Structural Flakeboards and Composites 



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.1 .2 .3 4 .5 .6 



LINEAR EXPANSION 1 (%) 



Figure 24-55. — Linear expansion, between 47 and 93 percent RH, of various flakeboard 

 constructions compared with southern pine veneer and southern pine plywood. 

 (Drawing after Suchsland et al. 1979.) 



24-21 FABRICATED JOISTS WITH THIN FLAKEBOARD 



WEBS 



Effective use of wood in lightweight I-beam-type composite joists requires 

 uniformly strong, stiff flanges and shear-resistant webs. 



Percival et al. (1977) glue-nailed pairs of western hemlock (Tsuga hetero- 

 phylla (Raf.) Sarg.) select structural stress-graded (1 ,800 f) 2 by 4 flanges to 16- 

 inch-deep structural particleboard webs to fabricate 16.5-foot-long garage 

 headers (fig. 24-56) and compared their performance with a double 2- by 12- 

 inch header of No. IC Douglas-fir {Pseudotsuga menziesii (Mirb.) Franco) 

 lumber, a beam once commonly used for framing a 16-foot garage opening. 

 One-half-inch-thick webs in the composite I-beams were one of three materials: 

 C-C exterior-grade Douglas-fir plywood; phenolic-bonded aspen waferboard; 

 and urea-bonded mixed-hardwood core-board containing flakes smaller than 1/2 

 -inch long. The ply wood- web beam was 71 percent stiff er, the aspen wafer- 

 board- web beam 100 percent stiff er, and the mixed-hardwood core-board-web 

 beam 84 percent stiffer than the double 2 by 12 header. The plywood-web beam 

 and the double 2 by 12 header failed at 799 pounds per lineal foot of uniform 

 load, the aspen beam at 1,008, and the mixed-hardwood beam at 1 ,714 pounds 

 per lineal foot. 



From this experiment and others, e.g., Hunt (1975), Johnson et al. (1976), 

 Superfesky and Ramaker (1978), and McNatt (1980), it is evident that compos- 

 ite wood I-beams can serve usefully. 



