In Japan, plain concrete piers with no reinforcing bars are still in service, and their damages have been reported in past earthquakes. The typical failure is the damage to the concrete edge below the cold joint, and no damage has occurred to the concrete above the joint. To prevent damage in future earthquakes, it is essential to clarify the failure mechanism and clarify whether the concrete above the joint can also fail. In this paper, the finite element analysis of the plain concrete pier

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... er two sinusoidal wave inputs with different frequencies was performed, and the failure mechanism was investigated. The results revealed that tensile failure is caused by friction force at the joint, and the direction of friction force changes depending on the input frequency. The friction force causes tensile stress at the concrete below the joint when the input frequency is low. Past earthquake damages to the concrete below the joint correspond to the case with the low input frequency. It was also found that the friction force causes tensile stress at the concrete above the joint when the input frequency is high. Therefore, it was found that the concrete above the joint can fail when a large earthquake with high frequency occurs. Finally, a shaking table test was conducted using a miniature model made of styrene foam, and the mechanism revealed by the finite element analysis was confirmed.