Nailed coNNectioNs · The reductions may be neglected if the nail diameter d is ≤ 6 mm or holes...

Nailed coNNectioNs

Table of conTenTs

1 General .......................................................................................................22 Pre-drilling ..................................................................................................23 Material properties ...................................................................................24 Loading .......................................................................................................35 Laterally loaded nails ...............................................................................4 5.1 Timber-to-timber connections .......................................................4 5.1.1 Kerto-to-Kerto connections ...................................................5 5.1.2 Kerto-to-timber connections ................................................5 5.1.3 Timber-to-Kerto connections ................................................6 5.2 Panel-to-timber connections .........................................................6 5.3 Steel-to-timber connections ..........................................................76 Block shear failure ....................................................................................8 6.1 Connection forces at the angle of grain .......................................97 Axially loaded nails ...................................................................................98 Combined laterally and axially loaded nails .......................................109 Fastener spacing and edge and end distances ..................................1110 Allowed tolerances of nailed connections..........................................1511 Bibliography .............................................................................................15

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

2 KERTO MANUALNAILED CONNECTIONSAPRIL 2013

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

NAILED CONNECTIONS

3. Material properties

Nails can be manufactured from non-alloy steel or austenitic stainless steel with diameter 1.9 mm ≤ d ≤ 8 mm,minimum tensile strength fuk ≥ 600 N/mm2 and head area Ah ≥ 2.5d2. For profiled nails the length of the treatedpart lg should be minimum 4.5d. In panel-to-timber connections the head diameter dh should be at least 2d.4

The following details are needed from nail manufacturer for design: •Thecharacteristicpoint-sidewithdrawalstrength fax,k [N/mm2] together with the characteristic density ρk [kg/m�] of the timber used or the type of wood based product used •ThecharacteristicvaluefortheyieldmomentMy,k [Nmm] •Thecharacteristichead-sidepull-throughstrengthfhead,k [N/mm2] together with the characteristic density ρk [kg/m�] of the timber used or the type of wood based product used •Thecharacteristictensilecapacity(fuk ≥ 600 N/mm2 ) ftens,k [kN] •Thenominaldiameterd [mm], the length L [mm], the head diameter dh [mm] and for profiled nails the length of the treated part lg [mm].

Steel plates need to be pre-drilled structural steel or austenitic stainless steel.

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

2. pre-drilling

Timber should be pre-drilled when: the characteristic density of the timber ρk is greater than 500 kg/m� or the diameter d of the nail exceeds 6 mm. The characteristic density of Kerto-S and Kerto-Q is 480 kg/m� and Kerto-T 410 kg/m�. The diameter of pre-drilled holes should be 0.5d - 0.8d, where d is the nail diameter.

Solid timber, glued laminated timber, flatwise Kerto-S and flatwise Kerto-T should be pre-drilled when the thickness t of the timber member is smaller than:

where: ρk is the characteristic timber density, in kg/m� d is the nail diameter, in mm

The minimum thickness of flatwise Kerto-Q is not limited for nails without pre-drilled holes.2

Edgewise Kerto-LVL should be pre-drilled when the thickness t of the timbermemberissmallerthanequation(2),for other nailed connections theEN1995-1-1:2004clause8.3.1.2(7)maybeneglected.

where: ρk is the characteristic timber density, in kg/m� d is the nail diameter, in mm

1. general

Nails are well suited for panel-to-timber and timber-to-timber shear connections. Nails are generally designed for single shear connections.

There should always be at least two nails in a connection. Nails and gluedonothaveaco-operativeaction.Unlessotherwisespecified,nailsshouldbedriveninatrightanglestothegrainandtosuchadepth that the surface of the nail heads are flush with the timber surface with a tolerance of -0 / +3 mm.

Forsquareandgroovednails,thenaildiameterd should be taken as the side dimension.

Smooth nails in end grain should not be considered capable of transmitting lateral forces. In secondary structures smooth nails may be used in end grain, for example, when connecting fascia to rafters. Thedesignvaluesoftheload-carryingcapacityshouldbetakenas1/3ofthevaluefornailsinstalledatrightanglestothegrain.

Profiled annular and screw nails may be used in end grain in struc-turesotherthansecondarystructures.Thedesignvaluesoftheload-carryingcapacityshouldbetakenas1/3ofthevaluesforsmoothnailsofequivalentdiameterinstalledatrightangletothegrain,providedthat: the nails are only laterally loaded; there are at least three nails per connection; the point side penetration is at least 10d; the connection isexposedtoserviceclass1or2.

(1)1

(2)3

[mm]

[mm]

⎪⎩

⎪⎨⎧

⋅−=400

)3013(7

max kdd

t ρ

⎪⎩

⎪⎨⎧

⋅−=200

)3013(14

max kdd

t ρ

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.



4. loading

Nails 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. The reductions may be neglected if the nail diameter d is ≤ 6 mm or holes are positioned on the compressed side of the member and filled with a material of higher stiffness.

In compressed Kerto-to-Kerto joints, 2/3 of the perpendicular compression force can be transferred directlythroughcontactfrommembertomember.IfthecontactsurfaceshavebeenCNC-machined, 3/4 of the perpendicular compression force can be transferred directly through contact from member to member. Splitting of the compressed side in sloped connections, such as ridge connections,shouldbepreventedbyshapingtheendofthememberorinstallingahardfibreboardor 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 nails in laterally loaded joints should, if possible, be positioned on the compressed side of the member. Generally, in this case there is no need to check the tension capacity perpendicular to the grain. See Figure 5.

