Bulletin No. 12. 



U. S. DEPARTMENT OF AGRICULTURE. 



DIVISION OF FORESTRY 



TIMBER PHYSICS SERIES. 



ECONOMICAL DESIGNING 



OF 



TIMBER TRESTLE BRIDGES, 



BY 



A. L. JOHNSON, C. E. 



PREPARED UNDER THE DIRECTION OF 



B. E. FERNOW, 



CHIEF OF DIVISION OF EORESTKY. 



W A S H I N G TON: 



GOVERNMENT PRINTING OFFICE. 

 I902. 



