By Joe Palese, MCE, P.E.
Director Engineering Analysis ZETA-TECH Associates
With the increased cost of track maintenance, as well as the reduction in maintenance budgets, it has become increasingly important for railroads to understand the life of track components, specifically crossties.
To help railroads do this, ZETA-TECH Associates Inc. has developed for the Railway Tie Association a user-friendly computer model TieLifeTM, for determining future crosstie requirements. The model was developed to assist the user in understanding the expected life of crossties under different track and traffic conditions, along with the corresponding annual tie requirements. The model was developed for the Windows operating system and is an easy-to-use and intuitive maintenance/planning tool.
The model evaluates track and traffic data as primary inputs, including length of track segment, climate of segment, type of fastening system and distribution of trackage with respect to degree of curvature and annual traffic density. This primary input screen is shown in Figure 1, which shows that the example analysis segment if 1,000 miles long with a weighted average annual traffic density of 12 MGT and has trackage distributed according to the matrix of degree of curvature and annual traffic density.
Based on the input data, the average life of a tie is determined for each category of trackage (distributed by curvature and tonnage) using an empirical model calibrated to historical freight railroad experience. It should be noted that the model allows the user to override these calculations should their individual experience be unique. Utilizing the tie life information and distribution of trackage, a matrix of annual tie requirements can be determined based on a steady state failure rate. This information is presented to the user as number of ties required annually (and percentage of total annual tie requirements) for each category in the trackage distribution matrix (see Figure 2). In the example shown, it can be seen that on average, a total of 110,947 ties would be required annually, as distributed by the matrix of curvature and tonnage.
Since ties do not fail uniformly, and are not replaced uniformly, it is further required to understand the actual annual crosstie requirements for a segment of track under analysis, given the historic installation of crossties on that segment. The model allows the user to input the quantity of ties installed on the analysis segment for the past 40 years, or for whatever time frame the data is available. Based on the specific tie installation history and the average tie life (distributed by curvature and tonnage), a forecasting algorithm is used to determine more accurately the quantity of ties required annually for the analysis segment. The forecasted tie requirements are presented in table and graphical forms as shown in Figure 3.
In the example shown, for the next three years, the analysis segment will require 112,125; 111,873; and 111,689 ties respectively.
It can be seen from these values that more than the steady state average number of ties will be required in the first three years. This further reinforces the fact that ties do not fail uniformly and that installations occur based on the actual failure history as a function of the specific track and traffic parameters. Therefore, TieLifeTM can be used to determine tie requirements based on expected failure rates and actual historical replacement rates.
TieLifeTM was developed as a user-friendly maintenance/planning tool to be used by railroads and suppliers for evaluating and determining the life of crossties under various conditions and the resulting annual crosstie maintenance requirements considering historical tie installations.
Editor’s Note: The Railway Tie Association (RTA) continues to be a leader in the services it develops for railroad usage. In addition to industry leading seminars, this new software package provides an incredibly powerful tool for Class I and regional/short line railroads for planning and budgeting purposes. With accurate input data, railroads can accurately forecast and budget for the replacements either system-wide or by smaller track segments. In addition to these obvious benefits, the forecasts can be used by railroads that are seeking capital expenditure financing to provide an analytical model for the source for such funding. With TieLifeTM, RTA continues to provide tools designed to assist railroads in making the best decisions possible in maintenance planning so that tie life can be maximized with minimal cost.