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1. • CommentAuthorDr. Zee
   • CommentTimeJan 12th 2007

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   If the poles are suspected of having crack(s), or if there have been catasrophic failures of the weldments (HAZ)in the past, poles with the same design at a project site should be by evaluated by ultrasonic testing or other forms of non destructive testing methods to identify additional suspect poles. MATCO highly recommends that all similar pole structure be inspected immediately and that cracked poles be taken out of service as soon as possible. There is only a small window of time when the cracks are both large engouh to detect, and small enough to not yet cause catasrophic failures. Replaced pole(s) should be designed so that the stress ranges due to the fatigue design loads are less than the fatigue thresholds for each detail, thus ensuring that fatigue will not occur even for a large number of load cycles. Thickness of the base plate can have significant affect on fatique life of a pole structure. Thicker base plates generally exhibit significantly longer time to failure.
   Since fatigue cracking is possible and have been observed frequently in certain design of pole structures, it is important that the materials used for anchor rods and load bearing members have some minimum level of resistance to fatigue, defined by notch toughness in order to avoid brittle fracture from small cracks. Using materials with additional notch toughness (above these minimum levels) would not significantly increase the time to failure of the structure by fatigue. This is because cracks grow at an exponential rate, and 95 percent of the life is consumed while the crack size is less than a few millimeters. Even though additional fracture toughness may correspond with a greater crack length at the time of failure, it does not correspond with a significantly longer time to failure. MATCO highly recommends that all similar pole structure be inspected immediately and that cracked poles be taken out of service as soon as possible. There is only a small window of time when the cracks are both large engouh to detect, and small enough to not yet cause catasrophic failures. Replaced pole(s) should be designed so that the stress ranges due to the fatigue design loads are less than the fatigue thresholds for each detail, thus ensuring that fatigue will not occur even for a large number of load cycles. Thickness of the steel plate can have significant affect on fatique life of a pole structure. Thicker plates generally exhibit significantly longer time to failure. At your request Matco can establish a program to inspect the poles with similar design for cracking at project sites to prevent catasrophic failures.