12_1_franke

1© Institution of Engineers Australia, 2011 Australian Journal of Structural Engineering, Vol 12 No 1 * Paper S09-040 submitted 11/11/09; accepted for publication after review and revision 5/02/10. Published in AJSE Online 2010, pp. 23-34. † Corresponding author Dr Steffen Franke can be contacted at [email protected]. Compression strength perpendicular to the grain of New Zealand Radiata Pine lumber * S Franke † and P Quenneville The University of Auckland, New Zealand ABSTRACT: The compression strength perpendicular to the grain is one of the important timber properties for structural design. Exceeding the strength value will not only lead to large deformations and thus a serviceability issue, but it can also lead to a failure and thus a safety issue. Only some compression strength values and little information about the complete behaviour for Radiata Pine from New Zealand can be found in the literature. To correct this lack of information, tests have been conducted to investigate the compression behaviour, whereby compression strength values perpendicular to the grain much lower than the ones published in the current standard were noted. To make the designers become aware of this issue, the paper presents the experimental results of compression tests perpendicular to the grain with New Zealand Radiata Pine lumber. The test results are compared with strength values of the national and different international standards, as well as experimental research results of different species. It also gives an overview of the testing standards in use in different countries, showing the diffculty to determine a consistent strength value. According to the experimental results, the use of about half of the strength value published in the current design standard for compression perpendicular to the grain is recommended for structural sawn timber from New Zealand Radiata Pine. 1 INTRODUCTION The compression strength perpendicular to the grain is one of the important timber properties used in structural design. The knowledge of the compressive strength is relevant to the design of structural joists or supports, and also for carpenter connections or connections with mechanical fasteners. In some cases, the compressive strength governs the design of the structure. For example, long span roof or foor systems or timber bridges have to transfer high concentrated loads at their supports, where they mostly have relative small bearing areas. For the investigation of existing or new connections and reinforcement possibilities to strengthen the load capacities, researchers need to know the complete stress-strain behaviour including the failure behaviour of wood. The signifcant elastic-plastic strength behaviour of timber under compression, the deformation and the loading conditions make it diffcult in determining a defned strength value caused by a failure. Furthermore, the current testing standards around the world use different test and evaluation methods that result in non-consistent strength values. There is still an active discussion about the test and design methods (see Larsen et al, 2008; Blaß & Görlacher, 2004). Many research studies outside of New Zealand and Australia are carried out to determine the compression strength perpendicular to the grain. But only a limited quantity of compression strength test values for Radiata Pine from New Zealand could be found in the literature. Based on that, compression tests were carried out to correct this lack of information. Compression strength values perpendicular to the grain much lower than the ones published in the current standard were noted. To make designers aware of this, the results for compression perpendicular to the grain are presented in this paper. 2 MATERIAL AND METHODS 2.1 Test standards The AS/NZS 4063:1992 (Standards Australia/ Standards New Zealand, 1992), draft AS/NZS 4063.1:2009 (Standards Australia/Standards New S09-040 Franke.indd 1 27/06/11 4:46 PM Australian Journal of Structural Engineering Vol 12 No 1 “Compression strength perpendicular to the grain of New Zealand ...” – Franke & Quenneville 2 Zealand, 2009), EN 408:2003 (CEN, 2003), ASTM D143- 09 (ASTM International, 2009), ISO 3132:1975 (ISO, 1975) and DIN 52192:1979 (DIN, 1979) are different test standards used to determine the compression strength of wood. Each standard uses different test confgurations and/or different evaluation methods, which shows the diffculty to determine consistent strength values and to compare these values. Many researchers distinguish between six different loading confgurations, as shown in fgure 1, and discuss the comparability of their compression strength values. This also includes an infuence of the specimen length and the length of the support on the stress-strain behaviour, and therefore on the strength value as well, as shown in fgure 2. All confgurations are loaded over the complete depth. Therefore, confguration A is fully loaded and called “pure block test”. All other confgurations are partly loaded and called “rail tests”. Each testing standard uses one of the confgurations A, B or D. A description, comparison and discussion of the specifc procedures of some of the test standards are given. 