Structural lumber from suppressed-growth

ponderosa pine from northern Arizona

Thomas M. Gorrnan' David W. Green' Aldo G. Cisternas Roland Hernandez

Eini C. Lowell"

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Abstract I.,urnber was sawn Sro~n 150 suppressed-growth ponderosa pine trees, 6 to 16 inches in diameter, harvested near Flagstaff,

Arizona. 'l'lris paper presents grade recover and properlies li)r clry 2 by 4's sawn from the logs and graded by a variety of stritclural glading syslerns. Flexural properties met or exceeded those listed in the National Design Specification. When graded as Light Flairling 43 percent of the 2 by 3's made Standard and Better arid as Stmctuial Light Framing, 34 percent made No. 2 and-better. Cb'a~p was the biggest factor limiting grade yield. About 7 percent of the lun~bcr would ~nake a rriachine stress-rated (MSR) lurnber grade of 1450f. bur x i th no established market such productio~i is not recomniended. If graded as laminating stock, about 8 percent of the lumber qualified as 1.3 or better. A cornparison of the results froni this study wilh those from a con~paizion study indicates that appearance grades ofl'er the highest vali~e alternative tbl- luinber produced from this resource.

Poadams ; i pine (PNms po,,rrili,rrta. I..) is o w of the most important soflwood species in westeni North America. It is found in commercial quantities in every state west of the Great Plains. Wood from mature trees is relatively light- weight, nondurable, nearly white, and has straight grain and a nledium texture. I t is easy to work nilh hand tools, glues well, and is average i n paint- and I'astener-Izoldinrrin abilities. It is a principal millwork species. being used for window karning, saslzcs. doors. moulding. s l~el \ - i r~g~ and paneling. I n round- wood fhr111; il is ilscd lor posts, poles, and house logs (Lowery 1984). 11s slructural lurnber. it 1s sold iis part ofthe Western Woods spcc.ies grouping (NI)S 2005).

Natural regencration 01' ponderosa pinc i s sporadic over rnuch of i t s range, with successfitl gcm~ination thought to be the resull o f the chance combination o fa heavy seed crop and hvorable \vcalhcr dilri~lg the Sollo\;\irrg growing seasou (l3urns and Ilonkala 1990). Iljslurically. the pondel-osa pine forests were gritriarily open stands of mature trees inter- spersed with pockets of younger trees arid grassland. Prior to the carly 1900s. f r e q ~ ~ m l low-intensity fires killed off corn- petirig vegetation, inclilding ponderosa pine seedlings. and help ~uainlaincd open stands of large, fire-resistant trccs (1:ictiler et a1. 1!)97). Fire silppression, along with livestock glszirlg :ind limber harvest: has pri>moted the conversicm of

