THE EFFECT OF EDGE KNOTS ON THE STRENGTH OF WESTERN SPF MSR LUMBER A THESIS IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF

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1 THE EFFECT OF EDGE KNOTS ON THE STRENGTH OF WESTERN SPF MSR LUMBER by Terry Courchene B.Sc. (Forestry) University of British Columbia, 1992 A THESIS IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE in THE FACULTY OF GRADUATE STUDIES Department of Wood Science We accept this thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA April 1996 Terry Courchene, 1996

2 In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of British Columbia, I agree that the Library shall make it freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the head of my department or by his or her representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. The University of British Columbia Vancouver, Canada DE-6 (2/88)

3 ABSTRACT Mill visits were conducted to evaluate the effect of Visual Quality Level (VQL) restrictions of edge knots on the yields of Machine Stress Rated (MSR) lumber. This initial study indicated that edge knots contribute significantly to the amount of MSR lumber that is being downgraded because of visual override requirements, representing in excess of $15,000 per month in lost revenue to MSR producers. Therefore, an experimental study was initiated to study the effect of large VQL (edge knots) on the strength properties of Spruce-Pine-Fir (SPF) MSR lumber. Two groups of material were studied that had been graded by a Continuous Lumber Tester (CLT) to receive a 1650E-1.5Fb MSR grade designation. One group called on-grade complied with the visual override requirements and the other group, VQL, should contained at least one edge knot with a VQL greater than 25 % of the cross sectional area. All specimens were nominal 38 mm x 89 mm SPF lumber collectedfromthe same MSR production run. Manual measurements of the VQLs was conducted on all 750 specimens and they were then tested nondestructively to determine flat-wise and edge-wise modulus of elasticity. All the specimens were randomly divided into either tension or third point bending testing since these are the most commonly used destructive tests. There were weak relationships noted between the measured VQL size and destructive strength values. Strength results were as expected in that tension strength proved to be more important and restrictive. Even when some boundaries were placed on the VQL size the tension specimens failed to meet the grade requirements while the bending specimens exceeded the requirements in all cases. This results from the fact that MSR production of SPF lumber is

4 governed by the MOE value determined by the CLT. It is not controlled by the bending strength as is the case for Douglas-fir; whose strength values were used in the VQL size determination. Two procedures, simulation and proportionality, were used to determine the amount of large VQL material that can be included with the current on-grade production and meet grade requirements. These procedures were conducted with the various VQL groups for both destructive tests and confirmed that tension strength is the governing factor. The results highlight the importance of the amount of VQL material to include in a grade; therefore, proper and thorough testing by organizations is required for large VQL inclusion. iii

5 TABLE OF CONTENTS Abstract Table of Contents List of Tables List of Figures List of Symbols List of Abbreviations List of Grades Acknowledgments ii iv vi vii x xi xii xiii 1. BACKGROUND 1 2. PRELIMINARY EVALUATION Visual Quality Level Assessment VQL Study VQL Falldown Results Economic Implications Conclusions MATERIAL AND METHODS Material And Sampling Testing Knot Area Ratio Flat-Wise Modulus of Elasticity Edge-Wise Modulus of Elasticity Slope of Grain Density Tension Bending 23 iv

6 4. METHODS OF ANALYSIS AND RESULTS Knot Area Ratio Modulus of Elasticity on Flat Modulus of Elasticity on Edge Slope-of-Grain X-Ray Tension Strength Bending Strength Weibull Analysis Closed Form Solution Simulation Studies DISCUSSION Knot Area Ratio Additional Knot/Board Analysis Inclusion Quality Control CONCLUSIONS Summary and Conclusions Future Research 71 LITERATURE CITED 73 APPENDIX 1 74 v

7 LIST OF TABLES Table 1. VQL Limits for MSR Lumber. 6 Table 2. Summary information for all the mills surveyed. 12 Table 3. Summary of information from Interior Region - Splitter Stock. 14 Table 4. Summary Statistics for MOE by Group. 28 Table 5. Summary Statistics for Bending and Tension Strength by Group. 35 Table 6. Statistics of VQL Breakdown into KAR Groups. 44 Table 7. Closed Form Solution Results for Bending Strength using KAR Group Table 8. Closed Form Solution Results for Tension Strength using KAR Group Table 9. Closed Form Solution Results for Edge MOE - Minimum using KAR 1 Proportions. 47 Table 10. Summary of Regression Results for Bending and Tension. 52 Table 11. Comparison of 5th Percentile Strength Values. 61 Table 12. Closed Form Solution Results for Tension Strength using KAR Group Table 13. Closed Form Solution Results for Tension Strength using KAR Group Table 14. Summary of Closed Form Solution for MOE on Edge of cases KAR 1 and Table 15. Summary Statistics for Quality Control Trials in Bending. 69 vi

8 LIST OF FIGURES Figure 1. Illustration of a CLT machine. 1 Figure 2. Illustrations of Edge Knots - greater that 1/2 of narrow face. 7 Figure 3. Illustrations of Re-location type Knots. 8 Figure 4. Illustrations of Multiple Knots in the same cross section. 8 Figure 5. Sequence Description of the Cook Bolinders AG-SF Grading Machine. 19 Figure 6. End and Side Representations of the Collimated X-ray Source for 22 the Visionsmart Model #1, X-ray Density Machine. Figure 7. Bending Strength versus Knot Area Ratio of VQL Specimens. 25 Figure 8. Tension Strength versus Knot Area Ratio of VQL Specimens. 25 Figure 9. Cumulative Probability Distribution of Average Flat-wise MOE. 27 Figure 10. Cumulative Probability Distribution of Minimum Flat-wise MOE. 27 Figure 11. Cumulative Probability Plot of Edge-wise MOE. 29 Figure 12. Pass 1 Slope of Grain Results for Specimen # Figure 13. Pass 2 Slope of Grain Results for Specimen # Figure 14. Pass 1 Slope of Grain Results for Specimen # Figure 15. Pass 2 Slope of Grain Results for Specimen # Figure 16. X-ray Density Plot for Specimen # Figure 17. X-ray Density Plot for Specimen # Figure 18. Comparison Plot of Weibull and Actual Data for Tension Strength of Group. Figure 19. Comparison Plot of Weibull and Actual Data for Tension Strength of VQL 36 Group. vii