2.1.1 AS/NZS 4063:1992 and draft AS/NZS 4063.1:2009 The valid testing standard from 1992 does not provide a testing procedure for evaluating the strength values for compression perpendicular to the grain. Also the latest version of the draft standard provides in the main section only a test setup for the determination of the bearing strength perpendicular to the grain. In this draft, the bearing strength is to be determined from the loading confguration with the dimensions of the specimen illustrated in fgure 3. This is equivalent to case B of fgure 1. The load F shall be applied at a uniform rate of loading through a steel bearing plate 50 mm in width placed at equal distances from the ends until failure or a deformation of 2.5 mm is reached typically within 2 to 5 minutes. The bearing strength f p shall be calculated from the load at a deformation of 2.0 mm of the test piece divided by 50 and the breadth of the test piece. It is not clear, if this is corresponding to an absolute deformation at 2 mm or to a 2 mm offset method. Additionally, a test method for the determination of the compression strength perpendicular to the grain is provided in the Appendix A of the standard informatively, as illustrated in figure 4. This is equivalent to the rail test case D of fgure 1. Until the 2008 draft, this method was used in the main section instead of the bearing test but with different defnitions, eg. for the calculation of the compression strength, which uses the lesser of the ultimate load or the load at 20 mm deformation. Since the 2008 draft version, the compression strength f c,90 shall be calculated using the lesser of the ultimate load or the load at a deformation of 0.1 × height (10% absolute method). This means that only tests smaller than F F F E F D F C F B F A Figure 1: Loading configurations for determining compression perpendicular to grain (Larsen et al, 2008). Figure 2: Different stress-strain behaviours under compression perpendicular to grain (Suenson, 1938). Figure 3: Test configuration for bearing strength perpendicular to grain of draft AS/ NZS 4063.1:2009 (Standards Australia/ Standards New Zealand, 2009). 200 mm in height can be analysed using this method. For calculating the yield compression strength f c,90,y , all drafts use the yield load, which is to evaluate the strength using a 2 mm offset method, as shown in fgure 4(c). The load F shall be applied at a uniform rate of loading through a pair of steel bearing plates until failure or a deformation of 20 mm is reached, typically within 2 to 5 min, which results in a much slower rate of loading compared to the bearing test. Lateral restraints may be used to resist the tendency of buckling. Except for the length-to-depth ratio of the test pieces, there are no specifications or restrictions for the dimensions. S09-040 Franke.indd 2 27/06/11 4:46 PM “Compression strength perpendicular to the grain of New Zealand ...” – Franke & Quenneville Australian Journal of Structural Engineering Vol 12 No 1 3 2.1.2 EN 408:2003 and DIN EN 408:2003 The European standard uses a tall pure block test, equivalent to case A of fgure 1, with b = 45 mm, h = 90 mm and l = 70 mm for structural wood, and b ≥ 100  mm, h = 200 mm and bl = 25000 mm 2 for glulam, as shown in fgure 5. The deformation is to be measured within a length h c ≈ 0.6h in the middle of the height of the specimen. The load shall be applied continuously using the displacement control method, so that the maximum load is reached within 5 ± 2 minutes. The compression strength is calculated from the yield load, determined using the 0.01h c offset method (1% offset), as shown in fgure 5(c). 2.1.3 ASTM D143-09 The American standard uses a full supported rail test with specimen of 50 × 50 × 150 mm, as shown in fgure 6. This is equivalent to case B of fgure 1. The load shall be applied in radial direction through a metal bearing plate 50 mm in width, placed across the upper surface at equal distances from the ends. The test shall be carried out continuously with a motion Figure 4: Informative test configuration for compression strength perpendicular to grain in Appendix A of draft AS/NZS 4063.1:2009 (Standards Australia/Standards New Zealand, 2009) – (a) loading configuration, (b) dimensions of steel-bearing plate, and (c) notation for load-deflection graph. Figure 5: Test configuration of EN 408:2003 (CEN, 2003) – (a) structural wood, (b) test principle, and (c) load-deformation curve. (a) (b) (c) (a) (b) (c) Figure 6: Test assembly for compression tests perpendicular to grain in the ASTM D143-09 (ASTM International, 2009). rate of 0.305 mm/min up to 2.5 mm displacement. There are no specifcations for the evaluation method to determine the compression strength. It is assumed to use the load at a deformation of 2.5 mm. It is noted that loading in the radial direction will not result in a compression strength value as low as loading in a direction of about 45°. S09-040 Franke.indd 3 27/06/11 4:46 PM Australian Journal of Structural Engineering Vol 12 No 1 “Compression strength perpendicular to the grain of New Zealand ...” – Franke & Quenneville 4 2.2 Comparison and discussion of the testing methods Due to the different specifications given in the various standards, which include different sizes of the test specimen, different loading confgurations and different evaluation methods, the compression strength value results obviously in different values. It is noted that only the test method of the European standard EN 408:2003 (CEN, 2003) with the pure block test (confguration A) results in a decisive or reference compression strength value. According to fgure 2 and the results in fgure 11, the rail test confgurations B and D used in the New Zealand and American standards result in higher compression strength values due to the bending effect of the adjacent fbres, but this increase effect should be taken into account using a configuration factor. The different evaluation methods determining the compression strength values according to the standards are summarised in table 1. 