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Some physical and mechanical properties of beech wood grown in croatia


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SOME PHYSICAL AND MECHANICAL PROPERTIES OF BEECH WOOD GROWN IN CROATIA

Slavko Govorčin- Tomislav Sinković-Jelena Trajković

Forestry Faculty in Zagreb

ABSTRACT
Beech-wood ( Fagus sylvatica L. ) is a typical European wood species found in the moderate oceanic and tender continental climate. Because of its


utilization in making army wagons and gun-stock it was once a synonym for 'military' wood in the tradition of the European nations, and millions of cubic meters were burnt in army stoves and field kitchens.

Distribution, quantity share and characteristic technological quality categorize beech-wood as one of the main species in industrial processing of wood in Croatia.

The number of previous studies of the technological properties of beech-wood grown in Croatia corresponds to its presence and importance, which is evident from a number of sites within the beech-wood range on which the studies were carried on. ( Fig.3 ).

Examinations of physical and mechanical properties of beech-wood from the site of Bjelolasica ( Gorski kotar ) were made on sampling material at three tree heights, which was different from previous studies. The maximum number of samples, looking from pith to bark i.e. in the radial direction, enabled an insight into distribution of beech-wood properties through characteristic zones of a tree during their life. Considering a great number of up to the present studies of beech-wood properties in Croatia on


different above-sea heights of the sites, a significant dependence of

properties on above-sea heights was observed.

KEY WORDS: Beech-wood ( Fagus sylvatica L. ), physical properties, mechanical properties, Croatia

INTRODUCTION


The area of natural distribution of ordinary beech-wood covers up almost the whole Europe. As mountain species, it reaches the South all the way to Sicily (=37 ), but it can't be found in Spain nor Greece. In the North, it spreads to the northern part of Scotland, southern part of Sweden ( up to =59 ), and in the Eastern Prussia up to Kaljingrad. The southern border goes from Kaljingrad towards Kisinjevo in Besarabia in the shape of an arc protruding out into the West. In the Southwest direction it spreads from the slopes of the Transilvanian Alps to the Danube, and then heads towards East through the northern part of Bulgaria to the Black sea. The southern border of its distribution goes to the Strandza mountains in Turkey to the West ,mainly to the Greek state borders and then spreads, beginning from Bitolj, to the South to the Pind mountains in Greece and from there to the Ionic sea. ( Fig. 1 ).




Fig.1: The distribution range of beech wood ( Fagus sylvatica L.) in Europa.
The conclusion is that beech wood represents a species of moderate oceanic and tender continental climate. But the distribution in the above mentioned area is not even. It can't be found in the French province of Provence, Italian Lombardia, the pine-wood area of the central Alps, the middle part of the Czech Republic. It is explained by the fact that beech-wood is a mezofit and it requires abundant rains during summer, which doesn't occur in the mentioned areas.

For the same reason, it can't be found in Croatian areas of the mediterranean and submediterranean climate ( Istria, Hrvatsko primorje, most part of Dalmatia ). From the North of Croatia, beech-wood grows in the direction of the SouthWest ( Hrvatsko Zagorje- Slavonia ) and in the middle part of Croatia ( Gorski kotar, Lika, Kordun and Banija ). In


Hrvatsko primorje it appears above 600 m above-sea, beginning with stunted forms. Its bottom border is distributed and registered on the above-sea height of 112 m near Bjelovar and on the above-sea height of 112 m near Novoselec and at 103 m above-sea near Karlovac. According to L. Abramović, the upper border of high-altitude distribution lies in the mountains of Velebit, at 1500 m above-sea (Fukarek 1965)( Fig. 2).



Fig.2: The distribution range of beech wood ( Fagus sylvatica L.) in Croatia.
The beech-wood forests of Croatia belong to the association of Croatian beech-wood forest Fagetum silvaticae croaticum Horv., which is recognized for its great number of distinctive species and thus represents the richest form of beech-wood forests in Europe.

