. See Figure 5.

Figure 1: Laterally loaded connection

4. laterally loaded bolts

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

Design capacity of the connection:

M

kd

RkRγ⋅

= 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.

(2)6

where

⎪⎪

⎩

⎪⎪

⎨

⎧

⋅

⋅

=

kh

kh

kh

kh

u

fftfft

t

,

,2,2

,

,1,1

min (3)7

t1 and t2 are the thicknesses of the outer timber members

fh,1,k and 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 two shear plane connection

d is the fastener diameter

The characteristic value for the yield moment:

);;min( ,,,2,,1,, kshkhkhkh ffff = (4)8

[Nmm] (5)9

where fu,k is the characteristic tensile strength of the bolt, in N/mm2

d is the fastener diameter, in mm

4.1 Timber-To-Timber connecTions

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

My = 0.3 · fu,k · d 2.6



⎪⎪⎪

⎩

⎪⎪⎪

⎨

⎧

⋅⋅⋅

⎥⎥

⎦

⎤

⎢⎢

⎣

⎡−

⋅⋅

⋅+⋅⋅⋅⋅

⋅⋅

=

dfM

tdf

Mdtf

dtf

R

khy

kh

ykh

kh

k

,

2,

,

,

3

14

23.1min

⎪⎩

⎪⎨⎧

⋅⋅⋅

⋅⋅⋅=

dfM

dtfR

khy

khk

,

,

2

4.0min

⎪⎪⎩

⎪⎪⎨

⎧

+

+

+

+

=

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

(6)10

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

where

[N/mm2]

In general

for Kerto-Q(7)11

for Kerto-Q fh,α,k = fh,45,k when 45° ≤ α ≤ 90° 14

ρk is the characteristic timber density, in kg/m3


α is the angle of the load to the grain

(9)13

(8)12

for Kerto-S and Kerto-T

for Kerto-Q

for softwood

for hardwoods

for flatwise connections

for edgewise connections

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.

[mm] (10)15

where: fh,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:

fh,k = 0.11 · (1 – 0.01d) · ρk [N/mm2]

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


(11)16

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

fh,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

(12)17

4.3 sTeel-To-Timber connecTions

The capacity of a steel plate should be checked according 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 installed 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 a 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).

(13)18

(14)19

ααα 2290

,0,,, cossin +⋅=k

ff kh

kh [N/mm2]

tpanel ≥ 80 ◊dfh,panel ,k

[–]

[–]



connectionshear multiple and other twomembersouter in only er with timbconnection

);2;2min();min(

21

21

⎩⎨⎧

=sttt

ttt

⎪⎩

⎪⎨

⎧

⋅

⋅=4

29.0

50

min

dta

n

nn

i

i

ef

⎪⎪⎪

⎩

⎪⎪⎪

⎨

⎧

<<⋅⋅⋅⎟⎟⎠

⎞⎜⎜⎝

⎛+

≥⋅⋅⋅

≤⋅⋅⋅

⋅⋅⋅

=

dtddfMdt

dtdfMdtdfM

dtf

R

tkhyt

tkhy

tkhy

kh

k

5.0for 15.0

for 3

5.0for 25.0

min

,

,

,

,

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.

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

(15)20

where: ni is the number of fasteners in the row i


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

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.

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

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} }





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 :

⎩⎨⎧

=

≥=

1 when ,2 when ,);min(

3

31

i

i

nanaa

a



⎪⎪

⎩

⎪⎪

⎨

⎧

≤⋅⋅

≤⋅⋅

=

lamellas middlefor 63.1

lamellas sidefor 68.0

,0,

,0,,

ikh

y

ikh

y

ief

tff

d

tff

dt

⎪⎪⎪

⎩

⎪⎪⎪

⎨

⎧

=

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

Q-Kerto edgewisefor 7.0S-Kertofor 7.0

vk

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

6. block shear failure

6.1 Timber failure caPaciTy of The 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:

RkM

RdEd FkFF ,0mod

,0,0 γ=≤ (19)25

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.