Inthisguidetimbermeanssolidtimber,gluedlaminatedtimber,Kerto-SandKerto-T.Duetoitscross-veneers,Kerto-Q has better splitting resistance when compared to other timber when used in flatwise connections.

Wood-basedpanelsshouldbeCE-markedinaccordancewithEN13986(plywood,particleboard,OSB-board,mediumfibreboardandhardfibreboard)ortheyshouldhavealocaltypeapprovalorstatement/certificatefromaninstitutionapprovedbylocalbuildingauthoritiesthatcoverstheiruseasload-bearingstructures.

Figure 1: Forces for nails

table 2: strength modification factors for service classes and load-duration classes kmod and partial factors γM for material properties and resistances.7

fasTener service class

1 2 3

Nails with d ≤ 4 mm None Fe/Zn 12c, Z275 Fe/Zn 25c, Z350

Nails with d > 4 mm 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: The minimum specifications for material protection against corrosion for fasteners. electro-plated zinc coating fe/Zn classes are according to iso 2081 and hot-dip coating Z classes according to en 10346.5 stainless steel according to en 10088-1 (grades 1.4401. 1.4301 and 1.4310)6.

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



5. laterally loaded nails

For calculating the lateral load-capacity of the connection, a capacity of the fastener and block shear in the timber member should be checked. See Figure 2.

5.1 Timber-To-Timber connecTions

This method can be used when the penet-ration depth t1 is; with non-pre-drilled nails≥7d, and with pre-drilled nails ≥ 4d and penetration depth t2 is; with non-pre-drilled nails ≥ 8d, and with pre-drilled nails ≥ 4d. For Kerto-Q without pre-drilled holes the penetration depth t1 may be ≥ 4d. See Figure 3.

figure 3: definitions of t, t1 and t2 (a) single shear connection, (b) double shear connection, (c) over-lapping nails8

The characteristic load-carrying capacity for nails in single shear, when penetration depths t1 ≥ 8d and t2 ≥ 12d

where: d is the nominal diameter of the nail, in mm

The penetration thicknesses t1 and t2 are defined in single and double shear connections as follows, see Figure 3:

•Insingleshearconnectionst1 is the thickness of the timber member at the head side and t2 is the penetration depth of the point side.•Indoubleshearconnectionst1 is the minimum of the following: thickness of the timber member at the head side or the penetration depth of the point side and t2 is the thickness of the central member•Inthree-memberconnections,nailsmayoverlapinthecentralmemberprovided(t - t2) is greater than 4d.

If using single side nailing in double shear connections the point side timber member should be tied, for example with screws or through bolts, if the penetration depth at the point side is less than 12d.

(6)12

(5)11

(4)10

(8)14

with the following limits: kt <_ 1.3 for smooth square nails kt <_ 1.1 for smooth round nails

(7)13

(3)9

for other nails.

The design load-carrying capacity when t1 < 8d or t2 < 12d

Iftimbermembersdonothavethesamecharacteristicdensitythesmallestvalueshouldbeused.ForKerto-SandKerto-Qthekρ=1.171andforKerto-Tthekρ = 1.082.

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 valueofk mod / γM should be used.

My is the characteristic fastener yield moment, in Nmmd is the nominal diameter of the nail, in mmRk is the characteristic load-carrying capacity for nails in single shear,equation(3)

(9)15

(10)16where:

kkhtM

d Rkkkk

R ⋅⋅⋅⋅= ,mod

ργ

The design load-carrying capacity when t1 ≥ 8d and t2 ≥ 12d

350kkρ

ρ =

⎪⎪⎩

⎪⎪⎨

⎧

−⋅+

−⋅+

=

ddt

ddt

kt

612

3.01

88

3.01max

2

1

kt ≤ 6.2160d

M y

⎪⎪⎩

⎪⎪⎨

⎧

≥−

=

Q-Kerto edgewiseFor 312

1

generalIn 0.1,

d

k kh

kkheM

d Rkkkk

R ⋅⋅⋅⋅= ,mod

ργ

⎪⎪⎩

⎪⎪⎨

⎧

=

dtdt

ke

12

8min2

1

[N]

figure 2: laterally loaded connection



5.1.1 KerTo-To-KerTo connecTions

table 3: the lateral load-carrying capacity values of single smooth wire nails without pre-drilling Rk and kmod · Rk [N] for Kerto-to-Kerto flatwise connection (Kerto-s or Kerto-Q). table values can be used when penetration lengths are t1 ≥ 8d and t2 ≥ 12d. the calculation has been done by using the Johansen yield theory according to eurocode 5. strength modi-fication factors for service classes and load-duration classes are according to table 2.

