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An analysis of variation in moduli of elasticity and rupture in young Douglas fir Littleford, Thomas William 1957-12-31

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AN ANALYSIS OF VARIATION IN MODULI OF ELASTICITY AND RUPTURE IN YOUNG DOUGLAS FIR by THOMAS WILLIAM LITTLEFORD B.A.Sc, University of B r i t i s h Columbia, 1950 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF FORESTRY i n the Department of Forestry We accept th i s thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA August, 1957 ABSTRACT The r e s u l t s of two hundred and f i f t y - e i g h t s t a t i c bending tests on young Douglas f i r were obtained from the Vancouver Laboratory of the Forest Products Laboratories of Canada. Twenty-two trees had been sampled; seven of approx imately six t y years of age from Port Moody, eight of about seventy years of age from Coombs (on Vancouver Island), and seven of approximately ninety years of age from Stave Lake. Stand s i t e q u a l i t y i n each l o c a l i t y was similar and above average for second-growth f i r from the coastal region of B r i t i s h Columbia. The laboratory's r e s u l t s were separated into two classes. Ninety-seven tests represented wood formed within the f i r s t f i v e inches of r a d i a l growth i n the tree. The remaining one hundred and sixty-one tests t y p i f i e d the older wood lying between the inner zone and the bark. Analyses of variance revealed highly s i g n i f i c a n t differences- i n properties between zones. Wood from the inner zone had a faster growth rate, lower density (though wider bands of summerwood) and less strength and less s t i f f n e s s i n bending than wood from the outer zone. The influence of ring width, summerwood width and s p e c i f i c gravity on the moduli of e l a s t i c i t y and rupture was assessed for each zone by regression analyses. Ring width and summerwood width accounted for a s i g n i f i c a n t amount of v a r i a t i o n i n modulus of e l a s t i c i t y and modulus of rupture i n the two zones. Their influence on both moduli, however, was completely due to th e i r association with s p e c i f i c gravity. S p e c i f i c gravity, alone, accounted for almost twice as much of the v a r i a t i o n i n e l a s t i c i t y and bending strength as did ring width and summerwood width combined. The presence of compression wood i n a few specimens from the outer growth zone weakened the relationship between modulus of e l a s t i c i t y and s p e c i f i c gravity i n t h i s zone but had no effect on the modulus of rupture — s p e c i f i c gravity r e l a t i o n  ship. In consequence, the influence of growth zone on modulus of e l a s t i c i t y could not be determined. The difference i n average values of s p e c i f i c gravity between zones did not f u l l y explain the similar difference between zones for average modulus of rupture values; an in d i c a t i o n that r a d i a l growth zone i n the tree had some influence on the bending strength independent to that exerted by density. In presenting t h i s thesis i n p a r t i a l fulfilment of the requirements fo r an advanced degree at the University of B r i t i s h Columbia, I agree that the Library s h a l l make i t f r e e l y available for reference and study. I further agree that permission for extensive copying of t h i s thesis for scholarly purposes may be granted by the Head of my Department or by his representative. It i s understood that copying or publication of t h i s thesis f o r f i n a n c i a l gain s h a l l not be allowed without my written permission. Department of Forestry  The University of B r i t i s h Columbia, Vancouver #, Canada. Date September 2 7 , 1 9 5 7 . ACKNOWLEDGEMENT Work and time given by members of the Timber Mechanics Section of the Vancouver Laboratory of the Forest Products Laboratories of Canada to the assemblage of data used i n t h i s thesis deserves and receives f u l l acknowledgement from the author. For the p r i v i l e g e of using such information, he i s indebted to Col. J. H. Jenkins and Messrs. K. G. Fensom and W. J. Smith a l l of the Forest Products Laboratories D i v i s i o n , Forestry Branch, Department of Northern A f f a i r s and National Resources. F i n a l l y , he wishes to thank Dr. R. W. Wellwood and Dr. J. H. G. Smith of the Faculty of Forestry at the University of B r i t i s h Columbia for t h e i r assistance i n the preparation and presentation of the th e s i s . CONTENTS Page. 1. Introduction . 1. 2 . Review of Literature 1. 3 . Purpose of Analysis 7 . 4. Source of Material 8. 5 . Testing Procedure 8. 6. Method of Analysis and Results 9 . 7 . Interpretation and Discussion of Results . 23» 8. Conclusions 26 . 9 . Future Work 28. 10. BIBLIOGRAPHY 29 . 11 . APPENDICES 33-APPENDICES Appendix Page. A. Measurements taken i n the f i e l d on twenty-two second-growth Douglas f i r trees 33. B. Results of two hundred and f i f t y - eight s t a t i c bending tests made on specimens from twenty-two second- growth Douglas f i r trees. . . . . . . 34. ILLUSTRATIONS Figure Page 1. Location of test specimens 11. 2. Relationship between modulus of e l a s t i c i t y and s p e c i f i c gravity for growth zones A and B 20. 3. Relationship between modulus of rupture and s p e c i f i c gravity for growth zones A and B 21. TABLES Table page 1. Summary of test r e s u l t s 10. 2 . Analysis of variance for properties between zones 13 . 3* Analysis of variance for the regression of modulus of e l a s t i c i t y ( Y e ) on s p e c i f i c gravity(Xa), average ri n g width(Xb), and average width of summerwood(Xc) 14. 4. Analysis of variance for the regression of modulus of rupture(Yr) on s p e c i f i c gravity (Xa), average ring width(Xb), and average width of summerwood(Xc) 15* 5. Analysis of variance for the regression of modulus of e l a s t i c i t y ( Y e ) on average ring width(Xb) and average width of summerwood (Xc) 17. 6. Analysis of variance for the regression of modulus of rupture(Yr) on average r i n g width (Xb) and average width of summerwood(Xc). . 18. 7 . Analysis of covariance for the regression of modulus of rupture(Yr) on s p e c i f i c gravity(Xa) 22 . AN ANALYSIS OF VARIATION IN MODULI OF ELASTICITY AND RUPTURE IN YOUNG DOUGLAS FIR 1. Introduction Wood strength depends i n large part upon wood density. Studies such as those of Newlin and Wilson (1919) and Markwardt and Wilson (1935) have repeatedly shown an association between the two. Although density accounts for a substantial part of the v a r i a t i o n i n strength of wood, an important amount s t i l l remains unexplained. This suggests that a d d i t i o n a l character i s t i c s of tree growth must also be related to strength. In t h i s t h e s i s , ring width, summerwood width, and r a d i a l growth zone i n the tree, were tested for sig n i f i c a n c e of t h e i r e f f e c t on the moduli of e l a s t i c i t y and rupture i n young Douglas f i r (Pseudostuga t a x i f o l i a Lamb. B r i t t . ) . 