Flexural properties of dimension lumber from a 50-year-old loblolly pine plantation stand were evaluated. The results indicate very impressive visual grade recovery, particularly No. 1, which amounted to about 44% yield. The results also indicate that the overall degrees of compliance of visually graded lumber to standard SPIB requirements of strength and stiffness are 99 and 94%, respectively

Biblis, Evangelos J.

Carino, Honorio F.

English

Wood and Fiber Science (E-Journal)

FLEXURAL PROPERTIES OF LUMBER FROM A 50-YEAR-OLD LOBLOLLY PINE PLANTATION1 Evangelos J. Biblis Professor and Honorio F. Carino Associate Professor School of Forestry and Alabama Agricultural Experiment Station, Auburn University, A L  36849-5418 (Received May 1998) ABSTRACT Flexural properties of di~ncnsion lumber from a 50-year-old loblolly pine plantation stand were evaluated. Thc results indicate very impressive visual grade recovery, particularly No. 1, which aniountcd to about 4 4 8  yield. The results also indicate that the overall degrees of compliance of visually graded lumbcr to standard SPIR requirements of strength and stiffness are 99  and 94%, respectively. K<,y~~ord.c:  Southern pine, dimension lumber, grade recovery, plantation stand, flexural properties, dcsign requirements, visual grade compliance. The quality and properties of dimension lumber from southern pine plantations, partic- ularly from loblolly pine (Pinus taeda L.) (Bendtsen 1978; Pearson and Gilmore 1971, 1980; Biblis et al. 1993, 1995, 1997) and slash pine (Pinus elliotti Engelm.) (MacPeak et al. 1990; Biblis 1990) have been evaluated. MacPeak et al. (1990) reported that all tested dimension lumber obtained from a 50-year-old planted slash pine stand met the flexural strength and stiffness values required by the Southern Pine Inspection Bureau (SPIB) for the corresponding visual grades. The loblolly pine studies by Biblis et al. (1993, 1995, 1997) involved two different stand densities and four stand ages ( 2 5 ,  30-, 35- and 40-year-old). The results indicate that the structural quality of loblolly pine dimension lumber increases with stand age and stand density. Moreover, there is conclusive evidence that dimension lumber obtained from loblolly plantation stands aged 40 years or less does not meet the SPIB's re- quired flexural design properties, particularly the stiffness values for the assigned visual grades. In loblolly plantations, even at age 35, the percentage compliances of lumber to flex- ural design strength (F,) and stiffness (E) re- quirements are only 89 and 52%, respectively. At age 40, the average flexural stiffness (MOE) of lumber meets the required average design (E) value for the corresponding grade. However, when individual pieces of lumber are considered, the results indicate that the percentage of pieces of lumber complying to required stiffness "E" is alarmingly low. On average, considering all grades and lumber sizes of an unthinned 40-year-old loblolly ' This paper is bascd on a study supported by USDAI plantation stand, only 66% of the lulnber CSRS Grant 92-37103-8030 and Mclntirc-Stennis funds (Project 974) and is nublished as Alabama Agricultural the required "E" ~ x ~ e r ~ m e n r  Stat~on ~ d u r n a l  series NO O-~8592u8. This study was undertaken to determine Wood I J I I ~ ~  I r h o  S< rr,rt< ?. 3 1 t 2). IYYY.  pp 20G103 ' 1 '  I Y Y V  hy the Soclcty of Ww,d Sc~encr and Technolog? 