load-duraTion class and service class

PermanenT acTion kmod · Rk

medium Term acTion kmod · Rk

shorT Term acTion kmod · Rk

insTanTaneous acTion kmod · Rk

d L Rk 1 and 2 3 1 and 2 3 1 and 2 3 1 and 2 3

square nails

2.5 60 753 452 377 602 489 678 527 828 678

2.8 75 915 549 458 732 595 824 641 1007 824

3.4 100 1278 767 639 1022 831 1150 895 1406 1150

4.2 125 1839 1103 920 1471 1195 1655 1287 2023 1655

5.1 150 2570 1542 1285 2056 1671 2313 1799 2827 2313

5.5 200 2927 1756 1464 2342 1903 2634 2049 3220 2634

6.0 225 3401 2041 1701 2721 2211 3061 2381 3741 3061

round nails 2.5 60 707 424 354 566 460 636 495 778 636

2.8 75 857 514 429 686 557 771 600 943 771

3.1 90 1018 611 509 814 662 916 713 1120 916

3.4 100 1186 712 593 949 771 1067 830 1305 1067

3.8 120 1425 855 713 1140 926 1283 998 1568 1283

4.2 130 1680 1008 840 1344 1092 1512 1176 1848 1512

4.6 145 1953 1172 977 1562 1269 1758 1367 2148 1758

5.0 160 2241 1345 1121 1793 1457 2017 1569 2465 2017

5.1.2 KerTo-To-Timber connecTions

table 4: the lateral load-carrying capacity values of single smooth wire nails without pre-drilling Rk and kmod · Rk [N] for Kerto-to-timber flatwise connection (Kerto-s or Kerto-Q and solid timber with strength class ≥ c24). table values can be used when the timber ison the point side of the nail and penetration lengths in are t1 ≥ 8d and t2 ≥ 12d. the calcu-lation has been done by using the Johansen yield theory according to eurocode 5. strength modification factors for service classes and load-duration classes are according to table 2.







square nails

2.5 60 576 346 288 461 374 518 403 634 518

2.8 75 698 419 349 558 454 628 489 768 628

3.4 100 972 583 486 778 632 875 680 1069 875

4.2 125 1394 836 697 1115 906 1255 976 1533 1255

5.1 150 1941 1165 971 1553 1262 1747 1359 2135 1747

5.5 200 2208 1325 1104 1766 1435 1987 1546 2429 1987

6.0 225 2562 1537 1281 2050 1665 2306 1793 2818 2306

round nails 2.5 60 528 317 264 422 343 475 370 581 475

2.8 75 639 383 320 511 415 575 447 703 575

3.1 90 758 455 379 606 493 682 531 834 682

3.4 100 885 531 443 708 575 797 620 974 797

3.8 120 1066 640 533 853 693 959 746 1173 959

4.2 130 1262 757 631 1010 820 1136 883 1388 1136

4.6 145 1470 882 735 1176 956 1323 1029 1617 1323

5.0 160 1691 1015 846 1353 1099 1522 1184 1860 1522



5.1.3 Timber-To-KerTo connecTions

table 5: the lateral load-carrying capacity values of single smooth wire nails without pre-drilling Rk and kmod · Rk [N] for timber-to-Kerto flatwise connection (Kerto-s or Kerto-Q and solid timber with strength class ≥ c24). table values can be used when the timber is on the head side of the nail and penetration lengths in are t1 ≥ 8d and t2 ≥ 12d. the calculation has been done by using the Johansen yield theory according to eurocode 5. strength modi-fication factors for service classes and load-duration classes are according to table 2.

5.2 Panel-To-Timber connecTions

The design capacity of single shear panel-to-timber connections, when the nail goes completely through the wood-based panel and the point side penetration depth into the timber member is at least 12d, can be calculatedaccordingtoexpression(11).Thismethodisnotallowedforedgewise wood-based panel connections.

(13)19

(14)20

(11)17

where: kmod is the modification factor for duration of load and moisture content γM is the partial factor for connection resistance Rk iscalculatedwith(12)fornailswithandwithout predrill. Rk = 120d 1.7 [N] d is the nominal diameter of the nail, in mm

When t2 is at least 12d the klcanbecalculatedwith(13),ift2 is less than 12d kl is 1.0.

(12)18

with the following limits: •kl ≤ 1.4 kρ for smooth square nails •kl ≤ 1.2 kρ for smooth round nails

t is the thickness of the wood-based panel

Forthecharacteristicdensitythevaluefromthepointsidetimbershould be used. For Kerto-S and Kerto-Q the kρ=1.171andforKerto-T the kρ = 1.082.

The nominal diameter d of the nail should not be more than 0.5t withplywood,particleboardandOSBandwithhardfibreboard0.67t.Additionally,withparticleboardandOSBthemaximumnominal diameter of the nail should be not more than 5 mm.