2 . Review of Literature Clarke (1939) has defined concisely the underlying 2. relationship between tree growth and wood properties. In the living tree the wood of the trunk has three main functions, namely, the mechanical support of the crown, the conduction of sap, and the storage of food. Special tissues are developed for these purposes and the properties of timber depend on the character and d i s t r i  bution of these tissues and on the nature of the material composing their c e l l walls. With this concept in mind, one can visualize the wide choice of variables available for correlation with strength. Some that have received close attention are reviewed in the following paragraphs. I n i t i a l l y , a knowledge of strength variation was necessary for the establishment of reliable working stresses for wood. Data obtained for this purpose by the United States Forest Products Laboratory were also used by Newlin and Wilson (1919) for derivation of empirical formulae relating specific gravity to strength. These formulae were of the type: S»KG n, where S is the desired strength property, G is the specific gravity, and K and n are constants dependent upon the strength property estimated, moisture content of the wood and tree species. Although Janka (1915)» and others, had previously recognized that density and strength were related, this later study was the f i r s t to express the relationship convincingly in the form of an equation. Douglas f i r and the southern yellow pines have been selected for most tree growth — wood strength studies, as they were (and s t i l l are) species of prime importance for structural grades of lumber. Also, their distinct growth rings with marked 3 delineation between springwood and summerwood lent themselves well to such work. Brust and Berkley (1935) made one of the more thorough studies of the southern yellow pines. After testing a t o t a l of about two thousand small clear specimens of L o b l o l l y pine (Pinus taeda Linn.), shortleaf pine (Pinus echinata M i l l . ) and longleaf pine (Pinus p a l u s t r i s M i l l . ) , they concluded that strength, e l a s t i c i t y and density decreased from the stump upwards i n the tree and increased with r a d i a l distance outwards from the p i t h . Their findings were i n good agreement with the concurrent work of Alexander (1935) on old-growth Douglas f i r and the much l a t e r work of Wangaard and Zumwalt (1949) on second-growth Douglas f i r . A year after these l a s t two authors published t h e i r r e s u l t s , Kraemer (1950) reported that r a d i a l growth zone i n the tree influenced the strength of red pine (Pinus resinosa A i t . ) ; s p e c i f i c a l l y , the modulus of rupture, modulus of e l a s t i c i t y and f i b r e stress at the proportional l i m i t determined from the s t a t i c bending t e s t . Another conclusion of Brust and Berkley was that r i n g width and strength showed no consistent r e l a t i o n s h i p to each other because of the larger overriding influences of age and species on strength. They did note, however, that a marked and sudden change i n growth rate was accompanied by a corresponding change i n strength. Bethel (1950) reasoned that i f the d i s t i n c t springwood and summerwood bands i n L o b l o l l y pine were considered as laminates 4. of l i g h t and dense m a t e r i a l , one combination of laminates c o u l d be more e f f e c t i v e than another of the same d e n s i t y i n r e s i s t i n g a p a r t i c u l a r s t r e s s . To t e s t h i s h y p o t h e s i s , he made a c u r v i l i n e a r r e g r e s s i o n of compression s t r e n g t h d i v i d e d by s p e c i f i c g r a v i t y on per cent summerwood. The r e g r e s s i o n was s i g n i f i c a n t . By t a k i n g the f i r s t d e r i v a t i v e of the curve and equating i t to zero, he s o l v e d f o r the percentage of summerwood that gave the maximum s t r e n g t h i n compression p a r a l l e l to the g r a i n independent of the d e n s i t y of the m a t e r i a l . T h i s v a l u e f o r L o b l o l l y pine was f o r t y - e i g h t per cent. As laminate combin a t i o n s l i k e l y vary w i t h f l u c t u a t i o n s i n growth r a t e , h i s r e a s o n i n g c o u l d e x p l a i n the abrupt changes i n s t r e n g t h found by B r u s t and B e r k l e y . F o r s a i t h (1933) observed a c o n n e c t i o n between s p r i n g - wood and summerwood width and e l a s t i c i t y . Working w i t h s m a l l m a t c h s t l c k - s i z e beams of southern yellow p i n e , he found t h a t the d e f l e c t i o n under load depended p a r t l y upon the amount of summerwood p r e s e n t . From a m i c r o s c o p i c examination of l i n e s of f a i l u r e i n the beams, he concluded a l s o t h a t springwood t r a c h e i d s f a i l e d i n a manner d i f f e r e n t to summerwood ones. Springwood t r a c h e i d s b u c k led under compressive s t r e s s whereas t r a c h e i d s i n the summerwood separated at the middle l a m e l l a . Garland (1939)) r e p o r t i n g on L o b l o l l y p i n e , noted t h a t s e p a r a t i o n i n specimens under compression was normally between the outer and c e n t r a l l a y e r s of the secondary w a l l . Both he and F o r s a i t h were i n agreement that bordered p i t s were not a source of weakness 5 i n the tracheid wall. Garland, i n addition, related the type of c e l l fracture to the f i b r i l angle i n the secondary wall, and was one of the f i r s t to introduce t h i s c h a r a c t e r i s t i c . Later, Kraemer (1950) found evidence that f i b r i l angle influenced the bending strength and s t i f f n e s s of red pine. As the studies of tracheid length made by Liang (1948) and Bisset, Dadswell and Wardrop ( 195D indicated i n t e r - r e l a t i o n s h i p s between growth rate, age, c e l l length and f i b r i l angle, t h i s l a s t character i s t i c of c e l l structure might well receive continued attention i n future growth — strength work. In many tree growth-wood property studies, such as those of Turnbull (1948), Chalk (1953) and Smith (1955 and 1956) , s p e c i f i c gravity was selected as the dependent v a r i a b l e . These studies are of interest because variables that influence density probably also influence strength. Of the variables that might be associated with density, for example ri n g width, summerwood percentage, and age, age remains the most contro v e r s i a l . After investigating the s p e c i f i c gravity of Pinus  in s i g