298 



TIMBER BRIDGES AND TRESTLES. 



CHAP. VII. 



WORKING UNIT-STRESSES FOR STRUCTURAL TIMBER EXPRESSED IN POUNDS PER SQUARE 



INCH.* 



Note. The working unit-stresses given in Table V are intended for railroad bridges and 

 trestles. For highway bridges and trestles the unit-stresses may be increased twenty-five (25) 

 per cent. For buildings and similar structures, in which the timber is protected from the weather 

 and practically free from impact, the unit stresses may be increased fifty (50) per cent. To 

 compute the deflection of a beam under long-continued loading instead of that when the load is 

 first applied, only fifty per cent of the corresponding modulus of elasticity given in the table is 

 to be employed. 



TABLE V. 



UNIT STRESSES FOR STRUCTURAL TIMBER EXPRESSED IN POUNDS PER SQUARE INCH. 

 AMERICAN RAILWAY ENGINEERING ASSOCIATION. 



REFERENCES. For additional details and information the following references may be 

 consulted : 



Foster's " A Treatise on Wooden Trestle Bridges," John Wiley & Sons, gives data and 

 details of the design of timber trestles. 



Jacoby's " Structural Details ; Design of Heavy Framing," John Wiley & Sons, gives data 

 and details of the design of timber trestles and timber structures, and is the best book on tim- 

 ber construction. Every engineer interested in the design of timber structures should have a 

 copy of Jacoby's " Structural Details." 



* Adopted, Am. Ry. Eng. Assoc., Vol. 10, 1909. 



t Partially air-dry. / = length in inches. d = least side in inches. 



