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Institution of Engineers Australia, 2011

* Paper S10-067 submitted 31/08/10; accepted for publicationafter review and revision 9/11/10.

Corresponding author Dr Steffen Franke can be contacted [email protected].

Bolted and dowelled connections in Radiata pine and

laminated veneer lumber using the European yield model*

S Frankeand P QuennevilleThe University of Auckland, New Zealand

ABSTRACT: Connections with mechanical fasteners are important for all cases of timberstructures. The failure of these connections may occur in either ductile or brittle manner. For thecalculation of the ductile failure strength or the load carrying capacity, the European yield model(EYM) is used in many standards and accepted as a very accurate model. In the current NewZealand timber standard NZS 3603:1993 (Standards New Zealand, 1993) and the Australian oneAS1720.1-1997 (Standards Australia, 1997), the design concept for bolted or dowelled connectionsis not based on the EYM, and depends only on the diameter, the timber thickness and the speciesgroup. The most important parameters for the EYM are the fastener yield moment and the timberembedment strength, but embedment strength values are not available for New Zealand Radiatapine or laminated veneer lumber (LVL). To obtain the missing information and to implement theEYM into the New Zealand and Australian standards, embedment tests parallel, perpendicular andunder various load-to-grain angles with different dowel diameters in Radiata pine lumber and LVLwere conducted and compiled to build a database of embedment strength values. This paper includesthe latest results of the investigations with dowel diameters extended up to 30 mm. Furthermore,different international testing standards are compared and their evaluation methods are used. Thetest results are also compared with the corresponding results using the Eurocode 5 formulas, andshow that adjusted formulas of the Eurocode 5 can be used to predict the load carrying capacity

of bolted and dowelled connections in Radiata pine lumber and LVL. Design examples comparingthe current methods from the New Zealand/Australian design standards and the proposed methodadopted from the EYM of the European design standard are given as well.

1 INTRODUCTION

For all connections, it is important to predict thefailure strength as accurately as possible. Thisincludes both the ductile and, in some casesespecially in timber construction, the brittle failure

as well. For the calculation of the ductile failurestrength, the European yield model (EYM) is usedin many standards and accepted as a very accuratemodel. It forms the basis of the European timberstandard Eurocode 5, EN 1995-1-1:2004 (CEN, 2004).The development of this approach is based on amultitude of embedment and joint tests with differentEuropean and North American wood species bymany researchers. Furthermore, a continuousadaptation and improvement was reported overseas(Hbner et al, 2008). The most important parametersfor the EYM are the fastener yield moment and the

timber embedment strength, which are known formost of the softwoods and tropical hardwoods.

In the current New Zealand and Australian timberstandards NZS 3603:1993 (Standard New Zealand,1993) and AS1720.1-1997 (Standards Australia, 1997),the design concept for bolted connections is not basedon the EYM, and depends only on the diameter, thetimber thickness and species group. They use slightlydifferent factors, but are similar in the general designmethods. Both do not predict the different types offailure and can lead to an overestimating of the jointstrength. Embedment strength values, which can beused for the Johansens yield theory to estimate theyield strength of joints, are not available for NewZealand Radiata pine. Furthermore, no formulas areavailable for the design of joints with the engineeredwood product laminated veneer lumber (LVL), whichuse becomes more important in structural members.To implement the EYM design concept in the currentNew Zealand and Australian design standardsfor mechanical connections, it is thus essential toinvestigate the material behaviour and to determine

Australian Journal of Structural Engineering, Vol 12 No 1

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Australian Journal of Structural Engineering Vol 12 No 1

Bolted and dowelled connections in Radiata pine and laminated ... Franke & Quenneville

the embedment values for Radiata Pine lumber andalso for Radiata pine LVL, which are main productsused in New Zealand and Australian constructions.The second important parameter, the fastener yieldmoment capacity, depends only on the ultimatetensile strength of the steel of the fastener and canbe adopted from the Eurocode 5 formulas.

To obtain the missing information about theembedment strength, almost 950 embedment testsparallel, perpendicular and under various load-to-grain angles with different dowel diameters withNZ Radiata pine lumber and LVL were conducted,analysed and their results compiled to build adatabase of embedment strength values that can beused to implement the EYM into the New Zealandor Australian standards. Further comprehensivedata about the connection behaviour that are usefuland needed in nite element (FE) calculations arealso provided.

The embedment strength was evaluated usingthe 5%-offset method according to the ASTMD5764-97a (ASTM International, 2007), the extendedproportional limit load following the DIN 52192:1979(DIN, 1979) and the maximum load, which is eitherthe ultimate load or the load at 5 mm displacement,according to EN 383:1993 (CEN, 1993) and ISO/DIS10984-2 (ISO, 2008), respectively. For the embedmentstrength from Radiata pine lumber, results from testsconducted in Auckland and from other researcherswere used. The paper also compares the resultswith the predicted embedment failure results

calculated using the current formulas of Eurocode 5for European spruce. Moreover, a comparison of thedifferent available test standards used to determinethe dowel embedment strength is presented.

Finally, design examples of a connection showing thedesign procedures and differences of the current NewZealand timber standard NZS 3603:1993 (StandardNew Zealand, 1993) and the adjusted EYM adoptedfrom the European timber standard Eurocode 5,EN 1995-1-1:2004 (CEN, 2004) are included. Theresults according to the Australian design standardAS1720.1-1997 (Standards Australia, 1997) are similar

and not calculated specically. The examples alsoserve to highlight some of the shortcomings of theNew Zealand and Australian design approaches.

Movable crosshead

Spherical loading block

Loading apparatus

Specimen

Dowel

Stationary cross head

LVDT

Figure 1: Test configuration full-holetest, ASTM D 5764-97a (ASTMInternational, 2007).

LVDT

Movable crosshead

Loading apparatus

Dowel

Specimen

Stationary cross head

Figure 2: Test configuration half-hole

test, ASTM D 5764-97a (ASTMInternational, 2007).

Full-hole test Half-hole test

1

2

3

4

1

2

3

4

1 Steel apparatus 3 Test piece2 Fastener4 Displacement gauge attached to the test piece

Figure 3: Test configuration, ISO/DIS 10984-2(ISO, 2008).