9 Figure 20. Comparison Plot of Weibull and Actual Data for Bending Strength of Group. Figure 21. Comparison Plot of Weibull and Actual Data for Bending Strength of VQL 38 Group. Figure 22. New Comparison Plot of Weibull and Actual Data for Tension Strength of VQL 39 Group without Specimen # Figure 23. Graphic Determination of Proportionality Results. 43 Figure 24. Cumulative Probability Plot of Simulated Grades in Bending using KAR 49 Group 1 Data. Figure 25. Cumulative Probability Plot of Simulated Grades in Bending using KAR 49 Group 4 Data. Figure 26. Cumulative Probability Plot of Simulated Grades in Tension using KAR 50 Group 1 Data. Figure 27. Cumulative Probability Plot of Simulated Grades in Tension using KAR 50 Group 4 Data. Figure 28. Average MOE Flat Profile for Specimen # Figure 29. Average MOE Flat Profile for Specimen # Figure 30. Photograph of Failure Location for Specimen # Figure 31. Photograph of Failure Location for Specimen # Figure 32. X-ray Density Plot of a Through Knot. 59 Figure 3 3. X-ray Density Plot of a Spike Knot. 60 Figure 34. Comparison Plot of Weibull and Actual Data for Tension Strength of VQL 64 KAR Group 4. Figure 35. Comparison Plot of Weibull and Actual Data for Tension Strength of VQL 64 KAR Group 5. viii

10 Figure 36. Plot of Bending Strength Level as a Function of the Percentage of VQL 66 KAR Group 1. Figure 37. Plot of Tension Strength Level as a Function of the Percentage of VQL 66 KAR Group 1. Figure 38. Plot of Edge MOE Strength Level as a Function of the Percentage of VQL 66 KAR Group 1. ix

11 LIST OF SYMBOLS A = deflection at the center (5 mm for the Cook Bolinders Machine) P = load L' = span between the center of the outer rollers (900 mm for the Cook Bolinder Machine) I = moment of inertia b = width of the section d = depth of the section L - test span = 21*d A = cross sectional area (b times d) Pmax ~ maximum load X = the strength level for a particular Pf m - scale factor K = shape factor Pf = probability of failure PfT = probability of failure of combined grades Pf/i65o = probability of failure for 1650 grade pi650 = proportion of 1650 material PfrvQL = probability of failure for VQL grade pvol = proportion of VQL material x

12 LIST OF ABBREVIATIONS Modulus of Rupture Modulus of Elasticity Continuous Lumber Tester Machine Stress Rated Spruce-Pine-Fir National Lumber Grades Authority Visual Quality Level Megapascal Standard and Better Economy MOR MOE CLT MSR SPF NLGA VQL MPa Std & Btr Econ 1450f-1.3E 1.3E 1500f-1.4E 1.4E 1650f-1.5E 1.5E 1800f-1.6E 1.6E 2100f-1.8E 1.8E 2400f-2.0E 2.0E Slope-of-Grain knot area ratio cumulative distribution function SOG KAR CDF 3-Parameter 3-P xi

13 LIST OF GRADES The MSR grade names follow standard rules and practices and are designated by a Fb - Eg classification system. The Fb is the assigned bending strength class and Eg is the assigned modulus of elasticity for the grade. The grades names appearing in this thesis are as follows: 1450f-1.3E 1500f-1.4E 1650f-1.5E 1800f-1.6E 2100f-1.8E 2400f-2.0E The values associated with the grades names refer to imperial units; therefore, the designated bending strength (f) is in pounds-per-square inch (psi) while the modulus of elasticity (E) for the grade is in million psi. xii

14 ACKNOWLEDGMENT This project is initiated and supported by the National Lumber Grades Authority (NLGA). I would like to thank them for their assistance, guidance and patience. Thanks also go to the mill and its personnel for their support and instruction in the sample collection. I would like to express my gratitude to Dr. Frank Lam for his guidance and input into this research. In addition, special thanks to Dr. J.D. Barrett who made this research possible. Other thanks goes to the technical staff of the Department of Wood Science, Bob Myronuk. xiii

15 1 BACKGROUND Machine stress rating of lumber began in the early 1960's when the well-known principle of positive correlation between bending strength (modulus of rupture-mor) and stiffness (modulus of elasticity-moe) properties of lumber was used to develop commercial grading machines. The production method involves bending lumber flat-wise and measuring the loads as the member passes through the grading machine (see Figure 1). The applied load and corresponding deflection will vary depending on the stiffness of the piece. For the Continuous Lumber Tester (CLT) the intent is to measure the load needed to cause a specified deflection. The grading machine will transform the load data, over the length of the piece, into an MOE profile. Next, the minimum MOE and average MOE are determined from the load profile. With this MOE information the board is put into a preliminary grade or a MOE class. UKS0ft<4 SWSOM SfKSOd I OPfMTIOKIl UtPUflfftS Figure 1. Illustration of a CLT machine, (from Galligan et al: Machine Stress Rating:Practical Concerns for Lumber Producer. USDA General Technical Report FPL 7.) 1

16 Since most machine graded wood products are used on edge (eg. truss members and floor joists) and the machine stress grading process is based onflat-wise MOE, visual grading rules have been established limiting selected defects that cause strength reductions when the material is used on edge. These rules are known as visual quality level (VQL) restrictions. Edge knots are but one of the restrictions. Ii" edge knots were a problem, the logical question to be raised is why isn't the lumber mechanically graded on edge to measure the MOE. The reason lumber is tested on the flat is so that the grading machine can induce a sizable deflection without creating large stresses. Some research in the early 1960's indicated that there was no significant difference between MOE measured on the edge and MOE on the flat (6). However, if an edge-wise MOE based grading machine were to be built there would be more difficulties with proper alignment of the lumber and there would be higher induced stresses on the member at easily measurable deflections. These facts contributed to the decision to build the prototype mechanical grading machines measuring flat-wise MOE. Besides strength related issues associated with the correlation of flat-wise MOE versus edge-wise strength, some non-structural appearance characteristics of machine stress rated (MSR) material are important to the intended end-use. Each piece of MSR lumber receives visual inspection for such critical features. The visual restrictions ensure that MSR lumber meets the same acceptable minimum standards of certain properties like wane, warp, and general appearance that are applicable to all lumber products (10). It is important to also note that the ends of the lumber that pass through a grading machine are not completely tested. The length of these untested ends will vary depending on the particular grading machine; however, for visual grading purposes the distance has been set at 0.6 m. These untested ends are a result of the mechanics and design of the testing machine and cannot be 2

17 avoided since the lumber must be supported before a load can be applied. The lack of machine MOE information for the ends of the lumber led to the development of more stringent visual grading rules for the end sections. These visual restrictions were imposed to ensure that the untested ends do not contain characteristics which will affect strength more seriously than defects in the test zone of the piece. It was recognized that knots, other than edge knots, may require some limitations to achieve consumer acceptance (7). It has been known for many years that the strength of lumber is affected by knots and slope of grain more than any other common defects. Past research has also shown that strength is affected by both size and location of knots. Littleford conducted an experimental program on dimension lumber of several western species and showed that edge knots have a large influence on MOR (9). This information forms part of the basis of the current visual stress grading requirement applied to MSR lumber. Orosz's research on the effect of knots on MOE provided some interesting results (13). The research used transverse free vibrations to determine the dynamic MOE of lumber. The material tested was 126 pieces of 38 x 89 mm western hemlock lumber; 3.6 meters long and seasoned to 12% moisture content. The samples were classified into two groups, either edge or center line knots. Each piece of test material contained either a single edge or center line knot in the center of the specimen length. The results indicated that knot position in the cross section had more effect on edge-wise MOE than on flat-wise MOE. In fact the MOE on edge was lower than MOE on the flat for pieces with edge knots, but not for pieces with centerline knots. It should be noted that specimens with other knot arrangements such as multiple knots and knot clusters were not considered; therefore, extending the conclusions to other knot arrangements may not be justified. 3

