Technology Digests / Fastener Spacing for Timber Ties on Open Deck Steel Bridges

TD22-028

October 1, 2022
Authors
  • Chris Johnson
  • Duane Otter
  • Dante DeVencenty
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Key Findings

  • Current AREMA recommendations for spacing of deck fasteners on open deck steel bridges are adequate for most load cases examined.
  • The effects of car load and car type are significant. The most challenging cases are long lightweight cars (such as autoracks) that have high wind loads, and empty cars in which light wheel loads reduce the amount of frictional resistance available.
  • As expected, the tie and hook bolt spacing had a large effect on the amount of lateral resistance in a bridge deck.
  • The case of a broken or missing hook bolt to allow for the realities of hook bolts breaking, twisting, loosening, or dropping was also considered, resulting in insufficient lateral resistance for nearly 10 percent more of the load cases.
  • The degree of curve had no significant effect, thus a consistent hook bolt spacing should be considered for all curves.

Fastener Spacing for Timber Ties on Open Deck Steel Bridges

MxV Rail (formerly TTCI) has been investigating new designs and materials to improve safety and efficiency and reduce the maintenance required for open deck bridges. Due to a lack of information on the lateral resistance provided by ties and fasteners on open-deck railroad bridges, there was no quantitative data to support guidelines or requirements for deck tie fastener spacing; specifically in decks with smooth girder top flanges (no rivets) and ties without daps. At the request of and with guidance from MxV Rail, researchers at Virginia Polytechnic Institute (Virginia Tech) conducted experimental testing on five tie materials, three hook bolt styles, and multiple vertical loading conditions to determine the lateral resistance of each combination. Through testing, lateral resistance provided by tie friction, hook bolt fasteners, and tie daps was quantified. Investigators at MxV Rail then used the lateral resistance values from this recent experimental testing to evaluate current American Railway…