The ;u!thors are. ~rspccr~vr ly , I'rol'essor ;mtl ilc+pt. I-lc:td, Ilcpt. of Forehr Product>. Lrnit.. or ld;~htr. h.lo>cow. Ida l~o ( ~ g i ~ m ; ~ n : ~ ~ ~ ~ ~ i d ; ~ l i < ) . ~Ju) : Supervis~ry Kcse;irch bnpinctr Emeritus. LiSDr\ Forest Scrv. f.'oscur Proclucls L;ih.. Iladi.;nr~. W ~ S C O ~ ~ S I I T ( Icvanpr.ccn:n h~ghcs . rict): In*lructor ProIi.sstli~, Dcpr. o f Wootl Eligif~ccring, F:rcully of rorcsrry, Ilnrl;. crf' Cllilc. S~~nrlagu. Cliilc (:~ci.;rtm~n i~chilc.cl); Sc- lticlr Enyinccr. I ECO, Sun I'r'arric. Wisconsr~l (mlund.l~cii~i~ncIcz/ti' rccotc~~ctl.cnm); itntl Rcsrarcl~ r:orcst I'rodt~ct.;Tcch~iolo~ist, I,'SD!I Forest Sorv., I'iicitic Northwcsr Kcscnrcli Sta.. I'ortlanil. Orcgon (c lnt+cl I ; i r , l i . f tc l .~~~) . F ~ ~ n t f i n g for this p~,o jcct was p r o v i d ~ d 1 % ~ I SDA Forclcr htrt . . Rcgion 3: n11d USDA Forest Scr\. .. Statr: and P ~ I b;ttc Forc-Iry, 'I CC I I I ~D I~J~ b la rkc t~~ ig I,'nit. %ladisnn. Wisconsin. l V c gtarcfi~ll!, ;~cknrrwlctlcc llic as5isiancc r m v ~ r l c d by rhc C'mnd C:nn?nl~ T;crrc>t\ I ) a n ~ l c n l ~ ~ p iu o h a ~ i n ~ ~ i g tlic I r r p , ~ l l e F r e ~ n o n ~ Can- 111ill ovthc C'trllln,, ( ' ~ v t i p a l i i c s 111 sawu~ip unrl L ~ l n drying. I SDA For- 2.1 C;c:r.\. Recirll~ h roi4 rnca?;llrcint.nrh ;~s\ist:incc. ilnd th? CC'cstrrn Wood I'rc~tlur~:. Slssoc. Iitrnhrr 91;td111~. TOC IZ';<~SIRIICC of %,IS. I'nlnclij I3>rti ln curi iplet l~~g thc staltstical onalysiq ot' this d ; ~ ~ n 1s n~i lc l l al~pr~ciifrcrl, Thc Furcd Prnduct5 I,ilh. is mai~i la~nct l in coop- crarlon w11li thc I jni i . of W~sctltlrin. This arliclc was written itnil prcparcd by 1 l . S . Gnvcnitnont emylayccs 011 crfticial tirnc, irnrf i t is rhcrci'o~.c in tlie p ~ ~ b l i c donii~in :mil nor suhicct 10 cnpyrigl~t. 'l'lie usc of undc or firm nnnlc\ in r l i ih p~it>licafion I\ li~r rcadcr inlbrmatinn and drrc.: r~ot 1n11)ly crliiorscmcnt hy ~ l l c U S U A of ally ~I.O(IIICI or sc~.\-icc. 7-his papcl ~vi~.; r-ccci\ctl I'nr ~ l t rb l ic :~ t ic~~l 111 Fcb~u;lry 2007. Ai-ticlc. Uo. 103 1 1. ,I.Forcxt Producrs Socicty blclnbcr, <';Forest Productr Society 2007.

Forest r'rod. J. 57(12):42-47.

DECEMBER 2007

the historical Ibrcst to dense stands containing a prcponder- ance of small-diameter trees. Under these conditions. tree growth is olieii suppressed. Because ponderosa pine is intol- erant of sh;ide. rapid growth of seedlings prior to crown clo- sure will produce a relatively large core of juvenile \vood. reneraily defined ;is the first 20-years of growth (Sliulzret al. - 19SO. Voorhies and Cironran 1989). Juvcnilc wood tencis to habc higher tllan normal longiti.uJixia1 shrinkage and rnay warp cxccssi\cly. 7his has bee11 idcntilicd as a primary problcni in the ~itili/iltioii ofs~nall-diameter ponderosa pine (F'ahcy er al. 1986).

Marlagemerrt goals for ponderosa pine Ibrcsls include re- ducing stand density to incr-easc resistance to insect and dis- ease attack, reduce the risk of catas(rop11ic wildfires: provide diverse n-tosaics ol' wildlik habitat. and provide eco~rornic benefit to local communities (Willits ct al. 1997). Increasing product utilization, along with reducing harvesting and pro- cessing costs, is critical ibr restoring ecological processes in ponderos;~ pine filrests (Ficdler et al. 1997. Larsort and Mirth 1998. Kummcr et al. 2003). Several studies have shown that old grctwth trees (generally defined as nlore than 150 years old) prociucc a larger proportion or high value "shop and se- Icct" grades 01' lurnhcr than do younger ('%lackjack") trees (Ernst ;tnd I'ong 11985, Fahey and Sachet 1993: Fahey et al. 1986). 1:aRey and Sachet (1993) conclucled that lumber from second growth pondelwsa pine logs is primarily in ttie Dimen- sion grades. These older stiidies. however, were riot specillc to suppressed stands and often were limited in the lumber grad- ing oplions investigated, t.speci;~lly for enginefled product applications. Reccnl studies have shobvn tliat srnall-diameter trees growing in dense stands may have higher aiinu;tl ring density and srnaller knots than more open-grown trees zund can be used as an input mw material li,r higher t~tlue products ranging 1;-om visually and mechanicaily gratled lumber to ve- neer l i ~ r structui.;~l con~posilc lumhcr (LVillits et al. 1997, IlTrickson ct al. 2000. Green el a!. 2005).