2 EMBEDMENT TESTS

2.1 Testing standards

There are different test standards for testing theembedment strength of wood for dowel-typefasteners; the ASTM D 5764-97a (ASTM International,

2007), the ISO/DIS 10984-2 (ISO, 2008) and EN383:1993 (CEN, 1993). A summary and comparisonof the specic procedures are given below.

2.1.1 ASTM D 5764-97a (2007)

The ASTM standard allows the choice of a full-holeor a half-hole testing setup, as shown in gures 1 and2. The minimum specimen dimensions are 38 mm or2din thickness, and the maximum of 50 mm or 4dinwidth and length, independent of the load-to-grainangle, where dis the dowel diameter.

The test is conducted as to reach the maximum loadin 1 to 10 minutes, using a constant rate of testingof usually 1.0 mm/minute. There is no furtherinformation about the loading procedure. The resultsare given as the yield load, determined using the5%-offset method, the proportional limit load and theultimate load. The embedment strength, calculatedfrom the yield load, is given by:

yield

h

Ff

dt (1)

2.1.2 ISO/DIS 10984-2

The tests according to this international standardshall be carried out using a full-hole test shown ingure 3(a), but it is a requirement of the test to avoid

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bending of the fastener under test. Thus it also allowsthe use of the half-hole test shown in gure 3(b). Theminimum specimen dimensions for tests paralleland perpendicular to grain can be found in gure 4.

The loading procedure to be used consists of onepreload cycle from 0.4F

max,est to 0.1F

max,est and the

force is to be increased or decreased at a constantrate. The maximum load is to be reached within 300 120 s. The standard includes formulas to calculatethe embedment strength, where F

max is either the

ultimate load or the load at 5 mm displacement,and the foundation modulus as below, where w isthe displacement:

maxh

Ff

bt (2)

, ,

,mod 0.4 0.1

0.4 0.4

4 3h est h est

i F F

f fK

w w w

(3)

2.1.3 EN 383:1993 or DIN EN 383:2007

The European testing standard is equal to the ISO/DIS 10984-2 (ISO, 2008), except that it does not allowthe half-hole test alternative.

2.2 Test series and specimen

2.2.1 Radiata pine LVL

The embedment tests series conducted include atotal of 494 tests with LVL and a dowel diameter d

a1

a1

a1

a1

l5

l5

a3

a2

Compressionperpendicular to grain

Tensionparallel to grain

Compressionparallel to grain

l4

l3

l2

l2

a d

a a d

1

2 3

= 3

= = 5

l l l d

l d

l d

1 2 3

4

5

= = = 7

= 30

= 10

Figure 4: Sizes of test specimen, ISO/DIS10984-2 (ISO, 2008).

of 6, 8, 12, 16, 20, 25 and 30 mm. They also compriseload-to-grain anglesof 0, 22.5, 45, 67.5 and 90.In addition to this, a test series with two dowelswere conducted to investigate the influence ofdowel spacing on the embedment strength for load-to-grain angles of 0 and 90 for selected doweldiameters. For this, the minimum distance of 3dwas

used for the bolt spacing. As a result of the splittingobserved on the specimens with both one and twodowels for the 90 loading angle, further tests weredone using specimen having twice the end distancerequirement. The labelling of each test is based tothe following denition:

LVL-E0-1x12-01

where LVL is the wood product (Radiata pine, LVL); Eis the kind of test (embedment), 0 is the load-to-grainangle (0), 1 is the number of bolts, 12 is the boltdiameter (12 mm), and 01 is the specimen number.

The tests were conducted according to the ASTM D5764-97a (ASTM International, 2007) as a half-holetest (gures 2 and 5), which involves pushing a bolt sothat no bending effects are observed. All specimenswere cut from billets of 46 mm thickness, so that forall test series, a constant thickness of 46 mm anda constant height of 70 mm were used. The widthof the specimens depends on the dowel diameter,the number of dowels and the load-to-grain angle.Perpendicular to the grain, the width of the specimenis 10dfor 1 dowel and 13dfor two dowels.

The density of the specimens, coming from the North

Island of New Zealand, covers a small range between550 and 640 kg/m3, with a mean of about 600 kg/m3and a coefcient of variation less than 2.5 %, as shownon gure 6. This reects the homogenisation of thematerial properties throughout the engineered woodproduct LVL. The specimens were conditioned to 20 Cand 65% relative humidity until mass consistency wasreached. The moisture content was measured to 10.8%on average. The specications, number, sizes anddensities of all groups are shown in table 1.

2.2.2 Radiata pine lumber

To obtain the embedment strength values of Radiatapine lumber and to compare it with the test results

width w

F

thickness t

heighth

Load to grain angle

Figure 5: Definition of embedment test variables and photo of test specimen during the test.

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Figure 6: Density distribution over all tests for Radiata pine lumber and LVL.

Table 1: Number, sizes and densities of embedment tests with Radiata pine LVL.

Group nameDiameterd(mm)

Load-to-grain

angle ()

No. ofdowel

No. ofspecimen

Width/height/thickness w/h/t(mm)

Density (kg/m)

Mean COV

LVL-E0-1x6

6

0.0 1 20 120/70/46 601 2.2%

LVL-E45-1x6 45.0 1 10 90/70/46 606 2.0%

LVL-E90-1x6 90.0 1 20 70/70/46 605 2.9%

LVL-E0-1x8

LVL-E0-2x8

8

0.01

2

32

12

120/70/46

150/70/46

608

610

2.0%

3.5%

LVL-E22.5-1x8 22.5 1 6 110/70/46 619 2.2%

LVL-E45-1x8 45.0 1 6 100/70/46 585 2.2%

LVL-E67.5-1x8 67.5 1 6 90/70/46 619 2.2%

LVL-E90-1x8

LVL-E90-2x890.0

1

2

32 (+2)

6 (+2)

80/70/46

104/70/46

599

603

1.9%

2.1%

LVL-E0-1x12

LVL-E0-2x12

12

0.01

2

32

12

120/70/46

150/70/46

599

603

1.9%

2.1%LVL-E22.5-1x12 22.5 1 6 120/70/46 607 2.0%

LVL-E45-1x12 45.0 1 6 120/70/46 611 1.9%

LVL-E67.5-1x12 67.5 1 6 120/70/46 602 2.1%

LVL-E90-1x12

LVL-E90-2x1290.0

1

2

32 (+2)

