Railroad Tie Lateral Resistance on Open-Deck Plate Girder Bridges

Abstract

Abstract On open-deck railroad bridges, the crossties (sleepers) are directly supported by the bridge superstructure and anchored with deck tie fasteners such as hook bolts. These fasteners provide lateral resistance for the bridge ties, and in railroad bridge design, their spacing is controlled by the required lateral resistance of the ties. Currently there are no provisions to assist in the calculation of lateral resistance provided by railroad ties on open-deck bridges, and as a result there are no specific requirements for the spacing of deck tie fasteners. This has led to different design practices specific to each railroad, and inconsistent fastener spacing in existing railroad bridges. A research plan was conducted to experimentally quantify the lateral resistance of timber crossties on open-deck plate girder bridges using different wood species and types of fasteners. Experimental tests were conducted on four different species of timber crossties (Beech, Sycamore, Southern Pine, and Oak) with three different types of fasteners (square body hook bolt, forged hook bolt, and Quick-Set Anchors). A structural test setup simulated one half of an open-deck bridge with a smooth-top steel plate girder, and hydraulic actuators to apply both vertical and horizontal load to a railroad tie specimen. The three main contributions to lateral resistance on open-deck bridges were identified as friction resistance between tie and girder due to vertical load from a truck axle, resistance from the fastener, and resistance from dapped ties bearing against the girder flange. Initial testing conducted at Virginia Tech isolated each component of lateral resistance to determine the friction coefficient between tie and girder as well as resistance from just the fastener itself. Results indicate that friction resistance varies based on the magnitude of vertical truck axle load, species of wood, and quantity of creosote preservative on the tie, while fastener resistance varies based on type of fastener and displacement of the tie. With the experimental results, a preliminary equation for calculating the overall resistance of open-deck timber crossties is developed, which allows for a recommendation of fastener spacing based on the type of fastener, wood species, and anticipated lateral loads on the structure.