22 



Figs. 3 and -A show designs recommended by the Forestry Division, 

 that in tig - . 3 being preferred, though slightly more expensive than lhat 

 in fig. 4. These diagrams illustrate an important point, i. e., that the 

 economical design of timber structures requires the judicious employ- 

 ment of different species as well as different sizes, in the same. 



With corbels: 



RECOMMENDED PRACTICE. 



Factor* of safely. 



Stringers in cross breaking 5 + 



Stringers in deflection *},,-, span 2 + 



St ringers in end bearing 4 •+- 



Cap in bearing value 3 + 



Posts in endwise crushing 7. 4+ 



'3Strs.LongLeafPine. 



3CORBfLS.WHITF.0AK 



Cap, White Oak 



Posts. Red CrPRtss. 



■DRIP HOLES 



—.Sills. 

 2 I White Oak 



Scale- j Inch - 1 Foot. 



Fig. 3.— Example of proposed practice with corbels. 



Bill of material. 

 TIMBER, EXCLUSIVE OF TIES AND GUARD RAIL. 



IRON. 



Size. 



Bolts (stringers), 8 pieces, 3"x31", at 4.96 .. 



Bolts (corbels) , 12 pieces, J"x28" at 4.48 



Driftbolts, 2 pieces, l"x 12" at 4.00 



Washers, 0. G., 40 pieces, 3" diameter, 1.25. 



Total 



Number Cost p?r 

 pounds. 



pound. 



39.7 

 53. 8 

 8 

 50 



151. 5 



4 



4 

 4 

 2 1 



Total 

 cost. 



$1.59 



2.15 



.32 



1.25 



5.31 