6 (+2)

120/70/46

150/70/46

571

596

0.8%

3.7%

LVL-E0-1x16

LVL-E0-2x16

16

0.01

2

12

6

120/70/46

150/70/46

600

574

3.5%

2.0%

LVL-E22.5-1x16 22.5 1 6 130/70/46 587 2.2%

LVL-E45-1x16 45.0 1 6 140/70/46 586 1.4%

LVL-E67.5-1x16 67.5 1 6 150/70/46 601 2.9%

LVL-E90-1x16

LVL-E90-2x16 90.01

2

12 (+2)

6 (+2)

160/70/46

208/70/46

613

608

1.9%

1.5%

LVL-E0-1x20

LVL-E0-2x20

20

0.01

2

12

6

120/70/46

150/70/46

587

585

3.8%

3.0%

LVL-E22.5-1x20 22.5 1 6 140/70/46 586 3.4%

LVL-E45-1x20 45.0 1 6 160/70/46 581 2.0%

LVL-E67.5-1x20 67.5 1 6 180/70/46 584 2.0%

LVL-E90-1x20

LVL-E90-2x2090.0

1

2

12 (+2)

6 (+2)

200/70/46

260/70/46

604

588

1.5%

1.4%

LVL-E0-1x25

25

0.0 1 20 120/70/46 607 2.6%

LVL-E45-1x25 45.0 1 20 140/70/46 594 2.5%

LVL-E90-1x25 90.0 1 20 250/70/46 604 1.5%

LVL-E0-1x3030

0.0 1 20 120/70/46 608 2.9%LVL-E45-1x30 45.0 1 20 140/70/46 546 3.4%

LVL-E90-1x30 90.0 1 20 300/70/46 607 2.2%

Total or average 494 599 2.4%

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from LVL, 270 tests with dowel diameters of 6, 8,25 and 30 mm and results of 184 embedment tests(Sufad, 2008; Mills, 2008) with dowel diametersof 10, 16 and 20 mm were used. All tests were alsocarried out following the ASTM D 5764-97a (ASTMInternational, 2007) procedure as a half-hole test. Inboth research studies (Sufad, 2008; Mills, 2008), only

load-to-grain angles of 0 and 90 were investigatedand the yield strengths with the 5%-offset methodwere evaluated. For the tests conducted with 6, 8, 25and 30 mm dowels, the same sizes and evaluationmethods as used with the LVL tests were used. Thepreparation and conditioning of the specimens werecarried out in the same manner as described for thetests with LVL. Referring to gure 5, the details ofthe specimens are shown in table 2. The distributionof the density is shown in gure 6.

2.3 Evaluation methods of

the embedment strength

For each test, the following characteristics, as shownin gure 7, were evaluated by means of the load-displacement curves: the stiffness or slip modulus K(as the slope of the linear elastic behaviour betweenapproximately 10% and 40% of the maximum load);the slope/stiffness T after the yield point (as theslope of a line tted to the load-displacement); theproportional limit load F

prop; the yield load F

5%; and

the maximum load Fmax

, either as the ultimate load(mostly for = 0 and 22.5) or the load at 5 mmdisplacement (mostly for 45). The proportional

Table 2: Number, sizes and densities of embedment tests with Radiata pine lumber.

Group nameDiameterd(mm)

Load-to-grain

angle ()

No. ofdowel

No. ofspecimen

Width/height/thickness w/h/t(mm)

Density (kg/m)

Mean COV

RP-E0-1x6

6

0 1 30 120/70/45 447 4.7%

RP-E45-1x6 45 1 15 90/70/45 518 3.2%

RP-E90-1x6 90 1 30 60/70/45 461 7.8%

RP-E0-1x8

8

0 1 30 120/70/45 439 4.0%

RP-E45-1x8 45 1 15 100/70/45 528 2.9%

RP-E90-1x8 90 1 30 80/70/45 415 5.5%

RP-E0-1x1010

0 1 32 45/90/45 525 12.5%

RP-E90-1x10 90 1 35 120/80/45 512 11.8%

RP-E0-1x1616

0 1 31 45/90/45 531 11.3%

RP-E90-1x16 90 1 27 120/80/45 506 10.3%

RP-E0-1x2020

0 1 30 45/90/45 524 12.0%

RP-E90-1x20 90 1 29 120/80/45 517 11.0%

RP-E0-1x25

25

0 1 20 120/70/45 522 11.9%

RP-E45-1x25 45 1 20 160/70/45 495 11.7%

RP-E90-1x25 90 1 20 250/70/45 532 6.5%

RP-E0-1x30

30

0 1 20 120/70/45 557 10.2%

RP-E45-1x30 45 1 20 160/70/45 523 4.0%

RP-E90-1x30 90 1 20 300/70/45 541 6.3%

Total or average 454 505 8.2%

[mm]uDisplacement

0.1F5 mm

F5 %

F5 mm

2/3K1

1

1

K

T

5 mm0.05 -offsetd

Load

[kN]

F

u0

Figure 7: Evaluating methods for embedmentstrength.

limit load is dened as the contact point of the testdata and a line with a slope of 2/3Kaccording toDIN 52192:1979 (DIN, 1979). The 5%-offset method,according to EN 383:1993 (CEN, 1993) and ISO10984-2 (ISO, 2008), respectively, was adopted toevaluate the yield load. The embedment strengthis calculated to the 5% yield embedment strength

fh,,5%and the maximum embedment strengthfh,,maxin this paper, respectively, where is the load-to-grain angle. The intersection point of the lineof the linear elastic part with the x-axis is used tocalculate the initial slip u

0, which is used to correct

all load displacement curves in further evaluations,comparisons or discussions. All presented resultsare per fastener.

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3 RESULTS AND DISCUSSION

3.1 Embedment behaviour

3.1.1 General

Typical load-displacement curves for the series

with one 16 mm dowel and different load-to-grainangles are shown in gure 8. The curves representthe average curve of each group. For all doweldiameters, the curves show a linear increase ofthe load up to the proportional limit. After theyielding point, the curves are almost constant for= 0 or increasing slightly for = 22.5 and 45,but increase signicantly for = 67.5 and 90. Thesame behaviour could be observed for all doweldiameters for load-to-grain angles of 45 andmore, whereas the behaviour parallel to the grainsignicantly depends on the dowel diameter, asshown in gure 9 and explained in section 3.1.2.For the tests with two dowels, the same behaviourwith almost twice the load of one dowel test wasalways observed.

