288 



TIMBER BRIDGES AND TRESTLES. 



CHAP. VII. 



Frame Trestles. The details of the standard frame trestle with open floor of the N. Y., 

 N. .H. & H. R. R. are given in Fig. 2. The bents are spaced 12 ft. center to center. The floor 

 system is the same as for pile trestles. The frame trestle may be supported on a pile foundation, 

 upon timber sub-sills (mudsills) or on concrete pedestals. Timber sub-sills soon decay and 

 should be used only for temporary trestles. Other data and details are shown on the plans. 



The plans of a standard frame trestle designed and built by the Illinois Central Railroad are 

 given in Fig. 3. The bents are spaced 14 ft. centers, while the stringers are 28 ft. long and cover 

 two panels. The details of the track and the guard rails are not shown. A complete bill of 

 timber and iron for one bent and one panel of the floor are given in Fig. 3. The standard frame 

 trestle may be carried on mudsills (sub-sills) as shown in Fig. 3, or on piles or concrete pedestals 

 as shown in Fig. 2. 



Detail plans of a pile trestle with ballasted deck are given in Fig. 4. 



TIMBER HOWE TRUSSES. Plans of a standard 150 ft. span Howe truss designed and 

 erected by the C. M. & P. S. Ry. are shown in Fig. 5, Fig. 6, and Fig. 7. This bridge was designed 

 for Cooper's E 55 Loading, with the allowable unit stresses as given in the American Railway 

 Engineering Association Specifications for Timber Bridges and Trestles. The bill of lumber is 

 given in Table I; the bill of castings and bolts is given in Table II; the bill of upset vertical rods 

 is given in Table III, and the bill of lateral rods is given in Table IV. The following additional 

 specifications were given on the plans. 



TABLE I. 



BILL OF TIMBER FOR ONE 150 FT. HOWE TRUSS SPAN. 