0 2 4 6 8 10 12 14 0 1 2 3 4 5 6 7 8 9 L o a d F [ k N ] displacement u [mm] A: h = 40 mm A: h = 120 mm 2.5 mm absolut 0.01h-offset 2 mm-offset 1 mm-offset Figure 7: Evaluation methods for two different heights. Table 1: Summary of the evaluation methods of the different standards. Standard Method AS/NZS 4063.1 draft 2009 yield: 2 mm offset compr.: 10% absolute (0.1h) EN 408:2003 yield: 1% offset (0.01h) ASTM D143-09 2.5 mm absolute Table 2: Load capacity according to different evaluation methods for specimens with different heights (kN). Absolute methods % offset methods Fixed offset methods 2 mm 2.5 mm 10% 0.5% 1% 2% 0.5 mm 0.8 mm 1.0 mm 2.0 mm A : h = 40 mm 9.9 10.1 10.7 8.5 9.2 9.7 9.4 9.6 9.8 10.2 A : h = 120 mm 7.2 8.3 – 9.4 10.2 10.8 9.2 9.6 10.0 10.7 Ratio of 120/40 0.73 0.82 – 1.11 1.11 1.11 0.98 1.00 1.02 1.05 For demonstration of the different evaluation methods, two different pure block tests (confguration A) will be discussed. For this, fgure 7 shows typical load-deformation curves for a specimen with 40 and 120 mm in height, together with the illustration of selected evaluation methods. The corresponding results obtained from the different evaluation methods are summarised in table 2. As shown, using an absolute method will lead to bigger differences in the strength values, whereas using the offset method leads to better comparable results. The height dependent offset methods (percentage offset) result in a constant difference of 11%, whereas the differences of the fxed limit offset methods, eg. 1 mm offset, vary depending on the limit. Using the 10% absolute method, the results have to be analysed at 4 and 12 mm displacement, respectively. It is obvious that the load can be outside of the recorded data of the test, and will furthermore lead to non-realistic and non-comparable results. Thus, the 10% offset method and the 2.5 mm absolute method were not considered for the evaluation of the results of the tests presented. This applies to the 20 mm absolute method as well, even though the results according to this method were analysed and presented to clarify the big differences between the different confgurations. Dependent on the height of the specimen, the evaluation method using an absolute limit includes either an elastic portion only or the complete S09-040 Franke.indd 4 27/06/11 4:46 PM “Compression strength perpendicular to the grain of New Zealand ...” – Franke & Quenneville Australian Journal of Structural Engineering Vol 12 No 1 5 elastic part, or even additionally a portion of the plastic deformations. Whereas using an offset method, the limit always includes the complete elastic deformations and a defned portion of the plastic deformations. For the example given, an offset method of about 0.8 mm will give the same strength values for both specimens. To ensure a good comparability between the different standards and different species of wood, it is recommended to use an offset method with a limit between 0.5 and 1.0 mm. 2.3 Determination of characteristic values The characteristic value is defned as the 5 th percentile value estimated at the 75% confidence level. Assuming a standard normal distribution, the 5 th percentile can be calculated as follows: 5% 1.6449 x x o = ÷ (1) where x is the mean value and σ is the standard deviation. It is also possible to calculate the 5 th percentile value according to the Weibull distribution using the procedure outline in ASTM D5457-04a (ASTM International, 2004). For simplicity, the characteristic values in this paper are calculated using the standard normal distribution. According to AS/NZS 4063:1992 (Standards Australia/Standards New Zealand, 1992), the characteristic strength values R k are given by equation (2), which provides 75% confdence in the derived percentile values. 