The range of Croatian beech-wood forests can be divided into 3 variations ( subassociations ), according to the above-sea height.The lowest area, i.e. the one up to ca. 700 m ab.s. belongs to the mountain beech forests, Fagetum croaticum montanum Horv. In the area from 700 / 1000 - 1.300/1.400 m. ab.s. grows a forest of beech-wood and fir-wood Fagetum croaticum abietetosum Horv. Above it, there is a mountain beech-wood forest, Fagetum croaticum subalpinum Horv., with pure beech which transforms into a elder bush*. On silicate grounds in the range of ca. 350-550 m. ab. s., there is a acidofilna association of hard fern and beech-wood, Blechno-Fagetum Horv., which transforms into a forest of sessile oak and sweet chestnut, Quercus-Castenum croaticum Horv., and the in the higher parts into a forest of hard fern and fir-wood. On the slopes heading towards the sea there is a coastal forest of beech-wood Fagetum croaticum seslerietosum Horv. which covers an area of ca. 600-1000 m-ab.s. and which, in higher parts, transforms into a forest of beech-wood and fir-wood Fagetum croaticum abietetosum Horv. ( Herman 1986).

The importance of beech wood as wood species in Croatia is evident in the total wood stock of Croatian forests of 39,9%, i.e. 80 million of cubic metres . It grows in the area of around 250 000 ha in pure stand, in mixed stand with sessile oak and hornbeams in the area of ca. 700 000 ha, and with fir-wood and spruces it covers the area of ca. 200 000 ha . The annual felling in Croatia makes 1,7 million m3 of gross mass, i.e. 500 000 m3 or 45% of saw-mill hardwood logs or ca. 32% of total produced mass of saw-mill logs in Croatia. For making sliced and rotary cut veneer , around 115 000 m3 of beech-wood logs were used i.e. 48,5% of the total produced mass of veneer logs ( Klepac 1986).

Mean values of some physical and mechanical properties of beech-wood at breast height determined by previous studies in Croatia are illustrated in Tab.6.

The values of some physical and mechanical properties of beech-wood taken from the previous published references : density 0=0,68 g/cm3 , volumetric shrinkage V max=17,6%, compression strength parallel to the grain 12%=62 MPa ( Kollman 1951, Bosshhard 1974 ) are out of date to a certain extent.

Density 0=0,70 g/cm3, volumetric shrinkage V max=17,6%, compression strength parallel to the grain 12%=46 MPa , static bending strength b14%=104 MPa ( Tsoumis 1991, Wood Handbook, FPL 1999 ) represent more recent data on the values of some physical and mechanical properties of beech-wood.

MATERIAL AND METHODS

From 1956 to the present time, physical and mechanical properties of beech wood have been studied on seven Croatian sites, by means of methods adequate to the period and the then possibilities. Almost the whole area of beech wood distribution in Croatia was covered (see Fig.3). According to the information gotten from the sites of the former studies, an area was chosen in which a study of beech wood properties hadn’t been carried on before. The site of Bjelolasica in Gorski kotar was chosen, with its 1150-1200 m above-sea height.




  1. Petrova gora

  2. Papuk

  3. Gorski kotar

  4. Senjsko bilo

  5. Zagrebačka gora

  6. Žumberak

  7. Velebit

  8. Bjelolasica


Fig.3: Map of sites for studies of physical and mechanical properties of beech wood in Croatia.
On the site of Bjelolasica ( Gajina lokva – division 47a, area 49,42 ha ) 15 specimens were taken out of 5 diameter classes. After felling, test small logs ( 70 cm of length ) and test wood discs ( 4 cm of thickness ) were removed from each tree at 3 sampling heights ( at 1,3 m – breast height, at ca. 5 m – the center of length between ground and the crown base, and at and at ca. 10 m – before the beginning of crown ). From the test logs two groups of samples were cut following ISO standards, prismatic ( symmetrical ) ones for determining physical properties and others to determine mechanical properties. From the test girdles, samples of unsymmetrical forms were cut in order to determine physical properties. While making samples of symmetrical and unsymmetrical forms, the principle of making the biggest possible number of samples in the radial direction was employed, in all four cardinal points, with material loss occurring only at the points of sawkerf.
RESULTS AND DISCUSSION

The results of physical and mechanical properties’ study are based on the values obtained by a very large number of samples. The values of properties distribution in the radial direction are given, for easier reference, in tables and graphs as mean values of 20 rings intervals. The results shown in this paper are based on the values of all studied samples at breast height ( 1,3 m ) in order to compare them with the so-far studies on other sites, depending on above-sea height of the sites.