where: ∑=

=m

iRkiRk FF

1,0,,0 (20)26

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

The capacity of inner part lamellas:

where: fh,0,k is the embedment strength of timber parallel to grain

Ah,ip = (n – n1) · d · t1

Fcv,k = Fv,k + (n2 – 1) · d · tef,i · fh,0,k

RkepRkipRki FFF ,,,0, += (21)27

( )( )⎪⎩

⎪⎨⎧

⋅

⋅=

aliitoksiss ssapuristetui ,;min

aliitoksiss ä vedetyiss,;min

,,0,,

,,0,,,

kcvkhiph

ktvkhiphRkip FfA

FfAF

in tension joints

in compression joints(22)28

(23)29

(24)30

(25)31

(26)32for Kerto-LVLfor glued laminated timber

(27)33

n is the number of fasteners

n1 is the mean number of fasteners in the rows parallel to grain (n1=n/n2)


ti is the lamella thickness ≤ penetration of the fastener

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

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

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

(28)34

( )( ) iipt tdanA ⋅−−= 22, 1

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

(29)35

(30)36

(31)37

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

The characteristic timber failure capacity of the joint area:

6.1.1 caPaciTy of inner ParT lamellas

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



⎟⎟⎠

⎞⎜⎜⎝

⎛−

=

4,1cosh

7.2

4

3

aa

send

⎪⎩

⎪⎨

⎧

=

4

365.0

1max

aashole

( ) ktiefend

kse fdatsn

F ,90,3,

9.01

, 5.014

⋅−⋅⋅=

( ) ktiefhole

ks fdatsn

F ,90,3,

9.01

, 5.014

⋅−⋅⋅=

⎪⎪

⎩

⎪⎪

⎨

⎧

≤⎟⎟

⎠

⎞

⎜⎜

⎝

⎛−⋅

≤⎟⎟

⎠

⎞

⎜⎜

⎝

⎛−⋅

=

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 lamellas. 38

6.1.2 caPaciTy of The edge ParT of lamellas

where:

(32)39( )( )⎪⎩

⎪⎨⎧

⋅

⋅=

aliitoksiss ssapuristetui ,;min

aliitoksiss ä vedetyiss,;;;min

,,0,,

,,,,0,,,

kcvkheph

kseksvktvkhephRkep FfA

FFFfAF

in tension joints

in compression joints

ieph tdnA ⋅⋅= 1,

khiefkvkcv ftdFF ,0,,,, ⋅⋅+=

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

epteptipt AkA ,,, ⋅= epvipv AA ,, =

( ) iept tdaA ⋅−= 4, 2

( )( ) iefepv taanA ,311, 12 ⋅+−=

(33)40

(34)41

(35)42

(36)43

(37)44

(38)45

and

epv

eptept

AAk

,

,,

1

1

+

=

a4 is the fastener edge distance

(39)46

The splitting capacities:

(40)47

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

(41)48

(42)49

(43)50

The capacity of the edge part of lamellas:

where:

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



Figure 4: definition of symbols for the edge parts of lamellas. 51

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:

dEdv FF ,90, ≤

dF ,90

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

1,EdvF 2,EdvF

where:

and are the design shear forces on

Figure 5: connection forces at the angle of grain. 54

(44)52

(45)53

either side of the connection caused by the connection force component (FEd · sin α) perpendicular to the grain

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.

⎟⎠

⎞⎜⎝

⎛−

⋅⋅=

hhhbF

e

ek

114,90 (46)55[N]

is the design splitting capacity



⎪⎩

⎪⎨⎧

⋅⋅⋅

⋅⋅⋅+⋅⋅=

ktbttnet

kvvnetkttnetkbt fktL

ftLftLF

,0,1,

,1,,0,1,,

7.0max

where: fv,k is the edgewise shear strength (fv,0, edge, k = 4.5 N/mm2)

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:

( ) ( )( )DanaL vnet −⋅−+⋅= 113, 12

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 bolted connections, where the amount of fasteners in a row paral-lel to grain is not more than four and the bolt spacing perpendicular to the grain a2 ≥ 5d, the block shear capacity does not need to be checked.