⎪⎩

⎪⎨

⎧⋅⋅⋅=

dtRkkR kl

Md

12

1min 2

mod

γ

⎪⎪⎪

⎩

⎪⎪⎪

⎨

⎧

⋅⎟⎠

⎞⎜⎝

⎛+

⋅⎟⎠

⎞⎜⎝

⎛+

⋅⎟⎠

⎞⎜⎝

⎛+

=

fibreboard hard 1-622 ENfor 8

7.0

plywoodbirch for 9

6.0

OSB ard,particlebo plywood,conifer for 12

5.0

ρ

ρ

ρ

kdt

kdt

kdt

kl

350kkρ

ρ =







square nails

2.5 60 536 322 268 429 348 482 375 590 482

2.8 75 651 391 326 521 423 586 456 716 586

3.4 100 908 545 454 726 590 817 636 999 817

4.2 125 1305 783 653 1044 848 1175 914 1436 1175

5.1 150 1824 1094 912 1459 1186 1642 1277 2006 1642

5.5 200 2077 1246 1039 1662 1350 1869 1454 2285 1869

6.0 225 2413 1448 1207 1930 1568 2172 1689 2654 2172

round nails 2.5 60 495 297 248 396 322 446 347 545 446

2.8 75 601 361 301 481 391 541 421 661 541

3.1 90 713 428 357 570 463 642 499 784 642

3.4 100 833 500 417 666 541 750 583 916 750

3.8 120 1005 603 503 804 653 905 704 1106 905

4.2 130 1188 713 594 950 772 1069 832 1307 1069

4.6 145 1385 831 693 1108 900 1247 970 1524 1247

5.0 160 1593 956 797 1274 1035 1434 1115 1752 1434



table 6: the lateral load-carrying capacity values of single smooth wire nails without pre-drilling Rk and kmod · Rk [N] for panel-to-Kerto flatwise connection (Kerto-s or Kerto-Q and conifer plywood t = 18 mm). if thicker conifer plywood or birch plywood is used, the calculated values are on the safe side. table values can be used when plywood is on the head side of the nail and the penetration length t2 ≥ 12d. the calculation has been done by using the Johansen yield theory according to eurocode 5. strength modification factors for service classes and load-duration classes are according to table 2.

5.3 sTeel-To-Timber connecTions

This method is for connections where the steel plate is on the head side. The capacity of the steel plate should be checked according to EN 1993. This method cannot be used for edgewise Kerto connec-tions. The edgewise steel-to-timber connections can be calculated according to the EN 1995.

The characteristic load-carrying capacity for nails in single shear for steel-to-timber connections

(19)24

(18)23

(15)

where: kmod is the modification factor for duration of load and moisture content γM is the partial factor for connection resistance Rkiscalculatedwith(16)fornailswithand without pre-drilled holes. Rk = 120d 1.7 [N] d is the nominal diameter of the nail, in mm

The characteristic capacity can be increased with ks if the point side penetration depth t2 ≥ 12d.

ksM

d RkkR ⋅⋅=γmod

(16)21

(17)22 Forthecharacteristicdensitythevaluefromthepointsidetimbermember should be used. For Kerto-S and Kerto-Q the kp=1.171and for Kerto-T the kp = 1.082.

The ks-factor with a steel plate thickness that lies between a thin and thick plate, where 0.5d < tt < d, should be calculated by linear interpolation. Theuseofthicksteelplatesinequations(17)or(18)isallowedifthe hole diameter D in the steel plate is not more than 1.1d. With conical nails, the hole can be bigger, but not more than the conic part diameter. For annular, anchor or screw nails with a conical head, when the cone length is at least d, cone diameter at least 1.3d and the conical head has a full bearing area with the steel plate hole, the thick steel plate equations can be used also with steel plate thickness 0.5d < tt < d.

For annular, anchor or screw nails with penetration depth 8d ≤ t2 ≤ 12d, the characteristic capacity can be increased with ks

dtdt

k

kk

t

ts ≥

≤

⎪⎩

⎪⎨⎧

⋅

⋅=

plate steelfor thick 5.0 plate steelfor thin

5.1

1.1

ρ

ρ

⎪⎪⎩

⎪⎪⎨

⎧

≥⋅⎟⎠

⎞⎜⎝

⎛⋅+

≤⋅⎟⎠

⎞⎜⎝

⎛⋅+

=dtk

dt

dtkdt

k

t

t

s plate steelfor thick

129.06.0

5.0 plate steelfor thin 12

9.02.0

2

2

ρ

ρ

350kkρ

ρ =







square nails

2.5 60 727 436 364 582 473 654 509 800 654

2.8 75 836 502 418 669 543 752 585 920 752

3.4 100 1082 649 541 866 703 974 757 1190 974

4.2 125 1464 878 732 1171 952 1318 1025 1610 1318

5.1 150 1971 1183 986 1577 1281 1774 1380 2168 1774

5.5 200 2223 1334 1112 1778 1445 2001 1556 2445 2001

6.0 225 2552 1531 1276 2042 1659 2297 1786 2807 2297

round nails 2.5 60 680 408 340 544 442 612 476 748 612

2.8 75 771 463 386 617 501 694 540 848 694

3.1 90 861 517 431 689 560 775 603 947 775

3.4 100 956 574 478 765 621 860 669 1052 860

3.8 120 1091 655 546 873 709 982 764 1200 982

4.2 130 1236 742 618 989 803 1112 865 1360 1112

4.6 145 1390 834 695 1112 904 1251 973 1529 1251

5.0 160 1556 934 778 1245 1011 1400 1089 1712 1400

6.0 200 2014 1208 1007 1611 1309 1813 1410 2215 1813



where:

fv,kistheedgewiseshearstrength(fv,0,edge,k = 4.5 N/mm2 )

𝑘𝑘!" =1.50, for solid wood and glued laminated timber

1.25, for Kerto-LVL

6. Block shear failure

Timber failure capacity within the joint area can be calculated using the method presented in RIL 205-1-2009 in section 8.2.4S Lohkeamismurto. For nailed steel-to-timber connections usually only the plug shear capacity should be checked. This method is not allowed for edgewise Kerto connections.

When connection force components are parallel to the grain, the timber failure should be checked at the ends of tension loaded members. There are two types of timber failure modes: block shear and plug shear.

It is not necessary to check block shear and plug capacity for connections where all the fasteners are in a single row parallel to the grain(n2 = 1).

