1

Behavior of Glulam in Compression Perpendicular to grain in Different Strength Grades and Load

Configurations

M. Augustin1, A. Ruli2, R. Brandner2, G. Schickhofer1 1 Institute for Timber Engineering and Wood Technology,

Graz University of Technology / Austria, Europe 2 holz.bau forschungs gmbh, Graz / Austria, Europe

Abstract In the European standard for glulam EN 1194:1999 the strength values perpendicular to the grain are specified in dependence on the tensile strength and grading class of the used boards respectively. By consideration of the test results given in this paper this correlation could not be confirmed. For all glulam strength classes the specification of a constant characteristic strength value perpendicular to the grain fc,90,g,k of about 2,1 N/mm² to 2,3 N/mm² can be recommended and has to be discussed. This is also the fact for the characteristic modulus of elasticity perpendicular to the grain where a constant mean value of 300 N/mm² valid for all glulam strength classes should be considered. For the design of structural members with different loading situations adjustments of these values are necessary. 1 Introduction In many practical applications timber and glulam respectively (resp.) is loaded perpen-dicular to the grain. For design purposes realistic strength and stiffness values have to be determined. It has to be mentioned that a definite point of failure due to stresses perpendicular to the grain can not be obtained and – apart from special configurations where a collapse as stability problem can occur – restrictions of deformations are needed. As a result for the determination of strength values for this type of loading serviceability limit states are rather crucial than ultimate limit states ([7], [8], [9]). In the relevant testing standard EN 408:2005 [16] the needed force Fc,90 and stress fc,90 resp. for reaching a defined deformation (in EN 408:2005: 1% of the specimens height h0) are specified as strength values for compression perpendicular to grain. For the determination of the stiffness parameters a secant (in EN 408:2005: between 0,1 Fc,90,max and 0,4 Fc,90,max) has to be approximated into the load-deformation-curve whereby the slope enables the calculation of the modulus of elasticity perpendicular to the grain Ec,90. The mechanical properties for this type of loading are depending on wood technological characteristics like the annual ring width and - curvature, in particular the position of the board to the pith and in local areas by the knottiness ([3], [5], [6]). Apart from this in particular the geometrical situation of the loaded area (at the end, at a distance from the end, “in the center”), the type of loading (full area loading, partial area loading) and the loading and bearing length resp. have a strong influence on the mechanical parameters in compression perpendicular to the grain ([1], [2], [4], [5], [11]). Because of the large variability of loading situations in practical cases basic values for the strength and stiffness

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perpendicular to the grain in the european codes are determined on cubic specimens loaded on the whole surface. For the design of structural members the so specified values have to be adjusted by coefficients for the loading configuration (in Eurocode: kc,90) and the loading length to represent the realistic situation. For the determination of strength values such in most codes for glulam also in the European standard EN 1194:1999 [14] the so called “beam model” is given. According to this model with increasing tensile strength and grading class of the boards resp. the bending strength of hence build-up glulam increases. Based on this relation also other characteristic values for glulam are defined. Because of the appearance of juvenile wood and the higher knottiness near to the pith resp. in general boards with higher tensile characteristics are from the outer zones of the log. Such a board can be characterized by flat curved annual rings where boards near to the pith have upstanding ones. Obviously these boards have lower stiffness perpendicular to grain and – because of the definition of the strength – also lower strength values (“spring-model”). That is in fact a contradiction to the given “beam model” based on the fact that boards of flat curved annual rings are characterized by lower compression strength perpendicular to grain but higher MOE and tensile strength. Therefore the above mentioned assumption is verified with tests on cubic specimens of different heights. In addition for the evaluation of a practical case tests on members with a continuous support on the opposite side of the loadings (sills) with different heights and various loading situations have been conducted. 2 Codes and Standards 2.1 EN 1194:1999 [14] The ”beam model“ in the European standard EN 1194:1999 applied on the compression strength perpendicular to the grain specifies the correlation between the tensile strength and grading class of the boards resp. and the strength of the glulam perpendicular to the grain by the following function:

5,0k,l,0,tk,g,90,c f7,0f ⋅=

fc,90,g,k ……characteristic glulam compression strength perpendicular to the grain [N/mm²] ft,0,l,k ……characteristic tensile strength of the used boards [N/mm²] For the glulam strength classes defined in this standard and the characteristic tensile strength of the boards needed for their lay-up the following stiffness and characteristic strength values for compression perpendicular to the grain can be calculated as listed in the following Tab. 1.