8ihli.c cr~ld Ctirirto-FLEXURAL PROPERTIES OF LOBLOLLY PINE LUMBER 20 1 whether dimension lumber from a 50-year-old loblolly plantation stand meets the required SPIB flexural strength and stiffness values for the assigned visual grades. MATERIALS AND METHODS The investigated loblolly pine plantation is located on a Piedmont site in West Georgia. The 50-year-old stand was established with 1.83- by 2.44-m (8-ft X 8-ft) spacing on a site index of 27.4 d 5 0  yr (90 fd50 yr). At age 18, the stand was lightly thinned at the rate of 19.6 m3/ha (3 cordslacre). In addition, the stand at age 40 was subjected to a severe storm that caused the untimely felling of a sig- nificant number of trees and consequent sal- vaging of sawtimber with an estimated scaled volume of 20.4 m3/ha (3,500 bf-Doylelacre). Later at age 48, the stand was subjected to another storm that again caused the untimely felling of additional trees and consequent sal- vaging of sawtimber with an estimated scaled volume of 11.7 mz/ha (2,000 bf-Doylelacre). Finally, at age 50 the stand had 271 standing treeslha (1 10 treeslacre) with an average di- ameter at breast height (DBH) of 37.3 cm (14.7 in.), basal area of 12.0 m2, (130 sq. ft) and volume of approximately 81 m31ha ( 13,900 bf-Doylelacre). Prior to the selection of sample trees, the timber size distribution for the stand was es- tablished by measuring DBH of all trees in four 0.1-hectare (114-acre) plots in the stand. Twelve trees representing the DBH distribu- tion for the stand were then selected as sam- ples for the study. These were properly iden- tified, harvested, and measured for size. Each sample tree was bucked into 3.66 m- long (12-ft) sawlog segments in the field. The large end of each sawlog was spray-painted with a different color to identify the location of the sawlog within a tree (i.e., first, second, third, or fourth log). Afterwards, the large- and small-end diameters outside bark were measured and recorded. All sawlogs from the sample trees were transported to the cooper- ating sawmill and sawn into lumber. All green lumber was sorted by width and length and then stacked and kiln-dried to approximately 15% moisture content (MC). Thereafter, all the lumber pieces were dressed to the mill's spec- ifications and subsequently graded to SPIB vi- sual grades by qualified lumber graders. The lumber, prior and during testing, was stored in the Auburn University Forest Products Labo- ratory at drier conditions; that resulted in MC during testing between 8 and 9%, as indicated in Table 1. All sawn lumber was transported and stored inside the laboratory for a minimum of 3 weeks prior to testing. Based on actual sizes, the 3.81- by 19.1-cm (2- X 8-in.) and 3.81- by 14.0-cm (2- X 6-in.) test pieces were trimmed to 3.5 m (138 in.) long, while all 3.81- by 8.9-cm (2- X 4-in.) pieces were trimmed to 2.44 m (96 in.) long. All test sam- ples that were trimmed to the desired size were regraded by a qualified lumber grader. A total of 356 pieces of lumber were destructively tested edgewise in flexure to failure with third- point loading according to ASTM D 198-84 (1994). The 3.81- by 19.1-cm (2- X 8-in.) and 3.81- by 14.0-cm (2- X 6-in.) pieces were test- ed over a span of 3.35 m (132 in.), and the 3.81- by 8.9-cm (2- X 4-in.) pieces were tested over a 2.29-cm (90-in.) span. A Tinius-Olsen hydraulic testing machine with a capacity of 54,480 kg (120,000 Ibs) was used to test the lumber. For flexure tests, the distances be- tween the load points were 76.2 cm (30 in.) for the 3.81- by 8.9-cm (2- X 4-in.) and 1.12 m (44 in.) for the 3.81- by 14.0-cm (2- X 6- in. and 2- X 8-in.) lumber. Load and corre- sponding deflection-to-failure data were ob- tained with a data acquisition system. The modulus of rupture (MOR), modulus of elas- ticity (MOE), MC, and specific gravity (SG, based on oven-dry weight and volume) for each tested piece of lumber were subsequently calculated. Flexural test results were used for making comparisons with the required bending strength value for each visually graded piece; that is, the obtained MOR value of every piece was compared to the required bending strength 202 WOOD AND FIBER SCIENCE. APRIL 1999, V .  