3.1.2 Splitting

The behaviour parallel to the grain dependssignicantly on the dowel diameter due to splittingeffects that were observed for different deformationsdepending on the dowel diameter. The larger thediameter, the earlier the splitting occurs, which thenleads to a load decrease and the shorter the loadplateau is. Because of this behaviour that affectsthe yield embedment results using the 5%-offsetmethod, additional tests with larger specimens werecarried out for every dowel diameter to investigatethe inuence on the embedment behaviour and thusthe embedment results. The larger specimens usedare constantly 200 mm wide, 115 mm heigh and 45mm thick. Regardless of the dowel diameter, thecurves of these larger specimens all show a constantload level after yielding and splitting occurred atmuch larger deformations in comparison to thesmaller ones, as shown in gure 10. The evaluation

of the embedment curves of the smaller and largerspecimens also shows that the yield loads of bothare in the same range for dowel diameters up to20 mm. For dowel diameters of 25 mm and more,the maximum loads are in the same range than theyield loads. This means that the maximum loadswere adopted as yield loads for dowel diametersof 25 mm or more.

The minimum width according to the testingstandards is 4dand 6dfor ASTM D 5764-97a (ASTMInternational, 2007) and ISO 10984-2 (CEN, 2008),respectively. The specimen width of the smallerspecimen (120 mm in width) is greater than 4d, butsmaller than 6d for dowel diameters greater than20 mm; whereas the width of the larger specimens(200 mm in width) is always greater than 6d for

0

5

10

15

20

25

30

35

40

0 1 2 3 4 5 6 7 8

LoadF[kN]

Corr. displacement u [mm]

LVL-E-1x16

=0

=22.5

=90

=67.5

=45

Figure 8: Typical load versus displacementcurves for a constant diameter anddifferent load-to-grain angles.

0

10

20

30

40

50

60

0 2 4 6 8

LoadF[kN]


LVL-E0-small specimen

1x30

1x25

1x20

1x16

1x12

1x8

1x6

Figure 9: Typical load versus displacement

curves for all diameters parallel tothe grain direction for the smallerspecimens.

0

10

20

30

40

50

60

0 2 4 6 8

LoadF[kN]


LVL-E0-large specimen

1x30a

1x25a

1x20a

1x16a

1x12a

1x8a

1x6a

Figure 10: Typical load versus displacementcurves for all diameters parallel tothe grain direction for the largerspecimens.

dowel diameters up to 30 mm. Therefore, a minimum

width of the specimen of 6d, as required in ISO

10984-2 (CEN, 2008), shall be used in order to prevent

splitting at small deformations, which inuences the

evaluation results.

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3.1.3 Slip modulus

The stiffness or slip modulus K of the connectiondepends on both the dowel diameter and the loadto grain angle, as can be seen in gures 8 to 12 andfrom the results in tables 3 and 4, but the load-to-grain direction is not considered in the formulas of

the Eurocode 5 calculating the joint slip using the slipmodulus Kser

per fastener and shear plane (equation(4), below). For the tests conducted, almost the samestiffness or slip modulus per fastener was observedin the one and two dowel tests. Due to the type oftest method used, the value of the slip modulus Kofthe tests cannot be directly compared with the slipmodulus K

sergiven in Eurocode 5 (equation (4)), but

it indicates the inuence of different parameters onthe slip modulus as mentioned before. It seems thatthe slip modulus parallel to the grain, especially forbigger dowel diameters, is much higher and wouldthus result in much less slip deformation. There is agood agreement for load-to-grain angles of 45 andhigher. The mean densities of the tests with the samediameter were used to calculate the slip modulus K

ser

shown in gures 11 and 12. However, further researchis being undertaken and ndings will be publishedat a later date.

3.1.4 Tangent modulus

The tangent modulus Trepresents the behaviourafter yielding. Negative values represent a softeninginduced, eg. by splitting, whereas positive values

represent a hardening due to the compressibility ofthe cells under the fastener. A constant load levelwould refer to a modulus of zero. Due to the splittingresulting from the specimen sizes, as described insection 3.1.2, the tangent modulus can be taken aszero instead of all negative values. This is consistentwith the evaluation of the constant load level forlarger specimens. These parameters are useful forthe denition of material laws used in FE analysis.

3.2 Embedment results for Radiata pine LVL

Table 3 shows the mean values and the coefcientof variation of the results evaluated for each testseries depending on the dowel diameter, thenumber of dowels and the load-to-grain angle.The last two columns include the ratio of the yield

to proportional limit embedment strength andof the maximum to yield embedment strengths,respectively. The ratios of the embedment strengthsare on average 35% and 20%, respectively. Thisalso illustrates the differences resulting from thedetermination of the embedment strength usingdifferent standards and/or evaluation methods.

There are only very small variations between theyield strength of the tests with 1 and 2 dowels witha maximum difference of 6%, which is within thesame range as the coefcient of variation. As alreadymentioned, this is also valid for the stiffness K. Also

the load-displacement curves of all wider specimenstested are within the range of the shorter specimens,so that the results of one dowel, two dowels, theshort and the long specimens are examined as onegroup E together in the subsequent discussionand comparison with the Eurocode 5 regarding theirload-to-grain angle and dowel diameter.

The mean values of the yield embedment strengthf

h,,5%and the maximum embedment strengthf

h,,max

are compared as a function of the dowel diameterin gure 13. Both show a reduction in the strength

values with an increase of the dowel diameter. Thedependency of the embedment strength on thevarious load-to-grain angles was more signicantfor the yield embedment strength than the maximumembedment strength. The yield embedment strengthfor load-to-grain angles between 45 and 90 are veryclose together.

In addition to these diagrams, the yield embedmentstrength values versus density are shown in gure

Figure 11: Comparison of the slip modulusof LVL.

Figure 12: Comparison of the slip modulusof lumber.

1.5

per fastener and shear plane for dowels, bolts, screws and nails with pre-drilling

23

serK d

(4)

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Table 3: Test results of Radiata pine LVL (MPa).