n i s Doug, and Pinus patula Schlech. and Cham., Turnbull (1948) proposed that the density of coniferous wood depended primarily on the number of rings from the p i t h . Chalk (1953) attempted to v e r i f y t h i s conclusion for Douglas f i r but found no evidence to support i t , neither did he f i n d a clear r e l a t i o n  ship between ring width and density; therefore Turnbull fs 6. hypothesis that a tree could be grown r a p i d l y without decreasing i t s density was not refuted. In a comprehensive survey of l i t e r a t u r e pertaining to growth rate and s p e c i f i c gravity i n conifers, Spurr and Hsuing (1954) concluded that growth rate had far less effect on s p e c i f i c gravity than did r a d i a l p o s i t i o n i n the tree or age of the wood. Recent studies by McKimmy (1955)» McGuinnes (1955) and Smith (1955 and 1956) have made good use of s t a t i s t i c a l methods to separate the interacting influences of growth rate, percentage of summerwood, and age on s p e c i f i c gravity. McKimmy used regres sion techniques to analyse s p e c i f i c gravity v a r i a t i o n i n second- growth Douglas f i r . He noted that age of the tree at the time the wood was formed seemed to greatly a f f e c t the s p e c i f i c gravity. He p a r t i c u l a r l y cautioned against predicting strength of material near the p i t h by either growth rate or percentage of summerwood because neither was an accurate estimate of s p e c i f i c gravity i n th i s zone. Smith (1956) also used methods of regression analysis. She found a d e f i n i t e r e l a t i o n s h i p between percentage of summerwood and s p e c i f i c gravity i n wide-ringed second-growth Douglas f i r . As this r e l a t i o n s h i p did not change s i g n i f i c a n t l y for three successive r a d i a l growth zones from the p i t h that she selected, she was able to show by a covariance analysis that differences i n percentage of summerwood accounted for differences i n mean s p e c i f i c gravity for whole annual rings from the three zones. By analysis of variance and covariance, McGuinnes (1955) 7. determined the influence of per cent summerwood, ring width, age, and crown class on s p e c i f i c gravity i n eastern white pine (Pinus strobus Linn.). After adjusting for per cent summerwood differences between decades, he found that age had no s i g n i f i c a n t e f f e c t upon density. His r e s u l t s concurred with those of Smith. The fact that McKimmy did not consider differences i n percentage of summerwood between decades could explain why his r e s u l t s were i n disagreement. 3« Purpose of Analysis Douglas f i r i s an important s t r u c t u r a l timber i n world markets. In the past, and to a lesser extent at present, the supply of timbers has come from large trees i n old-growth stands. If a supply i s to be maintained i n the future, an increasing proportion of the timbers w i l l have to be taken from second- growth stands because much of the limited amount of remaining old-growth material i s i n urgent demand f o r the manufacture of plywood. It i s quite possible that some of these young stands w i l l be subjected to s i l v i c u l t u r a l treatment. Thinning and pruning can be planned most e f f e c t i v e l y when, the desired pro perties of the f i n a l product are c l e a r l y defined and t h e i r relationship to tree growth i s well understood. This study attempts to add to the understanding of growth—strength relationships i n young Douglas f i r ; s p e c i f i c a l l y , i t i n v e s t i  gates the influence of r a d i a l growth zone i n the tree on two 8 . important mechanical p r o p e r t i e s , namely, the modulus of e l a s t i c i t y and modulus of rupture . 4 . Source of M a t e r i a l The basic data used i n th i s thes i s were obtained from the Vancouver Laboratory of the Forest Products Laboratories of Canada. They had been compiled from strength tests conducted on three shipments of second-growth Douglas f i r . Twenty-two trees had been t e s ted , seven of approximately s i x t y years age from Port Moody, eight of about seventy years of age from Coombs (on Vancouver I s l a n d ) , and seven of approximately ninety years of age from Stave Lake. Stand s i t e q u a l i t y i n each l o c a l i t y was s imi lar and above average for second-growth f i r from the coas ta l region of B r i t i s h Columbia. The trees were se lected over a period of twenty years (1931 to 195D by J . B. Alexander and W. J . Smith of the Timber Mechanics Sect ion of the Vancouver Laboratory. Dominant and co-dominant trees were taken because t h e i r larger s i ze permitted the desired number of test pieces to be cut from each t r e e . Age, height and diameter measurements of the trees are presented i n Appendix A* 5. Test ing Procedure Modulus of e l a s t i c i t y and modulus of rupture were determined from standard 2 " x 2 " x 30" specimens tested i n the green cond i t i on . These specimens were se lected (from a bo l t twelve feet long sawn from the butt end of each tree) and tested, over a twenty-eight inch span, by the procedure prescribed for s t a t i c bending i n Part IV of the A.S.T.M. Standards, 1955.1 S p e c i f i c gravity (volume at test—weight oven-dry), rings per inch and per cent summerwood were obtained by methods es s e n t i a l l y the same as those described by Rochester (1933)* S p e c i f i c gravity was computed on the basis of weight, moisture content, and dimensions of the specimen. Rings per inch and per cent summerwood were estimated from cross-sectional discs (examined under low-power magnification) taken from the piece containing the test specimen. The boundary between spring-wood and summerwood was determined v i s u a l l y without reference to any standard d e f i n i t i o n of summerwood; consequently, the experimental error for per cent summerwood contained a personal bias. 6. Method of Analysis and Results A t o t a l of two hundred and f i f t y - e i g h t s t a t i c bending tests had been made on specimens from the previously mentioned twenty-two trees. Ninety-seven specimens had been taken from young wood within the f i r s t f i v e inches of r a d i a l growth. Modulus of e l a s t i c i t y and modulus of rupture values determined from these specimens were grouped under the heading Growth Zone A. The remaining one hundred and sixty-one specimens had been obtained from the older wood lying between the inner zone and 1 Standard Methods of Testing Small Clear Specimens of Timber, A.S.T.M. Designation: D143-52. 10. Table 1. Summary of test r e s u l t s . Property Inner growth Outer growth A l l zone zone data A. B. A.