CONTENTS. 



Page. 



Introduction 7 



Data for trestle construction 8 



Present practice 8 



Recommended practice • 1 



Moisture classification 12 



Safe unit stresses 13 



Inspection 19 



Moisture conditions 19 



Weight 19 



Size of pieces 19 



Position in tree 19 



Defects 19 



Anatomical structure 20 



Methods of designing 20 



Present practice 20 



Recommended practice 22 



Stringers 23 



Cost of stringers of equal strength 24 



Cost of stringers of equal stiffness 25 



Corbels 27 



Posts and caps 28 



Appendix I. — Explanation of factors of strength 29 



Appendix II.— Review of the foregoing paper by Mr. G. Lindenthal, chief en- 

 gineer of the North River Bridge Company 31 



Appendix III.— Notes by Mr. Walter G. Berg, principal assistant engineer of 



the Lehigh Valley Railroad 34 



Appendix IV. — Report of Committee of American International Association of 

 Railway Superintendents of Bridges and Buildings on "Strength of bridge 



and trestle timbers " 41 



ILLUSTRATIONS. 



Fig. 1.— Diagram showing the relation between the coefficient of crushing end- 

 wise strength and the ratio of length to least width of solid timber columns 



of longleaf pine 17 



Fig. 2. — Example of present system of designing 21 



Fig. 3. — Example of proposed practice with corbels 22 



Fig. 4. — Example of proposed practice without corbels 23 



Fig. 5. — Diagram showing relative cost of stringers of different heights 24 



Fig. 6. — Showing construction with four vertical legs 32 



Fig. 7.— Showing construction with two vertical and two slanting legs 33 



5 