0.05 2.7 1 k CV R R n | | = ÷ | \ . (2) where CV is the coefficient of variation of the measured data, n is the sample size and R 0.05 is the 5 th percentile of the measured data. The normalised characteristic strength R k,norm is given by following equation: ( ) , 1.35 1.3 0.7 k k norm R R CV | = + (3) where φ is the capacity factor specifed in the limit state code. 2.4 Test series and specimens The compression test series perpendicular to the grain with Radiata Pine lumber includes a total of 90 pure block tests (case A), which are divided into 30 specimens. Each group predominantly for a radial (β = 0°), tangential (β = 90°) and not-oriented (β ≈ 45°) load-to-annual ring direction. For each cases of the confgurations B and D, 30 tests in total including a variation about the load-to-annual ring direction (0 ≤ β ≤ 90°) were carried out. The specimens were cut according to the load-to-annual ring direction, but without any further preselection from different slats (MSG 8) coming from around the North Island of New Zealand. The specimens are free from defects and cover a wide range of densities between 390 and 580 kg/m 3 mostly used for structural timber in New Zealand (fgure 12). A constant cross section of 40 × 40 mm was chosen for all confgurations for a better comparison between each other. The number, sizes and densities of all groups are shown in table 3. The labelling of the specimens, eg. RP-C-TL90-2, include the species of wood (RP = Radiata Pine), followed by the kind of testing (C = compression), the predominant load-to-annual ring direction or plane in load direction (T = tangential, R = radial, L = longitudinal, NO = not oriented), together with the load-to-grain angle α (90 = 90°), and finally the number of the specimen. The specimens of the confgurations B and D are all labelled with NO for the load direction, because each confguration includes all load-to-annual ring directions (0 ≤ β ≤ 90°), but they have the additional letter B or D according to the confguration. Prior to the tests, the specimens were conditioned to 20 °C and 65% relative humidity until mass consistency was reached. Confguration A is carried out according to the European standard EN 408:2003 (CEN, 2003), configuration B according to the ASTM D143-09 (ASTM International, 2009) and the AS/NZS 4063.1:2009 (Standards Australia/Standards New Zealand, 2009), and confguration D according to the procedures in the appendix of AS/NZS 4063.1 draft standard (Standards Australia/Standards New Zealand, 2009). Figures 8 and 9 show a test photo and the test setup for each case of the confgurations. The tests were loaded at a uniform rate of approximately Table 3: Number, sizes and densities of compression tests perpendicular to grain. Load case Species Load-to-annual ring angle No. of specimen Width (mm) Height (mm) Thickness (mm) Density (kg/m 3 ) Min Max A Radiata Pine β = 0°; RL 30 40 40 40 395 535 Radiata Pine β = 45°; NOL 30 40 40 40 410 575 Radiata Pine β = 90°; TL 30 40 40 40 396 547 B Radiata Pine 0° ≤ β ≤ 90°; NO 30 160 40 40 403 566 D Radiata Pine 0° ≤ β ≤ 90°; NO 30 160 40 40 416 560 S09-040 Franke.indd 5 27/06/11 4:46 PM Australian Journal of Structural Engineering Vol 12 No 1 “Compression strength perpendicular to the grain of New Zealand ...” – Franke & Quenneville 6 3.5 mm/min until 37.5% and 50% strains were reached, which are about 15 and 20 mm, respectively. The test duration was about 5 minutes. Due to the good accuracy of the preparation of the parallel opposite test sides of the specimens, the tests were done without using universal joints. The load was measured in the axis of loading and the deformation between the loaded steel plates. The moisture content of every specimen was measured and the overall average is 11.9%. 3 RESULTS AND DISCUSSION 3.1 Evaluation methods According to the different testing standards used, different evaluation methods were adopted. For each test, the yield load F c,90,1% or F c,90,2mm and the maximum load F c,90,max as the load at 20 mm displacement were evaluated, as shown in fgure 10. The line between approximately 10% and 40% of the maximum load represents the slope of the elastic part of the behaviour, and is used to calculate the initial slip u 0 . The 1% offset method (EN 408:2003) and the 2 mm offset method (AS/NZS 4063.1 draft) were adopted to evaluate the yield load. The results at a displacement of 20 mm were obtained to satisfy the test requirements of the previous New Zealand standard until the introduction of its 2008 draft (see section 2.1), and are shown to highlight the big differences between the different methods. In this paper, the yield compression strength values f c,90,1% or f c,90,2mm , and the maximum compression strength value f c,90,max , calculated using the corresponding compression load divided by the compression area, are reported. Figure 8: Test photos of the configurations A, B and D. Figure 9: Test setup of the configurations A, B and D. Load F [kN] Displacement u [mm] F c, 90,1% F c, 90,2mm 0.1 F c,max 0.4 F c,max F c,90,prop u 0 + 20 mm 0.01 h c - offset or 2 mm - offset F c ,90,max E -modul 2/3·E u 0 1 Figure 10: Evaluating methods for the compression strength. S09-040 Franke.indd 6 27/06/11 4:46 PM “Compression strength perpendicular to the grain of New Zealand ...” – Franke & Quenneville Australian Journal of Structural Engineering Vol 12 No 1 7 3.2 Compression strength Figure 11 shows the mean load-deformation curves of all test confgurations. All show a similar behaviour, whereas the radial oriented confguration A and the confgurations B and D show a higher stiffness. Figures 13 to 17 in Appendix A show all corresponding single load-deformation curves for the tests together with their mean curve. All displacements are corrected with the initial slip u 0 . The single compression strength values according to their density of all tests of the more important confguration A, which gives the reference strength values, are shown in fgure 12. It can be seen, that the not-oriented (NO) specimens have the lowest