31(2) . . I .ABLE I .  E'lexi4ral proi~erties and conlpliunce to visual grude requirements of lumber obtuined ,froin u 50-year-old thinned lobloll~ pine plurltation tesrt~d edgewise according to ASTM D 198 wit11 third-point louding over the spans of 228.6 c,m,fi)r 3.81- X 8.9-cni ( 2  X 4s) clnd 335.3 cmfor  3.81- X 8.9-cm (2  X 6s), and 3.81- X lY.1-cnl ( 2  x 8r). SPlB rrqu~red Meet \tandard\ SPlB Plrcc, > I\LI;LI g ~ : ~ i e  te\tetl MC 'X SC" M O E ~  tiua MORh M M D ~  BSV' Mu;, MOE tiwa "Fh" C/C "F-' "4 Lumber size (2" X 4") 3.81- X 8.9-cm 0.58 16.5 71.7 26.8 (0.2) (4.8) 0.50 13.7 44.8 21.7 (0.7) (5.5) 0.5 1 10.4 29.6 12.3 (1.3) (2.1) No. I No. 2 No. 3 All grades Lumber size ( 2  X 6 )  3.81- X 14.0-cm 0.55 15.5 58.6 23.9 (0.4) (2.1) 0.43 12.6 37.2 18.1 (3.4) (2 1 )  0.5 1 12.0 32.4 10.8 (1.2) (5.5) 0.53 8.3 26.9 (0.5) (3.4) No. I No. 2 No. 3 ECON All grades Lumber size (2" X 8") 3.81- X 19.1-cm 0.57 14.7 5 1 .0 10.1 ( 1 .0) (4.1 ) 0.49 12.4 44.1 17.4 (1.0) (4.8) 0.52 9.2 46.9 10.1 No. 1 No. 2 No. 3 All grade\ All lumber 356 99 94 ,' Obcr,-clr> h~~,), Numhr! \  (11 ~pdrer~the\~- .trr \titl~dard d r \ ~ i l t ~ o n  ' RSV 15 lhz I C C I I I I I . P ~  helidlng ~Irmgth value ohtalned hy multlplylng the "Fh" by 2.1 value (BSV) of the corresponding visual grade. The BSV was calculated by multiplying the SPIB required bending design value F, for each grade by the combined adjustment factor 2.1 for safety and duration of load. This com- parison is shown in Table 1 and is reflected by the percentage of the number of pieces meet- ing or exceeding the requirements to the total number of pieces tested. The percentages of the tested pieces with E values above those recommended by SPIB grading rules for the corresponding visual grade are also listed therein. the 50-year-old plantation stand of loblolly pine investigated. Table 1 shows the flexural properties of lumber by size class and visual grade category of all logs obtained from the stand. Also shown in these tables are the num- ber of lumber pieces tested and the average specific gravity (SG) and moisture content (MC) of lumber in the aforementioned clas- sifications. Although the moisture content of the tested lumber was 8.5%, it is not expected to significantly influence the results since any positive effect from the lower MC% on the strength and stiffness of the lumber is negated by the additional negative influence from the defects (Green et al. 1986). In addition, the table shows the bending strength value (BSV) required by SPIB grading rules (1994) for RESULTS AND DISCUSSION Table 1 summarizes the results of the flex- ural tests conducted on lumber produced from Rlhlrc crtld Cnrrrto-FLEXURAL PROPERTIES OF LOBLOLLY PINE LUMBER 203 each visually graded piece and the stiffness design value, E, recommended by SPIB grad- ing rules as the average value for each visual grade. Table 1 shows that the distribution of visual grades of all tested lumber is 44% for No. 1, 40% for No. 2, and 15% for No. 3 and below. The No. 1 grade lumber recovery in this case is exceptionally good compared to that of younger loblolly stands. Table 1 also presents what is considered to be the most important results of the study, i.e., a measure of the degree of compliance of vi- sually graded lumber to standard requirements of strength and stiffness set for a given visual grade classification. In terms