18 When studying the effect of knots it appears that the grain around the knot is of equal or more importance than the knot itself which means that the method of determining or interpreting knot sizes is very important. Bolger and Rasmussen conducted various tests on the Stress-O-Matic stress-rating system in 1962 (2). Lumber was fed through the machine and loaded on the flat face. The number of boards that failed and the causes of these failure were recorded. Next, the pieces that passed were tested in static bending. The boards were placed on edge with the largest defect loaded in tension. Again, the number and the cause of failures were recorded. The large majority of failures reported were a result of cross grain or cross grain around knots which indicated grain distortions around knots are important. Cramer and Goodman established a mathematical model to predict elastic properties and strength of wood with knots (3). They showed that edge knots have more effect on strength than center knots. However, more importantly, they also proved that localized grain distortions associated with knots is the main strength reducing effect of knots in lumber. Therefore, when measuring the size of a knot, the grain distortions associated with the knot must be considered. Littleford studied the visual restrictions on the size of edge knots (8). He stated that edge knot restrictions arise to "eliminate those pieces where the flat-wise stiffness measured by the machine might not be a good index of the actual strength for use on edge as, for example, joists and rafters". The restriction is intended to reduce the variability in strength. This research was conducted on unseasoned Douglas fir and western hemlock nominal 38 x 140 mm lumber. The material was graded by a CLT-1 stress rating machine. He showed that lumber below the average strength, for any MOE, can be attributed to edge knots. He recognized that the degree of seasoning and the species would have to be considered. In fact he stated, "restrictions on the maximum size of edge knots to be allowed in Douglas fir and western hemlock grades...it is 4

19 debatable, however, that such a restriction will prove to be so useful for lodgepole pine and western white spruce" (8). Littleford referred to in-house research work conducted by various grading authorities in the 1960's. These authorities included the West Coast Lumber Inspection Bureau, the Western Pine Association and the Western Wood Products Association. Unfortunately much of their work is unpublished and the basis of their grade restrictions was unpublished data collected by the machine manufacturers. Therefore, it has been impossible to study or review this unpublished literature. There have been some questions regarding the background and verification of procedures used in developing the visual override restrictions for Canadian Spruce-Pine-Fir (SPF) MSR lumber. This created interest in further researching the VQL restriction on edge knots. Results from the Canadian Lumber Properties In-grade Program indicate that SPF MSR material has greater strength in both bending and tension for the same MOE value than either the Doug. Fir- Larch or Hem-Fir species groups (1). This indicates that the current restriction, based on Doug. Fir-Larch and Hem-Fir data, may not be suitable for SPF material. The objectives of this study are to: 1) quantify howfrequentlyedge knots contribute to visual downgrading of SPF MSR lumber, 2) to evaluate the relationship between knot size and lumber strength and 3) to provide guidance for establishing alternate VQL (visual quality level) rules for SPF MSR lumber. 5

20 2 PRELIMINARY EVALUATION Mill visits were performed to evaluate mill practices of edge knot size determination. These visits also provided information on whether edge knot restrictions were actually a problem to the mills. The study involved assessing the proportion of visually downgraded material resulting from edge knotrestrictions. 2.1 VISUAL QUALITY LEVEL ASSESSMENT The NLGA has grading rules for MSR production. This study focused on the VQL restrictions placed on MSR lumber. The definition of a VQL, as provided by the NLGA (11), is a strength reducing characteristic partially or wholly at the edge of a wide face. The current size of edge knot VQL restrictions are based on the assigned modulus of rupture (MOR) values for each grade of MSR produced (see Table 1). 1 Net Cross Sectional Area Edge Displacement 1 Characteristic MOR Value (MPa) 1/ / / /6 >30.4 Table 1. VQL Limits for MSR Lumber. 6

21 Here the defect is not allowed to occupy more of the net cross-section than the specified edge displacement. For example, if lumber has been machine graded into the 1500f-1.4E group the associated MOR is 21.7 MPa; therefore, the maximum VQL currently permitted is 1/4 of the net cross sectional area. Implementation of the edge knot VQL determination follows the rule interpretation bulletin (12). It is stated that for a knot to be considered at the edge of the wide face, it must either: 1) occupy more than one-half of the edge (narrow face or thickness) (see Figure 2) or, 2) that there is less than one-sixth the size of the knot being studied of clear, straight grained wood on the edge (see Figure 3). A knot studied using the second condition is called a relocation knot. The procedure for the evaluation of re-location knots is to determine the cross sectional size of the knot itself and then to determine the cross sectional area of clear, straight grained wood between the knot and the edge of the piece. An edge condition would exist if the amount of wood on the edge is less than one-sixth of the knot itself. It should be noted that each knot is judged independently; therefore, if two or more knots occur in the same cross section, each knot is measured individually (see Figure 4). The concept of considering each edge knot individually extends both in the determination if they are edge knots and if each is less than the required size. Figure 2. Illustrations of Edge Knots - greater that 1/2 of narrow face. (From Interpretation Bulletin. National Lumber Grades Authority.) 7

22 Figure 3b. No Edge Knot condition. Figure 3. Illustrations of Re-location type Knots. (From Interpretation Bulletin. National Lumber Grades Authority.) EDGE KNOT condition: Knot occupies more than 1/2 narrow face. Combination narrow face (spike knots) measured individually and each is less than 1/2 the narrow face. Figure 4. Illustrations of Multiple Knots in the same cross section. (From Interpretation Bulletin. National Lumber Grades Authority.) 8

23 Typically a MSR producing mill -will only manufacture a few MSR grades or grade combinations at any one time. Two of the more popular grade combinations are: 1) 1650f-1.5E, 2100f-1.8E and 2400f-2.0E, 2) 1450f-1.3E and 1800f-1.6E. These correspond to different production methods where the first combination comes from natural stock or a typical mill run and the second combination resultsfromsplitter-stock (ie. splitting a 2x8 into two 2x4's). Based on the values in Table 1, the allowed VQL for combination 1 would be 1/4 for the 1650f-1.5E grade and 1/6 for the other grades, while for combination 2 the VQL size allowed is 1/3 for 1450f-1.3E grade and 1/6 for the 1800f-1.6E grade. It should be noted that the grades listed are only the MSR grades being produced where as other visual grades, including items such as Standard and Better (Std & Btr) as well as Economy (Econ), would also be manufactured simultaneously. When a piece of lumber with an oversized VQL is encountered during production, this piece must be downgraded and can only be downgraded into other grades that are currently being produced. After the VQL size is evaluated the piece is placed into a lumber grade where the maximum size restriction is not exceeded. Therefore, for combination 1, the downgrading of the 2100f-1.8E and 2400f-2.0E grades must go into the 1650f-1.5E grade or lower and downgrading the production of 1650f-1.5E is into Std & Btr or lower lumber grades. The downgrading of large VQL in combination 2 follows the same progression where 1800f-1.6E machine graded material goes into 1450f-1.3E or lower grades and the 1450f-1.3E material is downgraded into Std & Btr or lower. 9

