This study proposes a low-cycle fatigue life derived from measurement points on pipe elbows, which are components that are vulnerable to seismic load in the interface piping systems of nuclear power plants that use seismic isolation systems. In order to quantitatively define limit states regarding leakage, i.e., actual failure caused by low-cycle fatigue, in-plane cyclic loading tests were performed using a sine wave of constant amplitude. The test specimens consisted of SCH40 6-inch carbon steel pipe elbows and straight pipes, and an image processing method was used to measure the nonlinear behavior of the test specimens. The leakage lines caused by low-cycle fatigue and the low-cycle fatigue curves were compared and analyzed using the relationship between the relative deformation angles, which were measured based on each of the measurement points on the straight pipe, and the moment, which was measured at the center of the pipe elbow. Damage indices based on the combination of ductility and dissipation energy at each measurement point were used to quantitatively express the time at which leakage occurs due to through-wall cracking in the pipe elbow.

It is known that all of structures be old enough not to use as time elapses, and the degree of deterioration depends on the environmental conditions and maintenance activity. Specific repair for deteriorated structures should be applied and the performances are greatly affected by materials used and location of members allocated. This study is to evaluate the enhancement of steel pipe pile in terms of performance when they are reinforced by carbon-fiber composite for underwater.

It is known that all of structures be old enough not to use as time elapses, and the degree of deterioration depends on the environmental conditions and maintenance activity. Specific repair for deteriorated structures should be applied and the performances are greatly affected by materials used and location of members allocated. This study is to evaluate the enhancement of steel pipe pile in terms of performance when they are reinforced by carbon-fiber composite for underwater.