of strength, lum- ber obtained from the 50-year-old loblolly stand exhibited a very high level of compli- ance; on average (i.e., regardless of grade), 99% compliance. In terms of stiffness, which is considered a more sensitive parameter for lumber of younger loblolly pine plantation stands, on average 94% of the lumber pro- duced from the 50-year-old stand had E-values that exceeded the published "E" for the cor- responding grade. The results of this study reinforce the view that loblolly pine plantations managed for sawtimber production should have a 50-year harvest rotation. Such a management option is also more economically desirable than man- aging the same stand for pulpwood production based on a 20-year rotation (Biblis et al. 1998). CONCLUSION It can be concluded from the results of this limited study that dimension lumber produced from a 50-year-old loblolly pine plantation meets the flexural strength and stiffness re- quirements for the corresponding visual grades. ACKNOWLEDGMENTS The authors gratefully acknowledge contri- butions to this study made by The Fuller E. Callaway Foundation, LaGrange, GA; The Union Camp Corp., Opelika, AL; Mr. Owen Riley, Forester, Pine Mountain, GA. The as- sistance of Mr. Pat Patrick of Timber Products Inspection Inc., Conyers, GA, is acknowl- edged for determining the visual lumber grade of each piece. REFERENCES AMERICAN SOCIETY FOR TESTING A N D  MAT~RIALS (A TM). 1994. Standard methods of static tests of timbers in standard sizes. D 198-84. Standard method for estab- lishing structural grades and related allowable proper- ties for visually graded lumber. D 245-8 1. Annual Book of ASTM Standards, section 4, vol. 04.09. Philadelphia. PA. BENDTSEN, B. A. 1978. Properties of wood from irnprolcd and intensively managed trees. Forest Prod. J. 28(10): 61-72. BIBLIS, E. J. 1990. Properties and grade yield of luml3er from a 27-year-old slash pine plantation. Forest Prod. J. 40(3):21-24. , R. BRINKER, H. E CARINO, A N D  W. C. MCKEE. 1993. Effect of stand age on structural properties and grade compliance of lumber from loblolly pine planta- tion timber. Forest Prod. J. 43(2):23-28. , H. CARINO, R. BRINKER, AND W. C. MCKEE. 1995. Effect of stand density on flexural properties of lumber from two 35-year-old loblolly pine plantations. Wclod Fiber Sci. 27(1):25-33. -- , AND  . 1997. Flexural properties of lumber from two 40-year-old loblolly pine planta- tions with different stand densities. Wood Fiber Sci. 29(4):375-380. - , AND L. TEETER. 1998. Comparative eco- nomic analysis of two management options for loblolly pine timber plantations. Forest Prod. J. 48(4):29-33 GREEN, D. W., C. L. LINK, A. L. DEBONIS. A N D  T. E. MCLAIN. 1986. Predicting the effect of moisture content on the flexural properties of southern pine dimension lumber. Wood Fiber Sci. 18(1): 134-1 56. MACPEAK, M. D., L. E BURKART, AND D. WE:LDON. 1990. Comparison of grade, yield, and mechanical properties of lumber produced from young fast-grown and older slow-grown planted slash pine. Forest Prod. J .  40(1): 11-14. PEARSON, R. G., AND R. C. GILMORE. 1971. <:haractcriza- tion of the strength of juvenile wood of loblolly pine (Pinus tuedu L.) Forest Prod. J. 21(1):23-30. , AND - . 1980. Effect of fast growth rate on the mechanical properties of loblolly pine. Forest Prod. J. 30(5):47-54. SOUTHERN PINE INSPECTION BUREAU. 1994. Grading rules. SPIB, Pensacola, FL. 

Flexural Properties of Lumber from a 50-Year-Old Loblolly Pine Plantation

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Flexural Properties of Lumber from a 50-Year-Old Loblolly Pine Plantation

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