For non-pre-drilled steel-to-timber connections, where the amount of fasteners in a row parallel to the grain is not more than four or if the steel-to-timber connection is classified as a thin steel plate connection, the plug shear capacity does not need to be checked.

If the timber member t1 has fasteners inserted on opposite sides, and theeffectivethicknesstef ≥ 0.5t1. for steel-timber connections the block shear capacity should also be checked.

(23)29

(24)30

(26)32

(27)33

(28)34

The characteristic block shear capacity of timber member:

t1isthethicknessofthetimbermember(t1 ≤ 2tef)

The characteristic block shear capacity of a Kerto-Q member:

where:

Figure 4: a) block shear b) Plug shear 25

[N/mm2]

n1 is the number of rows parallel to the grain

n2 is the number of rows perpendicular to the grain

a1 is the fastener spacing parallel to the grain

a2 is the fastener spacing perpendicular to the grain

a3 is the fastener’s end distance

D is the pre-drilled hole diameter

ρk is the characteristic timber density, in kg/m�

d is the fastener diameter, in mm

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

(20)26

(21)27

(22)28

The characteristic plug shear capacity:

where:

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

( ) ( )DanL tnet −⋅−= 22, 1

kh

kef fd

Rt

,0,⋅=

⎩⎨⎧

−⋅

⋅−⋅=

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

,0, dd

f kkh

ρ

ktbttnetkbt fktLF ,0,1,, ⋅⋅⋅=

( ) ( )DanL tnet −⋅−= 22, 1

⎪⎩

⎪⎨⎧

⋅⋅⋅

⋅⋅⋅+⋅⋅=

ktbttnet

kvvnetkttnetkbt fktL

ftLftLF

,0,1,

,1,,0,1,,

7.0max

( ) ( )( )DanaL vnet −⋅−+⋅= 113, 12

(25)311.25, for Kerto-LVL

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

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

35 N/mm2 for Kerto-S

19 N/mm2 forKerto-Q(thickness21-24mm)

26 N/mm2 forKerto-Q(thickness27-69mm)

24 N/mm2 for Kerto-T1 grain direction

2 failure line



Figure 5: connection forces at an angle to the grain 37

Figure 6: nailing perpendicular to grain and slant nailing 39

6.1 connecTion forces aT an angle of 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 the grain, should be taken into account.

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

7. axially loaded nails

Nails used to resist permanent or long-term axial loading shall be threaded. The threaded nails used should be profiled or deformed overaminimumof4.5dofitsshankandhaveacharacteristicwith-drawal parameter fax,k greater or equal to 4.5 N/mm2 when measured in timber with a characteristic density of 350 kg/m3 conditioned to constantmassat20ºCand65%relativehumidity.

Threadednailsthathaveacharacteristicwithdrawalparameterfax,k less than 4.5 N/mm2 when measured in timber with a characteristic density of 350 kg/m3whenconditionedtoconstantmassat20ºCand65%relativehumidityshouldbecalculatedusingsmoothnailguidelines.

For smooth nails, the point side penetration tpen should be at least 12d. For threaded nails, the point side penetration should be at least 8d.

For threaded nails, only the threaded part should be considered capable of transmitting axial load. Nails in end grain should be considered incapable of transmitting axial load.

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

Theequation(31)doesnotneedtobecheckedforflatwiseKerto-QconnectionssinceflatwiseKerto-Qisnotsensitivetosplittingcausedbyconnectionforcesatanangletothegrainduetoitscross-veneers.

where: fax,k is the characteristic point side withdrawal strength fhead,k is the characteristic head side pull-through strength d is the nail diameter t is the thickness of the head side member tpen is the point side penetration length or the length of the threaded part within the point side member, excluding the length of the point itself. dhisthenailheaddiameter(ingeneraldh ≥ 2d)

For slant nailing the distance to the loaded end should be at least 10d. There should be at least two slant nails in a connection, see Figure 6. When nails are positioned symmetrically to both sides only axial load is present.

[N]

Fv, Ed1 and Fv, Ed2 are the design shear forces on either side of the connectioncausedbytheconnectionforcecomponent(FEd · sin α) perpendicular to the grain.

(29)35

(30)36

(31)38

(32)40

dEdv FF ,90, ≤

⎟⎟⎠

⎞⎜⎜⎝

⎛−

⋅⋅=

hhh

bFe

ek

114,90

The characteristic withdrawal capacity of nails, when nailing perpen-diculartothegrainshouldbetakenasthesmallerofthevalues.SeeFigure 6.

⎪⎪⎩

⎪⎪⎨

⎧

⋅

⋅+⋅⋅

⋅⋅

=

nails edfor threadnailssmooth for

nails allfor min

2,

2,,

,

hkhead

hkheadkax

penkax

k

dfdftdf

tdfR

where: F90,d is the design splitting capacity

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



For timber which is installed at or near fibre saturation point, and whichislikelytodryoutunderload,thevaluesoffax,k and fhead,k should be multiplied by 2/3.

