Evaluation and Repair of Wrought Iron and - Purdue e-Pubs ...

125remove the members and sandblast them before repainting and assembling them again tominimize future corrosion, as seen in Figure 5.11.5.6 Investigation and Repair of Elongated Eyebars and Diagonal BracingAnother problem that commonly occurs in existing historic iron truss bridgesdeals with the condition of the eyebars and diagonal members. Often over time thesemembers are elongated from heavy use and become slack or loose in the truss bridge.When these members are slack they no longer carry any load and other members areforced to carry greater loads than what they were originally designed for. This can createa dangerous and unsafe situation in the bridge.Shortening the loose or slack members in a metal truss bridge is a reasonablemethod to fixing this problem. Some bridges already have turnbuckles that weredesigned to correct the problem of elongating bridge members. A photograph of aturnbuckle can be seen in Figure 5.12. To shorten the member the turnbuckle is turnedand the two ends of the members are brought closer together. It is important not to turnthe turnbuckle too much and induce an unnecessary amount of strain in the member.Moreover, the turn-buckles themselves are often corroded and not easily maneuverable.Hence, it may be beneficial to add heat when trying rotate the turn-buckle and examinethe threaded region for section loss and cracking.In one of the Norfolk and Western Railway Bridges in Missouri, a method toshorten wrought iron eyebars without turnbuckles consisted of removing a piece of theeyebar and then welding the eyebar back together again with a pair of steel splice plates.Fatigue tests were completed on the splice plate repairs and determined that the repairswere adequate even though cracking occurred at the toe of the splice plate welds(Keating, 1984).