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Strength class of the glulam GL24h GL28h GL32h GL36h Tensile strength of the board acc. to EN 1194:1999

ft,0,l,k [N/mm²] 14,5 18,0 22,0 26,0

fm,g,k [N/mm²] 24,0 28,0 32,0 36,0 E0,g,mean [N/mm²] 11600 12600 13700 14700 E90,g,mean [N/mm²] 390 420 460 490

homogeneous build-up glulam

fc,90,g,k [N/mm²] 2,70 3,00 3,30 3,60 Tab. 1: Glulam strength classes defined in EN 1194:1999 and appropriate mechanical properties 2.2 EN 408:2005 [16] In the European standard EN 408:2005 regulations and an instruction for the testing procedure to determine the mechanical properties perpendicular to the grain are given. For glulam specimens specifications for the geometry (cubic specimens) and size (b · l = 25000 mm²; bmin = 100 mm; h = 200 mm) as well as a method for the calculation of strength and stiffness values is included. For the determination of the maximum compression load Fc,90,max in a first step an estimated load Fc,90,max,est is needed, then the values 0,1 Fc,90,max,est and 0,4 Fc,90,max,est can be calculated and drawn into the load-deformation-curve. Through the intersection points of these values with the recorded testing curve of the specimens a line 1 can be drawn. This line has to be shifted parallel on the x- coordinate by a distance of 0,01 h0 to get line 2. Where this line intersects the load-deformation-curve of the tested specimens a value Fc,90,max can be obtained. If this value is within a range of 5% of the estimated value Fc,90,max,est the procedure ends otherwise it has to be repeated until the value is within this tolerance limit.

F

1 2

w

Fc,90,max

0,4 Fc,90,max

0,1 Fc,90,max

0,01 h0

Fig. 1: Definition of the maximum compression load perpendicular to the grain in accordance with EN 408:2005

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By knowledge of the load Fc,90,max the strength perpendicular to the grain fc,90 can be calculated by

lbF

f max,90,c90,c ⋅

=

fc,90 ……... compression strength perpendicular to the grain [N/mm²] Fc,90,max …….. maximum compression load perpendicular to the grain [N] b, l ……... width, length of the specimens [mm] The modulus of elasticity perpendicular to the grain can be computed by

lb)ww(h)FF(E

1040

0104090,c −

−=

Ec,90 ……...… modulus of elasticity in compression perpendicular to the grain [N/mm²] F10, F40 …….. load at 0,1 and 0,4 of Fc,90,max [N] w10, w40 ……. corresponding deformations at the above mentioned loads [mm] h0 …………gauge length [mm] b, l ……….. width, length of the specimens [mm] 2.3 Execution and analysis of the tests In the below mentioned tests no gauges have been used as mentioned in EN 408:2005. Instead deformations in relation to piston ways of the testing machine have been measured. As a consequence the specimen height is equivalent to the gauge length and further the load-stiffness-behaviour of the testing apparatus has been determined and considered in the calculation of the test results. The characteristic MOE Ec,90,g,k and density ρk in accordance to EN 384:2004 [15] have been determined as mean and 5%-quantile value resp. For the determination of the characteristic compression strength perpendicular to the grain fc,90,g,k the required minimum number of 40 specimens could not be reached for all series. Therefore the calculation of the strength values in general has been carried out in accordance to prEN 14358:2006 [17]. The characteristic values of the sill-like specimens have been determined in the same way as it has been mentioned for the normative regulated cubic specimens. Thus the effect of the load spreading on the stiffness and strength has not been considered.

