DAMAGE OBSERVATIONS OF THE STRAIGHT PIPES SUBJECTED TO CYCLIC LOAD AMPLITUDES OF VARIOUS LEVELS

摘要

Fatigue failure accompanied by ratchet deformation is well known as one of the failure modes of pressurized pipes under high-stress level cyclic load. In this research, the process of failure of such pipes was investigated based on the experimental result in which a straight pipe failed by increasing cyclic input of displacement amplitude step-by-step. The strain behavior, moment-deflection relationship, and observed damage were compared with the stress levels prescribed in the seismic design of the piping system in Japan. As a result, no significant damage was observed and the moment-deflection relationship remained almost linear within the primary stress limit of 35m, although the strains at some measurement points reached to the plastic region. In the experiment, damage was observed at the applied load level of approximately 5Sm of the primary stress level, and 0.15 and more of the fatigue damage index, i.e., the usage factor based on the design. The test results showed that there is several times as much margin as its designed stress limitation before failure occurs to actual piping systems.