2668 



Chapter 22 



CASE I: BALLAST REMAINS 

 ESSENTIALLY IN PLACE. SHEAR AND 

 FLEXURE PROPERTIES ARE EQUALLY 

 IMPORTANT. 



CASE II: CENTER-BIND IS 

 CAUSED BY EROSION OF BALLAST 

 FROM BENEATH RAILSEATS. FLEX- 

 URE IS CRITICAL LOADING MODE. 



M 142 544 20 

 Figure 22-56. — Stability of ballast determines loading mode of crossties. (Left) With 

 ballast in place, shear and flexure properties are equally important. (Right) Center- 

 bind is caused by erosion of ballast from beneath railseats; flexure is the critical 

 loading mode. (Drawing after Tschernitz et al. 1979.) 



Table 22-20 — Size categories, thicknesses, and widths of sawn or hewn crossties and 

 switchties (National Hardwood Lumber Association 1965)'-^'^ 



Each railroad will specify species desired. 



^All thicknesses and widths apply to sections of the tie between 20 and 40 inches from the center of 

 the tie for standard gauge, 15 and 25 inches for narrow-gauge. All determinations of width will be 

 made on the top of the tie, which is the narrower of the horizontal surfaces, or the one with narrower 

 or no heartwood if both surfaces are the same width. 



^Each railroad will specify the size category desired in the lengths desired. The thicknesses, 

 widths, and lengths specified are minimums. Ties more than 1 inch thicker, wider, or longer than 

 specified will be rejected. 



"^None accepted for standard-gauge railway ties. 



^Seven- by 7-inch ties are designated size 3 A. 



Methods to secure rail to crosstie. — Before pressure treating with creosote, 

 top surfaces of crossties are machined flat (if necessary) at two locations to 

 receive steel plates (fig. 22-57) which distribute vertical traffic loads over a 

 larger area than the rail flange. The tie plates are also formed to restrain lateral 

 movement of the rails and are generally perforated with four holes on each side 