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3 Objective of the tests Because of the reasons mentioned above a verification of the specifications given in the European standard EN 1194:1999 has been conducted. Especially the correlation between the tensile strength of the boards and their grading class resp. and the compression strength perpendicular to the grain of glulam has been investigated. To clear-up the influence of the deformation limit (0,01 h0) on the strength perpendicular to the grain given in EN 408:2004 tests have been analysed also with the deformation limits 0,02 h0 (2%) and 0,05 h0 (5%). As mentioned the strength and stiffness values tested on cubic specimens are of less practical interest. In the field of timber engineering compression forces perpendicular to the grain often appear as local loadings in joints. Examples for such loading configurations are bearing areas of girders, loadings where the member rests on a firm foundation (sill) or are transmitted trough a member and below washers. For the calculation in the design process it is of importance how the members are loaded and on which length the load is applied. In the Eurocode this fact is considered by the kc,90-factor for the loading situation and a factor for the bearing length. The increased stiffness and strength perpendicular to the grain of practical loading configurations can be explained with the supporting effect of wood fibers beside the direct loaded areas (see Fig. 2).

Fig. 2: Illustration of the supporting effect of wood fibers beside the direct loaded area by means

of a loaded cellular material To find out the stiffness and strength values for a case of practical interest tests on sill-like specimens with loadings at the end, at a distance of 100 mm from the end and in an “adequate” distance form the end (“in the center”) have been conducted. The bearing length of all sill-like specimens has been 150 mm so that this influence can not be answered with the below mentioned tests. For the evaluation of a possible influence of specimens height on the strength perpendicular to the grain also tests with two different heights for the cubic and the sill-like specimens (h = 200 mm and h = 480 mm) have been performed.

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4 Testing programme 4.1 Material The investigated species has been spruce (Picea Abies) from a middle European provenience. All specimens have been conditioned before the tests to an equilibrium moisture content of u = 12 ± 2 % at 20°C temperature and 65 % relative humidity. The glulam specimens have been produced with a polyurethane adhesive (Purbond HB 110) in the lab. 4.2 Tests For the verification of the above mentioned questions two series (I and II) have been tested: 4.2.1 Series I For test series I 160 boards of dimensions l/b/h = 4000/175/40 mm have been obtained and graded into three stiffness classes (K1, K2, K3) by means of dynamical modulus of elasticity (MOEdyn) measurement determined with an ultrasonic apparatus (Sylvatest). Subsequently the boards have been cut as shown in Fig. 3 to obtain on one hand 90 specimens (= 30 specimens per stiffness class) for tensile tests according to EN 408:2005 (free testing length of 1600 mm; distance of the displacement sensors for the determination of the tensile MOE = 5 · b = 870 mm). On the other hand the remaining pieces have been used to produce 62 cubic glulam specimens (l/b/h = 160/160/200 mm) for the determination of the compression properties perpendicular to the grain in accordance to EN 408:2005. Threshold values of the MOEdyn for the three stiffness classes and the number of specimens for the tests of series I are given in Tab. 2. Stiffness class of the boards K1 K2 K3 MOEdyn of the boards [N/mm²] MOEdyn > 17200 15500 < MOEdyn

< 17200 MOEdyn < 15500

Number of tensile tests [-] 30 30 30 Series I - Specimens for tests perpendicular to the grain – cubic specimens (160/160/200 mm)

19 22 21

Tab. 2: Threshold values for MOEdyn and specimens number of series I

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Fig. 3: Geometry and lay-up for the specimens of series I

Fig. 4: Test configuration for the tensile tests (left) and the tests for the determination of compression properties perpendicular to the grain (right)

4.2.2 Series II Series II has been split-up into four sub-series with two heights (cubic specimens l/b = 160/160 mm; h0 = 200 mm and h0 = 480 mm) to investigate the influence of specimens height and various loading conditions resp. and geometrical influences (sill-like specimens l/b = 980/160 mm; h0 = 200 mm and h0 = 480 mm). The material consisted of machine graded boards (graded with the approved grading device Dimter Grademaster 403) of the strength grades MS10 (C24M), MS13 (C35M) and MS17 (C40M) in accordance to ON DIN 4074-1:2004 and EN 338:2003 resp. The cubic specimens have been cut, build-up as shown in Fig. 3 and tested as described for series I (tensile tests; compression tests perpendicular to the grain). Boards for the production of the sills have been cut as shown in the upper part of Fig. 3. With the longer parts (l = 3000 mm) tensile tests have been conducted and with the shorter parts (l = 1000 mm) sill-like specimens have been produced and tested in compression at the end, 100 mm from the end and “in the center” as shown in Fig. 5. A summary with the denotations of the sub-series, the dimensions and the number of specimen build-up with boards of the different grading classes is given in Tab. 3.