in a prekious paper we comj)ar.ed v o l ~ ~ m c and value recov- ery from 6- to 16-inch (152- to 406-rnm) iliameter brcast Iteight (DBH) suppressed-growth ponderosa pine harvested near C;Iagstat'f, Arizona iLowciI and Green 2001). which was manufactured into structural and nonstmctural lumber. 111 that paper, the structilral dimension Iim~ber was limited to the Structural Light Franiing grading system (WWPA 1998). The objective of this paper is to further investigate the yield ol structural lul-nber graded under $1 wider r;mge of structur;ll r r a d i n ~ .; .... 7 svstents.

Procedures Log selection and processing

rrces \liere sclcctcd fro111 the Fort Valley Research and Demonstratlcrn Forest, Flagstaff, Ar~zona, and harvested m silrrlmer 2006. I'he dcmonstrabon project contamed three ex- pet mental blocks 1~1th four treatment plots each. The expen- nren~al blocks represented drfSe~cnt ln~tial stand cond~trons: blackjack (young gro\vth). y e l l o ~ pprnc (old growth), and a rnlutrue of fhc tno age groups llle trcalments i%itllln hlochs 1% c ~ c d~f fe~en l Ilir~inrn~ prescriptions des~gned to retmn stands to prcse~llemerit cond~i~orrs 7 fils 111r oli.ccl thinning horn be- 106 111 \\ 111~11 the laige~ . older trees \\ ere I cla~ncd. Trees to be lcti fud been ntalked. bur no th~nn~ng tic~~tmctit had been ap- plied prior to sample bcicctlon for thrs study Yarnplz tlecs cankc from three oj die four treatlnwi plots 111 the nitxed agc bloch

.4 sa~nple of 150 trees ranging in DBH Ssom 6 to I6 inches (153 to 406 mm) was selected. A matrix of five 2-inch (1- nun) diameter cl:lsses was used, and the trees selected repre- sented those tliat would have been removed under the silvi- cultural prescription. The trees had an average age of 88 years. The sarnple was randoruly divided into LM:O ~i~bsaniples. onc to bc saLvn for dimension lumber and the other for appear- ance-grade lutnber. Only the 2 by 4's from the dimension luni- her sample are discussed in this report. The logs were sawn and the lumber kiln-dried by the Frernont [-umber CIompany, Lakeview. Oregon. owned by thc Collins C'onipanics. .4 more detailed discussion on selection and processi~ig proccdut-es and the overall resulk for both subsamples are presented in Lowell and Green (200 I 1. Simpson ancl Green (2001) give additional information on kiln-drying procedures in the Fre- monl Lumber Company sample.

Grading and testing

The d ~ y and surfaced 2 by 4's were sh~pped fi-onz the saw- m~l l to the l!n~.iers~ty of Idaho where they were graded as structural products by a lurnbcr lnapector ol the Western ?Vood Products Association (R'WPA). Each 2 by 4 \bas graded under ~ c ~ e r i ~ l slruchlral g~ading systems inclutltng Structural Light Framing. Light I*~nniin!. ant! the visual IT-

quiremen ts I'nr rnncliint3 s~ress-rated (MSK ) lumber and laml- nating grades r ATTC 1493. W I'A 199g). If the p a d e of the lunlher coidd be incn-ased by tr~rnming 2 to 4 feet (0.6 to I .2 111) Cram the cnd. the ~r~mnied leng~h and trlm~ned gradc wcre recorded. The lumber a a s cond~t~onecl t'os seceral months at applou~mately 70 "F (21 'C') and 55 percent relatrve hi~mld~ty.