For smooth nails with a point side penetration of at least 12d, the characteristicvaluesofthewithdrawalandpull-troughstrengthcanbedeterminedby(33).EquationsarenotvalidfornailededgewiseKerto connections.

flaTwise KerTo connecTion

edgewise KerTo

connecTion

d [mm] Rk KerTo-T kmod · Rk

Rk KerTo-s & KerTo-q kmod · Rk

Rk KerTo-s & KerTo-q

kmod · Rk

2.1 178 196 244 269 77 85

2.5 252 277 346 380 120 132

2.8 316 348 433 476 159 175

3.1 387 426 531 584 206 227

3.4 467 514 639 703 262 288

3.8 583 641 799 878 349 384

4.2 711 782 975 1073 454 499

4.6 854 940 1171 1288 577 635

5.0 1009 1110 1382 1520 720 792

5.1 1049 1154 1438 1582 759 835

5.5 1221 1343 1672 1840 929 1022

6.0 1452 1597 1991 2190 1175 1292

6.5 1704 1874 2337 2570 1460 1606

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

Ininternalthermalconditions(serviceclass1),wherethecharac-teristicpointsidewithdrawalstrengthisspecifiedat65%relativehumidity, the characteristic point side withdrawal capacity should be multipliedby0.4withsmoothnailsand0.7withthreadednails.

For smooth nails with a penetration depth of at least 12d in the edge ofKertowithoutpre-drilledholes,thecharacteristicvalueofthewithdrawal strength parameter may be calculated from the following equation

fax,k = 0.32d + 0.8 [N/mm2]

where: d is the nail diameter, in mm

Ininternalthermalconditions(serviceclass1),thecharacteristicpointsidewithdrawalcapacity(34)shouldbemultipliedby0.4withsmoothnailsand0.7withthreadednails.

In edgewise connections using Kerto-Q, the minimum nail diameter d is 3.1 mm for round nails and 2.8 mm for rectangular nails.

table 7: The characteristic withdrawal strength parameter fax,k [n/mm²]

values for some nails in edgewise Kerto 43

( )( ) 26

,

26,

1070

1020

kkhead

kkax

f

f

ρ

ρ

⋅⋅=

⋅⋅=

−

−

[N/mm2] (33)41

(34)42

fax,k 4.60 N/mm2 for Kerto-S and Kerto-Q

3.36 N/mm2 for Kerto-T

fhead,k 16.12 N/mm2 for Kerto-S and Kerto-Q

11.76N/mm2 for Kerto-T

table 8: The characteristic axial capacity values of a single smooth nail Rk and kmod · Rk [n]. Table values can be used when the point side penetration length tpen of the nail is at least 12d. The load-duration class is instantaneous and service class is 2. strength modification factors for service classes and load-duration classes are according to Table 2.

nail KerTo-s KerTo-q

Würth HDG ring nail 65x2,5 3.43 -

Würth HDG ring nail 90x3,1 1.97 -

Würth anchor nail 60x4,0 - 3.13

In Table 7, characteristic withdrawal strength parameter are presented for some annular and anchor nails.

(35)44

(36)45

8. coMBined laterally and axially loaded nails

For connections subjected to a combined axial load Fax and lateral load Fv the following expressions should be satisfied:

where: Fax,d is the axial load Fv,d is the lateral load Rax,d is the axial design load-carrying capacity Rv,d is the lateral design load-carrying capacity

1,

,

,

, ≤+dv

dv

dax

dax

RF

RF

12

,

,

2

,

, ≤⎟⎟⎠

⎞⎜⎜⎝

⎛+⎟

⎟⎠

⎞⎜⎜⎝

⎛

dv

dv

dax

dax

RF

RF

for smooth nails

for threaded nails



If staggering is not carried out, the load-carrying capacity parallel to the grainshouldbecalculatedusingtheeffectivenumberoffastenersnef .

where: n is the number of nails in a row

kef for solid timber, glued laminated timber, flatwise Kerto-S and flatwise Kerto-T, see Table 8

9. fastener spacing and edge and end distances

Due the possibility of splitting it is recommended to stagger nails perpendicular to grain by at least 1d.Inthiscasetheeffectivenumberof fasteners nef = n may be used. In flatwise Kerto-Q connections nails do not need to be staggered.

For nailed connections the allowed tolerances according to Table 12.

Figure 7: Nails in a row parallel to grain staggered perpendicular

to grain by d 46

(37)47

(38)48

efkef nn =

( )1

2003.01 1 ≤

−⋅−=

dad

kef

for edgewise Kerto connections

a1 is the spacing of fasteners in the grain direction, in mm

d is the nail diameter, in mm

sPacing a) kef kef

wiThouT Pre-drilling Pre-drilled

a1 ≥ 14 d 1.0 1.0

a1 = 10 d 0.85 0.85

a1 = 7 d 0.7 0.7

a1 = 4 d - 0.5

a) For intermediate spacings, linear interpolation of kef is permitted

table 9: Values of kef for solid timber, glued laminated timber, flatwise Kerto-s and flatwise Kerto-t 49



Figure 8: Minimum spacings and end and edge distances



table 10: minimum spacings and end and edge distances for flatwise nail connections 50 expressions are given in figure 8 and figure 9.