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Grading class of the boards according to ON DIN 4074-1:2004 and EN 338:2003 resp.

MS10 (C24M)

MS13 (C35M)

MS17 (C40M)

Tensile tests - Number of specimens 131 134 127 Series II/1 Number of cubic specimens (160/160/200 mm) 41 40 41

Series II/2 Number of cubic specimens (160/160/480 mm) 6 6 6

Series II/3 Number of sill-like specimens (980/160/200 mm) 18 18 18

Series II/4 Number of sill-like specimens (980/160/480 mm) 5 5 5

Tab. 3: Denotation of the sub-series, dimensions, grading classes and number of specimens of

series II

Fig. 5: Loading situations, dimensions (above) and test configuration (below) of the sill-like

specimens of series II (sub-series II/3 and II/4)

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6 Results The results given below in general have been calculated in accordance with the specifications given in EN 384:2004. Where this has not been possible because the number of specimens was lower than 40 the regulations of prEN 14358:2006 has been applied.

6.1 Series I Stiffness class of the boards K1 K2 K3 Boards Specimens number [-] 30 30 30

Mean [kg/m³] 481 450 408 COV [%] 4,36 4,61 5,43

Density ρl

ρl,k [kg/m³] 446 416 372 Mean [N/mm²] 14730 12290 10340 COV [%] 10,16 6,88 12,79

(Tensile-) MOE Et,0,l

Et,0,l,05 [N/mm²] 12270 10890 8160 Mean [N/mm²] 49,54 33,73 27,64 COV [%] 23,87 26,07 33,87

Tensile strength ft,0,l

ft,0,l,k; EN 14358 [N/mm²] 30,50 19,72 15,71 Glulam specimens Specimens number [-] 19 22 21

Mean [kg/m³] 490 439 418 COV [%] 5,02 4,99 11,98

Density ρg

ρg,k [kg/m³] 449 403 335 Mean [N/mm²] 299 301 320 COV [%] 19,86 12,02 22,91

MOE Ec,90,g

Ec,90,g,05 [N/mm²] 201 241 200 Mean [N/mm²] 3,10 3,01 3,12 COV [%] 22,10 17,58 18,01

Compression strength perpendicular to the grain fc,90,g fc,90,g,k; EN 14358 [N/mm²] 1,99 2,13 2,18

Tab. 4: Test results of series I

Comparison of the characteristic values fc,90,g,k

3,11

3,87

2,77

1,992,132,18

0

1

2

3

4

5

10 12 14 16 18 20 22 24 26 28 30 32f t,0,l,k [N/mm²]

f c,9

0,g,

k [N

/mm

²]

fc,90,g,k "EN1194"

fc,90,g,k "Tests"

Δ = 27% Δ = 46 % Δ = 94 %

GL

32h

GL

36h

GL

28h

GL

24h

Fig. 6: Comparison of the characteristic values fc,90,g,k calculated with the functions in

EN 1194:1999 and the test results of series I

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6.2 Series II In table 5 results from the tests of subseries II/1 and II/2 (tests on cubic specimens with heights h0 = 200 mm and h0 = 480 mm) are listed. Grading class of the boards MS 10

(C24M) MS 13

(C35M) MS 17

(C40M) Boards Specimens number [-] 131 134 127

Mean [kg/m³] 419 452 489 COV [%] 6,33 6,47 6,95

Density ρl

ρl,k [kg/m³] 375 404 433 Mean [N/mm²] 9690 11830 14400 COV [%] 12,17 7,82 12,98

(Tensile-) MOE Et,0,l

Et,0,l,05 [N/mm²] 7750 10310 11330 Mean [N/mm²] 22,05 30,32 43,21 COV [%] 30,76 24,01 33,19 ft,0,l,05; EN 384 [N/mm²] 11,40* 19,23* 24,03*

Tensile strength ft,0,l

ft,0,l,k; EN 14358 [N/mm²] 11,98 19,21 23,38 Glulam Specimens Subseries II/1 Specimens number [-] 41 40 41

