Railway Track & Structures - October 2007 - (Page 44)

Thermal forces Figure 2, above, shows deployment options for the RSM. Figure 3, left, shows typical RNT output from UP’s test installation. data at 10-minute intervals. The module, which stores its data for approximately six months, can be queried immediately via the hand-held reader to provide the track crew an insight as to what stress state the rail is in, as well as provide the same information and more to all others with access to the database. An important part of the RSM installation is the setting of the “zero” for the RSM, i.e., the reference for the absolute force measurements. This zero setting is automatic when RSM is part of a new rail installation or with a plug repair application since the initial condition of the rail is known. Any time the RSM is installed on a free rail (not constrained by being fastened to ties or welded into track), the initial condition is known as a zero stress condition with no longitudinal force applied to the rail. When the RSM is deployed on existing trackage, a zero reference point is also required. For such conditions (existing track installations), the zero setting can be established by using a third-party system that will provide a one-time measurement with some degree of additional effort. In some applications, not having a zero might be acceptable since a relative force or RNT change measurement might be sufficient. In all such cases, Salient Systems can provide the specific requirements for the appropriate zero conditioning of the RSM. concrete tie track curve where both rails were instrumented with RSMs. The data show the RNT variation with time for the two rails (red for the high rail and green for the low rail) exhibiting the key features of the initially high installation temperatures, the daily variations (the tooth-like spikes), the detection and influences of two rail breaks on the low rail (as shown by the sudden drop in RNT) and the successful and effective RNT restress adjustment after the second break. Other test data (not shown here) provided information on the effectiveness of achieving the planned or target installation temperatures when installing or relaying cwr, especially during cold laying temperatures. The RSMs also provided important information on curve movement effects on RNT changes, especially when curves pull-in under cold temperature conditions. Buckling hazard index The prevention of track bucklecaused derailments remains a key industry goal. In 2006, the 48 track buckle-caused derailments ranked third in dollar damage from all track-caused derailments at 11 percent of the total cost. Railroad efforts are continuing to focus on improving buckling prevention practices and on better identifying buckling-prone conditions. To assist in these efforts, Salient Systems recently developed a Buckling Hazard Index that provides a warning on potential buckles in terms of a yellow, orange or red alert. The yellow-orange-red alerts are based on having a prescribed buckling margin of safety. The BMS is determined by the StressNet™ database and is based on the RSM measured rail and neutral temperature data, as well as the track’s buckling strength algorithm based on the Volpe/FRA CWR-SAFE model. The BMS is a numerical temperature index on how close the track is to a critical buckling temperature level according to Table 1. As an example, consider the data in Figure 3 at the conditions shown (outlined data of 95 degrees F RNT on one rail, and 55 degrees F on the other). If this were the RNT condition on a hot summer day when the rail temperatures reach 140 degrees F (the maximum rail temperature for this territory), the StressNet™ would provide a BMS=22 degrees F indicating a yellow alert. As indicated by the green arrow on the figure, the Union Pacific readjusted the reduced 55 degrees F RNT value to 120 degrees F much before reaching the onset of high temperature conditions. Rail repair and restressing A major reason for the reduced and possibly unsafe neutral temperatures is the difficulty in resetting the RNT to the desired high target value after a rail break or after a rail-defect removal. There tend to be 20,000 to 30,000 rail www.rtands.com RNT monitoring, break detection Figure 3 is an example of a StressNet™ output of 90 days of RSM data at one location of Union Pacific test segment of newly-laid cwr on a two-degree 44 Railway Track & Structures October 2007 Monitoring curve movement and force buildup in longitudinally stiff track segments such as at tunnel approaches is critical. http://www.rtands.com

Table of Contents Feed for the Digital Edition of Railway Track & Structures - October 2007

Railway Track & Structures - October 2007 Contents On Track Industry Today Supplier News AREMA News NRC News TTCI R&D Crossties by the Billions Provide Essentials for Full Support Modern Tools Manage Risk M/W Challenges: Better Management of Thermal Forces in CWR TTCI Celebrates 25 Years as Facility, 10 as Part of AAR Products and Literature People Calendar Sales Representatives Website Directory Advertisers Index Professional Directory Classified Advertising Chicago Perspective

Railway Track & Structures - October 2007

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