+-B. 97 tests 161 t e s t s 258 tests Modulus of e l a s t i c i t y (1000 p.s.i.) n , Mean 1470.7 1650.1 1582.6 Maximum 2140 2483 2483 Minimum 938 969 938 Modulus of rupture (p.s.i.) _ Mean 6899.4 8180.7 7699.0 Maximum 9940 11238 11238 Minimum 5045 6439 5045 S p e c i f i c gravity ( v o l . green-Wt.O.D.) Mean 0.4171 0.4723 0.4516 Maximum 0.532 0.643 0.643 Minimum 0.338 O.367 0.338 Ring width (inches) Mean 0.2159 0.1487 0.1740 Maximum 0.333 0.333 0.333 Minimum 0.091 O.O63 O.O63 Summerwood width (inches) Mean 0.0764 0.0649 0.0690 Maximum 0.115 0.125 0.125 Minimum 0.037 0.028 0.028 LOCATION OF T E S T SPECIMENS SELECTED FROM TWBHTT-TWO TREES REPRESENTING THREE GEOGRAPHICAL AREAS X - S E C T I O H OF BUTT END OF BOLT N | | T E S T P I E C E FROM GROWTH ZOHE B : TOTAL OF 161 P I E C E S . S I Z E OF SPBCIMEHJ 2" x 2" x 30". Figure 1. 12 the bark. Moduli values for these specimens were grouped under the heading Growth Zone B. Zones A and B are i l l u s t r a t e d i n Figure 1. Test results are l i s t e d by shipment, growth zone and tree i n Appendix B. Maximum, minimum and average values for each property from both zones are presented i n Table 1. Width of ring and width of summerwood i n the r i n g were used i n preference to rings per inch and per cent summerwood. The d i s t r i b u t i o n of rings per inch was skewed i n the d i r e c t i o n of fast growth, decidedly so for the inner growth zone. The r e c i p r o c a l , width of r i n g , had a much less skewed d i s t r i b u t i o n . Summerwood width was used to f a c i l i t a t e the analysis of seasonal growth ef f e c t s on strength and e l a s t i c i t y . An example, giving the o r i g i n a l measurements and the ones used, w i l l c l a r i f y the method of transformation employed. Origi n a l Transformation Measurement used measurement 4 rings per inch r e c i p r o c a l =^ r i n g width= 0.2500 inches 30 per cent summerwood \ x 30/100 summerwood width = 0.0750 inches I n i t i a l l y , differences i n average values of modulus of e l a s t i c i t y and modulus of rupture from each zone were tested for s i g n i f i c a n c e . Analyses of variance revealed highly s i g n i  f i c a n t differences for both moduli (Table 2 ) . Similar analyses for the properties of ring width, summerwood width and density showed that t h e i r average values d i f f e r e d i n much the same manner (as can be seen also from Table 2 ) . 13. Table 2. Analysis of variance for properties between zones. Degrees of freedom Modulus of e l a s t i c i t y Total 257 Within 256 Between means 1 Modulus of rupture To t a l 257 Within 256 Between means 1 Spe c i f i c gravity Total 257 Within.. 256 Between means 1 Ring width Total 257 Within 256 Between means 1 Summerwood width Tot a l 257 Within 256 Between means..... 1 Sum Squares 314,414,301 215,031 ,731 99,3827570 680,074 495J.229 184,795 Mean square 21,464 ,420 19 .516.709 76,237 1,947,711 1,947,711 44 839,968 99,382,570 44 1,935 184,795 ±4 98,914,001 71.644,177 279,860 27,269,824 27,269,824 44 11,877,181 11.066.907 43,230 • ~~£Jl0,274 810,274 44 44 S i g n i f i c a n t at the 1% l e v e l . Table 3 Analysis of variance for the regression of modulus of e l a s t i c i t y ( Y e ) on s p e c i f i c gravity (Xa), average ring width(Xb), and average width of summerwood(Xc). Growth zone A. Regression on XaXbXc Regression on XbXc Xa after Xb and Xc Error F * 35.027 Regression on XaXc Xb after Xa and Xc F - 1.641 Regression on XaXb Xc after Xa and Xb F - 1 .055 R 2y.abc - 0.5377 Degrees of freedom 3 2 1 93 2 1 2 1 Sum squares 3,293,865 2.227.221 1,066,644 2,832,056 3 i 2 6 l , 7 3 l 32,134 Mean square 1,066,644 30,452 ,243.890 49,975 49,975 32,134 Growth zone B. Regression on XaXbXc 3 5,522,075 Regression on XbXc 2 4.552.481 Xa after Xb and Xc 1 969,594 969,594 Error 157 7,868,713 50,119 F = 19.346 AA Regression on XaXc 2 5.490.111 Xb after Xa and Xc 1 31,964 31,964 F = O.638 Regression on XaXb 2 5.203.091 Xc after Xa and Xb 1 31o,984 318,984 F - 6.365 A R 2y.abc " O- 4* 2 4 AA S i g n i f i c a n t at the 1% l e v e l A S i g n i f i c a n t at the % l e v e l Table 4 Analysis of variance for the regression of modulus of rupture(Yr) on s p e c i f i c gravity(Xa), average rin g width(Xb), and average width of summerwood(Xc). Growth zone A. Regression on XaXbXc Regression on XbXc Xa after Xb and Xc Error F = 86.390 M Regression on XaXc Xb after Xa and Xc F = 1.117 Regression on XaXb Xc after Xa and Xb F = 0.181 Degrees of freedom 3 2 1 93 2 1 2 1 Sum squares 60,440,710 35i431,396 25|009,314 26,922,726 Mean square 25,009,314 289,492 60.117.465 3231*245 323,245 60.388.287 52,423 52,423 R y. abc 0.6918 Growth zone B. Regression on XaXbXc Regression on XbXc Xa after Xb and Xc Error F - 251.524 AA Regression on XaXc Xb after Xa and Xc F = 0.723 Regression on XaXb Xc after Xa and Xb F = 0.017 3 2 1 157 2 1 2 1 94,341,556 40.950.076 537391,480 33,326,739 94.188.112 153,444 53,391,480 212,272 153,444 3,568 R y.abc = 0-7390 Aft S i g n i f i c a n t at the 1% l e v e l 16. To determine i f the between-zone v a r i a t i o n i n strength and e l a s t i c i t y was e n t i r e l y due to the accompanying differences i n ring width, summerwood width, and density, the ef f e c t of each of these l a t t e r variables on the two moduli i n both zones had to be known. Regression analyses were set up to obtain t h i s information. Modulus of e l a s t i c i t y and modulus of rupture were selected as the dependent variables, and s p e c i f i c gravity, r i n g width, and summerwood width were chosen as the independent variables. The influence of each of the independent variables on the two moduli was assessed by methods sim i l a r to those outlined by Snedecor (1956) . In both zones, the influence of s p e c i f i c gravity on modulus of e l a s t i c i t y (Table 3 , Xa after Xb and Xc) and modulus of rupture (Table 4, Xa afte r Xb and Xc) was highly s i g n i f i c a n t . Ring width (Table 4, Xb after Xa and Xc) and summerwood width (Table 4, Xc after Xa and Xb) had no s i g n i f i c a n t influence on modulus of rupture i n either of!the two zones. With the possible exception of summerwood width i n the outer zone (Table 3» Xc after Xa and Xb), the i r influence on modulus of e l a s t i c i t y was also n e g l i g i b l e . Following these analyses, the influence of s p e c i f i c gravity on the two moduli was evaluated i n d i r e c t l y by using only ri n g width and summerwood width as independent variables. The R values of Tables 5 and 6 indicated that approximately one- t h i r d of the v a r i a t i o n i n both moduli from each zone was removed by th e i r regression on rin g width and summerwood width. The Table 5 Analysis of variance for the regression of modulus of e l a s t i c i t y ( Y e ) on average ring width(Xb) and average width of summerwood(Xc). Growth zone A. Degrees of Sum Mean freedom squares square Regression on XbXc 2 2 ,227,221 Xb alone 1 2,048.722 