Mean [kg/m³] 417 447 493 COV [%] 7,71 6,04 6,04

Density ρg

ρg,k [kg/m³] 364 402 444 Mean [N/mm²] 265 292 318 COV [%] 21,24 15,64 16,81

MOE Ec,90,g (h0 = 200 mm)

Ec,90,g,05 [N/mm²] 172 217 230 Mean [N/mm²] 3,35 3,43 3,16 COV [%] 19,62 21,05 17,58 fc,90,g,05; EN 384 [N/mm²] 2,46* 2,45* 2,45*

Strength perpendicular to the grain fc,90,g (h0 = 200 mm) (EN 384 / EN 14358)

fc,90,g,k; EN 14358 [N/mm²] 2,33 2,33 2,30 Subseries II/2 Specimens number [-] 6 6 6

Mean [N/mm²] 272 255 312 COV [%] 10,87 9,63 19,48

MOE Ec,90,g (h0 = 480 mm)

Ec,90,g,05 [N/mm²] 223 214 212 Mean [N/mm²] 2,89 2,87 2,84 COV [%] 14,50 13,59 11,73

Strength perpendicular to the grain fc,90,g (h0 = 480 mm) fc,90,g,k; EN 14358 [N/mm²] 2,10 2,11 2,17 * The given values have been determined as 5%-quantile values by means of order statistics.

Tab. 5: Results of series II – subseries II/1 and II/2 In table 6 results of scenarios characterized by consideration of deriving deformation limits of 0,02 h (2%) and 0,05 h (5%) are listed. Further a comparison with values calculated in accordance to EN 408:2005 (deformation limit 0,01 h and 1% resp.) is included.

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Analysed deformation limit

In acc. to EN 408:2005

(1%)

Deformation limit 0,02 h

(2%)

In comparison to EN

408:2005 [%]

Deformation limit 0,05 h

(5%)

In comparison to EN

408:2005 [%]

Mean value MS 10 (C24M) 3,35 3,69 110 3,93 117 MS 13 (C35M) 3,43 3,74 109 3,97 116 MS 17 (C40M) 3,16 3,54 112 3,81 121 Characteristic value MS 10 (C24M) 2,33 2,65 114 2,89 124 MS 13 (C35M) 2,33 2,67 115 3,02 130 MS 17 (C40M) 2,30 2,64 115 2,96 129

Tab. 6: Compression strength perpendicular to the grain of subseries II/1 by consideration of

different deformation limits (0,02 h0 and 0,05 h0) Strength values determined from tests with the sill-like specimens depending on different loading situations (loading at the end, at a distance of 100 mm from the end and “in the center”) and the different grading classes of the used boards are given in Tab. 7. Grading class of the boards MS 10 (C24M) MS 13 (C35M) MS 17 (C40M) Type of loading (see also Fig. 5) 1 2 3 1 2 3 1 2 3 Subseries II/3 Specimens number 18 18 18 18 18 18 18 18 18

Mean [kg/m³] 422 461 475 COV [%] 6,17 6,27 5,19

Density ρg

ρg,k [kg/m³] 379 413 434 Mean [N/mm²] 374 574 629 387 580 650 416 609 675 COV [%] 8,25 13,11 13,95 7,88 9,08 9,08 8,57 7,40 8,51

MOE Ec,90,g (h0 = 200 mm)

Ec,90,g,05 [N/mm²] 323 450 485 337 493 553 357 535 580 Mean [N/mm²] 4,40 5,82 6,14 4,49 5,86 6,27 4,38 5,41 5,67 COV [%] 7,44 12,76 15,20 11,54 11,01 15,64 10,24 11,80 14,53

Strength perp. to the grain fc,90,g (h0 = 200 mm) fc,90,g,k;

EN 14358 [N/mm²] 3,79 4,51 4,51 3,59 4,71 4,63 3,59 4,29 4,32

Subseries II/4 Specimens number 5 5 5 5 5 5 5 5 5

Mean [N/mm²] 399 585 851 400 635 876 398 614 849 COV [%] 17,84 17,37 15,40 9,11 9,71 16,44 9,44 13,11 8,99

MOE Ec,90,g (h0 = 480 mm)

