Mechanical properties of Engelmann spruce


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Mechanical properties of Engelmann spruce
Physical Description:
Mixed Material
Drow, John T
Forest Products Laboratory (U.S.)
USDA Forest Service, Forest Products Laboratory ( Madison, Wis )
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Resource Identifier:
aleph - 29175706
oclc - 230966425
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JJH!N T. D1tJ01', Engineer

Forest Products Laboratoiry,- Forest Se'rvice
U. S. Department of Agriculture

Engelmann spruce is orne of the lightest of the imnp-rtant comnnerci-l
woods grown in the United States. The specific gravity or de-,sity
of wood is a measure of the ar..'unt of -mood substance :er unit vol.-I.e,
is might be expected, theref-ore, the strength propc-rties of 'wc:d are
related to its density, and a lightwvieight wjd s-uch As Engc-liar.r.n
spruce is not so strong as the heavier woods. In general, this
results in lightweight woods being used to the greatest exte:.t for
purposes where strength is not the main consideration and v;herb the
light color, uniform texture, and lower weight are an advar.tage.

The bar graphs in figure 1 show the relative weight, shrirnkage, and
strength of the clear wood of rngelmriann spruce and a number of other
commonly used species with which it is associated. The relations
shown are based on average values of species and are indicative only
of general trends. The properties of individual pieces or small
groups of material in all species mav vary considerably above or
below the average. As a consequence, some overlapping iEt.'eer. species
will occur, and differences of only a fevw percent in -r-:'oerty rela-
tions should not be considered too important.

The irportnce of strength differences depends upon the use t,. ..'hich
a wood is put. The fact that Engelmann spruce is li"'-ter and somewhat
weaker than many of the comrnonly used construction woods d:es not -e-n
that it cannot be utilized for purposes where stren.:th is of s:-.:e
importance. In housing, for example, 2- by h-inch stds of -L-.'-r.
spruce at the usual 16-inch spacing would be entirely satisf-ct:--ry,
since the size of these rimners is dictated more by custom t:.-n o". an
engineering req-iremient for a U-iece of that size. 3i-.-Iarly, the
strength of Engelmann spruce is fully .dequate to its use in
ordinary 1-inch lumber for wall a.d roc'f sheathirn, snbflooring, 3n
similar uses. For other housing'bers, such as flcor ceiling
joists or rafter, the lower strength properties can be c:_.'e:.sattd
for by sing shorter spans, by increasir.g the size of the -e-Xer to

'Maintained at Madison, Wis., in cooperation with th7 universityy of

Rept. io. 1944-4 -1- AgricutI'Ce-; son

provide adequate strength for a desired span, or by the use of a
better grade. These factors are taken into account in setting up
maximum allowable spans. The required spans for Engelmann spruce
floor joists, flat-roof joists, ceiling joists, and rafters for
residential construction are listed in the Federal Housing Administra-
tion pFblication, "Tables of Maximum Allowable Spans," FHA Bulletin
No. 2550.

For some other purposes the strength and physical characteristics of
Engelmann spruce are adequate to permit its use interchangeably with
comparable grades of other species having generally similar charac-
teristics. For examr.ple, spruce (which includes Engelmann spruce) is
listed amcng more than 20 other species that fall in group I of four
groups of woods commonly used for box construction. All of the other
species shown on the bar charts fall in group I also, and all woods in
that group can be used interchangeably as far as the thickness of
material and the size and spacing of nails are concerned. For such
use, the light weight of Engelmann spruce is a distinct asset, since
one of the objectives in construction of boxes and crates naturally
is to reduce the.weight of the shipping container to save shipping
costs and facilitate handling.

En6elniann spruce, like lodgepole pine, ordinarily has smaller knots
than ponderosa pine, but they are present in larger numbers. These
woods are in general use for containers requiring wider and thicker
slats, such as those used for shipping meat products, or for casket
boxes and the like. Engelmann spruce, because of its light weight,
would also be especially suitable for smaller containers in which the
component parts, for the sake of convenience of manufacture, are made
larger and thicker than actually required for the load to be carried.

Rept. No. 1944-4

(J C

0 -

October 1953