STRENGTH TESTS OF STRUCTURAL TIMBERS. 



13 



SPECIAL TESTS ON SMALL PIECES. 



Table 3 gives a condensed summary of the results of a special series 

 of tests on small clear specimen ts (2 by 2 inches in section) of Douglas 

 fir, longleaf pine, and shortleaf pine. The tests were made at 

 the Forest Products Laboratory to study the effect of the various 

 steps used in the treatment of the full-sized stringers. Eight sticks 

 were subjected to each of the processes shown in Table 3. One-half 

 of the sticks were tested shortly after treatment and one-half after 

 they had been piled in the laboratory long enough (5 months) to reach 

 a practically constant weight. 



All the processes caused a reduction in the strength values of the 

 unseasoned material of the three species with, in most cases, a recov- 

 ery after seasoning, except in the tension tests. In these the weaken- 

 ing in the unseasoned material remained after seasoning in all processes 

 but the creosote bath. 



Table 3. 



-Effect of various treatments on small clear sticks (results expressed 1 in per cent 

 of strength of untreated material) . 



Steamed at 



20 pounds - 



5 hours. 



Unsea- 

 soned, 



Air 

 dry. 



Steamed at 

 20 pounds 

 5 hours; 

 26-inch 

 vacuum 

 1 hour. 



Unsea- 

 soned. 



Air 

 dry. 



Steamed at 

 20 pounds 



5 hours; 

 26-inch 



vacuum 

 1 hour; 



creosote, 

 120 pounds 



pressure, 



Ah hours. 



Unsea- 

 soned. 



Air 

 dry. 



Creosote at 



atmospheric 



pressure, 



200° F., 



27 hours. 



Unsea- 

 soned. 



Air 

 dry. 



Creosote bath 



at atmos- 

 pheric pres- 

 sure, 200° F., 

 27 hours; 

 creosote at 

 145 pounds 

 pressure, 

 180° F., 

 If hours. 



Unsea- 

 soned. 



Air 

 dry. 



Bending: 

 Modulus of rupture — 



Douglas fir 



Longleaf pine 



Shortleaf pine 



Modulus of elasticity — 



Douglas fir 



Longleaf pine 



Shortleaf pine 



Compression: 

 Maximum crushing 

 strength — 



Douglas fir 



Longleaf pine 



Shortleaf pine 



Shear with grain — 



Douglas fir 



Longleaf pine 



Shortleaf pine 



Tension perpendicular to 

 grain- 

 Douglas fir 



Longleaf pine 



Shortleaf pine 



Shrinkage i in cross section 

 during treatment- 

 Douglas fir 



Longleaf pine 



Shortleaf pine 



During treatment and sea- 

 soning- 

 Douglas fir 



Longleaf pine 



Shortleaf pine 



96 

 LOO 



107 



100 

 106 

 104 



78 



.S3 



8.58 

 10.64 

 10.47 



8.35 



97 

 76 



104 



100 



ioi" 



92 

 "96" 



97 



112' 



91 



108 

 105 



102" 



102 



103" 

 L18 



ii4" 



116 



136" 



3.34 

 .08 

 .92 



90 



9.33 

 .66 



.75 



98 

 93 

 106 



108 

 100 



112 

 87 

 109 



125 

 115 

 115 



117 

 67 



7.39 

 6.18 

 5.94 



7.46 



7.50 



11.31 

 7.90 

 5.73 



1 Shrinkage given in per cents of areas when first measured. Corresponding shrinkage of untreated mate- 

 rial: Douglas fir, 6.40; longleaf pine, 8.48; shortleaf pine, 7.29. 



2 Increase in volume. 