values and represent the lower limit of the compression strength values, and the radial (RL) loaded specimens represent the upper limit with an average of 23% higher strength value. Both groups show an insignifcant dependency on the densities. The results of the tangential (TL) loaded specimens are located in between, but they show a strong dependency of the strength to the density. Considering the results of all groups together and the fact that mostly not-oriented members are used in the constructions, a constant compression strength value can be used regardless of the density and thus the strength classes. The mean and characteristic compression strength values as well as the coeffcient of variation for all load confgurations A, B and D are summarised in table 4. For the confguration A, the values according to each group, as well as the average for all three groups, are listed. Only 10 specimens of each of the confgurations A could be analysed for the evaluation of the maximum compression strength at 20 mm deformation as test results did not include data covering this range of deformation. Also, due to the range of measurements of the confgurations B and D, an extrapolation of the mean curves was made to obtain the maximum compression strength. As already mentioned for fgure 12 and comparing the values of configuration A individually, the not-oriented specimens show the lowest strength values with 5.1 and 4.0 MPa for the mean value and the characteristic value, respectively. Grouping all specimens of configuration A, the mean and characteristic strength values are 5.7 and 4.4 MPa, respectively. The yield strength results using the 2 mm offset evaluation method show on average a 0 5 10 15 20 25 0 3 6 9 12 15 L o a d F [ k N ] Displacement u [mm] RP-C-TL90- RP-C-NOL90- RP-C-RL90- RP-C-NO90-B- RP-C-NO90-D- Figure 11: Mean load-deformation curves. 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 380 400 420 440 460 480 500 520 540 560 580 600 1 % y i e l d s t r e n g t h f c , 9 0 , 1 % [ M P a ] Density [kg/m 3 ] RPCRL90 RPCTL90 RPCNOL90 Figure 12: Compression yield strength versus density. S09-040 Franke.indd 7 27/06/11 4:46 PM Australian Journal of Structural Engineering Vol 12 No 1 “Compression strength perpendicular to the grain of New Zealand ...” – Franke & Quenneville 8 9% higher value than the value obtained with the 1% offset method, whereas each group has a difference of not more than 10%. In contrast, the maximum strength shows on average a 90% higher value than the value obtained with the 1% offset yield strength, a difference of 63% to 130% for each group. The ratio between the yield strength values f c,90,1% and f c,90,2mm is smaller for confguration A (mean of 9%) than those for the confgurations B and D (19% and 16%, respectively). Because of the signifcant elastic-plastic strength behaviour of the specimens under compression (see figure 11), the strength values at 20 mm displacement are much higher than the yield strengths. Based on the different loading situations, the yield strength values f c,90,1% and f c,90,2mm of confguration B are 63% and 79% higher than the values of confguration A, respectively. Also for confguration D, the values are 49% and 60% higher than the one for confguration A. In many international standards, this difference is considered using the factor k c,90 , which is sometimes identifed as the bearing length factor. Depending on the loading situation, k c,90 will vary from 1.0 to 1.75. For the experimental results, the factor k c,90 would be about 1.70 for confguration B and about 1.50 for confguration D. These tests also show that the confgurations B and D cannot be used to determine the reference compression strength. 3.3 Comparison A comparison of the compression strength values of different standards from Europe, Canada, USA and Australia/New Zealand, and therefore different species of wood, as well as experimental values of different researchers, is provided in table 5. The values provided are compiled and adjusted to short- term or test duration of up to 10 minutes, respectively. In the European standard, the strength values depend on the density as well as on the grading and the structural use and are less than 3 MPa for sawn timber. In the Canadian and American design standards, a value between 3.1 and 7.2 MPa is used depending on the species of timber. Even in Australia, a strength value of 5.0 MPa is used for Radiata Pine imported from New Zealand. In summary, a strength value f c,90 for compression perpendicular to the grain of up to one-third of the current strength value used in the New Zealand design standard is used all over the world for likely a similar density of timber. 