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BUILT-UP WOOD 



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BY O. M. BUTLER 



ASSISTANT DIRECTOR, FOREST PRODUCTS LABORATORY 



RESEARCH in forest products, stimulated by war 

 requirements, forecasts a far-reaching movement in 

 the peace-time utilization of wood in new forms. 

 One field of possibilities in particular stands out. In it 

 lumbermen and foresters should be especially interested, 

 because rapid advancement within the next ten or twenty 

 years may be expected, and developments in this field 

 may have a marked influence on the industry and the 

 profession. This domain is the utilization of wood in 

 built-up forms. 



The trend of utilization is already strong in this direc- 

 tion. Built-up wood is by no means new. Before the 

 dawn of history, the Horse of Troy, we have been led 

 to believe, was a built-up wooden "steed of tremendous 

 height," and on through the ages wood has been used in 

 forms that were "built-up" in one sense or another. The 



in the same way. During the war, built-up structural 

 beams were approved by both the National and Chicago 

 Boards of Fire Underwriters to meet the shortage of the 

 large sizes of structural timbers, while lattice trusses of 

 light-weight timber with the principal supporting mem- 

 bers made of built-up stock were developed for govern- 

 ment use to span walls as far as ioo feet apart. Recogniz- 

 ing that it would be a mistake for lumbermen and archi- 

 tects generally to adopt this form of construction without 

 first having conclusive data as to the efficiency of Specific 

 types or standards of built-up designs, the Forest Prod- 

 ucts Laboratory now has under way, in co-operation with 

 the National Lumber Manufacturers' Association, a series 

 of mechanical tests on full-sized, built-up beams. 



A number of factors may be mentioned as influencing 

 this trend toward the larger use of built-up wood. New 



EXPERIMENTS ARK BEING CONDUCTED UPON A WIDE VARIETY OF WOODKX ARTICLES AT THE FOREST PRODUCTS LABOR- 

 ATORY TO DETERMINE THE EXTENT TO WHICH THEY MAY BE MADE FROM LAMINATED STOCK. THE AIRCRAFT PROPELLED 

 IS TYPICAL OF THE SUCCESSFUL COMMERCIAL APPLICATION OF LAMINATED CONSTRUCTION. THE OTHER ARTICLES ARK AS 

 YET PURELY EXPERIMENTAL IN CHARACTER ALTHOUGH THE TESTS ALREADY CONDUCTED INDICATE THE POSSIBILITY OF 

 SECURING VERY SATISFACTORY SERVICE FROM LAMINATED ARTICLES. 



term, as here used, however, refers to the fabrication 

 from smaller material of special forms or types of lumber 

 to replace or to serve as substitutes for full-sawn or 

 solid material. Two general methods of building up 

 wood in this manner are now in use ; one employs glue, 

 and the other, nails, bolts, wooden pins, and other forms 

 of fastenings, to hold the different parts or laminations 

 together. 



Glued laminations are quite widfely used for the manu- 

 facture of a great variety of material for inside pur- 

 poses, such as furniture, toys, mill work, etc.; but it has 

 not found extensive application commercially for exterior 

 or semi-exterior requirements, because the ready failure 

 of the glue used when joints became exposed to rain or 

 extreme changes of moisture conditions. 



Laminated beams, girders, and stringers are now built 

 up of thin pieces of lumber bolted together and used for 

 structural purposes in the same manner as solid timbers 

 of the same cross section. Tension members in truss 

 design and, in fact, entire trusses have also been built up 



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and more accurate knowledge of the mechanical and 

 physical properties of wood and of the materials and 

 methods essential in perfecting built-up construction is 

 stimulating interest in its commercial possibilities. The 

 knowledge gained through intensive research during the 

 war relative to making glues of great strength and mois- 

 ture-resistance and relative to methods of conditioning 

 and protecting wooden laminations or parts has turned 

 attention to the possibilities of the exterior use of built- 

 up wood. 



A second factor is the regional depletion of forests 

 and the necessity that manufacturing plants in those re- 

 gions resort to closer utilization of the remaining timber. 

 Experience has shown that in such localities utilization 

 becomes increasingly intensive, while the price of lumber 

 likewise increases, thus permitting forms of utilization 

 involving increased cost to manufacturers. Closely allied 

 to this factor is the decreasing supply of large-sized tim- 

 ber from which solid beams or timbers in structural sizes 

 can readily be obtained. War demands emphasized only 