Modulus of elastjoity (MOE) was dclernlined by transverse vibra~ion (Etv) using a E-Computer (Metl-iguard, inc.. Pull- I

nian, Washington) with specimens supported at the ends and vibrated in the flatwise orientation. Specimens were then tested to failure on edge in static bending using third-point I

loading and a span-to-depth ratio of 2 1: 1 following the pro- cedures of ASTM D 198 (ASTM 2005). The rate of loading was appl-oxinlately 2 inchcs (51 mm) per minute. In accor- dance with .ASTM Standards D 2305 and D 4442--97. overtdry moisture content (Mf:) 2nd specific gravity (SG) based on o\i-

! endry weight and ovendry voiinne were determined from sec- tions taken near the fiilure region a-fier testing (ASTM 2005). I

I !

MSR simulation I Simulat~ons of MSR grades wcre ~onducted f c ~ a lange of

potential grades hat mg statlc edgev Ise MOE \ alues rangrng from 1.0 to 3.4 x 10' PSI (6.9 to 16.5 (;Pa) Ind~t~clual pleces in the s~~nulation of MSK grades had to meet four cr~teria to qual~fy for a spec~fied grade. (1) fifth perceittrle (m~rumum) MOE, ( 2 ) fifth peree~~tlle ( r n ~ n ~ ~ n u t n ) lnodulus of rupture (MOR). ( 3 ) grade arelagc MOE. and ( 4 ) visual yrad~ng rc- qulrcnients tiw edge knots. Tmdilionally. Ibr mecl~anically graded lumlxr, the tjlth percentile non-psramctric pomr cslr- nlatr niust equal S? pet*ccnr of the target avcrage MOE value ( i t . . 0.SZ x iI\cmge pl-sidc MOE). Yiis l~tnrts the vannhilily of Lhc Iowcr Ilalf of'thc MOE distr~bu~ron ol'lht. gmtlt. to a coef- liclcnt of ia~iatlon (C'OV) of I 1 percent. Thus. he nurilmurn MOI, Ibr a 1.3E glade would be 0 82 x 1.3 - 1.07 ./ 10' p s ~ (7.4 GPa) I'he nilnlmum MOK value ~ o u l d be 2.1 tlit~es thc allowable bend~ng strength (Fb) for the speciiied grade. In

FOREST P R O D U C T S J O U R N A L VOL. 57. NO. 12

d

addition to ihc M O E aiid bf0K scquiremcnts. knot size is lirn- ited by grade category. More information on h4SR lumber may be fi)und in (ialligan and McDonald (2000) and ihe Sunl- ~ n e r 1997 issue of fZ:ooti P)rsih.n Focus (FPS 1097). A more cotriprclic~~isive discussion of our MSK sirnulalion procc- di~rcs. along with several grading altern;ttives, is glven in Cjreeri et al. (3005).

Laminating grades Traditional pondesosa pine lutnher i~sed in glulani is refer-

enced in glulam standards as pan ol'a species grouping calletl Western Spec~es. As pal? of this grouping, only i:isu;il grading ol' khc luriiber was conducted. The rules fbs visual rating arc bused entirely on tlie ch:lracteristics that rue readily apparent to the llulnan eye, such as knot size. slope of grain. and wane. The following iabulation is an exainple of the knot size limi- tations for visual glulam gradcs:

(iradc Maxinrurii knol STILL

1.. 1 I il width

L2 I!? \x:idth

I..? li2 \r,lt11h

Laminating lurnber assigned to the Soficvood Species grouping has rclalivcly lo& kalues for rncchanical properties. Thus poncieros;l pine i n this spccies grouping was I~istoi-ically restricted to hornogencous L3 combinations. (Ither species. such as 1)ouglas-fir (r"'.crudolsug(i nlcnzirsii (Mirb.) Pranco) and sorrtl!ern pine ( P i n ~ r s spp.). c~nploy rncasure~ne~it of MOE (E-rating) ofthe outer larn~nations to make efficient use of the timher resource. Recent rcsearch has demonstrated that it is possil?le to produce glulam beams with only ponderosa pine luntber using a combination of E-rated lumber arid visual characteristics (Ilel-nandey ct al . 2005). These grades alp ex- pressed i n tcrlns crI'M(>E followed by the limiting knot size. Thus, a2.01'- I/(> grade has a M01: of2.0 x 10"psi (13.8 (il'a) iuld a rnaxirnr~rm edgc knot size of 1;6 tlie lumber width. The 1,-grades lbr our lurnber wa-c tlcreonincd by the WWPA lurn- her inspector.

