9 



Table I. — Species of limber employed in the construction of wooden trestle bridges. 



[Compiled from reports from fifteen railroads of the United States.] 



Species used. 



White oak 



Burr oak 



lied cedar 



Redwood 



Longleaf pine 



Oregon or Douglas fir 



Red cypress 



White pine 



Norway pine 



Sugar pine 



Red spruce 



Mean 

 length 

 of life. 



Years. 



10 



Mean . 



STRINGERS. 



Douglas or Oregon iir 



Longleaf pine 



Shortleaf pine 



White pine 



Norway pine 



Red cypress 



Mean . 



16 



12 



9 



8-9 



Per cent 

 of re- 

 ported 

 roads 

 using this 

 species. 



9.0 



10 

 8 

 G 

 8 



70 



12 



31 



6 



25 



12 



6 



(i 



6 



(i 



6 



44 



56 







44 



6 



6 



Species used. 



CAPS. 



Douglas or Oregon fir 



Longleaf pine 



Shortleaf pine 



White pine 



Norway pine 



Colorado pine 



Red cypress 



Red cedar 



White oak 



Redwood 



Mean 



POSTS. 



Douglas or Oregon fir 



Longleaf pine 



Shortleaf pine 



White pine 



Norway pine 



Red cypress 



Red cedar 



White oak 



Redwood 



Mean 



Mean 

 length 

 of life. 



1 ears. 



10 

 8 



t; 



8 



8 



8 



10 



11 



8 



12 



8.9 



12 



in 

 6 



10 

 9 

 9 



11 

 9 



12 



9.s 



Per cent 

 of re- 

 ported 

 roads 



using this 

 species. 



25 

 41 



6 



38 

 12 



6 

 19 



t; 

 19 



6 



25 

 56 





 38 

 12 

 12 



6 

 19 



G 



Tahle II. — Showing the range in values of safe unit, stresses as reported by fifteen railroad 



companies of the United States. 



[The " factorof safety " given below is not what was reported by these companies, theirvalues ranging 

 from live to twelve", but what actually exists according to values based on the tests of the Forestry 

 Division as given in Table IV.] 



Species. 



Longleaf pine (Pinus palnstris) 



Shortleaf pine (Pinus echinata) 



White pine (Pin us strobus) 



Norway pine ( Pinus resinosa) 



Colorado pine (Pinus ponderosa) ... 

 Douglas fir (Pseudotsuga douglaki) 

 Redwood (Sequoia xempcrvirens) ... 

 Red cedar ( Juniperus irirginiana) . . 

 Bald cypress ( Taxodium aistichum) . 

 White oak ( Quercus <Ub<i) 



Factor of safety. 



Modulus of 



strength 



at rupture 



per square 



inch. 



Pounds. 



1,000-5,000 



500-1,000 



1,300 

 500-2, 100 

 000 

 1,750 

 1,000 

 3,300 



1.5-13.0 



Modulus of 

 elasticity 



per square 

 inch. 



Pounds. 



Crushing 



strength 



endwise per 



square 



inch. 



Pounds. 

 830 1,700 



000-1,000 

 050-2, 100 



000-1, 0(H) 



300 



1,000 



1,000 



1,400 



Crushing 



strength 



across the 



grain per 



square 



inch. 



Pounds. 

 050-1,000 



400- 420 

 350 



120- 420 



00 



530 



200 



GOO 



2. 6-25. 



0. 0-5. 7 



*The reporter of this value gave 10,000 pounds per square inch as the modulus of rupture, and said 

 in designing he was accustomed to use one-half the amount. 



Table II shows the ranee in values for the safe unit stresses as 

 reported by these railroad companies. This range is best appreciated 

 by an inspection of the range in value of the factor of safety for the 

 different factors of strength, given at the bottom of the table, which 

 is based upon the safe-load values given in Table IV. Supposing these 