3.4 Discussion The value for the compression strength perpendicular to the grain f c,90 reported in the New Zealand design standard NZS 3603:1993 (Standards New Zealand, 1993) is approximately twice the experimental value observed using f c,90,1% (1% offset method) or f c,90,2mm (2  mm offset method). Based on the fact that the current valid testing standard AS/NZS 4063:1992 (Standards Australia/Standards New Zealand, 1992) does not provide any methods for compression tests, it is not known if the current compression strength value in NZS 3603:1993 (Standards New Zealand, 1993) is different on the basis that the timber strength has changed over the last 20 years or if the value is based on a testing method using a confguration such as B or D and/or based on a maximum load F c,90,max at 20 mm displacement. Timber designers should be made aware of this particularity as it has serious repercussions in the limit state design of wood members. It is well known that for either a 2 mm or a 20 mm deformation, the limit state is not ultimate but related to a deformation only. For designers, it is very significant, if the strength values are reported for 2 mm or 20 mm deformations. In most cases, a 2 mm deformation is suffcient to lead to signifcant structural problems and designers around the world use this limit. Using the value evaluated using either f c,90,1% (1% offset method) or f c,90,2mm (2 mm offset method) would bring the NZS 3603:1993 (Standards New Zealand, 1993) value f c,90 in line with the Australian one used for New Zealand Radiata Pine. This compression Table 4: Compression strength values of the compression tests (MPa). Load case Load-to- annual ring angle Yield strength f c,90,1% Yield strength f c,90,2mm Max strength f c,90,max f c,90,2mm / f c,90,1% f c,90,max / f c,90,1% Mean CV (%) char. Mean CV (%) char. Mean CV (%) char. A β = 0° (TL) 5.7 16.7 4.6 6.2 18.0 5.0 10.1 a 20.8 a 7.4 a 1.10 1.63 β = 45° (NOL) 5.1 12.2 4.0 5.6 12.0 4.4 10.0 a 15.2 a 8.4 a 1.10 1.79 β = 90° (RL) 6.3 16.7 4.4 6.7 15.4 4.8 15.4 a 20.3 a 11.4 a 1.06 2.30 A (all) 0° ≤ β ≤ 90° 5.7 15.2 4.4 6.2 15.1 4.7 11.8 18.7 9.0 1.09 1.90 B 0° ≤ β ≤ 90° 9.3 16.6 7.3 11.1 16.1 8.9 34.0 b – – 1.19 3.06 D 0° ≤ β ≤ 90° 8.5 10.4 6.9 9.9 9.9 8.0 28.0 b – – 1.16 2.83 a based on 10 test results; b using F c,90,20mm of the mean curve extrapolated to 20 mm displacement. S09-040 Franke.indd 8 27/06/11 4:46 PM “Compression strength perpendicular to the grain of New Zealand ...” – Franke & Quenneville Australian Journal of Structural Engineering Vol 12 No 1 9 strength value is recommended by the authors to be reported in the current design standard and to be used by the New Zealand timber designers, not the one determined at a deformation of 20 mm or using a confguration such as B or D. According to the results, a strength value f c,90 for compression perpendicular to the grain of 4.5 MPa is recommended for use for dry visually or machine stress graded structural sawn timber from Radiata Pine. To take advantage of the higher load capacity in partially loaded confgurations, the factor k c,90 can be used to explain the increase in resistance depending on the length of the member adjacent to the loading area. Depending on the loading situation, k c,90 will vary from 1.0 to 1.75, and the one currently given in the New Zealand design standard NZS 3603:1993 (Standards New Zealand, 1993) or the one given in the European standard EN 1995:2004 (CEN, 2004) could be used. 4 CONCLUSIONS The paper presents experimental results of compression tests perpendicular to the grain with New Zealand Radiata Pine lumber. It also gives an overview of the testing standards of different countries, which shows the diffculty to determine a consistent strength value. The testing method of the European testing standard EN 408:2003 (CEN, 2003), the pure block test, gives the decisive or reference compression strength. The effect of higher loading capacities in other loading confguration or partially loaded confgurations should be taken into account using the confguration factor k c,90 . As shown with an example, it is recommended to a use a 1 mm offset method evaluating the yield compression strength. The tests presented include pure block tests according to the EN 408:2003 (CEN, 2003), and rail tests according Table 5: Comparison of the compression strengths perpendicular to grain given in international standards and research results for test duration (MPa). Standard Experiment Charact. value Mean value (char. value) f c,90,k f c,90,R f c,90,T Europe DIN 1052:2008 / DIN EN 338:2003 Spruce C 24 ρ = 350 kg/m 3 2.5 Spruce C 30 ρ = 400 kg/m 3 2.7 Spruce GL 24h ρ = 380 kg/m 3 2.7 Spruce GL 32h ρ = 430 kg/m 3 3.3 Baumann (1922) – Spruce 3.8 7.0 Eberhardsteiner (2002) – Spruce 6.4 Keenan & Jaeger (1978) – Douglas Fir 9.0 Reiterer & Stanzl-Tschegg (2001) – Spruce 3.5 Franke (2008) – Spruce 2.6 3.7 Canada CSA-O86-2009 Spruce, Pine, Fir: Timber, all grades 6.6 c Spruce, Pine: Glulam 7.2 c USA LRFD standard Douglas Fir 5.8 Southern Pine 4.5 Spruce, Pine, Fir 3.1 Australia AS 1720.1-1997 Radiata Pine (Australian) 6.2 Radiata Pine (New Zealand) 5.0 New Zealand NZS 3603:1993, Amendment 4 Radiata Pine visually graded: dry/green 8.9/5.3 Radiata Pine machine stress graded: dry 8.9 This paper – Radiata Pine 6.3 (4.6) 5.6 (4.4) c for comparison, the published values has been multiplied by a load duration factor of 1.25 to correct it to test duration. S09-040 Franke.indd 9 27/06/11 4:46 PM Australian Journal of Structural Engineering Vol 12 No 1 “Compression strength perpendicular to the grain of New Zealand ...” – Franke & Quenneville 10 to the ASTM D143-09 (ASTM International, 2009) and AS/NZS 4063.1 (Standards Australia/Standards New Zealand, 2009) to provide a comprehensive investigation of the different loading confgurations used in the different standards