Results Visual grading

Gr-cxrk? j:it.ld. In this paper. grade yield is based on the total volume of 7 by 4's pmduced from all the logs. rather than being relative to the volume of wood in each individual log as was done in our previous paper (Lowell and ($reen 2001 ). This was necessaly because only the 2 by 4 lumber was evalu- ated ti3r stn~cti~ral products. This decision also rcrnoves the sawing efficiency of a given sawmill as a limitation and makes the rcsulls more applicable LO other rnills that might have different equipment configirraliolis to process the logs.

Under the Structumi I.,ight 1:rarning system. most of the 2 by 4's wcre eiltlcr gradcs No. 2 or No. 3, tviih only a little Inore than 7 percent malting rhe higher grades of Select Structural No. 1 (Table I ) . Thcse results arc similar to those we previ- ously found Ibr lumber cut from small-diameter ponderosa pine froin (irangeville. Idaho ('I'ahle 2). Here tlie lumber that dicl not makc at least No. 3 grade is termed "No. 4"; to avoid conlirsion will1 the lurrlbcr that did not make at least Utility gradt: i n die Light Framing grading system. cvliich is called "Economy." The primary characteristics that limited grade wer-c warp (113'?*'0), wane ( 1 l'!.;,), and linots (7'!6). Likewise, when graded as Lighl l;rnr~iing (T'ublc I ) , only about 13 pcr- ccrit ot' the lu~riber made C:onslructioii grade. (.;rade iilniting

Table 1. - Grade yield for v~sually graded 2 b y 4's from suppressed ponderosa pine from Flagstaff, Arizona.

Grade No. of ~ I L L C C ~ \'0Iu111c Y ~ e l d

(131.) ( "b)

Structulal 11phl framing

Selcct rruclural 2 1 141 2.4

\(I, I 39 287 4.9

KL) 2 200 1555 26.7

N o . 3 2 24 188; 32.3

Yt,. 4 223 1961 33,7

'Co?aI 707 5827 100

characteristics were essei~tially the same as those for Stn~c- tural Light Framing. Thus. its has been shown in previous studies, warp is the primary grade limiting problem. Preven- tion of warp could significantly iscreiwr: utilizatiorl of lmnber from small-diameter ponderosa pine trees (Si~npson and tircen 2001. Simpson 2004).

Mi?chu~zic.rr~~~~"oj?~ii~/i~s. -- To reduce the amount of lun~ber that was tested, only the 2 by 4's that were broken in this study had potential for mechanical grading and glulani. Generally, these were at least a No. 3 visual grade and met other required visual characteristics. as cleterniiued by the WWPA lumber inspeclor. Ihify a small proportion 10%) of the No. 3 visual grade yl~i\lilicd for MSR and was tested. and only a few pieces ( = ~ ' i"~i11 ol' the No. 2 gl.:ldc were not tested. In IIIC Light Fram- ing systcrn, only one piece ol' Utility grade I ~ m ~ b e r qualilicd t i ~ r MSR. itl~creas only a I?\!. picces of Slandartl grade did riot qualif'y.

'I'able 3 sho\+s the tlcxural properties nlicn the lumber 1s graded as Structural Ltght Frarn~ng The lumber had a MC of atmilt 10 pcrcent The SC; of all the lumbe~ averaged aboul 0.41 based on ovendly we~ght and bolurne Tlirs 1s sl~ghtl\i lower than the value of 0.43 gven 111 the Nat~onal Des~gn Specificat~orls (NDS 2005). When adjusted to 15 percent MC as per ASTM Standard Dl990 (ASTM 7005. E\ans et al. 1989). the allowable bendmg strength. kb. and MCfF..s of the Structural Light Framing and I. lght Franinig glades here at least as h ~ g h as those specified In the N I X ('L'able 4). Property values are not shown for the No. 3 and Uttlltl grades because too niany p~eces rn the\e grades \ \ex not tested. L~ght frani~ng grades f o ~ ponderosa pme were not tested In the rn-grade pro- gram (Green and Gvans 1987). I