Xc after Xb 1 178,499 178,499 Error 94 3,898,700 41,476 F * 4.304 4 Xc alone 1 434.757 Xb after Xc 1 792,464 792,464 F = 19.107 44 R 2yibc s 0.3636 Growth zone B. Regression on XbXc 2 4,608,236 Xb alone 1 4.608.009 Xc after Xb 1 227 227 Error 158 8,782,779 55,587 F « 0.004 Xc alone 1 3.630.184 Xb after Xc 1 978,052 978,052 F - 17.595 44 R 2 y . b c - 0.3441 4 S i g n i f i c a n t at the % l e v e l 44 S i g n i f i c a n t at the 1% l e v e l Table 6. Analysis of variance for the regression of modulus of rupture(Yr) on average ri n g width (Xb) and average width of summerwood(Xc). Growth zone A. Regression on XbXc Xb alone Xc after Xb Error F = 14.141 *ft Xc alone Xb after Xc F = 60.026 AA Degrees of freedom 2 1 1 94 1 1 Sum squares 35,431,396 27.618.944 7,812,452 51,932,040 2.269.004 33,162,392 Mean square 7,812,452 552,469 33,162,392 R 2 y . b c = Growth zone B. Regression on XbXc 2 40 ,950,076 Xb alone 1 14.733.986 Xc after Xb 1 26,216,090 26,216,090 Error 158 86,718,219 548,849 F = 47.766 AA Xc, alone 1 1.006.738 Xb after Xc 1 39,943,338" 39,943,338 F = 72.777 AA R 2y.bc - 0.3208 M S i g n i f i c a n t at the 1% l e v e l 19. i n d i v i d u a l significance of r i n g width (Tables 5 and 6 , Xb after Xc) and summerwood width (Tables 5 and 6 , Xc after Xb) showed that an estimate of strength and e l a s t i c i t y made from the two together was more accurate than that made from either one separately. Because the d i r e c t influence of r i n g width and summer- wood width on the moduli of e l a s t i c i t y and rupture was i n s i g n i  f i c a n t , only s p e c i f i c gravity differences between growth zones required adjustment to assess the effect of growth zone on the moduli. This assessment was made by a method of covariance analysis outlined by Snedecor (1956) . The regression equations used, that i s , modulus of e l a s t i c i t y versus s p e c i f i c gravity and modulus of rupture versus s p e c i f i c gravity, and the slopes and positions of these straight l i n e equations through the basic data, are i l l u s t r a t e d i n Figures 2 and 3 respectively. Snedecor has pointed out that two assumptions are made i n carrying out such an analysis. 1. The two samples have a common mean square deviation from regression. 2 . The slopes of the two regressions are the same. It can be observed from Figure 2 that the dispersion of modulus of e l a s t i c i t y values about the regression l i n e i n the outer zone appears greater than i n the inner zone. This unequal dispersion was tested for s i g n i f i c a n c e , as Snedecor has suggested, by c a l c u l a t i n g the r a t i o of mean square deviations for the two zones. The r a t i o (72,687:33,672) was highly s i g n i f i c a n t for 159 and 95 1 M ! - n - n - , ! 1 1 i i i i i 1 ! I I l i l M i l E L A T 1 1 i ! ' 1 : 1 . • 1 . , • i MOD 3ROW ULUS H ZD ;ITY : t .j B. : kND S PECIF i i ! i i 1 F ONSH P B E SVilTY WE Eh Or! E N E S .ASTI I AND c i i i : i ! 1 1 I i i i i - i i i GR i i i >R: I 1 ; I I I i J i i _ U _ L -: 1 1 I 1 1 ' P i 1. , i i i i ! I I I I i i ; i i i 1 1 1 1 1 1 TESTS' - i : i 1 i i i i i LL..U. M I 1 ' ! I X L i l . ! . 1!' z° ' • 70 4E A KEQraESSIOr . i TION3. ; L •-— • i - — ! : i i ! 1 1 1 1 1 1 1 ! I ! 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J _ L 1 i "i i i - i . i p i - •--i i _ — — - >-a- i 1 I I I : r - - T l - - _ - - - 4- i •- r t.i H 1 Y t i - 0 - L © • i ' Q i i i i - G 1 1 i r 1.1. 1 i 0 - -j > L _ : i - - - G -- - - - ' "\ — - 1 j _ 1 : i i M I ; M M ) 1 - - - - i' - -l.-LL i i i - C i \ 1 i (. ! . i i i i I i ' i I i I r I Q 1 i i i i -a-- - T n j 9 + - • r i - - - i - - - - - - G -! 1 - . i - i i i - i i i - i i i — - - - - -- - — - - - - - — — I — - i 1 ,! - 7* r9 - -- - --- - - - - - - - - - - - -- - - - -- - - -- .! 1 • i i 1 ' ' - - - - - - i -- I 1 1 i i "\" :\ i j i i i - - -!.!: - - - -- - - -r r i - — 0 0 -- - - P. 5 0 — — < ) 0 0 - - - - -0 > M •'C yo MI C 5 ( R ft it 71 r i - — j J! >< ) - J y ) - -- i ) .... -• - ~! i - — - | - - - - - - --- - - - - - --• i i i i - - - - - - _ _ 0 Ll IM E < if i : Ii 4 V re C 1 T 0 VI N c ll n - - - - - - -- - - i i i i i i 1 i i i -- - - - -- - - - - - - - - - — -- - - -- - - - 1 i 1 J i i o 22. degrees of freedom. The variance was heterogeneous. As the data did not s a t i s f y the f i r s t assumption, no further attempt was made to determine the eff e c t of growth zone on modulus of e l a s t i c i t y . The two assumptions were f u l f i l l e d for the modulus of rupture data. Tests of significance are presented i n Table 7. Neither F = 1.374, which tested for heterogenity of variance, nor F = 1.416, which tested for unequal slopes, was s i g n i f i c a n t . The value F • 17.54, which tested for differences i n modulus of rupture between the two zones after adjustment to a common sp e c i f i c gravity, was highly s i g n i f i c a n t . Table 7. Analysis of covariance for the regression of modulus of rupture(Yr) on s p e c i f i c gravity(Xa). Regression Deviation from regression c o e f f i c i e n t (ZXaYr) 2 Degrees of I Yr - 2 Mean F freedom ZXa square Zone A. 18,670 95 28,392,995 298,874 1.374 Zone B. 16,895 159 34,587,731 217,533 Within 254 62,980,726 247,956 1.416 Regression c o e f f i c i e n t 1 350,758 350,758 Common 17,501 255 63,331,484 . 248,359 17.54 M Adjusted means 1 4,356,426 4,356,426 Total 256 67,687,910 ftft S i g n i f i c a n t at the 1% l e v e l 23. 7. Interpretation and Discussion of Results Table 4 showed that ring width and summerwood width had no influence on the modulus of rupture after the e f f e c t of s p e c i f i c gravity on the modulus had been removed. Thus the quality of wood substance, as measured by these gross anatomical features, did not seem to add to or detract from the load- carrying a b i l i t y of the tested beams. This i s i n agreement with the work on second-growth Douglas f i r of Wangaard and Zumwalt ( 1 9 4 9 ) and Schrader ( 1 9 4 9 ) who stated that rate of growth did not correlate mathematically i n any recognized r e l a t i o n s h i p with strength except as i t affected s p e c i f i c gravity. Clark ( 1 9 3 9 ) had made a similar study of the effects of s p e c i f i c gravity, growth rate, and amount of summerwood on the longitudinal com pressive strength of European ash (Fraxinus excelsior Linn.). His results also concur with those reported here, although obtained for a d i f f e r e n t strength property from a wood of e n t i r e l y d i f f e r e n t structure. Table 3 revealed that summerwood width was s i g n i f i c a n t l y related to the modulus of e l a s t i c i t y i n the outer zone aft e r the effects of s p e c i f i c gravity and ring width had been eliminated — a r e s u l t contrary to that for modulus of rupture. In other words, the quality of summerwood i n the