A serious fracture, extending halfway through the circumference of a steel pipe column, was discovered in a pedestrian bridge across a prefectural road in Japan. This paper presents the examination of the causes of the fracture and its retrofitting. In order to identify the causes of the fracture, observation of the crack surface, SEM observation, material property tests and measurement of strain were carried out. According to observation of the crack surfaces, the cracks originated from the toes of the boxing welds at the end of the rib plates. The failure surface was covered with a thick layer of corrosive products, but a large section of the crack surface in the fractured area was estimated as brittle failure and there was no evidence of cracks due to fatigue. However, the crack surfaces near the boxing welds on the opposite side of the fractured area were evaluated as having being caused by fatigue failure. The results of the measurements of stresses demonstrated that a relatively high stress range was caused near the boxing welds, when several people ran across the pedestrian bridge. The base metal was found to have very low Charpy-absorbed energy. The fractured steel pipe column of the pedestrian bridge was retrofitted by applying bolted splice rings and plates.
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