I Mechanical grading

There IS a good ~ e l a t ~ o n s h ~ p between MOE and btv and be- tween MOR and MOE (Table 5, Fig. 1) . Although the r Z hal- Lies arc a llttle lower than expected, our prcvious s tud~ t s on pondel osa plne from small-d~arneter trees found hlglier 1- val- ues; t l i~~s . tllere 1s no rcason to expect a yroblcrn with rnechan~- cally g r a d ~ n ~ [hi\ lumber The lo\+er 90 percent contidence ~ntcrval on (he Mob-MOK rclat~onsh~p is slio\\n In Flgurc 1. I'ne percent of tlie clata uould he expcclcd Lo be below l h ~ s

DECEMBER 2007

Table 2. - Grade yield of Structural Light Framing for 2 by 4's cut from small-diameter ponderosa pine trees from interior wesf locations.

--

( ,ra~lr ieI(l. ".;."

I.,oiation S ~ r u a [ r o ~ ~ 'iampic si/c S.S Kc>. I 'io ?- So.3 I:con Kc.fercnceC

~ , ~ I I I I I ~ L " 11) ~ ' l : k l l ~ ~ i i l ~ l ~ ~ i ' 2!)0 0 I ,O 11.4 31 0 55.1 I

C I I . ~ I I ~ C \ ilk. 11) f'lianlar~on" 388 0.2 14.0 33.2 3.2 40 4 - 7

4 4 - 7 , 33.? Flagst';ltT: AL S I ~ ~ ~ I , C S > C ~ 707 2.4 26.7 SL.J 3 ___ .... _._ _ ,,,, .......................... _ _- ........... _ - ................ _ - . '-

"Percen~ ul'thc RI) FT volllrne o f 2 by 4'\ in a gl.atlc rclati\c lo the total volu~i~e 01'2 hy 4's. "Pla~lted iiiiriallq at a p~vcn sp:lcing, nor a coml~~crciai plancation. ' I . 1-rickson CI al . 2000; 2. (;orman rlntl (irectl 2000; 3, current xtudy.

Table 3. - Mechanical properties of visually graded ponderosa pine 2 by 4's. .. ..................................................... ............. -, , - - - - - - - . - .- - - - -- .- - - ...... _-- .................. ...... --- ............ %,lOt.d (lO"psi'~ V1OK ( 10' ps0

(;I ade N R.IC (or ; ) Sc; (0l);Ol)) Mci111 SI) M can 51) -.- iiftll

Slruct~lrnl Ilght fcirning S'i 17 0.X 0.33 1 1.374 0.17.; 7.84 l 2.553 4 258

No. I 3 5 9.8 0.409 1.248 0.1 #I 5.5 I I 1.605 1.874

Nc). 2 181 0.7 0.407 1 .I Oh 0.181 4.418 1.811 2.062

Liglit framing

C:orrhtl.uclic~i~ 04 0 7 0.409 1.193 0.105 5.253 2.190 11.300

Standard 102 9.7 0.107 L .079 0. 100 3.198 1.791 I ,880 - ................................................................................................................................................................................. .......... - ....... ............ ..... ......... ..... ""- - 10 ' [psi 0,804 = kt1 1%. I O6 !psi \, O.XO4 -= (%Pa.

Table 4. - Fiexural properties of ponderosa pine 2 by 4's

.... " .... ". " .................... . .

-. .- ."

I 0 1 ' K,,. 2. I I , k h l~lOI1 l<c,G2.1"

Structural Ilghr li.ai~r ing S.S. 1.270 - - 1 2 0 1.078 2.056

No. 2 1 ,112 I 0.082 1 .O 1 0 12 O 932 1.160

Slandiird O.OOh O.RO5 0.9 (1 4115 - - . . ........ ................ --.A. . --- ................

"Wedcrn bVo0~1s sl?ccii':, g101111, NIIS. 2005 "(;rc.cn ant1 i:i:~!ls 1'187. ' !v~Ol~ ILL> L I ~ ? I I S ot.lO"phi. KO,; t~riris o t ~ l ! ) ' p ~ i z 103 1 ) ~ x (>.894= biPa.

