Measuring Rail Seat Pressure Distribution in Concrete Crossties Experiments with Matrix - Based Tactile Surface Sensors

Transportation Research Record: Journal of the Transportation Research Board, No. 2374, Transportation Research Board of the National Academies, Washington, D.C., 2013, pp. 190–200. DOI: 10.3141/2374-22 C. T. Rapp, M. S. Dersch, J. R. Edwards, and C. P. L. Barkan, Rail Transportation and Engineering Center, Department of Civil and Environmental Engineering, University of Illinois at Urbana–Champaign, 205 North Mathews Avenue, Urbana, IL 61801. B. Wilson, Amsted Rail, Inc., 1700 Walnut Street, Granite City, IL 62040. J. Mediavilla, Amsted RPS, 8400 West 110th Street, Suite 300, Overland Park, KS 66210. Corresponding author: C. T. Rapp, [email protected]. conditions including areas of high moisture that would cause accelerated decay of timber ties (1). The cast-in shoulders and molded rail seat of concrete crossties increase their ability to hold gage under these loading conditions (1). Concrete crossties are not without their design and performance challenges. As reported in surveys conducted by the University of Illinois at Urbana–Champaign (UIUC) in 2008 and 2012, North American Class I railroads and other railway infrastructure experts ranked rail seat deterioration (RSD) as one of the most critical problems associated with performance of the concrete crossties and fastening system (2, 3). Problems that arise from the deterioration of the concrete rail seat surface include widening of gage, reduction in the clamping force (toe load) of fastening clips, and insufficient rail cant (2). All of these problems have the potential to create unsafe operating conditions and an increased risk of rail rollover derailments (4). A suspected cause of RSD is high forces acting on the concrete rail seat surface, often in concentrated areas. To address this problem, a study was performed by the John A. Volpe National Transportation Systems Center on the effect of wheel and rail loads on concrete tie stresses and rail rollover. The study confirmed the possibility of concentrated loads producing stresses exceeding the 7,000-psi (48,260-kPa) minimum design compressive strength of concrete as recommended by the American Railway Engineering and Maintenance-of-Way Association [AREMA (4)]. The combination of static wheel loads and dynamic impact loads imparts forces into the rail seat that potentially damage the concrete surface (5). The magnitude of these loads can vary on the basis of track support variations, wheel defects, or rail irregularities (5). Well-maintained concrete crosstie track is typically stiffer than timber crosstie track. According to the AREMA Manual for Railway Engineering, the typical track modulus value for mainline concrete crosstie track is 6,000 lb/in (41.4 N/mm), which is twice the typical timber crosstie track modulus of 3,000 lb/in (20.7 N/mm) (6). A track superstructure that is stiffer, consisting of the rail, fastening system components, and crossties, produces a less resilient response to impact loads, resulting in the transfer of higher forces to the concrete rail seat surface. This theory assumes that the track substructures, consisting of the subballast and ballast layers, for both concrete and timber crosstie track provide adequate support conditions for each track type (7). Despite the superstructure’s being less resilient, a study performed to investigate the effect of replacing defective timber crossties with concrete crossties yielded results showing a drastic improvement on the remaining life of other crossties for this given section of track (8). A stiffer track structure may also be desired Measuring Rail Seat Pressure Distribution in Concrete Crossties Experiments with Matrix-Based Tactile Surface Sensors