CIB-W18 Timber Structures – A review of meeting 1-43 2 MATERIAL ...

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Conclusions The following conclusions can be made from the limited analyses carried out so far with respect to beam strengths. – The present project on the determination of along-member beam strengths seems to provide good prospects for the calculation of moment configuration factors. – It is desirable to gather information on the way and the extent to which the strength reductions due to defects may spread along a beam. – It is advisable to have information on the possible strength coefficients of variation (COVs) with respect to the regression analysis predictions. – It is necessary to study the effect of the possible subjectivity of manually selected defect positions on the generated strength results. This subjectivity occurs for beams with many smaller close depressions in the graph of force vs. the beam length. – The determination of valleys in the grading machine readings, which may correspond to defects, need to be automated. For this purpose objective criteria need to be developed. – Firmer conclusions can be made only when the strength predictions of all the 133 beams are simulated and a statistical analysis of results is carried out. 28-12-2 E Aasheim, K H Solli Size factor of Norwegian glued laminated beams Background A research project where the aim was to determine the size factor kh, of Norwegian glued laminated beams has been carried out by The Norwegian Institute of Wood Technology in co-operation with two Norwegian producers of glued laminated timber. The purpose of this project was to compare the laboratory results with the corresponding values of kh given in Eurocode 5: h � � 0,2 600 k � h with the following limits: 1�kh� 1,15 The limits correspond to h = 600 mm ( kh � 1) and h = 300 mm ( k � 1,15 ). h Conclusion Based on Eurocode 5 it should be expected that kh � fm, k,300 fm, k,600 � 1,15 The result from this project shows a lower value of k h . By using the values from the Weibull-3 parameter distribution the following value of k h was given for a depth of 300 mm: f mk , ,300 34,1 � � � 1,07 f 32,0 CIB-W18 Timber Structures – A review of meeting 1-43 2 MATERIAL PROPERTIES page 2.128 k h mk , ,300 The corresponding size factor calculated from the mean values was kh � 1,12 . Based on observations of the lamellae and their distribution of defects it is assumed that much of the size effect can be explained by the test method and the grading accuracy. If this assumption is correct, then the size factor k h is not only a function of the depth, but also of the grading accuracy and the strength class. 29-6-1 N Burger, P Glos Effect of size on tensile strength of timber Introduction When designing timber members according to Eurocode 5 the size of the member has to be taken into account by means of size factors. These factors were derived from investigations mainly carried out in North America and Great Britain using wood species and grading rules common in these countries. Since it is most likely that size effects may also depend on wood quality, grading rules and, perhaps, wood species, the purpose of this study was to investigate whether these size factors also apply to wood species and grading rules currently in use in Germany. Towards this end the influence of specimen size on the tensile strength was investigated using 750 specimens from timber of native spruce and 200 specimens from timber of native Douglas fir, with varying crosssectional dimensions and lengths. Discussion of Results Results from the tension tests conducted in the course of this study reveal systematic effects of specimen dimensions on tensile strength. On the one hand tensile strength decreases with increasing test length, which corre-
sponds to the statistical approach according to the Weibull theory. On the other hand an increase in tensile strength with increasing specimen width was apparent. This observation contradicts the Weibull theory and can be attributed to the influence of decreasing knot ratio concomitant with the increase in specimen width. 31-12-1 B Källsner, O Carling, J Johansson Depth factor for glued laminated timber-discussion of the Eurocode 5 approach Abstract In Eurocode 5 the bending strength of glued laminated timber depends on the depth of the beam. This paper gives comments on some European investigations of glued laminated timber of spruce (Picea Abies) where the influence of depth has been studied. The test results indicate that the depth factor kh based on 5-percentiles should be lower than given in Eurocode 5. Further, there is a tendency of lower coefficient of variation in the bending strength of deep beams than of shallow beams. This has an effect on the partial safety factor which could be handled by reducing kh. Based on this it could be argued that the depth factor kh should be removed from Eurocode 5. Conclusion The Austrian and the Norwegian investigations indicate that the depth factor kh based on 5-percentiles should be about 1,06. In both investigations machine graded timber was used. A Swedish investigation with well-matched laminations on the tension side of the beams indicates that kh may be even lower when there is a low variation in the strength of the laminations. This means on the other hand that kh may be somewhat higher for visually graded timber where there is a somewhat higher variation in the strength of the timber. There is a tendency towards a lower coefficient of variation in the bending strength for deep beams than for shallow ones. This has an effect on the partial safety factor which could be handled by reducing kh by about 3 %. Based on the discussion above it is proposed that the depth factor kh should be removed from EC5. For other wood species than spruce (Picea Abies) where other sawing patterns are used and where large single traversing knots appear in the laminations, it cannot be excluded that the depth factor kh is different. CIB-W18 Timber Structures – A review of meeting 1-43 2 MATERIAL PROPERTIES page 2.129