It!' psi x 6.803 : (il'a "KO. IS t i le ~?o~i -~)~f i~ t~ ic t~ . jC fitill ~ C I C C ' I I I ~ I C

Table 5. - Property relationships for 2 by 4's cut from sup- pressed-growth ponderosa pine. -. -. - -. ... - ...... " .-uu-,,,-.,--,,-,-, ""--- ...... - .

Prcloer~u - A -A- RX

1'1-ope~ly ' X Sarnplc sire .\ - - - -. -. - - -. 13 r' R V I S I - ~ ............. . ..... . -,,, "- ,--,.--.-

MOE I,.tv 193 0 I70 k7?7 0.53 0.124 'IOl? MOI' 2%; -3.340 7.00.3 0.40 1 576 ........ ............ - - - - . .......... . .- .... ....................

'hlOi:, i rv Ii:ls urlith o i 10" psi. MOIC tla\ tlnlt:, ol' 10' psi. 10' psi 6.894 -- blI';i, 10" ~ p i (3 894 - (;P:+,

''I<ooI 111c~i11 sq11>1re crrol-, i l l i 0' p i .

"I6 ? - Mean trend --- 90% l o w C 1

Ftgure 1. - Relationship between modulus of rupture (MOR) and modulus of eiasticity (MOE) in static bending for 2 by 4's cut from suppressed-growth ponderosa pine.

lo~vest MSR grade with much of an established market is 14501- 1.3E (James 200 1). Only about 7 percent of the volume (425 BF) of these 2 by 4's would make 1450f. With no estab- lished market Ihr ponderosa pine (or Western Woods) MSK, it would not be economical to consider such production. This conclusion is corisiste~lt with what we Sound in our previous study for ponderosa pine from near Grangeville, Idaho (kick- son cl al. 2000).

line and is the basis for establishing rnecl~anical grades. Tllc equation that we used fi)r the lower conlidence intcn;al is: Table 6 shows the distributior~of flatwise Etv values for our

data by edge knot size classes. Most of the pieces were either MC)Ro~,Jl c.1 :- 7.093 x hMOE - 5.780 in the classes with li6- or 1/2-in. edge knots, anti had Ehl

This lumber was evaluated for the production of'a ntr~nbcr values below 1.3 million pounds per square inch (9.8 CiPa). of MSK grading alternari\~es (Cisternas 7000). While a sig- When graded by the visual glulani grades, only about 1 0 per- nificamt arnount o i the lumber would rnakc a grade of'900Fb- cent of the lunlber would make at least an L3 grade (Table 7). 1 .OF;,, therc is ci~rrently no m a r k e t for such a grade. In Pact; die The largest single grade-lirniting factor for glulam with this

FOREST PRODUCTS JOURNAL VOL. 57. NO. 12 45

I . 3 4 percent oftlie 2 by 4's graded as 80.2 and better (43% as Standard and I3ettzr). Warp (43(!i,) and wane (17'!6) were the primary grade li~liilirrg defeccs. with oiily 7 per- cent of the grades being limited by knots.

2. Sawing the 2 by 3 's slightly over size, and kilil-drying with a top load of I SO to 200 pouiids per ft' would likely have improved the yield ofdilnension Itm~ber.

3. The fexural properties o f tills lurnber met 01. exceeded thc allowablt. properties assigned to the species group- ing containing ponderosa pine (tt'cstern Woods).

4. While about 7 percent of the 2 by 4's could qualify as 1 450t:l-r- 1.3E MllS Iinnbcr. such production i s riot rec- ommended. This is the lowest grade of MSR lu~nber cur- rently sold in any volurne, and no inarket is cun-cnlly established for this species group. For those already pro- ducing struct~n-a1 lumber grading, Light Framing. or Strt~ctural Light Framing grades are better alternatives.

5. If a marliet is readily available, this lumber is suitable for the pmductlou o r slack lirr glulam beains. Howeber, earel'ul attention rnust be paid to the reduction of warp and wunc.

6. Appcara~ice grades offer tile higlic~l valuc alterrlative for lumber production frorr~ this supprebsed-growth re- source. A premium of abour $ 5 3 per 1000 cubic fee2 (gross log scale) was estimated in a previous st~ldy.