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

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

The characteristic block shear capacity of a timber member:

ktbttnetkbt fktLF ,0,1,, ⋅⋅⋅=

where: is the tension strength of timber member without the size effect

ktf ,0,

(47)57

(48)58

⎩⎨⎧

=LVL ,25,1

liimapuu ja Sahatavara ,5,1btk

( ) ( )DanL tnet −⋅−= 22, 1

n2 is the number of rows perpendicular to the grain

a2 is the fastener spacing perpendicular to the grain

D is the hole diameter

t1 is the thickness of the timber member (t1 ≤ 2tef)

The characteristic block shear capacity of Kerto-Q member:

(49)59

(50)60

(51)61

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

where:

(52)62

( ) ( )DanL tnet −⋅−= 22, 1

kh

kef fd

Rt,0,⋅

=

(53)63

(54)64

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

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

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

fh,0,k is the characteristic embedment strength

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,

≤Rdt

Ed

NN

2,

9.0

M

unetRdu

fAN

γ

⋅⋅=

⎟⎟⎠

⎞⎜⎜⎝

⎛−= 5.2;7.14.1min

0

21 d

pk

⎟⎟⎠

⎞⎜⎜⎝

⎛−= 5.2;7.18.2min

0

21 d

ek

7. steel plates

7.1 Tension sTrengTh

where: NEd is the tension force design value

the design tension capacity for gross area:

the design tension capacity for net area

A is the gross area of cross-section

Anet is the 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)

⎪⎩

⎪⎨⎧

=Rdu

RdplRdt N

NN

,

,, min (56)

0,

M

yRdpl

fAN

γ

⋅= (57)

(58)

7.2 embedmenT sTrengTh

The design embedment strength for a single fastener:

2

1,

M

ubRdb

tdfakFγ

⋅⋅⋅⋅=

where:

parallel to force:

- for plate’s end fasteners

- others

perpendicular to force:

- for plate’s end fasteners

- others

;3 0

1

de

d =α

41

3 0

1 −=dp

dα

(59)

(60)

7.3 block Tearing

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

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

(61)

8. axially loaded bolts

The axial load-bearing capacity and withdrawal capacity of a bolt should be taken as the lower value of: the bolt tensile capacity; the load-bearing capacity of either the washer or (for steel-to-timber con-nections) the steel plate.

The bearing capacity of a washer should be calculated assuming a characteristic compressive strength on the contact area of 3fc,90,k .

The bearing capacity per bolt of a steel plate should not exceed that of a circular washer with a diame-ter which is the minimum of: 12tt , where tt is the plate thickness; 4d, where d is the bolt diameter.

Washer with a side length (in the case of square washers) or a diameter of at least 3d and a thickness of at least 0.3d should be used under the head and nut. Washers should have a full bearing area.

fu is the ultimate tensile strength of the steel plate

fub is the ultimate tensile strength of the fastener


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 3)

⎟⎟⎠

⎞⎜⎜⎝

⎛= 0.1;;min

u

ubdb ff

a α



64 RIL 205-1-2009, sivu 11565 EN 1995-1-1:2004, taulukko 8.5 ja VTT 184/03 Rev. 24 March 2009, sivut 20-21

9. 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

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° (4+|cosα|) d (4+3|cosα|) d d) 4 d

a2 0°≤ α ≤ 360° 4 d a) 4 d a) 4 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° (1+6 sin α)d (1+6 sin α)d 4 d

150°≤ α ≤ 210° 4 d 4 d 4 d

210°≤ α ≤ 270° (1+6 |sin α|)d (1+6 |sin α|)d 4 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 < 5d.

b) For bolts 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 bolts 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: bolt minimum spacings and edge and end minimum distances 66

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 bolted moment resisting multi shear kerto-to-kerto flatwise connections with circular patterns of fasteners, the following minimum values of distances and spacings may be used. 67

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

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

10. allowed tolerances of bolted connections

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

Bolt connection

bolt locationhole locationtightening

simultaneous drilling a)

separate drillingparts to contact

± 5 mm b)

± 1.5 mm c)

tilted gap max. 3 mm

a) Drilling through all the parts without stopping or using a predrilled part as a template.

b) On rows parallel to the grain, the fasteners can have a maximum tolerance of 5 mm to each other in the parallel direction.

c) Prerequisite that the timber members have 1 mm bigger holes than the bolt diameter and metal plates have 1.5...2.0 mm bigger holes than the bolt diameter.

11. 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.