Ec,90,g,05 [N/mm²] 282 418 635 340 533 639 336 482 724 Mean [N/mm²] 4,59 5,69 6,11 4,79 5,90 6,66 4,59 5,70 6,29 COV [%] 10,17 14,22 5,93 5,47 8,98 12,53 6,98 6,63 6,33

Strength perp. to the grain fc,90,g (h0 = 480 mm) fc,90,g,k;

EN 14358 [N/mm²] 3,53 3,93 5,32 4,20 4,78 4,95 3,86 4,84 5,43

Tab. 7: Results of series II – subseries II/3 and II/4 (1… loading at the end, 2 … loading in a

distance 100 mm from the end, 3 … loading “in the center”)

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In table 8 the results of the sill-like specimens with different loadings (subseries II/3 and II/4) are listed expressed as increasing factors in relation to the results obtained from the cubic specimens with the same height. Grading class of the boards MS 10 (C24M) MS 13 (C35M) MS 17 (C40M) Type of loading (see also Fig. 5) 1 2 3 1 2 3 1 2 3 Subseries II/3 Mean value MOE Ec,90,g,mean (h0 = 200 mm) [-] 1,41 2,17 2,37 1,33 1,99 2,23 1,31 1,92 2,12

Strength perp. to the grain fc,90,g,k; EN 14358 (h0 = 200 mm) [-] 1,31 1,74 1,83 1,31 1,71 1,83 1,39 1,71 1,79

5%-quantile and characteristic value resp. MOE Ec,90,g,05 (h0 = 200 mm) [-] 1,88 2,62 2,82 1,55 2,27 2,55 1,55 2,33 2,52

Strength perp. to the grain fc,90,g,k; EN 14358 (h0 = 200 mm) [-] 1,63 1,94 1,94 1,54 2,02 1,99 1,56 1,87 1,88

Subseries II/4 Mean value MOE Ec,90,g,mean (h0 = 480 mm) [-] 1,47 2,15 3,13 1,57 2,49 3,44 1,28 1,97 2,72

Strength perp. to the grain fc,90,g,k; EN 14358 (h0 = 480 mm) [-] 1,59 1,97 2,11 1,67 2,06 2,32 1,62 2,01 2,21

5%-quantile and characteristic value resp. MOE Ec,90,g,05 (h0 = 480 mm) [-] 1,26 1,87 2,85 1,59 2,49 2,99 1,58 2,25 3,42

Strength perp. to the grain fc,90,g,k; EN 14358 (h0 = 480 mm) [-] 1,68 1,87 2,53 1,99 2,27 2,35 1,78 2,23 2,50

Tab. 8: Increasing factors for mechanical properties of the sill-like specimens concerning different

loading situations in relation to the cubic specimens of the same height

Comparison of the characteristic values fc,90,g,k

3,383,07

2,33 2,33 2,302,11 2,172,10

0

1

2

3

4

5

10 12 14 16 18 20 22 24 26f t,0,l,k [N/mm²]

f c,9

0,g,

k [N

/mm

²]

fc,90,g,k "EN1194"fc,90,g,k "Tests (h = 200 mm)"fc,90,g,k "Tests (h = 480 mm)"

Δ = 4 % resp. 15 %Δ = 32 % resp. 45 % Δ = 47 % resp. 56 %

GL

32h

GL

36h

GL

28h

GL

24h

2,42

Fig. 7: Comparison of the characteristic values fc,90,g,k calculated with the function in

EN 1194:1999 and the test results of series II/1 and II/2

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The following diagram (Fig. 8) shows the correlation between the density and the compression strength perpendicular to the grain of the cubic specimen from series I and II/1. Additionally to the regression line also their 95%-confidence interval and the 95%-interval for the regression model is drawn.

fc,90,g = 0,0033 ρ + 1,7377R2 = 0,0498

0,00

1,00

2,00

3,00

4,00

5,00

6,00

7,00

300 350 400 450 500 550 600

Density ρ [kg/m³]

Com

pres

sion

str

engt

h pe

rpen

dicu

lar

to g

rain

f c,9

0,g [

N/m

m²]

Fig. 8: Correlation between the density and the compression strength perpendicular to grain of the cubic specimen of series I and II/1 with 95%- confidence interval for the regression line and 95%-interval for the regression model