Figure 9: spacings and end and edge distances, (a) spacing parallel to grain in a row and perpendicular to grain between rows, (b) edge and end distances. 51

(1) loaded end, (2) unloaded end, (3) loaded edge, (4) unloaded edge, 1 fastener, 2 grain direction

wiThouT Pre-drilled holes Predrilled holes wiThouT Pre-drilled holes

Predrilled

holes

Spacing or distance

Angle α Kerto-S Kerto-T

Kerto-Q Kerto-SKerto-T

Kerto-Q Timber ρk ≤ 420 kg/m³

Timber 420 < ρk≤ 500 kg/m³

Timber

Spacing a1 (parallel to grain)

0° ≤ α ≤ 360° d < 5 mm:(5+5|cosα|)d d ≥ 5 mm:(5+7|cosα|)d

(5+2|cosα|)d (4+|cosα|)d (4+|cosα|)d d ≤ 5 mm:(5+5|cosα|)d d ≥ 5 mm:(5+7|cosα|)d

(7+8|cosα|)d (4+|cosα|)d

Spacing a2 (perpendicular to grain)

0° ≤ α ≤ 360° 5d 5d (3+sinα)d (3+sinα)d 5d 7d (3+|sinα|)d

Distance a3.t (loaded end)

-90° ≤ α ≤ 90° (10+5cosα)d (4+3cosα)d (7+5cosα)d (4+3cosα)d (10+5cosα)d (15+5cosα)d (7+5cosα)d

Distance a3.c (unloaded end)

-90° ≤ α ≤ 270° 10d 4d 7d 4d 10d 15d 7d

Distances a4.t (loaded edge)

0° ≤ α ≤ 180° d < 5 mm:(5+2sinα)dd ≥ 5 mm:(5+5sinα)d

(3+4sinα)d d < 5 mm:(3+2sinα)dd ≥ 5 mm:(3+4sinα)d

d < 5 mm:(3+2sinα)dd ≥ 5 mm:(3+4sinα)d




Distance a4.c (unloaded edge)

180° ≤ α ≤ 360° 5d 3d 3d 3d 5d 7d 3d

Pre-drilling is required if the characteristic density of the timber ρk is greater than 500 kg/m3 or the diameter of the nail d exceeds 6 mm. See more details at section 2.



table 11: minimum spacings and end and edge distances for edgewiseKerto nail connections 52 expressions are given in figure 9.

Minimum nail spacings a1 and a2, Table 10 and Table 11, for non-pre-drilled panel-to-timber flatwise and edgewise nail connections may be multiplied by a factor of 0.85. The edge and end distance may not be reduced.

Minimum edge a4,c and end distances a3,c in plywood members should be taken as 3dforanunloadededge(orend)anda4,t and a3,t =(3+4sinα)dforaloadededge(orend),whereα is the angle bet-weenthedirectionofloadandtheloadededge(orend).Minimumedge and end distances in other wood-based board are according to Table10andTable11unlesstheboardCE-markstatesotherwise.

Minimum nail spacings a1 and a2, Table 10, for non-pre-drilled steel-to-timber flatwise nail connections may be multiplied by a factorof0.70.Theedgeandenddistancemaynotbereduced.

10. allowed tolerances of nailed connections

table 12: allowed tolerances of nail connections - allowed deviations from designed position, unless structural design otherwise states53

Nailed timber-to-timber connection

Fastener position Connector spacing a1 and a2 a)

End distance a3Edge distance a4

± max(10 %; d)

- 0 / + 10 mm- d / + 10 mm

Nailed steel-to-timber connection

Hole locationSteel plate position

Holes in steel plateBoth directions

± 3 mm± 5 mm

a) Nails in a row parallel to the grain should be staggered perpendicular to the grain by at least 1d if a1 is less than 14d.

calculation exaMple: laterally loaded tiMBer-to-tiMBer nail connection

figure 10: structural model

figure 11: Timber-to-timber connection

locaTion: a-roof Truss

wiThouT Pre-

drilled holes Pre-drilled holes

Spacing or distance

Angle α Kerto-S Kerto-QKerto-T

Kerto-S Kerto-QKerto-T

Spacing a1 (parallel to grain)

0° ≤ α ≤ 360° (7+8|cosα|)d 1.4 (4+|cosα|)d

Spacing a2 (perpendicular to grain)

0° ≤ α ≤ 360° 7d 1.4 (3+|sinα|)d

Distance a3.t (loaded end)

-90° ≤ α ≤ 90° (15+5cosα)d 1.4 (7+5cosα)d

Distance a3.c (unloaded end)

-90° ≤ α ≤ 270° 15d 9.8d

Distance a4.t (loaded edge)

0° ≤ α ≤ 180° d < 5 mm:(7+2sinα)dd ≥ 5 mm:(7+5sinα)d

d < 5 mm:1.4 (3+2sinα)dd ≥ 5 mm:1.4 (3+4sinα)d

Distance a4.c (unloaded edge)

180° ≤ α ≤ 360° 7d 4.2d

11. BiBliography

1 EN 1995-1-1:2004. Eurocode 5: Design of timber structures - Part 1-1:General-Commonrulesandrulesforbuildings.2004.

2 EN 1995-1-1:2004/A1:2008. Eurocode 5: Design of timber structures-Part1-1:General-Commonrulesandrulesforbuildings.2008.

3VTTCERTIFICATENO184/03.Revised24March,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.

7EN14592:2008+A1:2012.Timberstructures-Dowel-typefasteners - Requirements. 2012.

8VTT-S-04487-13.Initialtestingofwithdrawalstrengthofnailsforedgewise connections of Kerto-LVL. 2013.

inclination 1:2.5

on both sides



Checkingthepossibilityofusing2.5x60wirenails.

Pre-drilling

d ≤ 6 mm

ρk ≤ 500 kg/m3(Kerto-S480kg/m3)

pre-drilling is not required.

