Solid Wood Products 2669 



of the rail location (eight in all) to receive spikes which secure the rail and plate 

 to the crosstie (usually only two spikes are installed on each side of the rail). Tie 

 plates vary in size depending on rail weight (9 to 1 38 pounds per lineal foot). For 

 the lighter rails tie plates commonly measure 5 by 1 1 inches; for the heaviest rail, 

 7 by 12 inches — occasionally 7 by 16 inches. 



Before pressure treating, '/z-inch-diameter guide holes for spikes are drilled. 

 The spikes, which typically are made of high carbon steel, measure 6 inches 

 long, ys- by -Vs-inch in cross section, and have chisel points. Spike heads 

 commonly measure 1-5/16 inches wide and 1-9/16 inches long. Force to 

 withdraw such spikes immediately after driving in creosoted oak crossties is 

 usually in excess of 4,500 pounds. Withdrawal resistance lessens after repeated 

 loadings from passing trains. Readers interested in lateral resistance of steel rails 

 secured to red oak crossties will find Murphy's (1979) analysis useful. 



Crosstie life. — Bescher (1977) summarized available data on the life of the 

 creosoted crossties installed in mainline tracks. Tests beginning in 1909 and 

 1910 by the Chicago, Burlington, and Quincy Railroad showed that untreated 

 ties had a life of about 5 years; those treated with zinc chloride had lives of 15 to 

 16 years, and those with creosote 27 to 30 years. Tie life varied not only with 

 treatment, but by species (fig. 22-55 top). 



Crosstie life also varies significantly with the quality of track and ballast 

 maintenance, and with severity of traffic; accordingly, crossties in tracks of a 

 midwestern railroad that traditionally made a profit and maintained its tracks had 

 service lives varying from 25 to 60 years depending on the amount of traffic (fig. 

 22-55 bottom). 



Tie life is longest in side and yard tracks (60-year average), intermediate in 

 branch lines (about 30 to 35 years), and shortest on heavily-used mainline tracks 

 (about 25 years — possibly 35 years); on curved portions of mainline tracks, 

 crosstie life is shortest. With increasing weight of rolling stock, this life is 

 expected to drop to 20 to 25 years. 



Howe (1979) noted that the life of a softwood tie was about 20 years in curves 

 of 4 degrees and over on western sections of Canadian National Railroad tracks 

 in the days of steam locomotives. The crosstie would continue to hold gauge 

 (maintain correct distance between rails) after the respiking necessitated by one 

 rail replacement and two transpositions (turning rails end for end to equalize rail 

 wear). With the advent of multiple diesel engines pulling 50 to 150 cars each 

 weighing 220,000 to 263,000 pounds, Canadian National's experience indicates 

 a life of only 6 years for softwood crossties on mainline curved track sections 

 carrying heavy commodity loads. i 



For further discussion of the service life of treated crossties, see sec. 21-4. 



Reasons for crosstie failure. — Tie life depends in part on quality of track 

 maintenance. Clean, large, well-tamped ballast tends to have less water in its 

 lower levels, and therefore the crossties resting in the ballast change moisture 

 content to a lesser degree between wet and dry weather than if the ballast 

 contains fines and is not well-maintained. Changes in moisture content 

 contribute to formation of splits and checks which are the major defects leading 