The illustrated values of volume shrinkage and density of owen dry wood are founded on the results obtained by studying of symmetrical and unsymmetrical forms, while the values of growth rate, compression strength parallel to the grain and static bending strength are based on the results gotten from the study of symmetrical forms.
Growth rate
Distribution of mean ring width in the radial direction at breast height is given in Tab.1.


RANGE OF RINGS

RING WIDTH (mm)




n

MV

SD

1-20

1 194

0,9

0,494

21-40

1 200

0,85

0,529

41-60

1 124

0,76

0,534

61-80

1 040

0,74

0,460

81-100

1 040

0,75

0,520

101-120

984

0,81

0,534

121-140

960

0,86

0,570

141-160

960

0,97

0,647

161-180

880

1,15

0,739

181-200

676

1,40

0,822

201-220

320

1,61

0,818

221-254

208

1,50

0,456
MEAN

10 586

0,93

0,63


Tab. 1: Statistical characteristics of ring width for range of rings.

n-number of samples

MV-mean value

SD- standard deviation


It is evident that growth rate decreases in the radial section from the pith to the bark ( 70 years of age ), while the trend of value increase is evident towards the bark ( Fig. 4 ). The maximum mean value of the growth ring interval ( 1,61 mm of width ) is 117% bigger than the minimum mean value of the interval ( 0,74 mm of width ).





Fig. 4: Ring width (mm)

Volumetric shrinkage
The volume shrinkage values are illustrated in Tab. 2, while a graphic illustration given in Fig.5 reveals a general decrease of the volumetric shrinkage values in the radial direction from pith to bark, with a significant decrease of value in the first ca. 80 rings. The maximum mean value of the volumetric shrinkage interval ( 18,3 % ) is 14,4 % bigger than the minimum mean value of the interval ( 16,0 % ).

RANGE OF RINGS

VOLUMETRIC SHRINKAGE (%)




n

MV

SD

1-20

47

18,3

2,90

21-40

91

17,4

2,35

41-60

69

17,2

2,34

61-80

50

17,4

1,81

81-100

61

17,3

1,24

101-120

53

16,8

1,30

121-140

59

16,7

1,77

141-160

65

16,5

1,58

161-180

59

16,4

1,67

181-200

57

16,4

1,82

201-220

33

16,0

1,61

221-254

20

16,7

2,06
MEAN

664

17,0

2,01


Tab.2: Statistical characteristics of volumetric shrinkage for range of rings.

n-number of samples

MV-mean value

S
D- standard deviation



Fig. 5: Volumetric shrinkage (%)

Density
Distribution of the density values of owen dry wood in the radial direction is given in Tab. 3. The graphic illustration (see Fig.6) shows a significant decrease of the density values in the first ca. 70 rings from pith to bark, at a somewhat slower rate. The maximum mean value of the density interval in absolute dry conditions ( 0,714 g/cm3 ) is 11,6 % bigger than the minimum mean value of the interval ( 0,640 g/cm3 ).