Group nameStiffness

K(N/mm)

Tangentmodulus

T(N/mm)

Proportionallimit strength

fh, ,prop

Yield strength

fh, ,5%

Max. strength

fh, ,max

fh, ,5%

/

fh, ,prop

fh, ,max

/

fh, ,5%

Mean COV Mean COV Mean COV

LVL-E0-1x6 18013 28 36.2 11.2% 46.5 7.6% 52.0 6.7% 1.29 1.12

LVL-E45-1x6 8949 1291 26.3 13.1% 32.8 10.6% 50.3 8.3% 1.25 1.53

LVL-E90-1x6 5935 1838 26.1 9.6% 32.2 9.8% 55.0 11.1% 1.24 1.71

LVL-E0-1x8 27028 62a 28.6 11.4% 39.1 7.6% 42.0 7.9% 1.36 1.08

LVL-E0-2x8 26294 196 27.8 12.3% 40.6 5.8% 46.1 6.3% 1.46 1.13

LVL-E22.5-1x8 22263 187 29.3 14.8% 37.5 9.1% 41.1 8.1% 1.28 1.09

LVL-E45-1x8 12788 742 22.3 7.2% 28.7 7.8% 37.2 7.7% 1.29 1.29

LVL-E67.5-1x8 11100 2031 23.4 9.0% 31.2 8.2% 52.0 5.4% 1.34 1.67

LVL-E90-1x8 8881 2042 22.5 8.6% 30.1 6.5% 50.6 6.6% 1.34 1.68

LVL-E90-2x8 6432 1088 23.8 12.2% 29.4 9.9% 42.4 7.5% 1.24 1.44

LVL-E0-1x12 34131 49a 33.6 11.9% 44.2 8.2% 45.6 7.2% 1.32 1.03

LVL-E0-2x12 34408 34 37.5 11.4% 47.0 8.9% 48.1 9.0% 1.25 1.02

LVL-E22.5-1x12 33078 275 31.3 5.9% 43.2 5.3% 46.4 5.4% 1.38 1.07

LVL-E45-1x12 17997 1162 25.8 8.1% 33.5 3.5% 41.6 2.5% 1.30 1.24

LVL-E67.5-1x12 14398 2158 21.1 6.6% 28.3 7.5% 38.3 9.0% 1.34 1.35

LVL-E90-1x12 10593 1832 19.4 8.3% 26.7 7.1% 38.0 8.1% 1.37 1.42

LVL-E90-2x12 10822 1548 21.9 8.8% 28.1 7.3% 36.9 8.0% 1.28 1.32

LVL-E0-1x16 41213 108 32.5 6.5% 42.6 5.4% 43.6 5.7% 1.31 1.02

LVL-E0-2x16 32965 265 29.6 3.7% 39.2 3.0% 40.4 3.7% 1.32 1.03

LVL-E22.5-1x16 25029 1250 26.0 2.2% 34.9 4.3% 36.4 5.1% 1.34 1.04

LVL-E45-1x16 14953 266 21.1 8.4% 29.0 4.6% 33.5 6.2% 1.37 1.16

LVL-E67.5-1x16 15364 1412 20.3 7.5% 27.6 8.5% 34.2 8.1% 1.36 1.24

LVL-E90-1x16 12176 1982 19.9 9.3% 27.2 7.8% 35.1 6.7% 1.37 1.29

LVL-E90-2x16 10921 1332 19.6 5.6% 27.1 4.9% 34.3 5.4% 1.39 1.26

LVL-E0-1x20 55752 82a 28.8 33.7% 40.4 5.9% 40.6 5.7% 1.40 1.01

LVL-E0-2x20 70920 485a 30.7 15.2% 41.9 5.6% 42.4 5.3% 1.36 1.01

LVL-E22.5-1x20 40486 1073 25.0 5.9% 33.2 7.9% 33.8 8.3% 1.33 1.02

LVL-E45-1x20 21882 524 20.7 7.6% 28.0 5.1% 29.9 3.8% 1.35 1.07

LVL-E67.5-1x20 16000 1373 17.8 5.9% 24.6 8.0% 28.7 9.6% 1.38 1.17

LVL-E90-1x20 15078 1885 20.0 6.1% 27.5 5.5% 33.2 6.0% 1.37 1.21

LVL-E90-2x20 12296 1476 18.4 6.0% 25.8 6.6% 30.7 7.7% 1.41 1.19

LVL-E0-1x25 77217 4805a 27.1 11.3% 38.2 9.0% 38.2 9.0% 1.41 1.00

LVL-E45-1x25 27611 535 17.9 11.4% 25.9 7.7% 28.4 8.4% 1.45 1.09

LVL-E90-1x25 25591 1909 17.0 13.3% 26.7 6.8% 31.4 6.5% 1.57 1.18

LVL-E0-1x30 117342 5771a 31.8 11.6% 41.8 6.1% 41.8 6.1% 1.31 1.00

LVL-E45-1x30 34556 297 19.6 9.7% 25.8 7.3% 26.6 7.6% 1.32 1.03

LVL-E90-1x30 25297 1739 18.9 21.9% 27.5 12.8% 30.4 10.0% 1.45 1.11

Average 10.1% 7.5% 7.0% 1.35 1.20aA value of 0 shall be taken to consider the embedment behaviour for larger specimens.

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14. The strength values parallel and perpendicularto the grain direction show more or less positivecorrelations with the density. The use of a constantvalue could be appropriate because the relative smallrange of the density from LVL investigated (mostly560 to 620 kg/m) is to be taken into account for ageneral conclusion.

3.3 Embedment results for Radiata pine lumber

Table 4 shows the mean values and the coefcientsof variation of the results of the test series dependingon the dowel diameter dand the load-to-grain angle. Figure 15 contains the mean values of the yield

embedment strength fh,,5%

as a function of thedowel diameter and gure 16 as a function of thedensity. The results are almost constant regardlessof the dowel diameter, which agrees with studiesfor other species of wood (Harada et al, 1999;Sawata & Yasumura, 2002), whereas in a previousstudy (Whale et al, 1987), the embedment strengthwas observed to decrease as the dowel diameterincrease. The results corresponding to the densityare similar to the one of Radiata pine LVL and showpositive correlations, although the inuence of thedowel diameter on the correlation between theembedment strength and the density is lower fordiameters of 25 mm or more.