24 2.2 VQL STUDY MSR production of 1450f-1.3E, 1650f-1.5E, 1800f-1.6E, 2100f-1.8E and 2400f-2.0E grades from a SPF timber supply was studied because of it's large production volumes and economic importance to the MSR producers. Since SPF is such a broad classification, it was necessary to look at production from different regions in BC. The areas studied included the Interior region, the Cariboo, and the Kootenay or Rocky Mountain region. These areas should give a good representation of the SPF timber supply in the province. Originally it was hoped to study lumber as it was being graded. However, the speed of production prohibited the identification and recording of the visual restriction imposed by the graders in real time. Attempting this method of study would have caused problems, including disrupting the grading process and production. Alternatively, in each area visited,finishedpackages of MSR lumber were studied. The majority of the packages were classified as Std & Btr grade. The material had been put through a CLT machine but failed to meet the requirements for MSR lumber (falldown). It was only possible to go through a few packages at each location due to time restrictions. These packages are assumed to be representative of MSR production at the mills studied. When looking at the lumber in the packages, a MSR certified or qualified lumber grader was on hand to identify the reason for downgrading. The majority of the pieces were downgraded for the NLGA visual restrictions on MSR lumber. The CLT spray mark was used to identify the original MSR grade. A record of the original machine grade, the final grade, and the visual restriction that caused downgrading were recorded. 10

25 2.3 VQL FALLDOWN RESULTS While the NLGA lists all the possible VQL reasons, not all were encountered; so for the purposes of this study the reasons for downgrading were limited to the following: Edge Knots Other Knots Wane Shake and Splits Slope-of-Grain Manufacturing Natural Drying Species Unknown These categories follow the NLGA rules with some slight differences. The category "Other Knots" includes grain distortions and knots located in the untested ends. The knots located in the untested ends were placed into this category because they could have been trimmed to make the MSR grade. Defects that are naturally occurring such as rot or unsound wood, pockets, stain and compression wood were classified as "Natural". The class of defects termed "Mkiufacturing" included skip, tear (either Chip-N-Saw or planer), and machine damage. The category "Drying" includes warp, crook, twist, etc. The majority of material in the "Species" category was Interior Douglas-fir. This material is put into the Std & Btr grade because the mills did not have the appropriate grade stamp. The final category, "Unknown", contains all of the lumber that was either on grade (e.g. it should not have been downgraded or makes the CLT spray that it carries) or the reason for downgrading could not be identified. Some of the material was not machine sprayed and this lumber is listed separately. 11

26 Combined summary data for all the mills that were visited are shown in Table 2. Here the factors causing downgrading are listed followed by the total number of pieces and, finally, the percent occurrence of each factor. The percentage is calculated on a variety of different bases. First, as part of the Grand Total which includes the material that was not machine sprayed. Next, as part of the Total which neglects the material that was not machine sprayed (Not Sprayed). Li these two cases the top three reasons for downgrading (the highest percentage) are the categories: Other, Wane, and Edge Knots, respectively. Since a large amount of the lumber in the "Other" category is actually on grade, it should not be included in the calculations of the percentages. With this material removed, the results show that Wane is the number one reason and Edge Knots are solidly in second place. The relative percentages are 31.76% and 18.15% respectively. Downgrade Total % of Grand % of Total % of Total Rank Reason Total (without other) Edge Knot Other Knots Wane Shake SOG Manufacturing Natural Drying Other* Total (less other) 551 Total Not Sprayed Grand total * includes: J-Grade, Species, Moisture Content, Unknown causes and material determined to be On-Grade. Table 2. Summary information for all the mills surveyed. 12

27 The summary presented in Table 2 was generated from data on the individual packages that were studied at each mill. The results by package for each mill are tabulated in Appendix 1. Within each package there were different CLT spray marks to indicate different machine MOE ratings. The ratings encountered were 1.5E, 1.8E, and 2.0E (all MOE values are in million psi) in both the Rocky Mountain and Cariboo regions, and 1.3E and 1.6E were produced in the Interior region. The reasons for downgrading are listed for each rating, followed by the number of pieces and the percentages. The first percentage calculated is based on the total of all the pieces in the package. Next, the percent was calculated based on the total pieces in each machine class. However, some packages were not that representative of the mill production and the reasons for this have been noted on the respective results. When these extraneous factors are eliminated, the percentages show the same results as previously in the Total of all the mills. Wane and Edge Knots constitute a large percent of the reason for downgrading. The reason for separating the packages into the different machine rating E-classes was to help identify which E-class has the greatest problem with edge knots. While packages of 1.5E were studied they contained very little falldown from the 1.8E and 2.0E classes, therefore the results were not recorded. The majority of the results were from studying packages of Std & Btr where there was more falldown material from the 1.5E class than from the 1.8E or 2.0E classes. These results indicate that edge knots are more of a problem in the 1.5E than in any other class. It should be noted that Table 2 includes material from both mill run and splitter-stock production. The amount of splitter-stock evaluated was quite low compared to mill run. The splitter stock occurred in the Interior region only (see Appendix 1). Table 3 is a summary of all of the packages surveyed in the Interior Region. Here two grades of splitter-stock are produced, 1.6E and 1.3E. The results showed that there was very little downgrade of the 1.6E group into 13

28 1.3E, however Edge Knots were one of the factors causing downgrading. One package of Std & Btr 3.7 m long was sampled. Within this package 44% was machine graded 1.3E and 12% was machine graded 1.6E. Here the results indicate that Wane and Edge Knots are again the highest factors causing downgrading. Downgrade Reason # pieces per reason % of Total Rank Edge Knot Other Knots Wane Shake/Splits Manufacturing Natural Total 91 Table 3. Summary of informationfrominterior Region - Splitter Stock. 2.4 ECONOMIC IMPLICATIONS An informal survey was used to assess the economic implications of downgrading MSR lumber because of edge knot VQL's. To calculate the increased revenue requires three pieces of information: 1) the amount of MSR material that is currently downgraded, 2) the proportion of downgraded material that will remain in it's original MSR grade and 3) the price difference between the types of material. By telephone some MSR producing mills indicated their MSR production volumes and their MSR grading efficiency. With this information the amount of MSR material that is downgraded was calculated. Next, a conservative estimate of the amount of material that is downgraded because of edge knots was taken from the VQL study results. Finally, a three month average price difference between 1650f-1.5E and Std & Btr was calculated from the publication 14

