New Design Values In Effect

New empirical design values for southern pine lumber, the result of the North American In-Crade Testing Program, become effective Aug. t5.

The program, which began in 1977. involved the Southern Pine Inspection Bureau (SPIB). the west Coast Lumber Inspection lJureau, the Western Wood Products Association and Canadian agencies working in close cooperation with the U.S. Forest Products Laboratory in Madison. Wi. More than 70.000 full size, in-grade pieces were tested to the breaking point, including some I 8,000 pieces of southern pine. (See Bttildins Products Digast, Jan. 199 | , p. r9)

The test results varied from species to species, but validated most of the southern pine visual design values in use. Adjustments on these values willaffect only a limited number of end up applications. llasically,

Dorlgn Yrlur Comprrlronr

all southern pine lumber moisture designations will now have identical design values but each size of dimension lumber will now have a different design value and there will be three density classifications instead of two.

New design values for bending and tension parallel to grain will go up for narrows and higher grades and down for wides and lower gradesi compression parallel to grain values will increase significantly and modulus of elasticity (MOE) valu€s will remain unchanged or go down slightly.

SPll] has published the new design values in Supplement No. l9 to the grading rules for southern pine. In September they will publish complete southern pine grading rules incorporating the supplement and final changes such as compression parallel to grain fior southern pine MSR lumber which will be considered by the American Lumber Standards Committee Board of Review this month. The National Forest Products Association will publish the l99l National Design Specification for Wood Construction reflecting all design value changes for U.S. and Canadian dimension lumber in September.

The Southern Pine Marketing Council has begun distribution of a four page booklet explaining the changes and a two page sheet of revised values for southern pine dimension lumber. Design values for western species will be included in the l99l Western Lumber Grading Rules book being published this month. Industry associations will cooperate to conduct a series of seminars for building professionals.

Floor Jolrt Spen Gonpedronr

il0.2 E0ulhrn nna fDlt 2rl0t 10"0.c. l0 9rl O rsl old l8'-0' l0'.5' nd l0'.0' l0'.1' It chinCo 0 -zlt t10.3 Southrn Pln! fDl0 2r12t 10"0.c. t0 9rl l0 prl old t 7'.10' 1640' ncw 16'-2' 14'-6" It chen0c - 9't - Itt

Noh thrr both tho old rnd tlrc new Soutlern Pine eprn lcngthr for tle 80 pcf llve load crto sne e'xectly tlte mme. The mw f,p.n lengtl for the 40 psf livc load cer ie only two percont lower than lpforc, ud lr not rigniftcrnt from a prec' tical rtrndpoint. Ar rhown carllcr in thc dceign volue comparironr, e No.2 2rl0 erpericnccd a l3S decrtere in bending rtrengtl, but kept tlrc reme vrlue for modulue of elerticity.

Thir No.3 2xl2 example reprclent! one of the mort drgmatic decrem in a constnrction ap pliotion uring the new Soutlrern Pino deaign value. Trur Span

Comparltonr

2r4 llo.l XDl5

Soulhrrn Plnr

4/12 Slop.

25110110 prf Lo.drno

21" o.c.,1151( Lord Duntlon

0ld na{Y % chanoc

31',-8', 3r,-3" - llt

Note that the maximum truss span for this particular Soutlrern Pine example dcreaser slightly.

'This 1.6 crartolc wea oxcoadod irm lar gxtmolo lruss span cqrpsris Irbb6 p|.6llshod in Wdwdds, lhc ffilellor ol lhs Wood lru$ C4rcil ol &rr.ica. Tho cqtdoto $l ol cdnp.riod lablss lrchrdss a varioly ol lru$ lypcE. hrmber speci€s. lo6d drrralbns and ffignlor rp.cino3. Over.ll. lhe Southgrn Plre lru$ spaG ch..tgod rolalhlly lilll€ (wilhin 15 l lor tho kadilinl 2,1'ffienle. lrus8 spacirlg. wkler, 96'mootor lru$ sp.cings wre irpacledbydocr66ssol up to 2o%, Firo.it &€ lo lh€ ffi d66ion eq@lioos.