Bulletin No. 12. 



U. S. DEPARTMENT OF AGRICULTURE. 



DIVISION OF FORESTRY. 



TIMBER PHYSICS SERIES. 



ECONOMICAL DESIGNING 



UK 



TIMBER TRESTLE BRIDGES, 



HY 



A. L. JOHNSON, C. E. 



PREPARED UNDER THE DIRECTION OF 



B. E. FERNOW, 



CHIEF OF DIVISION OK FORESTRY. 



WASH I NGTON: 



GOVERNMENT PRINTING OFFICE, 

 I902. 