Figure 13: Mean yield and maximum embedment strength versus dowel diameter for Radiata pine LVL.

Figure 14: Embedment strength versus density for d= 6, 12, 20 and 30 mm for all loading angles in

Radiata pine LVL.

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Table 4: Test results of Radiata pine lumber (MPa).

Group nameStiffness

K(N/mm)

Tangentmodulus

T(N/mm)

Proportionallimit strength

fh, ,prop

Yield strength

fh, ,5%

Max. strength

fh, ,max

fh, ,5%

/

fh, ,prop

fh, ,max

/

fh, ,5%

Mean COV Mean COV Mean COV

RP-E0-1x6 12439 1a 29.7 15.0% 39.1 10.0% 44.5 6.9% 1.32 1.14

RP-E45-1x6 6074 934 21.5 14.7% 26.5 9.6% 39.3 7.8% 1.23 1.48

RP-E90-1x6 5005 997 17.8 14.7% 22.0 14.7% 35.8 15.7% 1.23 1.63

RP-E0-1x8 14160 117 24.0 10.7% 32.8 8.5% 36.9 7.2% 1.37 1.13

RP-E45-1x8 8130 730 18.0 13.5% 23.2 6.8% 31.4 8.5% 1.29 1.36

RP-E90-1x8 5275 584 12.1 16.6% 15.7 16.0% 21.9 14.2% 1.30 1.40

RP-E0-1x10 34.6 15.8%

RP-E90-1x10 18.0 18.6%

RP-E0-1x16 35.2 15.0%

RP-E90-1x16 16.9 17.6%

RP-E0-1x20 34.0 16.3%

RP-E90-1x20 17.9 16.6%

RP-E0-1x25 56237 3048a 21.4 21.3% 32.2 16.6% 32.4 16.5% 1.50 1.01

RP-E45-1x25 20174 476 13.0 19.0% 18.9 17.7% 20.1 12.0% 1.46 1.06

RP-E90-1x25 21786 936 12.2 18.7% 18.8 11.7% 21.2 12.5% 1.54 1.13

RP-E0-1x30 81005 3618a 26.3 19.2% 35.5 14.3% 35.5 14.2% 1.35 1.00

RP-E45-1x30 26827 418 17.5 13.9% 22.0 12.4% 22.8 11.2% 1.26 1.04

RP-E90-1x30 20938 820 15.2 9.6% 20.8 8.5% 21.9 9.1% 1.37 1.05

Average 15.6% 13.7 % 11.0% 1.35 1.20aA value of 0 shall be taken to consider the embedment behaviour for larger specimens.

Figure 15: Mean yield embedment strengthversus dowel diameter for Radiatapine lumber.

4 EMBEDMENT STRENGTH

VERSUS EUROCODE 5

The comparison of the mean test values with thecorresponding embedment strengths according to theEurocode 5 formulas are shown in gure 17. Each of

the graphs shows the embedment strengthfh,0

and the

reduction factor k90

, calculated from the embedmentstrength for = 0 and 90, as well as their linearregression (for LVL as one group for one and twodowels together). The Eurocode 5 embedmentstrength was calculated using:

fh,0,k

= 0.082(1 0.01d)k (5)

,0,, , 2 2

90 sin cos

h kh k

ff

k

(6)

where

90

1.35 0.015 for softwood

1.30 0.015 for LVL

0.90 0.015 for hardwood

d

k d

d

(7)

and dis the dowel diameter, the mean density of597 kg/m3for Radiata pine LVL and 505 kg/m3forRadiata pine lumber, and the load-to-grain angle.

For the LVL results shown in gure 18, there is a goodagreement for the average values. The slope of theyield embedment strength is parallel to the predictionof the Eurocode 5, whereas the trend of the reductionfactor k

90is almost constant or even slightly opposite

in trend. For the Radiata pine lumber results, is not

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Figure 16: Embedment strength versus density for d= 6, 10, 20 and 30 for all loading angles in Radiatapine lumber.

Figure 17: Comparison of the test results parallel and perpendicular to the grain with the Eurocode 5.

Figure 18: Embedment strengthfh,0

parallel to the grain and reduction factor k90

in comparison withEurocode 5.

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as good agreement and the results show an almostconstant value regardless of the dowel diameter forthe yield embedment strength parallel to the grain.The reduction factor k

90, evaluated using Eurocode

5, is much lower than the factor evaluated based onthe test results for small diameters and shows thesame trend as the LVL results.

5 SUMMARY AND DESIGN PROPOSAL

Based on the results presented for Radiata pinelumber and LVL, the method from the Eurocode5 with adjusted formulas for the estimation of theembedment strength f

h,0 can be used, as shown in

equation (8). As for the results of the reduction factork

90, we propose to use a constant factor of 2.0 and

1.5 for Radiata pine lumber and LVL, respectively,for simplicity and ease of use in the design. TheHankinson formula shown in equation (9) can be

used to calculate the embedment strength values fordifferent load to grain angles. A summary is givenwith equations (8) to (10).

,0,

0.072 1 0.0024 for Radiata pine lumber

0.075 1 0.0037 for Radiata pine LVL

k

h k

k

df

d

(8)

,0,, , 2 2

90 sin cosh k

h k

ff

k

(9)

where

90 2.0 for Radiata pine lumber1.5 for Radiata pine LVLk

(10)

and kis the characteristic timber density in kg/m3,

dis the bolt or dowel diameter in mm, and is theload-to-grain angle.

Figure 19 shows the comparison of the test resultswith the embedment strengths, obtained usingthe proposed method according to equations (8)to (10) for the mean density and a lower density todemonstrate the inuence of using a characteristicdensity in the design. Using densities of 500 and

340 kg/m3for Radiata pine LVL and Radiata pinelumber, respectively, which are the characteristicdensities for an equivalent New Zealand gradeof MSG10, the results are always on the safe side,especially for Radiata pine lumber.

6 DESIGN EXAMPLE

The following example is used to demonstrate thedesign procedure and differences of the currentNew Zealand timber design standard NZS 3603:1993(Standards New Zealand, 1993) and the proposedadjusted EYM adopted from the European timberstandard Eurocode 5, EN 1995-1-1:2004 (CEN, 2004).According to the connection as shown in gure 20and their parameters, the design joint capacity R

90,d

is to be calculated. Splitting will not be consideredor checked.