RANGE OF RINGS

DENSITY OF OWEN DRY WOOD (g/cm3)




n

MV

SD

1-20

47

0,714

0,0720

21-40

91

0,689

0,0646

41-60

69

0,670

0,060

61-80

50

0,674

0,0467

81-100

61

0,664

0,0288

101-120

54

0,651

0,0386

121-140

59

0,651

0,0472

141-160

66

0,662

0,0565

161-180

59

0,665

0,050

181-200

57

0,657

0,0529

201-220

33

0,640

0,0454

221-254

20

0,654

0,0407
MEAN

666

0,669

0,055


Tab. 3: Statistical characteristics of density of owen dry wood for range of rings.

n-number of samples

MV-mean value

SD- standard deviation




Fig.6: Density of owen dry wood (g/cm3)
Compression strength parallel to the grain
The values of compression strength parallel to the grain are illustrated in Tab. 4, and the graphic illustration in Fig.7 reveals a slight increase of the values in the first 70-80 rings, followed by a more severe decrease of the values, with the minimum value around the bark. The maximum mean value of the compression strength parallel to the grain ( 52,0 MPa ) is 14% bigger than the minimum mean value of the interval ( 45,6 MPa ).


RANGE OF RINGS

COMPRESSION STRENGTH PARALLEL TO THE GRAIN (MPa)




n

MV

SD

1-20

25

46,9

4,94

21-40

45

49,4

4,54

41-60

46

52,0

6,33

61-80

66

50,5

4,73

81-100

49

50,7

4,21

101-120

64

50,4

4,37

121-140

61

49,9

4,40

141-160

69

48,8

4,64

161-180

66

47,3

3,75

181-200

52

45,6

3,61

201-220

19

47,2

2,25

221-254

14

46,9

2,04

MEAN

576

49,1

4,77


T
ab. 4:
Statistical characteristics of compression strength parallel to the grain for range of rings.

n-number of samples

MV-mean value

SD- standard deviation


Fig.7: Compression strength parallel to the grain (MPa)

Static bending strength
The values of static bending strength are illustrated in Tab. 5, and the graphic illustration in Fig. 8 reveals a slight increase of the values in the first ca. 70 rings, followed by a more severe decrease of the values, with the minimum value around the bark. The maximum mean value of the static bending strength ( 107,4 Mpa ) is 25,6% bigger than the minimum mean value of the interval ( 85,5 Mpa ).


RANGE OF RINGS

STATIC BENDING STRENGTH (MPa)




n

MV

SD




1-20

11

96,7

16,74




21-40

19

105,1

13,23




41-60

21

107,4

19,24




61-80

27

104,2

11,39




81-100

22

100,8

10,40




101-120

30

102,2

8,34




121-140

21

97,1

13,02




141-160

31

96,8

10,18




161-180

31

98,0

7,95




181-200

17

92,4

10,99




201-220

10

95,1

14,76




221-254

5

85,5

10,62




MEAN

245

99,8

12,64





Tab. 5: Statistical characteristics of static bending strength for range of rings.

n-number of samples

MV-mean value

SD- standard deviation




Fig. 8: Static bending strength (MPa)

Dependence of some physical and mechanical properties of beech wood grown in Croatia on the height above sea level
The values of some physical and mechanical properties obtained in this study, together with the identical properties gotten from the so-far studies on other Croatian sites, are illustrated in Tab. 6.(Horvat 1959,1965,1969, Štajduhar 1973). The presence of different above-sea heights of the sites on which the studies were done offers an insight into a characteristic dependence of some properties on the above-sea height of the site in question ( Fig..9 – 13 ).


LOCATION

HIGHT ABOVE SEA [m]

n


ring width (mm)

n


volumetric shrinkage (%)

n


density (g/cm3)

N


compression strength parallel to the grain (MPa)

N


static bending strength (MPa)

PETROVA GORA

390

165

2,29

169

17,45

165

0,703

111

65,6

82

132,4

PAPUK

560

224

1,60

100

22,12

224

0,702

225

72,3

115

139,3

GORSKI KOTAR

620

231

2,00

91

22,00

231

0,698

231

57,5

116

130,5

SENJSKO BILO

780

63

1,77

63

16,91

63

0,674

33

68,7

33

132,4

ZAGREBAČAKA GORA

830

242

2,70

211

22,09

238

0,706

237

80,2

113

145,1

ŽUMBERAK

918

107

1,51

108

17,27

108

0,672

95

66,9

55

130,4

VELEBIT

1055

291

1,29

289

16,88

289

0,651

200

62,7

204

119,8

BJELOLASICA


1157

10 586

0,93

664

16,97

666

0,669

576

49,1

245

99,76


Tab. 6: Statistical characteristics of some physical and mechanical properties of beech on eight locations.




