CHAPTER VII. 

 TIMBER BRIDGES AND TRESTLES. 



Definitions. The following definitions have been adopted by the American Railway Engi- 

 mvring Association. 



Wooden Trestle. A wooden structure composed of upright members supporting simple 

 horizontal members or beams, the whole forming a support for loads applied to the horizontal 

 members. 



Frame Trestle. A structure in which the upright members or supports are framed timbers. 



Pile Trestle. A structure in which the upright members or supports are piles. 



Bent. The group of members forming a single vertical support of a trestle, designated as 

 pile bent where the principal members are piles, and as framed bent where of framed timbers. 



Post. One of the vertical or battered members of the bent of a framed trestle. 



Pile. (See definition under subject of Piles and Pile Driving.) 



Batter. A deviation from the vertical in upright members of a bent. 



Cap. A horizontal member upon the top of piles or posts, connecting them in the form of a 

 bent. 



Sill. A lower horizontal member of a framed bent. 



Sub-Sill. A timber bedded in the ground to support a framed bent. 



Intermediate Sill. A horizontal member in the plane of the bent between the cap and sill 

 to which the posts are framed. 



Sway Brace. A member bolted or spiked to the bent and extending diagonally across its 

 face. 



Longitudinal Strut or Girt. A stiff member running horizontally, or nearly so, from bent to 

 bent. 



Longitudinal X-Brace. A member extending diagonally from bent to bent in a vertical or 

 battered plane. 



Sash Brace. A horizontal member secured to the posts or piles of a bent. 



Stringer. A longitudinal member extending from bent to bent and supporting the ties. 



Jack Stringer. A stringer placed outside of the line of main stringers. 



Tie. A transverse timber resting on the stringers and supporting the rails. 



Guard Rail. A longitudinal member, usually a metal rail, secured on top of the ties inside 

 of .the track rail, to guide derailed car wheels. 



Guard Timber. A longitudinal timber framed over the ties outside of the track rail, to 

 maintain the spacing of the ties. 



Packing Block. A small member, usually wood, used to secure the parts of a composite 

 member in their proper relative positions. 



Packing Spool or Separator. A small casting used in connection with packing bolts to 

 secure the several parts of a composite member in their proper relative positions. 



Drift Bolt. A piece of round or square iron of specified length, with or without head or 

 point, driven as a spike. 



Dowel. An iron or wooden pin, extending into, but not through, two members of the struc- 

 ture to connect them. 



Shim. A small piece of wood or metal placed between two members of a structure to bring 

 them to a desired relative position. 



Fish-Plate. A short piece lapping a joint, secured to the side of two members, to connect 

 them end to end. 



Bulkhead. A wall of timber placed against the side of an end bent to retain the embankment. 



STRUCTURAL TIMBER. 



Definitions. The following definitions have been adopted by the American Railway Engi- 

 neering Association. 



Timber. A single stick of wood of regular cross-section. 



Cross-Section. A section of a stick at right angles to the axis. 



True. Of uniform cross-section. Defects are caused by wavy or jagged sawing or consist 

 of trapezoidal instead of rectangular cross-sections. 



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