outer zone appeared to a f f e c t e l a s t i c i t y but not strength. It can be noted from Appendix B and Figure 2 that a few of the test pieces from the outer zone of Trees 5,7 and 8 i n Shipment 98 (marked # i n Appendix B) exhibited unusual properties. They had wide bands of summerwood 24. and high density but very low values of elasticity. Although this shipment had been tested in 1952, several small specimens were found that had been used originally for estimating growth rate and per cent summerwood. One of these specimens had come from the test piece which had the low value of elasticity in Tree 7. This specimen was sectioned and examined under the microscope by Miss E . I. Whittaker of the Vancouver Laboratory. She found compression wood in three of the rings. Pillow and Luxford (1937) had observed that the greater slope of the f ibr i l s in the cel l wall accounted for the deficiency of strength in compression wood and that the decrease in modulus of elasticity with increasing f i b r i l angle proceded at a more rapid rate than did the decrease in modulus of rupture. Their observations suggest that the amount and severity of compression wood present in Tree 7 (and probably present also in Trees 5 and 8) was sufficient to affect modulus of elasticity but not modulus of rupture in the outer zone. Tables 5 and 6 disclosed the fact that ring width and summerwood width were significantly related to the moduli of elasticity and rupture i f the influence of specific gravity on these last two properties was not f irst eliminated from the analyses. That is , ring width and summerwood width, through an association with density, appeared to have an indirect influence on the modulus of elasticity and modulus of rupture. Kramer and Smith (1956) investigated the strength properties of plantation-grown slash pine and reported that the separate use 25. of rings per inch and per cent summerwood gave as r e l i a b l e an in d i c a t i o n of modulus of rupture as did the use of both combined. In the present study, the estimate of t h i s modulus made from ring width alone was improved, i n a l l cases, by the additional use of summerwood width. As rin g width and summerwood width are not exactly comparable with rings per inch and per cent summerwood, there was no assurance that differences i n growth conditions between the naturally-grown Douglas f i r and the plantation-grown slash pine were responsible for the contrasting r e s u l t s . Table 7 showed that a highly s i g n i f i c a n t difference i n strength remained between zones when the average values of modulus of rupture for each of the two zones were adjusted to a common s p e c i f i c gravity. This discrepancy i n strength was somewhat anticipated. F o r s a i t h (1933) had already noted i n his work on matchstick-size beams of southern pine that the wood formed early i n the l i f e of the tree was weaker than that produced during the la t e r years. Clarke (1939) had indicated that the effect of c e l l - wall composition, l i g n i n content i n p a r t i c u l a r , on the long i t u d i n a l compressive stress of ash was quite independent of s p e c i f i c gravity. Wardrop ( 195D had found that the t e n s i l e strength, c e l l length, and c e l l u l o s e content of tangential sections from stems of Pinus radiata D. Don. increased with successive growth rings from the p i t h . Their results suggest that the difference i n modulus of rupture between zones was due to changes i n chemical composition and microscopic structure 2 6 of the c e l l walls which occurred with advancing age. 8. Conclusions Ring width and width of summerwood i n the r i n g have some value i n predicting e l a s t i c i t y and bending strength i n young Douglas f i r but one must be used i n combination with the other i f the estimate i s to be r e a l i s t i c . Moduli of e l a s t i c i t y and rupture tend to increase as ring width decreases and width of summerwood i n the ring increases. Thus, there i s no basis for concluding, for example, that wood having s i x rings per inch i s stronger or s t i f f e r than wood having four rings per inch unless, i n addition, the width of summerwood i s known for the wood of each growth rate. There i s also one further compli cation — summerwood width cannot be determined as accurately as ring width. Because ring width and summerwood width were related to both moduli only through t h e i r association with density, density i t s e l f would be the l o g i c a l variable to estimate e l a s t i  c i t y and bending strength. Density accounted for almost twice as much of the v a r i a t i o n i n these properties as that explained by ring width and summerwood width. Unfortunately, the s p e c i f i c gravity of s t r u c t u r a l timbers i s d i f f i c u l t to determine accurately and quickly. Moisture content fluctuates considerably from piece to piece excluding the weight of a timber as a r e l a t i v e measure of i t s density. Although i t may not be fea s i b l e to set up separate 27 stress grades by density classes for a l l Douglas f i r timbers, consideration could be given to segregating by density the material used i n laminated construction. This material i s conditioned to a specified moisture content; therefore, the s p e c i f i c gravity of each laminate might be determined quite precisely from i t s size and weight. Corrections for minor fluctuations i n moisture content could be made from moisture meter readings. If working stresses recognized the fact that e l a s t i c i t y and bending strength increase as density increases, laminated beams could be designed very e f f i c i e n t l y . The densest material could be used advantageously i n the outer and most highly stressed laminations. The influence of age on the moduli of e l a s t i c i t y and rupture requires further study. No res u l t s were obtained for modulus of e l a s t i c i t y . The presence of compression wood i n a few specimens from the outer growth zone probably caused the heterogeneity of variance between zones which n u l l i f i e d any attempt to examine the eff e c t of age on e l a s t i c i t y . The r e s u l t s for modulus of rupture were not decisive but they did suggest that age had some influence on the modulus. That i s , difference i n average modulus of rupture values between growth zones was not explained by the similar difference i n average s p e c i f i c gravity values between zones. Current grading rules for Select Structural Douglas f i r timbers specify that such timbers be selected for close grain. 2 Standard Grading and Dressing Rules. No. 56 B r i t i s h Columbia Lumber Manufacturers Association. Vancouver, B.C. June 22 , 1956. 