29 Random Lengths. With these three pieces of information the extra revenue for added MSR production was calculated to be between $15,000 and $25,000 per month. In excess of this amount may be possible depending on the particular mill production. It should be noted that a conservative value of the amount of material downgraded for edge knots was used since it is recognized that it is not possible to completely eliminate the restrictions on large edge knot VQL's. 2.5 CONCLUSIONS The purpose of the mill visits was to evaluate the edge knot restriction on MSR lumber. All of the mills visited use the same NLGA approved method of Edge Knot size determination. By inspecting finished packages of mainly Std & Btr grades of lumber, it was determined that edge knot restrictions are an important cause of downgrading MSR lumber production. From the different MSR material studied it is evident that downgrading from the 1650f-1.5E machine grade is the most significant, both in terms of volume and more importantly in terms of value. Many of the mills raised concerns in regards to the potential impact of this research work since they tended to view edge knots as not being a major problem influencing the falldowns. The results from this study do not support the claim by some industry personnel that edge knots were only a problem in splitter-stock production. Li fact the results indicate that edge knots are a problem in both mill run and splitter-stock production. A possible reason for this may be the inconspicuous nature and relatively low frequency of edge knots. For example, it is much easier to spot and recognize other defects like shake and wane than it is for edge knots. However, the packages that were inspected showed that 3.70 to percent of pieces are being downgraded for edge knots. 15

30 3 MATERIAL AND METHODS 3.1 MATERIAL AND SAMPLING SPF material was sampled from an interior British Columbia MSR lumber sawmill with a Metriguard Continuous Lumber Tester (CLT). The material was kiln dried and nominally dimensioned 38x89 mm (2x4) with a 1650F-1.5E grade designation. The sample MSR lumber was separated into two different types which will be called the visual quality level (VQL) sample and on-grade or 1650 sample. The VQL material had at least one edge defect with a displacement of greater than 1/4 of the net cross section as defined by current lumber grading rules and practices. This group contained approximately 450 specimens. The other material studied consisted of one package, 294 specimens, of lumber that is on-grade for current visual override rules. Only 4.8 meter material was considered which well represents the productionfrominterior "small log" sawmills where lumber is typically cut in three to six meter length. The 4.8 meter material typically represents the long lumber lengths from short logs and the shorter material from longer logs. The choice of uniform specimen length further removed length effects as a variable. All material was gathered during a production run at the same time production volume data were recorded. This included the total number of boards processed through the CLT and the MSR machine production of all grades, including the 1650F-1.5E grade. It should be noted that during sample collection, the CLT was set to classify lumber into three grades; 2400F-2.0E, 16

31 2100F-1.8E and 1650F-1.5E. Finally, information on the amount of production into all grades after visual grading was also recorded. 3.2 TESTING Knot Area Ratio All specimens were numbered on the board face and close to the specimen end. The following information was also recorded during testing in the laboratory: the species, the CLT machine grade, the specimen dimensions and the location and size, to the nearest 1.6 mm (1/16th of an inch), of the largest strength reducing edge defect Fiat-Wise Modulus of Elasticity A Cook Bolinders SG-AF grading machine was used to determine the flat-wise modulus of elasticity of each board. Specimens were oriented on their edge (narrow face) as they proceeded through the grading machine. When the system was turned on there was a short warm-up period after which a Pass 1 light was illuminated and signified the machine could begin to accept lumber. As the lumber entered the machine, it encountered a set of pinch rolls A (see Figure 5). These rolls gripped and drove the material. The next roll that the lumber passed was the deflection roll B and the final set was the pinch rolls C. The opening of the air pressure operated pinch rolls and deflection roll were set for 38 millimeters material. As the lumber initially entered a set of pinch rolls they were under low pressure arid 17

32 when the material was fully within a set of pinch rolls the pressure was automatically changed to high. The grading machine has 2 photocells, before the first pinch rolls J and after the deflection roll K. The machine recognized that the lumber was fully within the second set of pinch rolls after the leading lumber edge interrupted the photocell K. At this time the material would be adequately clamped; therefore, the computer started recording load information. A flat-wise deflection distance of 5 mm was set for the 38 millimeters material before operation. The machine measured and recorded the varying load required to achieve the set deflection. The recording continued along the board length and the final load measurement was taken after a prescribed distance from when the material's trailing end passed photocell J. Each specimen was rotated about the longitudinal axis and fed again into the machine again, on edge, for pass 2. Here the same procedure occurred as for pass 1 operation. All specimens were steadied and accelerated to the machine speed before entering the first set of pinch rolls. The numbered end was the leading edge for all specimens. The machine's calibration was set at the start of the test and checked daily with an aluminum bar of known MOE. No major adjustments were required throughout the testing. The load profile for each specimen was stored on a personal computer connected to the grading machine. These load profiles consisted of the data for the required load at 2 mm increments for the length of the sample except for 500 mm on both ends which was required to ensure adequate clamping. 18

33 3D ' 1! :, R 7, s IZ,1 ' Is D K I i / \ \ H / 6 1 I. 1 I G 1 -> -r-, -j JL K7 P r v '7. I F i 1 i Figure 5. Sequence Description of the Cook Bolinders AG-SF Grading Machine Edge-Wise Modulus of Elasticity The 224kN bending machine was used to determine the edge-wise MOE of all specimens. The machine was set up in a third point loading configuration with a span to depth ratio of 21. This means that the distance between end reactions was set at 1.87 meters (21 times width) because the depth is based on the surfaced dry lumber width of 89 mm. The reaction and loading heads were of the roller type and 15 cm long by 10 cm wide. The maximum stroke of the hydraulic actuator was 254 mm. All specimens were longitudinally centered within the machine configuration. A yoke was suspended between nails that were spaced at a distance of 7 times the member width. A 19

34 linear variable differential transformer (LVDT) was centered within the yoke and measured mid-depth displacement to the nearest mm (0.001"). This yoke displacement, the actuator stroke displacement and the applied load were recorded by data acquisition software at a sampling rate of 3 Hz on a personal computer. The stroke actuator rate was 25 mm per minute while the maximum load per specimen was 2 kn; therefore, the loading time was approximately 1 minute Slope-Of-Grain A total of 100 specimens were tested with a Metriguard model 5100 Slope-Of-Grain indicator system. These randomly selected specimens consisted of 50 pieces from the VQL group and 50 pieces from the on-grade group. The system consists of two detector heads that rotate at 60 revolutions per second. Slope-of-grain (SOG), in degrees, is computed electronically as the absolute value of the difference between the signal phase and the reference phase. The two detector heads are oriented on the machine to provide both face and edge measurements of SOG for each piece of lumber. Both the edge and face heads were calibrated prior to measurements. Infeed and outfeed roller tables with guides were set to ensure accurate board placement through the machine. A variable speed controller drove the feed rolls and therefore the specimens at a speed of 14.6 meters per minute. Each specimen was accelerated to approximately the machine speed upon entry into the drive rollers. A personal computer recorded data for edge SOG, face SOG and their corresponding distance along the specimens length. To get SOG measurements on 4 sides, 20