In Fig. 9 the results of series II for the different loadings (cubic specimens – full area loading; sill-like specimens: loading at the end, 100 mm from the end and “in the center”), the different strength classes of the boards and specimens heights h0 = 200 mm and h0 = 480 mm are shown.

cubic specimen -full area loading

sill-like specimen -loading at the end

sill-like specimen -loading 100 m from

the end

sill-like specimen -loading in the

center

2,0

4,0

6,0

8,0

Max

Mean

Minfc,90,g,k

1 2 3 4 5 6 1 2 3 4 5 6 1 2 3 4 5 6 1 2 3 4 5 6

1 ... MS10 (h=200 mm)2 ... MS10 (h=480 mm)3 ... MS13 (h=200 mm)4 ... MS13 (h=480 mm)5 ... MS17 (h=200 mm)6 ... MS17 (h=480 mm)

Abbreviations:

Com

pres

sion

stre

ngth

per

pend

icul

arto

gra

in f

[N/m

m²]

c,90

,g

Fig. 9: Comparison of the results for the compression strength perpendicular to the grain depending on the different loading situations, strength classes of the boards and specimens heights

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7 Summary and Discussion As can be seen from the results in Fig. 6 and Fig. 7 the proposed correlation in EN 1994:1999 between the tensile strength and grading class of the boards resp. and the compression strength perpendicular to the grain for glulam could not be confirmed. For a specification in standards a value between 2,1 N/mm² and 2,3 N/mm² for cubic specimens (loaded on the whole surface) independent from the glulam strength class is recommended and has to be discussed. For the mean MOE Ec,90 a constant value of about 300 N/mm² (for the cubic specimens) valid for all glulam strength classes (see Tab. 4 and Tab. 5) should be introduced. These values confirm exactly the results published by [10]. From the wood technological point of view no definitely characteristic influencing the mechanical properties of this type of loading has been found. Between the density and the strength perpendicular to grain a slightly correlation with pronounced fuzziness of the test data could has been observed. The analysis of the board’s annual ring pattern used for the lay-up of the cubic specimens has been shown a slightly dependence on the mechanical properties perpendicular to grain. Specimens with upstanding annual ring pattern resulted in slightly higher stiffness and strength than those with flat-lying annual rings. If the analysis is done with a deformation limit of 0,02 h0 and 0,05 h0 resp. the characteristic compression strength values are increasing by about 15% and 30% resp. compared with those calculated in accordance with the procedure given in EN 408:2005 (0,01 h0 deformation limit). The results from the cubic specimens with two different heights (h0 = 200 mm and h0 = 480 mm) showed no significant difference. Thus a dependence on the height of the characteristic stiffness and strength values for the cubic specimens could not be observed. The tests on sill-like specimens revealed a strong dependence on the loading situation. This can be explained with the supporting effect of wood fibers beside the loaded area. For specimens with a height of h0 = 200 mm the mean stiffness values increased by a factor of 1,35 for the specimens loaded at the end, 2,03 for those with a distance of 100 mm from the end and 2,24 for those loaded “in the center”. For the characteristic compression strength perpendicular to the grain values increased by a factor of 1,58 (at the end), 1,94 (at a distance 100 mm from the end) and 1,94 (load “in the center”). The corresponding factors for the specimens with height h0 = 480 mm are: 1,44 (at the end), 2,20 (at a distance of 100 mm from the end) and 3,10 (load “in the center”) for the mean MOE values and 1,82 (at the end), 2,12 (at a distance of 100 mm from the end) and 2,46 (“in the center”) for the characteristic compression strength perpendicular to the grain. It has to be mentioned that these values are linked to a bearing length of 150 mm. Unlike to the results of the cubic specimens those of the stiffness and strength values perpendicular to the grain for the sill-like specimens showed an increasing tendency with increasing height. This fact is a consequence of the definition of the mechanical parameters and due to the spreading of the load under the loading area resp. Furthermore if the distance of the loaded area is more or equal than 100 mm from the end no significant difference of the mechanical properties could be found.