28. C l o s e g r a i n i s d e f i n e d as p i e c e s h a v i n g not l e s s t h a n s i x r i n g s per i n c h ( p i e c e s h a v i n g from f i v e t o s i x r i n g s per i n c h and c o n t a i n i n g o n e - t h i r d o r more summerwood a r e a c c e p t e d as e q u i v a l e n t t o s i x r i n g s per i n c h ) . I n t h e f u t u r e , some c o n t r o l may be e x e r t e d over growth r a t e i n young stands o f Douglas f i r . The i n d i c a t i o n t h a t s t r e n g t h i n c r e a s e s w i t h age makes i t a d v i s a b l e t o d e t e r m i n e whether o r not t h e s e p r e s e n t s p e c i f i c a t i o n s w i l l d i s c r i m i n a t e a g a i n s t wood formed r a p i d l y a f t e r a s t a n d has been t h i n n e d a t a l a t e r age. 9. F u t u r e Work A subsequent s t u d y o f v a r i a t i o n i n t h e s t r e n g t h p r o p e r t i e s o f f a s t growth Douglas f i r has been i n i t i a t e d . The method of a n a l y s i s i n t h i s i n v e s t i g a t i o n d i f f e r s from t h a t employed i n the study r e p o r t e d h e r e . Average age and range i n age o f t h e wood i n each t e s t p i e c e a r e a l s o c o n s i d e r e d . One s p e c i f i c o b j e c t i v e of t h i s p r o j e c t i s t o f i n d out whether or not age o f t h e wood i n t h e t r e e has a s i g n i f i c a n t i n f l u e n c e on s t r e n g t h i n r a p i d l y grown t r e e s . I f i t h a s , a second o b j e c t i v e w i l l be t o d e t e r m i n e a t what age t h i s r e l a t i o n s h i p becomes s t r o n g e s t . 29. 10. Bibliography- Alexander, J.B. 1935. The ef f e c t of the rate of growth upon the s p e c i f i c gravity and strength of Douglas f i r . Canada Dept. Int. Forest Serv. C i r c . 44. 8pp. 1950. The physical and mechanical properties of second-growth Douglas f i r . Amer. Soc. Test. Mat. Bull.1 6 9 : 3 3 - 3 8 . Bethel, J.S. 1950. The influence of wood structure on the strength of L o b l o l l y pine wood. North Carolina State College of Forestry Tech. Rpt. No.3. 6pp. Bisset, I.J.W., H.E. Dadswell and A.B.Wardrop. 195l« Factors influencing tracheid length i n conifer stems. Australian Forestry 15 (1 ) :17 -30 . Brown, H.P., A.F.Panshin and C.C.Forsaith. 1952. Textbook of wood technology. Volume I I . McGraw H i l l Book Company Inc. New York. 783 pp. Brust, A.W. and E.E. Berkley. 1935. 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Marts. 1931* Controlling the proportion of summerwood i n Longleaf pine. Jour. Forestry 29(5)^784-796. and D.M. Smith. 1950. Summary of growth i n r e l a t i o n to q u a l i t y of southern yellow pine. U.S.F.P.L. Rpt. No. D1751. 19 pp. Pillow, M.Y. and R.F. Luxford. 1937. Structure, occurrence, and properties of compression wood. U.S. Dept. Agr. Tech. B u l l . 546. 32 pp. 31 Rochester, G.H.1933* The mechanical properties of Canadian woods. Canada Dept. Int. Forest Serv. B u l l . 82. 88 pp. Schrader, O'.H. 1939. V a r i a t i o n i n the s p e c i f i c gravity of springwood and summerwood i n southern pines. Thesis, Univ. of Wis., 1932. Published i n part under similar t i t l e by B.H. Paul i n Jour. Forestry 37(6):478-482. 1949. Some strength properties of second-growth Douglas f i r . Report of Symposium on Wood. Office of Naval Research Dept. of the Navy. Wash. D.C. pp.304-310. , J.W. A l l e n and W.G. Hughes. 1949. Strength properties of second-growth f i r . Trend i n Engineering 1(2):16-20. Smith, D.H. 1955* Relationship between s p e c i f i c gravity and per cent of summerwood i n wide-ringed second-growth Douglas f i r . U.S.F.P.L. Rpt. No. 2045. 14pp. _ 1956. E f f e c t of growth zone on s p e c i f i c gravity and percentage of summerwood i n wide-ringed Douglas f i r . U.S.F.P.L. Rpt. No.2057 9 pp. Snedecor, G.W. 1956. S t a t i s t i c a l methods. Iowa State College Press. Ames, Iowa. 534- pp. 5 ed. Spurr, S.H. and W. Hsuing. 1954. Growth rate and s p e c i f i c gravity i n conifers. Jour. Forestry 52(3)»191-200. Turnbull, J.M. 1948. Some factors a f f e c t i n g wood density i n pine stems. Jour. So. African Forestry Assoc. 16:22-43. Vikhrov, V.E. 1949. Stroenie i . Fiziko-mekhanicheskie Svoistva Rannei i Pozdnei Drevesiny S i b i r s k o i Listvennitsy (The structure and the physical and mechanical properties of the springwood and summerwood of Siberian l a r c h ) . Akademiia nauk SSR, Trudy i n s t i t u t a l e s a (Academy of Sciences of the U.S.S.R. Transactions of the Wood I n s t i t u t e ) , v o l . 4:174-194. Translated from the Russian by H.P. Kippe, U.S.F.P.L. Translation No. 31 . 1951. Wangaard, F.F. and V.E. Zumwalt. 1949. Some strength properties of second-growth Douglas f i r . Jour. Forestry 47(1):18-24. Wardrop, A.B. 1951. C e l l wall organization and the properties of the xylem. 1. C e l l wall organization and the v a r i a t i o n of breaking load i n tension of the xylem i n conifer stems. Australian Jour. S c i . Res. Series B — B i o l o g i c a l Sciences 4(4):391-414. 32 Wardrop, A.B. and H.E. Dadswell. 1952. The nature of reaction wood I I I . C e l l d i v i s i o n and c e l l wall formation i n conifer stems. Australian Jour. S c i . Res. Series B — B i o l o g i c a l Sciences 5 (4 ) :385-398 . Wellwood, R.W. 1952. The eff e c t of several variables on the s p e c i f i c gravity of second-growth Douglas f i r . Forestry Chronicle 28 (3 ) : 34-42. Yandle, D.O. 1956. S t a t i s t i c a l evaluation of the effect of age on s p e c i f i c gravity i n L o b l o l l y pine. U.S.F.P.L. Rpt. No. 2049 4pp. Zobel, B.J. 1956. Genetic, growth and environmental factors a f f e c t i n g s p e c i f i c gravity of L o b l o l l y pine. Jour. For. Prod. Res. Soc. 6(10):442-447. 33. 11. Appendices Appendix A. Measurements taken in the field on twenty-two second-growth Douglas f i r trees, Shipment number Tree number Height at stump ft. and in. Age at stump years D.b.h. i n . Total tree height ft . 78. Port Moody 1 2 3 4 6 7 8 1- 0 2- 0 1-6 1-0 1-4 1-3 1-6 60 58 58 61 58 62 62 Missing 24 23 24 26 Missing Missing 133 139 137 141 132 139 146 93• Stave Lake 1 2 3 4 6 7 9 2-4 2-4 2- 6 3 - 3 2-6 2-4 2-3 85 85 82 86 89 87 92 37 30 35 29- 30 33 33 178 182 177 181 175 173 164 98. Coombs, V . I . 1 2 3 4 5 6 7 8 4-0 6-0 3-0 3-0 3- 0 4- 0 4-0 3-0 79 73 71 72 71 71 71 72 27 28 25 25 30 30 28 27 129 137 127 140 133 125 131 127 34. Appendix B. Results of two hundred and f i f t y - e i g h t s t a t i c bending t e s t s made on specimens from twenty-two second-growth Douglas f i r trees, Shipment number 78 . Port Moody. Growth zone A. Modulus of rupture p . s . i . 6519 7429 6098 6867 8883 7481 6902 7324 7780 7613 6064 6530 6159 6443 5976 7520 7088 6116 6534 5518 5810 5996 6140 6602 6602 5880 6865 5892 7140 7219 6470 7086 5962 8021 Tree no. Rings Per cent Basic Modulus per inch summerwood sp e c i f i c of gravity e l a s t i c i t y 1000 p . s . i . I. 4 35 0.387 1316 6 36 .442 1499 4 32 .387 1441 4 34 .392 1523 5 43 .500 1959 2 . 