Building Design and Construction Handbook - Merritt - Ventech!

4.46 SECTION FOUR
it is usually at or near glue lines. The presence of wood-fiber separation indicates
adequate glue bonds, and not delamination.
In general, checks have very little effect on the strength of glued-laminated
members. Laminations in such members are thin enough to season readily in kiln
drying without developing checks. Since checks lie in a radial plane, and the majority
of laminations are essentially flat grain, checks are so positioned in horizontally
laminated members that they will not materially affect shear strength. When
members are designed with laminations vertical (with wide face parallel to the
direction of load application), and when checks may affect the shear strength, the
effect of checks may be evaluated in the same manner as for checks in solid-sawn
members.
Seasoning checks in bending members affect only the horizontal shear strength
(Art. 10.5.13). They are usually not of structural importance unless the checks are
significant in depth and occur in the midheight of the member near the support,
and then only if shear governs the design of the members. The reduction in shear
strength is nearly directly proportional to the ratio of depth of check to width of
beam. Checks in columns are not of structural importance unless the check develops
into a split, thereby increasing the slenderness ratio of columns.
Minor checking may be disregarded, since there is ample safety factor in allowable
design values. The final decision as to whether shrinkage checks are detrimental
to the strength requirements of any particular design or structural member
should be made by a competent engineer experienced in timber construction.
4.35 COMMERCIAL GRADES OF WOOD
Lumber is graded by the various associations of lumber manufacturers having jurisdiction
over various species. Two principal sets of grading rules are employed:
(1) for softwoods, and (2) for hardwoods.
Softwoods. Softwood lumber is classified as dry, moisture content 19% or less;
and green, moisture content above 19%.
According to the American Softwood Lumber Standard, softwoods are classified
according to use as:
Yard Lumber. Lumber of grades, sizes, and patterns generally intended for ordinary
construction and general building purposes.
Structural Lumber. Lumber 2 in or more nominal thickness and width for use
where working stresses are required.
Factory and Shop Lumber. Lumber produced or selected primarily for manufacturing
purposes.
Softwoods are classified according to extent of manufacture as:
Rough Lumber. Lumber that has not been dressed (surfaced) but has been
sawed, edged, and trimmed.
Dressed (Surfaced) Lumber. Lumber that has been dressed by a planning machine
(for the purpose of attaining smoothness of surface and uniformity of size)
on one side (S1S), two sides (S2S), one edge (S1E), two edges (S2E), or a combination
of sides and edges (S1S1E, S1S2, S2S1E, S4S).
Worked Lumber. Lumber that, in addition to being dressed, has been matched,
shiplapped or patterned:
Matched Lumber. Lumber that has been worked with a tongue on one edge of
each piece and a groove on the opposite edge.