Fig. 9: Dependability of average rings width and height above sea level.



Fig.10: Dependability of average volumetric shrinkage and height above sea.



Fig.11: Dependability of density of owen dry wood and height above sea level.




Fig.12: Dependability of average compression strength parallel to the grain and height above sea.
F
ig.13
: Dependability of average static bending strength and height above

sea.


CONCLUSIONS
The evident trends of some functions of the illustrated physical and mechanical properties of beech wood in the radial direction reveal a characteristic and typical distribution ( A.J. Panshin and C. de Zeeuw 1970 ) as well as a strong mutual connection between properties. Trends are different from the density function trend at equal functions of the outlined mechanical properties in the first ca. 70 rings. The reasons are to be found in dimension changes of the elements of wood material in that part of a tree ( B. Petrić and V. Šćukanec 1980 ), as well as in the influence of range of rings in the radial direction ( Tab. 1, Fig. 4 ).

A distinct variability of the given properties observed in the radial direction from pith to bark were significant, and they were particularly evident at static bending strength.

A comparison of the data was made possible owing to the accessibility of the values of some up to the present studied physical and mechanical properties obtained from other sites of beech wood in Croatia. A strong dependence of some physical and mechanical properties of beech wood on the above-sea height of the site was reported. A general conclusion is that the values of the studied physical and mechanical properties get reduced with the increase of the above-sea height of the site.

REFERENCES




  1. Bosshard,H.H., 1974.: Holzkunde 1.Birkhauser Verlag.Basel und Stuttgart, 94 pp.

  2. Forest Products Laboratory, 1999: Wood handbook-Wood as an

engineering material. Gen. Tech.Rep. FPL-GTR-113. Madison, Wl:U.S.

Department of Agriculture, Forest Service, Forest Products Laboratory.

463 pp.


  1. 3. Fukarek,P.,1965.:Biološke i ekološke karakteristike bukve i bukovih šuma

u Jugoslaviji.Savjetovanje o proizvodnji,preradi i trgovini bukovim

drvom.Beograd, 1-18 pp.

4. Herman,J.,1971.:Šumarska dendrologija.Stanbiro. Zagreb,230-237 pp.

5. Horvat,I.,1959.:Osnovne fizičke i mehaničke karakteristike bukovine s

područja Žumberka,Petrove Gore,Senjskog bila i Velebita. Zagreb, 1-

94 pp.


6. Horvat,I.,1966.:Izvještaj o ispitivanju nekih fizičko-mehaničkih svojstava

bukovine s područja šumarija Virovitica,Nebljusi i Perušić, manuskripts,

Zagreb.

7. Horvat, I., 1969: Osnovne fizičke i mehaničke karakteristike



bukovine.Drvna industrija, 20 (11-12):183-194.

8. Klepac,D.,1986.:Uvodni referat na simpoziju o bukvi.Kolokvij o

bukvi.Velika- Zagreb. Sveučilište u Zagrebu, Šumarski fakultet. Zagreb

11-15 pp.

9. Kollmann,F.,1951.: Technologi des Holzes und Holzwerkstoffe Erste

band. Springer-Verlag. Berlin und Munchen.

10. Panshin,A.J.and De Zeeuw,K.,1970.: Texbook of Wood

Technology.Vol.1.Mcgraw-Hill book Company.New York, 251-255 pp.

11. Petrić, B., V. Šćukanec, 1980: Neke strukturne karakteristike domaće

bukovine (Fagus sylvatica L). Drvna industrija 31(9-10): 245-246.

12. Štajduhar,F.,1973.:Prilog istraživanja fizičko-mehaničkih svojstava

bukovine u Hrvatskoj.Drvna industrija 24(3-4):43-59.



13. Tsoumis, G., 1991.: Science and technology of wood: structure,

properties, utilization.Chapman&Hall. New York, 111-115 pp.


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