Improved Model Tests to Investigate the Failure Modes of Pipes Under Beyond Design Basis Earthquakes

In order to investigate the failure modes of piping systems under the beyond design basis seismic loads, the authors proposed an experimental approach to use pipes made of the simulation material instead of steel pipes in the previous study. Though the ratchet-collapse (ratchet and subsequent collapse) was successfully obtained as the failure mode through the shaking table test using the pure lead (Pb) pipes as the simulation material pipe specimens, there was concern that characteristics of pure lead was somewhat extreme considering the analogy with the stress-strain relationship of steel. In order to resolve such concern, a modified experimental procedure has been developed. In the modified procedure, lead-antimony (Pb-Sb) alloy is used as the simulation material. Through the shaking table tests on single elbow pipe specimens made of Pb-Sb alloy, it is found that the typical failure mode is the ratchet and subsequent collapse, as same as the results by the shaking table tests of the Pb pipe specimens. The results indicate that the lower input frequency than the specimen’s natural frequency is prone to cause failure to the specimen, while the higher input frequency hardly causes the failure. The tendency of the global behavior of specimens is similar each other between the Pb pipe specimens and the Pb-Sb alloy specimens, but the strength of self-weight collapse of the Pb-Sb alloy pipe specimen is much higher than that of the Pb pipe specimen. Due to such higher strength of Pb-Sb alloy pipes, a prospect to conduct an excitation test on a more complicated piping system model is obtained.