This paper addresses an explanation to the ice failure process of the phase-locked dynamic ice loading events on Molikpaq in 1986. The ice failure is illustrated as a ductile damage-collapse process with the general features that the ice failure is a discrete ductile process that can be separated into damage and collapse phases; in the damage phase cracks propagate in the ice but the ice does not break and in the collapse phase the ice is pulverized into powder; the ice crushing is a ductile process with the typical simultaneously failure characteristic; the failure has a specific failure length which is related to displacement of the structure. The full-scale data show that the ductile damage collapse failure happens at the ice drift velocity lower than 0.1 m/s. The failure is simultaneous along ice-structure interface and induces high global ice load without width effect. It also induces saw teeth ice load and caused dynamic response of the platform. The response is not an oscillation process and is different to the lock-in vibration of the jacket platform and light house because the caisson is close to an over damped or critically damped system. The field measurement also shows that failure length of the ice is about 5 cm for those events. A simple analysis shows that displacement of the structures is approximately ½ to 1 times of the failure length.

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