PeneTraTion dePTh

t1=27mm>8d = 20 mm

t2=60mm-27mm=33mm>12d = 30 mm

The design load-carrying capacity calculated when t1 ≥ 8d and t2 ≥ 12d

Rk = 120 · d 1.7=570Nkmod = 0.8, γM = 1.2(Kerto-S)

required amounT of nails

27no.of2.5x60wirenailsforeachsideoftheconnectionisselected.

nail PosiTioning

With Kerto-S the nails are to be staggered by d. Nails are positioned in the compressed side of the rafter. Withtheserulestheriskofsplittingisavoided.SeeFigure12andFigure13.

Nails spacing in the tension member a1:

tensionmember(α = 0) a1 ≥ a1,min=(5+5|cosα|)d = 25 mm

main rafter a1 ≥ a2,min / sin 22º = 5d / sin 22º = 33.4 mm

a1 = 40 mm is chosen.

Nail spacing in the main rafter ap:

tension member ap ≥ a2,min / sin 22º = 5d / sin 22º = 33.4 mm

mainrafter(α = 22º) ap ≥ a1,min=(5+5|cosα|)d = 25.1 mm

ap = 40 mm is chosen, in this case the tension members perpendicular direction a2=15mm(=40mmsin22º)

end disTance in The Tension member

tensionmember(α= 0) a3,min=(10+5cosα )d=37.5mm 50mmischosen

edge disTances

main rafter, loaded edge a4,t≥(5+2sinα )d=14.4mm(α = 158º)

a4,t = 204 mm is chosen

other edges: a4,c ≥ 5d = 12.5 mm

tension member a4,c = 40 mm is chosen

main rafter upped edge a4,c = 166 mm chosen

10.1612

3.01;88

3.01max

06.1

2

10.1

1 =⎪⎭

⎪⎬

⎫

⎪⎩

⎪⎨

⎧−

⋅+−

⋅+= ddt

ddt

kt

NNRkkk

R ktM

d 48957010.1350480

2.18.0mod =⋅⋅⋅=⋅⋅⋅= ργ



Figure 13: nailing

endnotes

Figure 12: general view of connection

1 EN 1995-1-1:2004 (8.18)2 VTT 184/03 REV. 24 MARCh 2009 pAgE 193 EN 1995-1-1:2004 (8.19)4 EN 14592:2008+A1:2012 6.1.3 AND EN 1995-1-1:2004 8.3.1.35 EN1995-1-1:2004 TAbLE 4.16 EN 14592: 2008+A1:2012 TAbLE A.17 EN 1995-1-1:2004/A1:2008 TAbLE 3.1 AND EN 1995-1-1:2004/NA TAbLE 2.3(FI)8 EN 1995-1-1:2004 FIguRE 8.4 AND 8.59 RIL 205-1-2009 (8.5.1S) AND (8.5.2S)10 RIL 205-1-2009 (8.5.3S)11 RIL 205-1-2009 (8.5.4S)12 RIL 205-1-2009 (8.5.5S)13 RIL 205-1-2009 pAgE 10414 VTT 184/03 REV. 24 MARCh 2009 pAgE 1815 RIL 205-1-2009 (8.5.3S)16 RIL 205-1-2009 (8.5.6S)17 RIL 205-1-2009 (8.5.8S)18 RIL 205-1-2009 (8.5.1S)19 RIL 205-1-2009 (8.5.7S)20 RIL 205-1-2009 (8.5.4S)21 RIL 205-1-2009 (8.5.1S)22 RIL 205-1-2009 (8.5.9S)23 RIL 205-1-2009 (8.5.10S)24 RIL 205-1-2009 (8.5.4S)25 RIL 205-1-2009 pAgE 9926 RIL 205-1-2009 (8.4.6S)27 RIL 205-1-2009 (8.4.3S)28 RIL 205-1-2009 (8.4.7S)29 EN 1995-1-1:2004 (8.32) AND VTT 184/03 REV. 24 MARCh 2009 pAgE 2030 RIL 205-1-2009 (8.4.1S)31 RIL 205-1-2009 (8.4.2S)32 RIL 205-1-2009 (8.4.3S)33 RIL 205-1-2009 (8.4.1S) AND (8.4.34)34 RIL 205-1-2009 (8.4.5S)

35 EN 1995-1-1:2004 (8.2)36 EN 1995-1-1:2004 (8.3)37 EN 1995-1-1:2004 FIguRE 8.138 EN 1995-1-1:2004 (8.4)39 RIL 205-1-2009 FIguRE 8.840 EN 1995-1-1:2004 (8.23) AND (8.24)41 EN 1995-1-1:2004 (8.25) AND (8.26)42 VTT 184/03 REV. 24 MARCh 2009 (C.1)43 VTT-S-04487-1344 EN 1995-1-1:2004 (8.27)45 EN 1995-1-1:2004 (8.28)46 EN 1995-1-1:2004 FIguRE 8.647 EN 1995-1-1:2004 (8.17)48 VTT 184/03 REV. 24 MARCh 2009 pAgE 1849 EN 1995-1-1:2004 TAbLE 8.150 VTT 184/03 REV. 24 MARCh 2009 pAgES 18-19 AND EN 1995-1-1:2004 TAbLE 8.251 EN 1995-1-1:2004 FIguRE 8.752 VTT 184/03 REV. 24 MARCh 2009 pAgES 18 AND EN 1995-1-1:2004 TAbLE 8.253 RIL 205-1-2009 TAbLE 10.2S

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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