35 the material had to be passed through the machine twice. Between passes the material is rotated about its longitudinal axis Density The same 100 specimens that were passed through the SOG machine were also density tested using an x-ray system. Initially, these specimens were weighed with an electronic balance to an accuracy of 0.22 kilograms. A belt infeed with roller guides and hold downs directed each specimens through the machine ensuring accurate placement. A roller table was used at the machine's outfeed to keep the specimens straight and level. The yisionsmart model #1, x-ray density machine consists of a collimated electric x- ray tube mounted as shown in Figure 6. The curtain slit of radiation travels from the source perpendicular to the sample feed direction. Below the specimen is an array of detectors that measures the amount of x-ray energy that penetrates the specimens. It should be noted that more energy is absorbed by the dense specimen; therefore, less radiation energy reaches the detectors. The machine was calibrated before the actual testing to ensure accuracy. As the specimen entered the machine it triggered a photocell. This signaled the machine to start the data collection process transferring of detector information to a PC. The detector array is a 200 mm strip with 128 pixels. The system scans this array every 2 milliseconds producing one line of information. Scanning or recording of the array values continues until a total of 1725 lines are accumulated which is the size of each PC file. 21

36 Xray Source r ~ Detector Array I Erd s i d e View V i e w Figure 6. End and Side Representations of the Collimated X-ray Source for the Visionsmart Model #1 X-ray Density Machine Tension Within each of the 2 groups, the specimens were randomly assigned to destructive testing in either tension or bending mode. The sample sizes for the on-grade and VQL group were 146 and 220, respectively. The Metriguard Model 403 Tension Proof Tester was used. It is a hydraulically actuated machine capable of kn of tensile force. It consists of 2 clamping assemblies which are air activated and 61 cm in length. The Tester uses mechanical wedge gripping action in the clamps therefore there is only one hydraulic pump required for machine operation. The hydraulic flow was adjusted to achieve sample failure within three to five minutes. Tension loads within 0.22 kn accuracy were determined by a hydraulic pressure gauge and fed to a readout display. A daily machine calibration check was carried out. 22

37 Specimens were tested at full 4.8 meter length. The lumber was lightly sanded for 61 cm on the ends to ensure that they did not slip within the grips. Since 61 cm on both ends were within the grips, test gauge length was reduced to 3.7 m. Moisture content, peak load, cause and location of the failure (based on the Forintek coding system (5)) were recorded Bending The 224 kn bending machine was used to determine the bending strength of 148 ongrade specimens and 220 VQL specimens. The machine was setup in the third point loading configuration with a span to depth ratio of 21. Therefore, the distance between the center of the end reactions was 1.87 meters. Samples were trimmed to 2.04 meters, to ensure adequate coverage of the reactions and to ensure the worst defect in a specimen could be placed within the middle third of the test length or as close to this as possible. All samples were longitudinally centered within the machine configuration The actuator stroke displacement and the applied load were recorded at a rate of 3 Hz on a personal computer by data acquisition software. The stroke actuator rate was 22.9 mm per minute to achieve failure in approximately one minute. The moisture content, failure location and failure cause were recorded. 23

38 4 METHODS OF ANALYSIS AND RESULTS 4.1 KNOT AREA RATIO A Fortran program was written to analyze the manual knot measurements. This program can be used to determine the knot size as a percentage of the cross sectional area and classify a knot as either an edge knot or other knot, based on current grading practices. Measurement of the knot size as a percentage of the cross sectional area is known as the knot area ratio (KAR). It should be recalled here that for a knot to be classified as an edge knot it must either occupy at least one-half of the edge or that the amount of clear, straight grained wood on the edge is less than onesixth the size of the knot size under study. The program translated the manual knot measurements into the Forintek knot coding system. Figures 7 and 8 are graphs of the knot area ratio (KAR), as a percentage of the cross section, for specimens with edge knots. 4.2 MODULUS OF ELASTICITY ON FLAT For each specimen, the load and corresponding board location for both passes were stored in computer files. The nature of the machine and the necessity to ensure proper clamping meant that there is no load information for 500 mm on either end of the piece. 24

39 Figure 7. Bending Strength versus Knot Area Ratio of VQL Specimens If 3 0 ft. < 25 4 I 20 S I 40 I 50 I VQL - KAR (%) Figure 8. Tension Strength versus Knot Area Ratio of VQL Specimens. 25

40 The computerfileswere analyzed and a single average load profile was created, based on the average of two passes. This was then converted to MOE by the following formula: 48/A where, A = deflection at the center (5 mm for the Cook Bolinders Machine) P = load L' = span between the center of the outer rollers (900 mm for the Cook Bolinder Machine) 7= moment of inertia. For a rectangular beam section: [1] bd 12 where, [2] b = d = width of the section depth of the section From this MOE profile a single average MOE and single minimum MOE were obtained. The location of the minimum MOE along the board was also determined. A cumulative distribution function (CDF) of the average MOE was created for both the 1650 and the VQL groups. These resulting values are graphed (see Figures 9 and 10), while the average MOE values are listed by groups in Table 4. 26

41 VQL Figure 9. Cumulative Probability Distribution of Average Flatwise MOE. VQL Modulus of Elasticity (MPa) Figure 10. Cumulative Probability Distribution of Minimum Flatwise MOE. 27

42 MOE Flat-wise MOE Edge-wise VQL 1650 VQL 1650 Mean (MPa) Median (MPa) Standard Deviation (MPa) Coefficient of Variation (%) Minimum (MPa) Maximum (MPa) Count Fifth Percentile (MPa) Table 4. Summary Statistics for MOE by Group. 4.3 MODULUS OF ELASTICITY ON EDGE For each specimen the load and yoke displacement information were stored on computer files. Determination of MOE on edge involved calculating a linear regression of these variables between a load range of to kn When the actuator and load initially contacted the sample there was some unevenness; however, between the selected range the load-deflection curve was linear elastic. The regression provided the slope of the load-deflection curve. With this P/A value, MOE on edge was calculated using the following standard engineering formula: MOE^. = edge PL 3 432A7 [3] where, A = deflection P =load L = test span = 21 *d I = moment of inertia for a rectangular beam 28

43 These MOE results are in Table 4 separated by groups. A CDF for each grade was developed and these are provided in Figure Modulus of Elasticity (MPa) Figure 11. Cumulative Probability Plot of Edge-wise MOE. 4.4 SLOPE-OF-GRAIN There are two computer files containing SOG information for each specimen. Each file contains data for one edge and one face with their corresponding distance along the specimen. All of thesefileswere graphed and some examples are presented in Figures

44 Figure 12. Pass 1 Slope of Grain results for Specimen # FACE2 -EDGE Position (m) Figure 13. Pass 2 Slope of Grain results for Specimen #