Literature Cited AIT(;. 1993. Standard specification.; for structural gluetl-laminaled t i~n-

ber of snfiwood specizs. Standard 1 17-0. bI:lani~Sacturing. A~nerican Inst. of 'l'in~ber C'onsrruction. tngiewood, ('olorado.

ASTM. 2005. Annual llook of Standards. Volunre 04.10. West C'i~n- slioliockcn. Pcnnsyli ania: i\mci icrin Soc. frlr Testing and Marc~ial,. D 108-05. Stanclnrrl nrethod.; of static tests of1~111ibe1- in structural si/es. I) 1 i~cKJ-OO. Standard practices for cstablibhinp allowable properties fi-oil1 in-grade tests offull-sl/c specimens. 1) 2395-02. Standard test iiiethods for zpccitic gravity 111' ~ w o d ;~ncl \.~oc)d-basecl inaterials. D 4442-92. Stand:~rcl test methotis Tor direct nloisture content ~ncasurenrcrrt of w c ~ ~ t l :~nd wood-hascti n~iitcrials.

Burns. R.M. and B.H. t,lc?nkalii. 1900. / t i : Silvics of N(11t11 Auierica. Vol. I. Conikrs. Agri. Handbook NO. 654. Ll'ashington, D.C.: LSDA Forest Scrv. f ' i t ~ ~ F ~ o ~ ~ ~ c I ~ o . Y ( I . M!.W. Oiivcr and K.A. Rykcr. pp. 313-424 Sumrnilry of tree characieristics. Burns and ilonkala. pp. 646-630

C'isternas, A,(;. 2000. Mechanical properties of ponderosa pine dimen- sion lu~nher tiom sn~all-dian~etcr, ovcrstockcd stands i n Arizona. Mas- ter's tllcqis. L)rpt. of Forest Products, Cniv. of Idaho. Mosco\+, Idaho.

Evans. S.W.. J.K. E\:rins, and D.W. (ireen. Ic)Xc). C'omputcrprograms for a(lju5ting the 1ncc1i:inical properties of ?-inch di~itensia~~ lu~nhcr for charrgcs in lnoibturc contcnt. <;en. Tech. Rcpt. FI'1.-(iTR-63. 1,SDA i'oresl Scrv.. I:orcst I'roilucts Lab., Madisoil. Wisconsin. v\..\vn.I. f~~l.f,.l'cd.us:~clti.intclactircmc.htrnl.

t:vicl\so~i~ R.(i. . 'I .bl. C;orm:in, D,b\ . ( ireen. rin1.1 I). (.irahiirn, 2000. Vz- chanicnl grlding of lumber sawti from stnail-tlra~lietcr Ioilgepole pine. i x ~ ~ i d c ~ o w p~ne. and gr:~nil f i ~ - ti-or11 nilrtl~crn liiaho. I'cwcst Prod. J. SO(7: 8):5il-05.

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and J.K.R. Sachcr. 1993. Product recovery of puntlci-osa pinc i n Ar~/anaand Ncu Mexico. Rcs. I';rp. PNW-R1'-407. C!SI)A For- est Serb., I'i~ciljc Nortl~~rcst Sfa.. Portland. Clrcgon.

l'icctlcr. C'.C.. C'.Fi. Kecgan, and S.F. Arno. 1!)')7. I!tlli~alion as a com- poncnt o r restoring ccolosicai processes in pondcrosa pine firrcsts. (;en. Tech. Itept. FPL-(iTR-I 00. l jSDA Forcht Serv.. Forest I'roducts Lab., Madison. Wisconsin.

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(irtlligan, 1V.L. ant1 K.A. blcDonald. 2000. Machine grading: Practical concerns for lumber Prodocers. (ien. Tech. Rpt. FPI.-GTR-7. USDA Forcst Sen.; Forcst I'roilucts Lab.. Madison, Wisconsin. www.fpl. ti.fed.us~doct1ri~1its~fplgtr/Fplgtr07.pdf.

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(ireen, D.W. and S.W. E\.ans. lOS7. klcchanical properties of ~isualiy gracied lumher: Vol.1. A sumlnary. I'ub. PI3-8X--159-307. Dcpr. <>f Commerce. hational 'Tech. Information Scrv., Springfield, Virginia. 76 PI?.

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