and the effect of using different defnitions for the characteristic strength reported. For the same matter, the yield compression strength, using the 1% offset method (EN 408) and the 2 mm offset method (AS/NZS 4063.1 draft), as well as the maximum compression strength are reported. The experimental results, as well as a comparison with different standards, show clearly that the current New Zealand compression strength value perpendicular to the grain is too high for the New Zealand softwood Radiata Pine. A strength value of one-half to one-third of the strength value used in the New Zealand standard is used all over the world for likely similar densities of timber. Timber designers should be made aware of this, particularity as it has serious repercussions in the limit state design of wood members. According to the experimental results, the use of a strength value f c,90 for compression perpendicular to the grain of 4.5 MPa is recommended for dry visually and machine stress graded structural sawn timber from Radiata Pine in New Zealand. When considering the higher load capacity in partially loaded configurations, the factor k c,90 , which is sometimes identifed as the bearing length factor and used in many international standards, can be used. Depending on the loading situation, k c,90 will vary from 1.0 and 1.75, and should not be changed in the New Zealand standard NZS 3603:1993 (Standards New Zealand, 1993). 5 OUTLOOK The research results presented in this paper can lead, on one side, to some changes in current testing standards or at least have an infuence on the reviewing process of the new testing standard of Australasia, the AS/ NZS 4063.1 (Standards Australia/Standards New Zealand, 2009). The same testing methods should be used around the world to make results comparable. On the other side, these results will result in a change to the currently used compression strength values in the New Zealand design standard NZS 3603:1993 (Standards New Zealand, 1993). Based on the lower compression strength values for Radiata Pine, the next question is: How do these results infuence the strength values for laminated veneer lumber (LVL) made from Radiata Pine? The paper shows, that there is still some need for research, both for the compression strength values and also for the complete strength behaviour of LVL. A further paper will be published presenting the results about the complete behaviour under compression for New Zealand Radiata Pine lumber, including different load-to-grain angles α and more mechanical properties. REFERENCES AF&PA American Wood Council, 2008, LRFD Standard for Load and Resistance Factor Design for Engineered Wood Construction, 1996 Edition. ASTM International, 2004, ASTM D5457-04a Standard Specification for Computing Reference Resistance of Wood-Based Materials and Structural Connections for Load and Resistance Factor Design, West Conshohocken, PA, USA. ASTM International, 2009, ASTM D143-09 Standard Test Methods for Small Clear Specimens of Timber, West Conshohocken, PA, USA. Baumann, R. 1922, “Die bisherigen Ergebnisse der Holzprüfung in der Material¬prüfanstalt an der Technischen Hochschule Stuttgart”, Forschungsarbeiten auf dem Gebiet des Ingenieurwesens, Heft 231, Verlag des Verein Deutscher Ingenieure, Berlin. Blaß, H. J. & Görlacher, R. 2004, “Compression perpendicular to the grain”, Proceedings of the 8 th World Conference on Timber Engineering, Lahti, Finland, Vol. 2, pp. 435-440. Canadian Standards Association (CSA), 2009, O86- 09 Engineering design in wood, Toronto, ON, Canada. Deutsches Institut für Normung (DIN), 1979, DIN 52192:1979-05 Prüfung von Holz; Druckversuch quer zur Faserrichtung (Testing of wood; compression test perpendicular to grain), Berlin, Germany. Deutsches Institut für Normung (DIN), 2003, DIN EN 338:2003 Bauholz für tragende Zwecke – Festigkeitsklassen; German version of EN 338:2003 Timber structures – Strength classes, Berlin, Germany. Deutsches Institut für Normung (DIN), 2008, DIN 1052:2008-12 Entwurf, Berechnung und Bemessung von Holzbauwerken – Allgemeine Bemessungsregeln und Bemessungsregeln für den Hochbau (Design of timber structures – General rules and rules for buildings), Berlin, Germany. Eberhardsteiner, J. 2002, “Mechanisches Verhalten von Fichtenholz, Experimentelle Bestimmung der biaxialen Festigkeitseigenschaften”, Springer Verlag, Wien. European Committee for Standardization (CEN), 2003, EN 408:2003 Timber structures – Structural timber and glued laminated timber – Determination of some physical and mechanical properties, Brussels, Belgium. European Committee for Standardization (CEN), 2004, EN 1995-1-1:2004 Eurocode 5 Design of timber structures Part 1-1: General – Common rules and rules for buildings, Brussels, Belgium. S09-040 Franke.indd 10 27/06/11 4:46 PM “Compression strength perpendicular to the grain of New Zealand ...” – Franke & Quenneville Australian Journal of Structural Engineering Vol 12 No 1 11 Franke, S. 2008, “Zur Beschrei bung des Tragverhaltens von Holz unter Verwendung eines photogrammetrischen Messsystems”, Doctoral Thesis, Bauhaus Universität Weimar, Weimar, Germany. International Organization for Standardization (ISO), 1975, ISO 3132:1975 Wood – Testing in Compression Perpendicular to