45 15 O in -FACE 1 -EDGE Position (m) Figure 14. Pass 1 Slope of Grain results for Specimen # t on & 0 O O CO FACE 2 -EDGE Position (m) Figure 15. Pass 2 Slope of Grain results for Specimen #

46 4.5 X-RAY For each specimen there is a computer file which contains the raw x-ray detector data. A new file containing actual density information is created for each data file. The conversion is accomplished using the provided machine software and is based on the calibrationfileswhich were created prior to sample testing. There are four calibration files and each contains x-ray information on a material of known density. The corrected x-ray densityfileswere graphed in contour plots (see Figures 16 and 17) to identify high density areas which corresponded to knots. 32

47 33

48 o OOQOOOW) ir. m IT, ir, o iri ts i -5 I.a s e O a 5 U a < (ram) qrpm Figure 17. X-ray Density Plot for Specimen #

49 4.6 TENSION STRENGTH The tension strength was calculated using the peak load information and the following formula: where, P a = A [4] P = maximum tensile load A = cross sectional area (b times d) Summary information, separated by groups is presented in Table 5 and corresponding CDF's are in Figures 18 and 19. Bending Tension VQL 1650 VQL 1650 Mean (MPa) Median (MPa) Standard Deviation (MPa) Coefficient of Variation (%) Minimum (MPa) Maximum (MPa) Count Fifth Percentile (MPa) Table 5. Summary Statistics for Bending and Tension Strength by Group. 35

50 Weibull Actual Tension Strength (MPa) Figure 18. Comparison Plot of Weibull and Actual Data for Tension Strength of 1650 Group. Weibull Actual Tension Strength (MPa) Figure 19. Comparison Plot of Weibull and Actual Data for Tension Strength of the VQL Group. 36

51 4.7 BENDING STRENGTH Each sample's computer file was analyzed to determine the maximum recorded load. This was used in conjunction with the ensuing standard engineering formula to deterxnine bending strength of a rectangular beam section under third point loading: ^"max ^ m a x ~ bd 2 where, [5] Pmax = maximum load Figures 20 and 21 are CDF's for both lumber groups studied and the summary information is in Table WEIBULL ANALYSIS A Fortran program based on the maximum likelihood procedure (4) was used to fit the bending and tension strength data of both lumber grades to 3-parameter (3-P) Weibull distributions. The 3-P Weibull was chosen because it was judged to provide the bestfitto the data among the various distributions tried, including 2-parameter Weibull and Lognormal. Figures show thefitted3-p Weibull distribution to the various groups of strength data. 37

52 Weibull Actual Bending Strength (MPa) Figure 20. Comparison Plot of Weibull and Actual Data for Bending Strength of 1650 Group. Figure 21. Comparison Plot of Weibull and Actual Data for Bending Strength of the VQL Group. 38

53 Figure 21 indicates that there is one sample that is an outlier because of its extremely low strength. This affected both the actual and its associated 3-P Weibull distribution resulting in lower strengths at the 5th percentile level. It was found that this sample did not fail at or due to the measured knot but at a through knot which also had a very large tearout. The sample was removed and a new 3-P Weibull was detennined (Figure 22). Figure 22 shows that with this outlier removed both the data and the 3-P Weibull fit better at the lower tail of the strength distribution. Weibull Actual Tension Strength (MPa) Figure 22. New comparison Plot of Weibull and Actual data for Tension Strength of VQL Group without Specimen # Figures show that the 3-P Weibull distribution did a good job of fitting to the actual data and can be thought of as conservative since the resulting Weibull CDF is to the left 39

54 of the actual data at the lower strength levels. This means that the Weibull information had a slightly lower strength value at the fifth percentile strength level. From visual inspection it is concluded that the difference in strength between the fitted 3-P Weibull and the actual data is not significant. This is especially the case when considering the material variability which is indicated by the coefficient of variation values in Table 5. This resulting "good fit" of the 3-P Weibull to the actual data helps to validate the following exercises. 40

55 4.9 CLOSED FORM SOLUTION In this section methods are presented to calculate the strength properties obtained by combining selected proportions of the VQL and 1650 sample to form a new "combined" grade. A method to determine the strength attributes of a new combined grade will be called the closed form solution (proportionality). It is also based on the 3-P Weibull distribution parameters that were fitted to the various strength data sets. The 3-P Weibull variables allow for the determination of probability of failure since a 3-P Weibull distribution has the following form: X=m{-la(l-P^} ijk + Location where, [7] X = the strength level for a particular Pf m = scale factor K = shape factor Pf = probability of failure Knowing the 3-P Weibull distribution parameters, the probability of failure for a given X, strength level, can be determined. 41

56 The new combined grade is a mixture of the 1650 and VQL grades. The combination is done where a specified percentage of the total is VQL material and the remainder is 1650 material. These percentages, called proportions, and their associated Pf determines the probability of failure for the new grade (PJT) as follows: PfT = Pj71650pl650 + Pf/VQLpVQL [8] where, P/r = probability of failure of combined grades Pfi65o - probability of failure for 1650 grade pi65o = proportion of 1650 material PpvQL = probability of failure for VQL grade PVQL ~ proportion of VQL material pl650 + pvql 1 Given a strength level X, the associated Ppi6so and PJTVQL were estimatedfromthe respective CDF's as shown in Figure 23. If the portion of VQL (PVQL) was known, the probability of failure of the combined grade could be calculated. Hence the CDF of the combined grade could be evaluated from equation 8 when a range of strength levels were considered. 42

57 i> 0.7-ja g =3 fa 0.4 OJ i 0 X Strength Level -New Grade I Figure 23. Graphic Determination of Proportionality Results. 43

58 The amount of VQL material in the new grade combination was determined by evaluation of different knot area ratios (KAR). In essence some boundaries were placed on the VQL group resulting in separation of the VQL into different groups based on KAR. These group characteristics and names, as well as the amount of material in each group and the corresponding percentages are summarized in Table 6. The percentage was calculated from the total production of 1650f-1.5E material during VQL collection and equaled 2642 pieces. KAR Group Name Group Characteristics Number of Specimens Containing Group Characteristics Percentage of Specimens Containing Group Characteristics KAR 1 KAR > 25% 263/ % KAR 2 50%>KAR>25% 246/ % KAR 3 40%>KAR>25% 197 / % KAR %> KAR> 25% 128/ % KAR %> KAR> 25% 124/ % Table 6. Statistics of VQL Breakdown into KAR Groups. To produce an MSR lumber grade it is known that the material's lower fifth percentile values for both tension and bending strength are required to equal or exceed the grade specified values (11). Therefore, probability of failure for the combined grade was set to five percent, synonymous to the fifth percentile, and the corresponding tension and bending strength was calculated. The calculation procedure involved using Microsoft Excel solver function which uses an optimization routine. Here it simultaneously calculates the P/for each of the 2 grades and when these are multiplied by their respective proportions it gives the strength of the new combined grade. Solver was set to find the strength value of the new combined grade with a associated Pf equal to Since this grade is a combination of the other two grades, the Pf 44

