Dowel-Laminated Crossties-Performance in Service, Technology of Fabrication, and Future Promise

Railroads must substantially increase their rate of tie renewals if roadbeds are to be maintained in acceptable condition. To accommodate faster trains and heavier loads, future mainline ties may average larger than the 7- by 9-inch size now in common use; fewer 6- by 9-inch ties will be utilized. A logical source of wood for these ties is the enormous inventory of underutilized small hardwoods in the south, east, and midwest. The process of dowel-lamination can permit manufacture of wane-free 7- by 9-inch mainline ties from logs with small-end diameters of only 8.3 inches–a size plentiful in this inventory. Bigger ties can easily be fabricated from logs only slightly larger. Through use of the shaping-lathe headrig, lumber recovery can approach 10 board feet per cubic foot of log input, with six half-ties produced per minute. Mainline ties dowel-laminated from two half-ties (interface vertical when in place) have suffered no failures in extensive service tests extending over 15 years, and their service life should be at least as long as the usual for one-piece ties. Laboratory tests indicate that dowels withdrawn from dry wood have greater withdrawal resistance if they are inserted in green (rather than dry) wood. When 1/2-inch fluted-steel dowels were inserted in green wood and withdrawn from dry wood of four species, withdrawal forces were highest in hickory and blackgum (average 1,935 pounds per inch of penetration) and least in southern red oak and sweetgum (average 1,468 pounds per inch of penetration). Handling costs can be reduced if half-ties are dowelled green rather than dry as is the present practice. Six half-inch fluted-steel dowels per tie should be adequate.

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