HEAVY AXLE STUDY: IMPACT OF HIGHER RAIL CAR WEIGHT LIMITS ON SHORT-LINE RAILROAD BRIDGE STRUCTURES

摘要

The fundamental objective of this study, sponsored by the Pennsylvania Department of Transportation's Bureau of Rail Freight, Ports, and Waterways, is to establish and implement a methodology to quantify the financial impact of higher gross car weights (GCW) on the infrastructure load carrying capacity of short-line railroads (SLRRs) operating within the Commonwealth of Pennsylvania. The research team developed a stratified random sampling methodology to establish a bridge sample due to the large number of railroad bridges in Pennsylvania. A stratified random sampling plan was developed to ensure that the bridge sample contained bridges of each material type and bridge type expected to significantly influence the strengthening cost estimate. Collecting and creating a complete database of railroad bridges was a large task due to the number of SLRRs and inconsistent record keeping by many SLRRs. There are an estimated 2000 bridges serving Pennsylvania SLRRs of which the eventual study population included 1174 bridges for consideration. The 25 sample bridges, drawn from this population, were evaluated structurally based on the American Railway Engineering Association (AREA) 1996 Specification and field inspections conducted by the research team. The structural evaluations were used as a basis to establish load-carrying capacity predictions and required strengthening for under-capacity structures. Five of the 25 sample bridges will not safely support either the 1273-kN (286,000-lbf) or the 1402-kN (315,000-lbf) GCW load. Bridge strengthening schemes were developed for each of the five under-capacity bridges. Cost estimates for each strengthening scheme were obtained from contractors and based on recent similar work completed in the Commonwealth of Pennsylvania. Upgrade costs for the bridge sample were then extrapolated to the entire SLRR bridge population, resulting in an estimated state-wide bridge upgrade cost of $8,500,000 with a 32% width for a 95% confidence level. The study presents a procedure adaptable to transportation agencies faced with a significant inventory of SLRR bridges that may be subjected to increased railcar loading.