Bridge No. 33, a late 1890 Warren pin connected through truss, is located at the end of an industrial line that provides access to U.S. Army Holsten ammunitions plant in Kingsport, Tennessee. Overtime, the pin plates began to wear and the associated truss members loosened around the pin to the point where the truss members oscillated under live load. This movement created fatigue cracks, sheared connection bolts within the floor system, and accelerated deterioration of the joint and nearby joints. Joint L4, located mid-span, developed the most significant wear, oscillation of the joint members became visible from the below road and requires annual maintenance and inspection. Conventional rehabilitation methods for freezing of the pin joint proved problematic due to the lower chord being composed of non-uniform eye-bars and existing utilities hanging off the field side of the trusses, restricting access to members. Joint L4 was repaired using sets of machined hairpins and compression struts (hairpin assembly). The hairpin assembly interlocks around the pin to create a cradle that will allow an alternate load path for loading, bypassing the pin plates via hairpin assembly, and transfer to the main load carrying members. This repair was installed with minimal disruption to rail traffic. This paper will discuss the design and construction challenges encountered during the course of this unique repair that will extend the life of an aging truss.
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