⎪⎪⎩

⎪⎪⎨

⎧

=⋅

⋅

=

⎪⎪

⎩

⎪⎪

⎨

⎧

⋅

⋅

= mm51

mm/N63.34mm/N63.34mm51

mm/N63.34mm/N63.34mm51

min

2

2

2

2

,

,2,2

,

,1,1

kh

kh

kh

kh

u

fft

fft

t

calculation exaMple

laTerally loaded Timber-To-Timber bolT connecTion

Location: Roof truss, lower chord tension joint.

Capacity of laterally loaded bolt group

Figure 10: connection detail drawing

Checking the possibility of using M12 bolts, d = 12 mm

Bolt grade is 8.8, fuk = 800 N/mm2

Timber beams: Kerto-S flatwise connection.

Service class: 2, load-duration class: medium term action.

The thicknesses of connection timbers, double shear plane connection. t1 = 51 mm > 4d = 48 mm t2 = 51 mm > 4d = 48 mm ts = 63 mm > 5d = 60 mm and ts > min(t1,t2) = 51 mm

The thicknesses of the connecting timber members are OK.

The characteristic embedment strength:

fh,0,k = 0.082 · (1-0.01·d) · ρk = 0.082 · (1-0.01·12) · 480 = 34.63 N/mm2

fh,1,k = fh,2,k = fh,s,k = fh,0,k = 34.63 N/mm²

fh,k = min( fh,1,k; fh,2,k; fh,s,k ) = 34.63 N/mm²



( )73.1

73.12

minmm1250mm63mm85

2

2min

50

min4 2

9.04

29.0 =

⎩⎨⎧

=⎪⎩

⎪⎨

⎧

⋅

⋅⋅=

⎪⎩

⎪⎨

⎧

⋅

⋅⋅

=

dta

n

nn

i

i

ef

shear/kN76.62.1

shear/kN12.108.0mod1, =

⋅=

⋅=

M

kd

RkR

γ

shear/kN12.10N15973N10123

min =⎩⎨⎧

=kR

( )

⎪⎪⎩

⎪⎪⎨

⎧

⋅⋅⋅

⋅⋅

⋅+⋅⋅⋅⋅

=

mm12mm/N63.34Nmm1534902

mm51mm12mm/N63.34Nmm1534903

1mm12mm51mm/N63.344.0min

2

222

kR

⎪⎪⎩

⎪⎪⎨

⎧

⋅⋅⋅

⋅⋅

⋅+⋅⋅⋅⋅

=

dfM

tdf

Mdtf

R

khy

ukh

yukh

k

,

2,

,

2

314.0

min

The design capacity per bolt per shear plane:

kmod = 0.8 and γM = 1.2

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

The characteristic value for the yield moment:

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

The design capacity of timber-to-timber connection:

Rd = amount of bolts · per shear capacity · shears = (2 · 1.73) · 6.76 kN/shear · 2 shears = 46.77 kN

Utilization rate against timber-to-timber capacity is 86 %. –> OK

a = min( a1; a3 ) = 85 mm

t = min( 2t1; 2t2; ts ) = min( 102mm; 102 mm; 63 mm ) = 63 mm

ni = 2

%8640 ,, ==⇒=

d

dvdv R

FkNF η

My = 0.3 · fu,k · d 2.6 = 0.3 · 800 · 122.6 = 153490 Nmm



kN98.67,mod

, == kbtM

dbt Fk

Fγ

When the lateral timber-to-timber load-carrying capacity is calculated according to the effective number of bolts in a row parallel to grain, the block shear capacity can be calculated according to section 6.3 using equation (47).

The characteristic load-bearing capacity of block shear:

The design load-bearing capacity of block shear:

( ) ( ) mmmmmmDanL tnet 37)1350()12(1 22, =−⋅−=−⋅−=

%5940,

,, ==⇒=

dbt

dvdv F

FkNF η

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).

Utilization rate against block shear capacity is 59 %. –> OK

1 EN 14592:2008+A1:2012 6.5.22 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)7 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)19 RIL 205-1-2009 (8.37.2S)20 RIL 205-1-2009 (8.37.3S) - (8.37.5S) 21 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

Fbt,k = Lnet,t · t1 · kbt · ft,0,k = 37 mm · 63 mm · 1.25 · 35 N/mm² = 101.98 kN

kmod = 0.8 and γM = 1.2

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