21 



Substituting the values for these quantities, we have 



>'» X 98,600X12 

 1,000X289 



where the height is assumed for trial. 



This will make three stringers under each rail, 8i by 17 inches in 

 cross section, posts, caps, and sills all being 12 by 12 inches in cross 

 section. 



The following factors of safety are indicated by their practice: 



Stringers in cross breaking 7. 6 



Stringers in deflection ^ span 3.1 



Stringers in bearing value 2. 7 



Cap, bearing value under stringers 1.5 



Cap, bearing value under posts 1.9 



Posts crushing endwise :* '. 6 



'3 StrsIongLeafPine 

 Cap.Reo Cypress 



PostsXong Leaf Pine. 



-Sills. 

 ReoCypress 



Scale- ■£- Inch = I Foot . 

 Pig. 2. — Example of present practice of designing. 



Bill of material. 

 TIMBER, EXCLUSIVE OF TIES AND GUARD RAIL. 



IRON. 



Size. 



Bolts, S pieces, J" x32£", at 5.20 



Driftbolts, 2 pieces, l"x23", at 7.5 



Washers, O. <;., 16 pieces, 3" diameter, 



Total 



at 1.25. 



Number 

 ■pounds. 



41.6 



15 



24 



80. 



Cost per 

 pound. 



Cents. 



4 



4 



^3 



Total 



cost. 



81.66 

 . 60 

 .60 



2. 86 