6.1 New Zealand timber designstandard NZS 3603:1993

R90,d

= N* = nnsk

1k

12k

13Q

sk= 73.3 kN

with

parallel to the grain:

211 10.4kN

min0.5 19.5kN

cj

kl

e cj

k f dQ

b f d

perpendicular to the grain:1.5

11 8.0kNmin0.5 7.0kN

pj

kp

e pj

k f dQb f d

where N* is the design load of the joint; Qsk is the

system characteristic strength per bolt, which isequal to the lesser of Q

kl or Q

kp; is the strength

reduction factor, 0.7; nis the number of bolts, 9; nsis

the number of shear planes, 2; k1is the load duration

factor, 1.0 (brief loads); k11

is the factor consideringjoint group classication, 2.0 (J5, parallel) and 14.9(J5, perpendicular); k

12is the factor for the design in

green timber, 1.0 (not green); k13

is the modication

Figure 19: Comparison of the test results with the new proposal for calculating the embedmentstrength for different densities.

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Fw,c

=Awf

c,90= 10.0 kN (A

efaccording to Eurocode 5 is

not considered)

whereFax,Rk

is the governing load to consider the ropeeffect; F

v,Rkis the characteristic load-carrying capacity

per shear plane per fastener (Johansen theory); Fb,ax

isthe characteristic axial load-carrying capacity of thefastener; F

w,cis the characteristic load-bearing capacity

of the washer;My,Rkis the characteristic fastener yieldmoment;Ais the area (b= bolt, w= washer); k

modis the

modication factor for duration of load and moisturecontent, 0.9 (brief loads);

M is the partial factor for

material properties, 1.1 (steel failure governs); nis thenumber of bolts (effective number in load directionhas to be taken into account), 9; n

sis the number of

shear planes, 2; ti is the timber or board thickness

or penetration depth for member i(t1= 70 mm and

t2= 90 mm); d is the fastener diameter, 12 mm;

k

is the characteristic timber density, 340 kg/m3 (forC22, which is equivalent to NZ grade MSG10); f

h,i,k

is the characteristic embedment strength in timbermember iaccording to the load-to-grain angle;f

h,0,kis

the characteristic embedment strength parallel to thegrain;f

u,kis the ultimate tensile strength, 400 MPa (mild

steel);fc,90

is the characteristic compression strength ofthe wood, 4.5 MPa (considering recent research results,published in Franke & Quenneville (2010)); k

90is the

reduction factor, 2.0 (Radiate pine lumber); iis the

load-to-grain angle for member i(1= 90 and

2= 0);

and is the ratio between the embedment strength ofthe members 1 and 2.

6.3 Comparison

The two design examples show that using theproposed EYM results in a 28% higher joint capacity(93.6/73.3 = 1.28), but using, for example, a loweror higher timber grade as well as an higher steelgrade for the fastener, which is only consideredin the European model, will change the ratio ofthe capacities. Furthermore, changing the memberthicknesses is not always considered in the NZdesign method. For example, the joint capacity forthe proposed model ranges between 87.2 kN (MSG8and steel grade of f

u,k

= 400 MPa) and 116.9 kN(MSG15, with an equivalent density of 400 kg/m3,and steel grade off

u,k= 600 MPa). This shows that the

capacity can result between 118% and 160% of thejoint capacity according to the current NZ design. Itseems that in the most of the cases considered here,the NZ design method is conservative; however,there are also cases where the joint capacity of theproposed method can be much less, thus, the currentNZ design is then overestimating the joint capacity.

For a comparison, the design joint capacity accordingto the Australian design standard results in 91.1 kN

(joint group JD4,

= 0.75, k16= 1.0, k17= 1.0) and isalso independent on the timber or steel grade. Thisis 24% higher than the capacity according to the NewZealand standard and 3% less than the one accordingto the proposed model.

1

2

240

7 7

6

0

60

60

60

190

90

35 60 60 35

90R

9 Bolts 12

[mm]

40

Figure 20: Sketch and parameters of the

connection for the comparison of thedesign standards.

factor for multiple numbers of bolts, 1.114 0.031n=0.835 (9 bolts);f

cjis the bolt bearing strength parallel

to the grain, 36.1 MPa;fpj

is the bolt bearing strengthperpendicular to the gain, 12.9 MPa; d is the boltshank diameter, 12 mm; and b

eis the effective timber

thickness, 90 mm (smaller of 2b1and b

2).

6.2 Proposed method adopted fromthe European timber standard

EN 1995-1-1:2004 (Eurocode 5)

mod ,90, 93.6 kN

s v Rk d

M

k nn FR

with

,1, 1

,2, 2

,,1, 1

2,1, 1

,

,

,, ,1,

9.99 kN

0.5 12.84 kN

4 21.05 2 1

2min

6.35 kN

42

1.15 2 7.48 kN1 4

h k

h k

y Rkh k

h kv Rk

ax Rk

ax Rky Rk h k

f t d

f t d

Mf t d

f dtF

F

FM f d

,0,,1, 2 2

90

11.89 MPasin cos

h kh k

ff

k

,0,,2, 2 2

90

23.77 MPasin cos

h kh k

ff

k

fh,0,k

= 0.072(1 0.0024d)k= 23.77 MPa

,2,

,1,

2h k

h k

f

f

My,Rk

= 0.3fu,k

d2.6= 76,745 Nmm

Fax,Rk

= min{Fv,RkJohansen

; Fb,ax

; Fw,c

} = 5.08 kN

Fb,ax

=Abf

u,k= 45.2 kN

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The governing case of the EYM also providesinformation about the specific failure of theconnection, ie. a combined embedment failure of theouter timber member occurs together with bendingof the bolts in the example presented (3rdcase). Thisinformation also allows the designer to consider thecontribution of the so-called rope effect of the fastener.

This means that the characteristic load-carryingcapacity for bolts per shear plane and fastener for thefailure cases 3 and 4 (3rdand 4thequation of F

v,Rk) is

increased by 25% of the lesser of the axial withdrawalcapacity of the fastener, the bearing capacity of thewasher or the joint capacity of the Johansens part.Furthermore, it gives the opportunity to increase thejoint capacity by specically changing the parameterthat mostly inuences the governing case.

