In the early 1960s, state departments of transportation (DOTs) began using aluminum trichord overhead structures to support signs along U.S. highways. Aluminum is lightweight, costs less than steel, and is inherently resistant to rusting, but is also prone to fatigue as a design factor. Over time, wind forces can create stresses on aluminum structures, eventually causing cracks to appear in the welded joints of the truss diagonals. If these cracks are not discovered and repaired, a welded joint could fail and cause an aluminum diagonal to fall onto the roadway. This article describes an inexpensive way to repair problematic structures, developed by the New York State DOT working with private industry and the University of Utah, to increase their safe and useful lives by employing a fiber-reinforced polymer composite to wrap cracked joints. By this means, workers can restore the structural integrity of a cracked joint to virtually the same strength as the original aluminum weld. The cost of the material is minimal and the repair can be conducted in the field.
Abstract