The new concrete crosstie rules require, in FRA Class 1-5 track standards, specific performance requirements that address the unique characteristics of fastener reliability, concrete crosstie, and roadbed stability. [Inspectors] should be aware of the three modes of concrete crosstie failure: support, stability, and electrical isolation. The compressive strength of concrete and the amount of prestress in its section composition provide the strength and stiffness necessary to support expected wheel loads. There’s a balance between excessive stiffness that can lead to higher stresses at the bottom of the crosstie and at the rail seat.
Conversely, a loss of stiffness, caused by ever increasing axle loading, can lead to excessive rail deflections and damage to the ballast and subgrade. Inspectors should be aware that failure modes are not isolated to crosstie defects. Combinations of compliant but irregular track and rail geometry, poor drainage, insufficient ballast depth and subgrade soil conditions may contribute to failure or root causal factors.
The new concrete crosstie regulations contained in Part 213.109(d) and a section by section description is as follows:
§ 213.109 CROSSTIES
d) Concrete crossties counted to satisfy the requirements set forth in paragraph (b)(4) of this section shall not be—
(1) Broken through or deteriorated to the extent that prestressing material is visible;
(2) Deteriorated or broken off in the vicinity of the shoulder or insert so that the fastener assembly can either pull out or move laterally more than 3/8 inch relative to the crosstie;
(3) Deteriorated such that the base of either rail can move laterally more than 3/8 inch relative to the crosstie on curves of 2 degrees or greater; or can move laterally more than 1/2 inch relative to the crosstie on tangent track or curves of less than 2 degrees;
(4) Deteriorated or abraded at any point under the rail seat to a depth of 1/2 inch or more;
(5) Deteriorated such that the crosstie’s fastening or anchoring system, including rail anchors (see § 213.127(b)), is unable to maintain longitudinal rail restraint, or maintain rail hold down, or maintain gage due to insufficient fastener toeload; or
(6) Configured with less than two fasteners on the same rail except as provided in § 213.127(c).