Railway Track & Structures - July 2008 - (Page 36)

Heavy haul m/w 120,000 psi tensile strength. AREMA Committee 5 is currently working on a new screw spike specification for Chapter 5 of the manual. Most railroads have specifications for screw spikes that were developed uniquely for each road. In 2001, a “North American Common Standard” screw spike drawing was released by three U.S. Class 1s. That part has seen some widespread use, but other parts and variations on the Common Standard part are still in widespread use, even among the railroads issuing the spec. “While the prospect of reaching a universal standard on screw spikes seems unlikely, there have been some trends,” Austin said. “The use of smaller diameter screw spikes has diminished in favor of 15/16 inch. Most Class 1 standards now require higher strength materials with tensile strength requirements ranging from 74,000 to 120,000 psi. “Screw spikes have become very common throughout special trackwork, especially in heavy traffic areas,” Austin said. “The biggest growth in screw spike usage has been in curves, with several Class 1s now using screw spikes in curves with various limits of curvature and traffic where they are specified. One railroad is using screws in curves as low as two degrees in very heavy tonnage areas, while two Class I roads have not adopted screw spikes in any curves. Other rail rollover protection is generally used in those cases. “The loading environment that screw spikes operate under is not well defined,” he noted. “They tend to work loose with dynamic loading and eventually break. Broken screw spikes are frequently found in groups. The consensus is that a few broken spikes tend to leave the surrounding spike more vulnerable and a chain reaction results. It is not usually clear whether broken screws are an issue with the screw, installation or other factors caused by the track conditions.” Inadequately restrained cwr has been known to break screw spikes as curves or special trackwork move under thermal loads. Excessive movement of track because of ballast and subgrade conditions can also cause premature failure of screw spikes. “The Evergrip spike developed by Lewis Bolt has seen some success in curves,” he said. “The spike was developed to have similar performance to a conventional screw spike and be installed with a machine typically used for standard track spikes. The result is a 15/16-inch screw spike with steep quadruple lead threads and a set of four fins just above the threads. “The angle of the threads causes the spike to turn as it is driven in,” Austin noted. “The fins are oriented to resist rotation that would back the screw out. The head is configured with a double washer arrangement to allow a set of jaws to pull it out. On top of the washers is a square drive to fit a 7/8inch socket. The top of the head has a dome that protects the square drive from damage when driven. The material is low carbon steel with tensile

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Railway Track & Structures - July 2008

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