Reuse o[ Structural Lumber

By Lyman \il. \(/ood, Ensineer Forest Products Laborotory, 1 Fosest Service U. S. Department of Agriculture

The reuse of second-hand lumber is a subject deserving of present attention. Although this is not a new practice, it is now of particular importance because of the large quantities of such lum,ber being released by the Army as temporary rvartime buildings are put up for sale. In using this material, however, certain precautions should be observed.

Preference of the industry for new over second-hand lumber is wholly understandable, Old lumber may be unattractive in appearance; it requires careful inspebtion before use; and in some cases it has been subjected to service that- may have rendered it unfit for further use. Cost of reworking or of repairing damage may make it no cheaper than new lumber. On the other hand, the salvage of old lumber and timbers is not difficult, and if suitable precautionS are taken, satisfactory results may be expected.

The Army, in 1943, had buildings totaling more than a billion square feet of floor area, the major portion of which was wood construction. Many of these buildings have been made available for reuse, and more may become available as time goes on. Lumber salvaged from World War I cantonments is still in use in some places.

It may be pointed out that since old lumber is generally well seasoned, it can be refabricated with assurance that it will maintain its size and shape. This is especially important in the thicker timbers used in heavy construction where air seasoning is slow.

Salvaging old material need not be costly. Nails can usually be pulled out of lumber without serious damage to it. At Fort Lewis, Washington, it was found that a dynamite charge inside a barracks building loosened nailed joints with less damage than the usual wrecking-bar methods. Construction employing ,bolts or connectors can be disassembled and reerected with little difficulty. -Repairs or reinforcements, when needed, can be made a part of the operation.

'Maintained at Madison, Wis., in cooperation with the University of Wisconsin.

Among the precautions necessary if. reuse of lumber or structural timbers is to be satisfactory, the most important is against decay. Since the effect or decay upon strength cannot be estimated visually, material in which decay or rot is found should not be used where strength is important. Much old lumber is darkened or discolored from exposure; this is not in itself harmful, though the discoloration may have resulted from moisture conditions that were also favorable to decay. Decay or rot can usually be identified by the appearance of brown or white spots or irregular zones, the development of brash or brittle texture, and the occurrence of collapsed or abnormally shrunken areas. Likely locations are near the bases of columns and other places where moisture may collect and remain.

It has been shown from tests and service records that wood protected from decay does not deteriorate with time. The Forest Products Laboratory tested railway bridge stringers after 23 years of service and found them as strong as the averag'e of new material. Roof timbers from a market in Alexandria, Va., were found generally serviceable after nearly a century of use. Wooden structures of still greater age are in servi'ce in many places.

Inspection of structural lumber for reuse should include a recheck of grade to see that it meets the strength requirements of the new use. Resawed material must be regraded.

Short deep beams that are heavily loaded are highly stressed in longitudinal shear. Such shear stresses are concentrated at the base of notches or around bolt holes, such as may be present in used timbers. In the previously mentioned Forest Products Laboratory tests, some of the old bridge stringers failed from this cause. Where the new

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