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CONTENT 2.1 COMPRESSION PERPENDICUL
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23-12-4 H Riberholt, J Ehlbeck, A F
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30-17-1 F Rouger A new statistical
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CIB-W18 Timber Structures - A revie
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2.1 COMPRESSION PERPENDICULAR TO GR
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for solid sawn lumber and glulam ha
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The discussion is supplemented by t
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Figure 3. Load-deformation curves f
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The results indicate a clear affini
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which has been already mentioned ab
Page 21 and 22:
served when testing whole CLT panel
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2) The mechano-sorptive effects in
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and codified; optimised strategies
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36-11-1 R H Leicester, C H Wang, M
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For handling of moisture effects in
Page 31 and 32:
- The short-term tests had a mean m
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criteria, they may offer decisively
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Conclusion The relation between the
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the laminations were determined and
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27-12-3 E Serrano, H J Larsen Influ
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shear stress offered by competing s
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e alarmed when a significant check
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Measurement of shear deflections du
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41-12-2 M Frese, H J Blass Bending
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tures". The Centre Technique du Boi
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By setting γG = γQ1 = γQ2 = …
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ment. For instance, extreme distrib
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method which was commonly used in c
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2.7 LOAD DURATION 6-9-3 T Feldborg,
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son curve", derived from small clea
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19-9-4 U Korin Non-linear creep sup
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24-9-1 T Toratti Long term bending
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Summary Based on the analysis of th
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when a dry period is followed by a
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- Jansson and Leijten both demonstr
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- The used methods and technologies
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ISO, generally through the technica
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ed. The significance of the choice
Page 77 and 78: However, there is another equally i
Page 79 and 80: 25-17-3 D W Green, J W Evans Moistu
Page 81 and 82: tion of settings. Since this proced
Page 83 and 84: posed approach is that the reliabil
Page 85 and 86: Conclusion It was concluded that th
Page 87 and 88: - The difference between E in edge
Page 89 and 90: On the basis of long-term experienc
Page 91 and 92: Conclusions The possibilities of vi
Page 93 and 94: Finland and Norway). Consequences w
Page 95 and 96: Fig. 1. A wind-induced compression
Page 97 and 98: emphasis on the modelling of the ef
Page 99 and 100: some trends are apparent. Based on
Page 101 and 102: - A higher COV of the raw material
Page 103 and 104: Visual grading of wood into strengt
Page 105 and 106: 4 X(1 � X) Y �1� X � 3s�1
Page 107 and 108: F112 and F122. It is however shown
Page 109 and 110: strength tends to increase with ris
Page 111 and 112: y assuming a normal distribution. E
Page 113 and 114: 19-12-3 F Colling Influence of volu
Page 115 and 116: - WF/Ww: 2:1 The single span three
Page 117 and 118: 40-6-2 M Poussa, P Tukiainen, A Ran
Page 119 and 120: 2.12 SIZE AND CONFIGURATION FACTORS
Page 121 and 122: While the estimates of the size eff
Page 123 and 124: ters for all grades and species. Si
Page 125 and 126: Modelling of length-wise distributi
Page 127: different things that affect the si
Page 131 and 132: fects. As a summary we may, for the
Page 133: More important than the volume effe
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