6 BULLETIN" 286, U. S. DEPARTMENT OF AGRICULTURE. 



RESULTS OF TESTS. 



The results of the bending tests on the natural and treated stringers 

 are shown in figures 3 to 7. 



The diagrams were made by first plotting the values for modulus of 

 rupture of the natural beams (solid lines) arranged from the highest 

 to lowest, beginning with the highest value on the left at the top of 

 the figure. The modulus of rupture of the treated half (dotted 

 lines) of the test pieces was then plotted in the same vertical line as 

 the untreated pieces. The two values are marked to distinguish 

 butts (B) from corresponding tops (T). The other values (fiber 

 stress at elastic limit and modulus of elasticity) for the same beams 

 are plotted in the same vertical lines. 



Conclusions should not be drawn regarding the comparative effect 

 of creosoting on the strength of the different woods, since they were 

 not treated under similar conditions. It should also be kept in mind 

 that the test material was not selected for the purpose of comparing 

 the various species. 



LOBLOLLY PLNE. 



Figure 3 gives a comparison of the strength and stiffness of natural 

 and treated loblolly pine stringers for partially air-dry and seasoned 

 material. In drawing conclusions from the diagrams it should be 

 kept in mind that butt stringers are naturally stronger than second- 

 cut or top stringers. This point was considered when the method of 

 selecting the test material was determined upon and butts and tops 

 were arranged to alternate in serving as treated and untreated 

 material. It will be noted from figure 3 that when the butts were 

 treated the breaking strength of the butts and tops fell rather close 

 together, while when the tops were treated the breaking strength 

 values were much farther apart. This shows an evident weakening 

 due to the treatment, even when the lower breaking strength of the 

 top stringers is taken into account. The tests are too few to make 

 a definite statement as to the amount of weakening for the specific 

 treatment under consideration. It is probably not more than 17 

 per cent. The fiber strength at elastic limit and the stiffness both 

 show a greater weakening due to treatment than docs the breaking 

 strength. The weakening is more marked in both strength and 

 stiffness in the air dry than in the partially air-dry stringers. Both 

 the treated and untreated stringers showed a strength about 30 per 

 cent greater in the seasoned material than in the partially air-dry 

 material. 



I ONGLEAF PLNE. 



In figure 4 the strength of treated and untreated longleaf pine 

 si ringers is compared for both partially air-dry and seasoned material. 

 It does not appear that the breaking strength was affected by the 

 1 rea I ment used with these stringers. There is a slight reduction in the 



