Dowel-laminated crossties: performance in service, technology of fabrication, and future promise

Abstract

It is generally agreed that railroads of the United States must be substantially increase their rate of tie renewals, if roadbeds are to be maintained in acceptable condition. To accomodate 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 8-inch ties will be utilized. A logical source of wood for these ties is the enormous inverntory 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 a new type of conversion machine - the shaping-lathe headrig-lumber recovery can approach 10 bd. ft/ft³ 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 that usual for one-piece ties. Laboratory tests indicate that dowels withdrawn from dry wood have greater withdrawal resistance if they are inserted in gree (rather than dry) wood. When 1/2-inch fluted-steel dowels were inserted in green wood and withdraw from dry wood of four species, withdrawal forces were highest in hickory and blackgum (Average 1,935 lb./in. of penetration) and least in southern red oak and sweetgum (Average 1,468 lb./inch. of penetration). These findings are useful, because handling costs can be reduced if half-ties are doweled green rather than dry, as is the present practice. Six half-inch fluted-steel dowels per tie should be adequate.

Citation

Howe, John P.; Koch, Peter. 1975. Dowel-laminated crossties: performance in service, technology of fabrication, and future promise. Forest Products Journal, Vol. 26(5): 23-30