Railway Track & Structures - November 2007 - (Page 19)

TTCI R&D Update: Impact of bridge deck fasteners under heavy axle load on open-deck bridges Open-deck bridge tie life and maintenance depend on the right mix of hardware. sing the right mix of hardware on bridge deck fasteners on open-deck bridges can significantly lower maintenance time and help extend bridge tie life. As reported in an earlier RT&S article (“Bridge Deck Fastener Evaluation at FAST,” July 2005), about nine million feet of bridges on the major U.S. and Canadian railroads have millions of deck fasteners in service. Little information was available to compare the performance of the fasteners until now. Engineers at the Transportation Technology Center, Inc., as part of the FAST Heavy-Axle-Load Program, have been evaluating the performance of bridge deck fastening systems for several years. To U date, eight variations of bridge deck fastener systems have been under evaluation on the steel bridge at the Facility for Accelerated Service Testing. Over most of the bridge, every fourth deck tie is fastened to the top flanges of the girders. The systems with the best performance have withstood more than 500 mgt of HAL traffic, with no maintenance required. The poorest-performing systems have withstood less than 40 mgt before several fasteners became loose, turned, or broken. Figure 1 summarizes the performance of the eight systems tested to date. Results from this test have shown that small differences in hardware can offer a tremendous reduction in required maintenance. The potential savings in labor and track time is particularly important on many bridges that require special equipment or scaffolding to properly tighten the fasteners. Where fasteners are not kept tight, railroads Figure 1, left, shows deck fastener maintenance intervals at FAST. Figure 2, top right, shows the original Conrail System using a hook bolt and a washer nut. Figure 3 shows a turned hook bolt. have noted splitting and/or skewing of ties, thereby reducing tie life. Performance of fastener systems The original Conrail hook bolt configuration used when the deck was installed consisted of a 14-inch hook bolt with a washer nut. Figure 2 shows the hole in the washer nut for a nail to be driven in to prevent the washer nut from turning. The lower portion of the hook bolt neck is fluted to prevent turning. This system withstood about 275 mgt of HAL traffic before the hook bolts had to be straightened and the nuts tightened. At the time of the first tightening, there was one broken by Duane Otter, principal investigator, TTCI and Brian Doe, engineer, TTCI November 2007 19 www.rtands.com Railway Track & Structures http://www.aar.com http://www.rtands.com

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Railway Track & Structures - November 2007 Contents On Track Industry Today Supplier News AREMA News NRC News TTCI R&D Seattle Retrofits Downtown Transit Tunnel Switch Stand, Switch Machines Planning M/W with Modern, High-Tech Tools Products & Literature People Calendar Advertisers Index Sales Representatives Website Directory Professional Directory Classified Advertising Chicago Perspective

Railway Track & Structures - November 2007

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