7 CONCLUSION AND RECOMMENDATION

A comprehensive investigation of the embedmentbehaviour and determination of the embedmentparameters provides a database with sufficientinformation to adopt the EYM predicting ductilejoint capacities. The research results observed covera wide range of different dowel diameters, loadto grain angles and wood products, as well as avalid reference number of test specimens of eachconguration. A comparison of smaller and largerspecimen shows that it is recommended to use aminimum specimen width of 6dfor test in paralleldirection in order to prevent splitting, which thus

inuences the evaluation results. The results alsoshow different slip moduli depending on the load-to-grain direction, which is not considered in theEurocode 5 formulas and could be implemented.

Based on the results obtained, adjusted formulascould be evaluated and their use demonstratedwithin the example. It is thus recommended toimplement the EYM into a revised New Zealandor Australian design standard for the prediction ofthe resistance of the ductile failure mode of boltedand dowelled connections. For a comprehensive useof the EYM model, one also needs to evaluate the

embedment strength values for nails and screws.Further research is also required for predicting brittlefailures which many researchers have observed.

ACKNOWLEDGEMENT

The authors would like to thank the StructuralTimber Innovation Company (STIC) for supportingthis research study.

REFERENCES

ASTM International, 2007, ASTM D 5764-97aStandard Test Method for Evaluating Dowel-BearingStrength of Wood and Wood-Based Products , WestConshohocken, USA.

Deutsches Institut fr Normung (DIN), 1979, DIN52192:1979-05 Prfung von Holz; Druckversuch querzur Faserrichtung (Testing of wood; compression testperpendicular to grain), Berlin, Germany.

European Committee for Standardization (CEN),1993, EN 383:1993 Timber structures Test methods.

Determination of embedment strength and foundationvalues for dowel type fasteners, Brussels.

European Committee for Standardization (CEN),2004, EN 1995-1-1:2004 Eurocode 5 Design of timberstructures, Part 1-1: General Common rules and rulesfor buildings, Brussels.

Franke, S. & Quenneville P. 2010, Compressionstrength perpendicular to the grain of New ZealandRadiata Pine lumber,Australian Journal of StructuralEngineering, Online, pp. 23-34.

Harada, M., Tomoyuki, H., Masahiko, K. & Kohei,K. 1999, Dowel-bearing test of glued laminatedtimber with a drift-pin, Summaries of TechnicalPapers of Annual Meeting Architectural Institute ofJapan, pp. 49-50.

Hbner, U., Bogensperger, T. & Schickhofer, G. 2008,Embedding strength of European hardwoods,Proceedings of CIB-W18, Paper 41-7-5, St. Andrews,Canada.

International Organization for Standardization (ISO),2008, Draft ISO/DIS 10984-2 Timber structures Dowel-

type fasteners Part 2: Determination of embeddingstrength and foundation values, Geneva.

Mills, M. 2008, Bolted timber connections,internal research report, Department of Civil andEnvironmental Engineering, University of Auckland,New Zealand.

Sawata, K. & Yasumura M. 2002, Determinationof embedding strength of wood for dowel-typefasteners, Journal of Wood and Sciences, Vol. 48, pp.138-146.

Standards Australia, 1997, AS1720.1-1997 TimberStructures Part 1: Design methods and Amendment 4Nov. 2002, Sydney, Australia.

Standards New Zealand, 1993, NZS 3603:1993 TimberStructures Standard, Wellington, New Zealand.

Suffiad, J. 2008, Bolted timber connectionsperpendicular to the grain, internal research report,Department of Civil and Environmental Engineering,University of Auckland, New Zealand

Whale, L. R. J., Smith, I. & Larsen, H. J. 1987, Designof nailed and bolted joints proposals for the revisionof existing formulae in draft Eurocode 5 and the CIBcode, Proceedings of the CIB-W18 meetings, paper 25-7-2, Dublin, Ireland.

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STEFFEN FRANKE

Dr Steffen Franke is a Postdoctoral Research Fellow at the University ofAuckland. He is a civil engineer with special interest in structural constructions,timber engineering and nite element analysis. Steffen graduated in structuralengineering at the Bauhaus-University Weimar (BUW), Germany, in 2001. In2008 he completed his PhD at the BUW, the Chair of Timber and Masonry

Engineering. His research focused on the investigation of timber with anown developed photogrammetric measuring system as base for numericalsimulations. He has been in the academic and research eld since 2001, teachingcourses in the area of structures and design, including theory of structuresand materials, structural design of steel, unreinforced and reinforced concrete,masonry, and mainly structural timber design. He has supervised severalundergraduate and graduate theses, authored national and internationalscientic and research papers and co-authored a book titledHolzkonstruktionenin Mischbauweise (Timber Composite Constructions) published in Germany.Since 2008, he has been working as Postdoctoral Research Fellow in TimberDesign with Prof Quenneville at the University of Auckland in New Zealand.

PIERRE QUENNEVILLE

Pierre Quenneville is the newly appointed Professor of Timber Design in theCivil and Environmental Engineering Department at the University of Auckland.Pierre graduated with a BEng (First Class Honours) in Civil Engineering at theRoyal Military College of Canada in 1983, and accepted an ofcer commissionas a military engineer with the Canadian Armed Forces. During his service,he graduated with a MEng at Montreal University in Structural Engineeringin 1986 and then served with an engineering unit, where he became involved

with timber structure repairs. He was then transferred to the Royal MilitaryCollege to take on a lecturer position within the Civil Engineering departmentin 1988. He engaged in PhD studies at the same time at Queens Universityin Kingston and graduated in 1992. His research was on timber connectionsand he became involved with the Canadian Wood Design standard in 1993.Since 1996, he has been chairing the Fastenings sub-committee of the TechnicalCommittee for the Canadian design standard. His research on connectionsfocuses on bolted connections and he became known for his novel approachto their design. During his academic career, Pierre had two sabbatical leaves,one of which was with a Canadian timber fabricator. He kept his involvementwith this timber structure fabricator until his move to New Zealand and wasinvolved with the design of many interesting timber projects. He has also beeninvolved in consulting work since 1999.

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28 Bolted and dowelled connections in Radiata pine and laminated ... Franke & Quenneville

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