59 of these will change; however their proportions are fixed and used for the determination of the new combined grade. Tables 7 and 8 contain summary information on tension and bending strengths of the combined grade considering all material with a KAR of greater than 25 percent. These tables are with the KAR 1 proportions of the VQL and 1650 groups Group KAR Group 1 Combined Grade * Fifth percentile requirement specified by the NLGA (11) for 1650f-1.5E. Table 7. Closed Form Solution Results for Bending Strength using KAR Group 1. 45

60 1650 Group KAR Group 1 Combined Grade Strength (MPa) Requirement* (MPa) * Fifth percentile requirement specified by the NLGA (11) for 1650f-1.5E. Table 8. Closed Form Solution Results for Tension Strength using KAR Group 1. A nonparametric approach was used for the MOE on edge since the 3-P Weibull did not provide a good fit at the lower end of the distribution. Here the actual data including the strength level and its corresponding probability of failure were input to the optimization routine of the solver function. A linear interpolation between the actual recorded strength levels enabled exact percentile determinations of the new combined grade. Table 9 is the fifth percentile (minimum) summary information of MOE on edge for the combined grade using all samples in the 1650 group and all of the VQL samples (tested in either bending or tension) with KAR 1 group properties. 46

61 1650 Group VQL Group Combined Grade * Fifth percentile requirement specified by the NLGA (11) for 1650f-1.5E. Table 9. Closed Form Solution Results for MOE on Edge - Minimum using KAR 1 Proportions SIMULATION STUDIES Simulation was an exercise performed to determine lumber strength values while at the same time resembling actual mill MSR production. Here a Fortran program was developed and used to randomly select specimens based on the 3-P Weibull distribution attributes. This was carried out on both the tension and the bending data. The goal was to detennine the characteristics of a new lumber grade that contains a mixture of both 1650 and VQL groups. The procedure worked by initially developing two populations: the 1650 group and the VQL groups. Based on their corresponding 3-P Weibull distributions 5,000 samples for each group were drawn randomly. From these two simulated populations a new grade combination consisting of 5,000 specimens was created where a percentage of the samples is drawnfromthe VQL group and a corresponding percentagefromthe 1650 group. This means that the difference between the KAR VQL percentage and 100 percent was the amount of 1650 material simulated for the new grade combination. For example, the new 47

62 combined grade using group KAR 1 would contain 9.05 % from the VQL and % from the 1650 group. It is important to note that different 3-P Weibull distributions were developed for each KAR group. Figures 24 to 27 provide the results of this exercise using the KAR 1 and KAR 4 percentages for the material tested in tension and bending, respectively. 48

63 Figure 24. Cumulative Probability Plot of Simulated Grades in Bending using KAR Group 1 Data. Bending Strength (MPa) Figure 25. Cumulative Probability Plot of Simulated Grades in Bending using KAR Group 4 Data. 49

64 Tension Strength (MPa) Figure 26. Cumulative Probability Plot of Simulated Grades in Tension using KAR Group 1 Data. Tension Strength (MPa) Figure 27. Cumulative Probability Plot of Simulated Grades in Tension using KAR Group 4 Data. 50

65 5 DISCUSSION 5.1 KNOT AREA RATIO The determination of knot area ratio (KAR) showed that many of the knots that were manually measured did not meet the criteria for MSR edge knots. These criteria are that the knot must either occupy at least one-half of the edge or that the knot cannot be relocated. Relocation is only possible if the amount of clear, straight grained wood on the edge between the knot and the board surface is greater than one-sixth the size of the knot size under study. It was found that the large majority of knots to qualify met the 1/2 of the edge coverage rule and only 18% of the knots were classified as edge knots because of relocation. This finding is not particularly revealing since the relocation rule was intended more towards the MSR material that is produced from splitter-stock. However, the people doing visual grading may benefit from this information and may need more instruction on interpretation and implementation of this 1/6 relocation procedure. The selection procedure of specimens for the VQL group was that the material be machine graded 1650f-1.5E and should contain at least 1 edge knot greater than 25 percent of the cross sectional area. From the total of 440 VQL specimens it was determined that only 263 actually contained edge knot greater than 25%. During the VQL production the lumber grader felt that he was only 75-80% accurate in selecting VQL samples for edge knots alone. This would mean that approximately 340 specimens should have had a large edge knot which is substantially above the actual number of 263 large edge knots. Some of this discrepancy 51

66 can be explained by the fact that there was more time and accuracy involved in the manual measurements than the visual assessment done by lumber graders in the mill. With the knot area ratio determined for the VQL specimens these values were graphed against the specimen's strength either in bending or tension (Figures 7 and 8). These figures show a very large variation and when regression analysis was conducted the resulting coefficients of determination were below 10% (see Table 10). However, it can be seen from the figures that the relationship between knot size or KAR and strength is the weakest for bending strength. Furthermore, during bending tests, the orientation of the worst defect in a specimen in either tension or compression edge is randomly selected and in some cases the worst defect may be placed outside the maximum stress zone as governed by its location within the specimen. These factors further complicate the relationship between KAR and bending strength. R Square Standard Error (MPa) Number of Observations P Value Tension Bending Table 10. Summary of Regression Results for Bending and Tension. 52

67 5.2 ADDITIONAL KNOT/BOARD ANALYSIS There was evidence of some potential relationships among the SOG, MOEfut, and x- ray results. Graphs of these three types of measures for two different specimens are presented in Figures 12 to 17 and 28 to 29. Specimen number 1230 is from the VQL group and 2213 is from the 1650 group. A great deal of information is available from these graphs. Detailed studies (beyond the scope of the current project) can be conducted to utilize the collected information to predict board strength and knot location. Relationships involving SOG will not be discussed here. Figures 28 and 29 are the average value of both passes through the Cook Bolinders machine (MOEflat). When the pass average is reduced to a single specimen average it is clear that specimen number 2213 has a higher average value. A general trend was found, as expected, in the fact that a larger MOEflat is associated with higher strength in either bending or tension. It is precisely this concept on which MSR technology was based. 53

68 IT % U I 10 -MOE-Avg. O Position (m) Figure 28. Average MOE Flat Profile for Specimen # (GPa) Flat H O 9 -MOE-Avg Position (m) Figure 29. Average MOE Flat Profile for Specimen #

69 Both of the samples were tested in tension. Figures 30 and 31 are photographs of the failure location for samples number 1230 and number 2213, respectively. For specimen 2213 the failure was at 3.5 m and the failure was classified as a tension type. There is no indication of the failure location by examination of the SOG, x-ray or MOE data. Specimen 1230 failed because of a knot located at m. Examination of the data for this sample reveals that this location is the lowest value for the flat-wise MOE average and high SOG readings, especially for pass 2. The edge knot causing failure is easily identifiable in the x-ray contour plot. 55

70 Figure 30. Photograph of Failure Location for Specimen #1230.