Grain, Geneva, Switzerland. Keenan, F. J. & Jaeger, T. A. 1978, “Effect of transverse stress on shear strength and failure mechanism of Douglas-Fir”, Proceedings of the International Conference on Wood Fracture, Alberta, Canada, pp. 73-78. Larsen, H. J., Leitjen, A. J. M. & van de Put, T. A. C. M. 2008, “The design rules in Eurocode 5 for compression perpendicular to the grain – continuous supported beams”, Proceedings of the CIB-W18 conference, St. Andrews, Canada, Paper 41-6-3. Reiterer, A. & Stanzl-Tschegg, S. E. 2001, “Compression behaviour of softwood under uniaxial loading at different orientations to the grain”, Mechanics of Material, Vol. 33, pp. 705-715. Standards Australia, 1997, AS 1720.1-1997 Timber structures – Part 1: Design methods and Amendment 4 Nov. 2002, Sydney, Australia. Standards Australia/Standards New Zealand, 1992, AS/NZS 4063:1992 Timber – Stress graded – In grade strength and stiffness evaluation, Sydney, Australia, and Wellington, New Zealand. Standards Australia/Standards New Zealand, 2009, AS/NZS 4063.1:2009-03 (draft) Structural timber – Characteristic values of strength graded timber, Sydney, Australia, and Wellington, New Zealand. Standards New Zealand, 1993, NZS 3606:1993 Timber Structures Standard, Wellington, New Zealand. Suenson, 1938, cited in Blaß, H.-J., Görlacher, R. & Steck, G. 1995, “Holzbauwerke, Bemessung und Baustoffe nach Eurocode 5, Step 1”, Informationsdienst Holz, Arbeitsgemeinschaft Holz e.V., Düsseldorf, Germany. APPENDIX A 0 5 10 15 20 25 30 0 5 10 15 20 L o a d F [ k N ] corr. displacement u [mm] RP-C-TL90-# Exp. curves Mean curve Figure 13: Load-deformation curves for configuration A – tangential. 0 5 10 15 20 25 30 0 5 10 15 20 L o a d F [ k N ] corr. displacement u [mm] RP-C-NOL90-# Exp. curves Mean curve Figure 14: Load-deformation curves for configuration A – not-oriented. 0 5 10 15 20 25 30 0 5 10 15 20 L o a d F [ k N ] corr. displacement u [mm] RP-C-RL90-# Exp. curves Mean curve Figure 15: Load-deformation curves for configuration A – radial. 0 5 10 15 20 25 30 35 0 5 10 15 20 L o a d F [ k N ] corr. displacement u [mm] RP-C-NO90-B-# Exp. curves Mean curve Figure 16: Load-deformation curves for configuration B. 0 5 10 15 20 25 30 0 5 10 15 20 L o a d F [ k N ] corr. displacement u [mm] RP-C-TL90-# Exp. curves Mean curve Figure 17: Load-deformation curves for configuration D. S09-040 Franke.indd 11 27/06/11 4:46 PM Australian Journal of Structural Engineering Vol 12 No 1 “Compression strength perpendicular to the grain of New Zealand ...” – Franke & Quenneville 12 STEFFEN FRANKE Dr Steffen Franke is a Postdoctoral Research Fellow at the University of Auckland. He is a civil engineer with special interest in structural constructions, timber engineering and fnite element analysis. Steffen graduated in structural engineering at the Bauhaus-University Weimar (BUW), Germany, in 2001. In 2008 he completed his PhD at the BUW, the Chair of Timber and Masonry Engineering. His research focused on the investigation of timber with an own developed photogrammetric measuring system as base for numerical simulations. He has been in the academic and research feld since 2001, teaching courses in the area of structures and design, including theory of structures and materials, structural design of steel, unreinforced and reinforced concrete, masonry, and mainly structural timber design. He has supervised several undergraduate and graduate theses, authored national and international scientifc and research papers and co-authored a book titled Holzkonstruktionen in Mischbauweise (Timber Composite Constructions) published in Germany. Since 2008, he has been working as Postdoctoral Research Fellow in Timber Design with Prof Quenneville at the University of Auckland in New Zealand. PIERRE QUENNEVILLE Pierre Quenneville is the newly appointed Professor of Timber Design in the Civil and Environmental Engineering Department at the University of Auckland. Pierre graduated with a BEng (First Class Honours) in Civil Engineering at the Royal Military College of Canada in 1983, and accepted an offcer commission as a military engineer with the Canadian Armed Forces. During his service, he graduated with a MEng at Montreal University in Structural Engineering in 1986 and then served with an engineering unit, where he became involved with timber structure repairs. He was then transferred to the Royal Military College to take on a lecturer position within the Civil Engineering department in 1988. He engaged in PhD studies at the same time at Queen’s University in Kingston and graduated in 1992. His research was on timber connections and he became involved with the Canadian Wood Design standard in 1993. Since 1996, he has been chairing the Fastenings sub-committee of the Technical Committee for the Canadian design standard. His research on connections focuses on bolted connections and he became known for his novel approach to their design. During his academic career, Pierre had two sabbatical leaves, one of which was with a Canadian timber fabricator. He kept his involvement with this timber structure fabricator until his move to New Zealand and was involved with the design of many interesting timber projects. He has also been involved in consulting work since 1999. S09-040 Franke.indd 12 27/06/11 4:46 PM