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For design purposes of loaded sills the application of the strength perpendicular to the grain of fc,90,g,k = 2,30 N/mm² and a factor kc,90 = 1,50 for the loading situation at the end and a factor kc,90 = 1,80 for loadings at a distance of ≥100 mm from the end can be suggested. As a conservative approach the mentioned kc,90-factors can also used for the calculation of the stiffness. It has to be mentioned that the given data for the sills can be explained in an excellent way with the theoretical model given in [12]. 8 Acknowledgement The presented research work of series I was in the main part carried out within the diploma thesis of A. Ruli [13] at the Institute of Timber Engineering and Wood Technology at Graz University of Technology / Austria. Additionally A. Ruli and R. Brandner were employed during the time they were working on Series II at the competence centre holz.bau forschungs gmbh which is supported with funds from the Federal Ministry of Economics and Labour (BMVA), of the Province of Styria and the City of Graz as a part of the programme Centres and Networks of Excellence for Technology Development of the BMWA in Austria. We would like to thank our colleagues G. Meinhardt for the co-supervision on A. Ruli’s thesis and B. Heissenberger, Y. Halili and H. Krenn (all holz.bau forschungs gmbh) for their support during the tests in the lab and the analysis of the data. Special thanks goes also to E. Gehri for his valuable discussions and his helpful suggestions during the tests and the analysis of the data. 9 Literature [1] Graf, O.

„Beobachtungen über den Einfluss der Größe der Belastungsfläche auf die Widerstandsfähigkeit von Bauholz gegen Druckbelastung quer zur Faser“,

Der Bauingenieur, 18 (1921), p. 498-501 [2] Suenson, E. “Zulässiger Druck auf Querholz”, Holz als Roh- und Werkstoff, 1 (1938), No. 6, p. 213-216 [3] Kennedy, R.W. „Wood in Transverse Compression“, Forest Products Journal, Vol. 18, No.3, p. 36-40, 1968 [4] Korin, U. “Timber in Compression Perpendicular to Grain” Proceedings of the CIB-W-18, Paper 23-6-1, Lisbon, Portugal, 1990 [5] Pellicane, P.J.; Bodig, J.; Mrema, A.L. “Behavior of Wood in Transverse Compression”, Journal of Testing and Evaluation, Vol. 22, No. 4, p. 383-387, 1994

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[6] Ethington, R.L.; Eskelsen, V.; Gupta, R. “Relationship between compression strength perpendicular to grain and ring orientation”, Forest Products Journal, 46 (1), p. 84-86, 1996

[7] Gehri, E. “Timber in compression perpendicular to the grain”

International Conference of IUFRO S 5.02 Timber Engineering, Copenhagen, Denmark, 1997

[8] Leicester, R.H.; Fordham, H.; Breitinger, H. “Bearing Strength of Timber Beams“ Proceedings of the CIB-W-18, Paper 31-6-5, Savonlinna, Finland, 1998 [9] Madsen, B. “Behaviour of Timber Connections” Timber Engineering Ltd., Vancouver, Canada, 2000 [10] Damkilde, L.; Hoffmeyer, P.; Pedersen, T.N. “Compression Strength Perpendicular to Grain of Structural Timber and Glulam” Holz als Roh- und Werkstoff, 58 (2000), p. 73-80 [11] Blass, H.-J.; Görlacher, R.

“Compression perpendicular to the grain“, Proceedings of the 8th World Conference on Timber Engineering, Vol. II, Lahti, Finland, 2004

[12] van der Put, T.A.C.M.; Leijten, A.J.M. “Evaluation of Perpendicular to Grain Failure of Beams caused by Concentrated Loads of Joints”, Appendix II

Proceedings of the CIB-W-18, Paper 33-7-7, Delft, The Netherlands, 2000

[13] Ruli, A. “Längs und quer zur Faserrichtung auf Druck beanspruchtes Brettschichtholz”,

Diploma thesis, Institute for Timber Engineering and Wood Technology, Graz University of Technology, Graz, 2004

[14] EN 1194:1999

“Timber structures – Glued laminated timber; Strength classes and determination of characteristic values”

[15] EN 384:2004

“Structural timber – Determination of characteristic values of mechanical properties and density”

[16] EN 408:2005

“Timber structures – Structural timber and glued laminated timber; Determination of some physical and mechanical properties”

[17] prEN 14358:2006 “Timber structures – Calculation of 5-percentile values and acceptance criteria for a sample”