6 42 0.451 1847 5 40 .429 1601 6 46 •431 1779 7 38 .483 1881 8 42 .423 1805 3 . 4 28 0.393 1407 4 32 .385 1493 4 33 .380 1563 5 34 .400 1523 4 . 3 24 0.362 1309 4 29 .414 1666 4 33 .405 1372 4 20 .391 1372 4 36 .419 1759 6 . 5 36 0.372 1339 5 42 .390 1355 6 31 .391 1200 5 34 .384 1428 5 40 .408 1523 6 44 .421 1671 7 . 4 34 0.363 1264 5 38 .411 1715 5 40 .396 1368 7 43 .427 1715 11 41 .440 1816 8. 6 42 0.411 1434 5 40 .394 1569 3 32 .360 1207 4 34 .373 6 47 .497 1267 7 47 .428 1686 Appendix B 35. Shipment number 78 . Tree no. Rings Per cent per inch summerwood 1. 7 36 10 39 7 40 6 37 6 35 8 39 2. 6 39 6 40 5 40 7 43 6 33 8 40 3. 10 43 5 35 5 40 8 50 6 38 6 38 8 43 4. 9 50 5 36 6 33 6 40 6 39 6. 6 42 7 42 7. 6 45 5 42 8. 7 48 5 42 5 43 5 48 Port Moody. Growth zone B. Basic Modulus Modulus specific of of gravity e l a s t i c i t y rupture 1000 p.s.i. p.s.i. 0.467 1599 8157 .448 1649 7742 ^511 1824 8390 .460 1978 8436 .471 1881 8587 .458 1885 7409 0.474 1912 7530 .499 2033 8374 .454 1199 7592 .440 1614 7481 .472 1307 8138 .457 1892 7147 0.454 1690 7589 .462 1666 8061 .466 1352 8369 .497 1452 8724 ' .487 1503 9880 .436 1444 7639 .448 1614 7560 0.487 1881 8211 .463 1759 7900 .401 1622 7413 .445 1688 8061 .435 1853 8022 0.470 1876 7766 .432 1588 7204 0.476 1750 8262 .403 1554 6461 0.497 1750 7595 .445 1215 7508 .414 1187 7131 .463 1260 7823 36. Appendix B. Shipment number 93 . Stave Lake. Growth zone A. Tree no. Rings Per cent Basic Modulus Modulus per inch summerwood s p e c i f i c of of gravity e l a s t i c i t y rupture 1000 p . s . i . p . s . i . 6. 7. 9. 4 39 0.427 971 6381 5 41 .410 989 5988 5 34 .400 1536 6627 4 45 .436 1011 7418 4 38 .369 938 5870 4 43 .388 1351 6339 3 27 0.415 1318 7032 3 33 .392 1318 6574 3 29 .398 1420 6587 7 41 .479 1657 8578 7 48 .488 1726 8621 4 23 .392 1318 6217 7 40 .466 1695 8357 8 46 .471 1695 8943 4 31 .379 1266 6149 3 28 0 .349 1181 5069 3 34 .386 9989 6217 3 31 .382 1230 6064 5 42 .389 1434 6510 4 33 0 .372 1274 6030 4 33 .375 1434 6304 4 38 .467 1796 7993 8 50 .462 1681 7655 4 25 0.364 1072 5749 5 47 .394 1409 7024 4 31 .374 1405 6817 10 37 .396 1548 6844 11 43 .391 1585 7539 4 33 .397 1172 6829 3 31 0.407 1201 6090 5 48 .461 1506 7693 4 34 .410 1365 6739 4 36 .398 1115 5944 4 18 0 .338 1014 5606 4 24 .390 1239 5534 3 23 .359 1332 5940 4 24 .345 1199 5692 3 22 .355 1189 5744 4 32 .413 1593 7496 Appendix B. Shipment number 93 . Stave Lake. Growth zone B. 37. Tree no. Rings Per cent Basic Modulus Modulus per inch summerwood s p e c i f i c of of gravity e l a s t i c i t y rupture 1000 p . s . i . p . s . i . 6 42 0.410 1318 6625 5 46 .445 1003 7650 5 42 .392 1024 7314 5 40 .404 1448 6739 4 37 .395 1199 6701 3 42 .367 989 5578 7 38 .377 1379 6439 6 35 .418 1233 6458 6 42 .419 1461 6991 5 40 .400 1494 6387 5 33 .411 1593 6713 7 42 0.467 1648 7950 10 46 .487 1882 8877 8 39 .488 1648 8994 11 43 .497 1841 9397 11 49 .503 1822 8398 9 36 .477 1988 8785 8 44 .468 1764 8531 5 46 0.409 1425 6931 11 43 .460 1758 8103 5 47 .428 1673 6999 6 46 .459 1771 7796 10 45 .479 1887 8551 5 45 .463 1811 8109 11 53 .499 1809 8311 16 46 .504 2100 8881 10 42 .478 1698 8473 5 46 0.451 1802 7732 11 51 .502 2130 8706 11 48 .545 2132 9008 10 45 .508 2100 9288 9 57 .503 2194 9691 13 50 .520 2112 9252 9 46 .492 1707 8358 13 46 .504 2087 8792 12 47 .485 2172 8759 8 52 .504 2241 9206 12 47 .516 2001 8558 38. Appendix B. Shipment number 93«(cont.) Stave Lake. Growth zone B. Tree no. Rings Per cent Basic Modulus Modulus per inch summerwood s p e c i f i c of of gravity e l a s t i c i t y rupture 1000 p . s . i . p . s . i . 5 42 0.425 1536 7131 6 46 .407 1454 7448 6 45 .444 1164 8068 5 47 .480 1350 9398 11 34 .393 1648 7542 8 40 .429 1754 7400 12 33 .390 1601 6956 7 47 .467 1665 7682 7 42 .408 1442 7669 9 42 .435 1447 8383 7 39 .445 1521 7950 5 49 0.485 1681 8275 6 49 .541 1298 9056 6 63 .524 1838 8574 5 41 .464 1601 7887 12 53 .453 1802 7797 10 50 .490 1524 9135 6 55 .521 1502 8915 9 61 .471 1606 7705 6 44 .484 1630 8120 9 51 .544 1999 8844 5 48 .448 1365 7131 8 50 .489 1601 8844 10 61 .513 1763 8239 5 45 0 .396 1511 6510 6 36 .436 1707 7314 7 43 .426 1420 6973 9 40 .466 1582 8109 5 37 .427 1506 7179 5 37 .421 1365 6634 6 37 .438 1454 7241 8 38 .429 1715 8006 6 25 .458 1617 8123 5 37 .414 1325 7323 10 38 .472 1665 7810 5 39 .447 1491 8321 9 42 .450 1517 8395 9 36 .440 1681 7836 39. Appendix B. Shipment number 98. Coombs, V.I. Growth zone A. Tree no. Rings per cent Basic Modulus Modulus per inch summerwood s p e c i f i c of of gravity e l a s t i c i t y rupture 1000 p . s . i . p . s . i . 1. 8 41 0.405 1443 7042 3 26 .354 1088 5625 2 . 5 29 0.449 1548 7619 10 38 .474 1650 7663 9 36 .448 1682 7954 3 . 4 39 0.451 1741 8063 5 38 .461 1690 7784 7 39 .433 1585 6926 4 . 5 53 0.532 2140 9940 5. 5 42 0.463 1660 7369 5 41 .460 1782 7644 4 42 .482 1531 6944 5 42 .457 1250 6728 5 31 .437 1539 7084 6. 4 46 0.454 1658. 7308 5 55 .509 1813 8232 7 48 .448 1750 8288 5 42 .433 1093 6784 7. 7 40 0.444 1628 7644 8. 7 36 0.483 1724 9101 10 42 .476 1862 8254 5 41 .480 1707 5045 40. Appendix Shipment number 98. Coom' Tree no. Rings per cent per inch summerwood 3. 7 42 10 47 10 47 11 38 12 40 8 47 8 49 6 33 8 45 9 40 4 44 8 32 6 41 8 40 8 45 9 38 9 38 8 42 8 39 8 38 4 44 12 41 9 57 9 50 7 57 5 47 6 43 # 5 54 # 5 50 # 6 38 # 4 56 7 35 # 7 49 # 7 62 8 36 B. is, V.I. Growth zone B. Basic Modulus Modulus s p e c i f i c of of gravity e l a s t i c i t y rupture 1000 p . s . i . p . s . i . 0.476 1716 8811 .485 1613 9078 .531 1633 9550 .496 1950 8855 .476 1899 8670 .474 2030 8318 .478 1347 9137 0.457 1588 7746 .432 1819 8173 .531 1770 8765 .459 1640 8164 .438 1668 7833 .497 1732 8400 .531 2109 8750 .539 2044 8663 .466 1556 8208 .464 1735 8154 .503 I696 7924 0.461 1652 8759 .454 1648 7695 .471 1740 8299 .496 1903 8452 0.643 2376 10420 .602 2483 11301 .603 2252 11238 0.504 1787 8935 .506 1774 8119 .508 1098 8114 .484 1053 8378 .584 1216 9767 .536 1116 9686 .460 1600 8005 .549 1197 8862 .557 1211 9173 .477 1652 7971 41. Appendix B. Shipment number 98 (cont.). Coombs, V.I. Growth zone B. Tree no. Rings Per cent per inch summerwood 7 43 6 7 54 6 55 8 54 7 43 8 40 11 39 6 42 7 43 4 50 ## 5 52 9 41 7 44 10 38 6 47 # 5 50 # 5 62 Basic Modulus Modulus s p e c i f i c of of gravity e l a s t i c i t y rupture 1000 p . s . i . p . s . i . 0.506 1868 9413 .486 1581 8275 .499 1974 9610 .524 1877 9609 .500 1920 8332 .470 1796 7940 .480 1804 8196 0.440 1787 7355 .458 1648 8383 .453 1712 7502 .501 1433 8816 .535 1067 8501 .494 1770 7899 0.483 1715 9135 .493 1721 8388 .491 1418 9163 .518 ' 1131 8332 .589 969 9759 # S i g n i f i e s that compression wood was probably present i n the testpp.iece. ## S i g n i f i e s that compression wood was present i n the test piece. 

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