Clarification of Deterioration Mechanism and Seismic Performance of Telecommunication Steel Conduit

This study evaluates the seismic response of conduits considering the aging deterioration of steel-pipe threaded joints for communication. To model the displacement-load characteristics of the aged steel-pipe threaded joint, fracture experiments were conducted using specimens with a burial period of 30 to 50 years. The obtained results showed that the maximum tensile load tended to decrease as the burial period became longer and as the internal corrosion became severe. The deterioration of steel pipe threaded joints was represented by a model in which the yield load and maximum load decrease as the pipe thickness decreases in proportion to the 0.5th power of the burial period t due to corrosion. The seismic response of the system is investigated by modeling the pipe with beam elements and the deteriorated joints as well as the pipe-soil interaction with spring elements. It is shown that joints with a burial period of more than 20 years are plasticized with a ground strain of 0.3%, and joints with a burial period of 50 years are destroyed with a ground strain of 0.5%. As a result, the effect of joint deterioration on the seismic performance of the steel pipe conduits was quantitatively clarified.