An Experimental Study on Ice-Structure Interaction

Abstract

ABSTRACT To date, despite a number of studies regarding dynamic ice-structure interaction problems, it seems that a practical and effective solution for the problems has not yet been established. It is considered that, at present, more experimental data is needed for the establishment of a solution for the problem. In our experimental study, intensive model ice loading tests were conducted at the Saroma Lagoon in Hokkaido, Japan. Three model pile structures having different natural frequencies were laterally loaded with ice sheets at wide-ranging strain rates of ice. Significant relationships were observed between the. strain rate of ice and both the ice force and the response of the model structure. The test results were analyzed using a rather simple analysis model which took the strain rate dependent ice force into consideration. The analysis model reasonably predicted the dynamic response of the model structure due to ice loading. INTRODUCTION During the last two decades, the dynamic ice-structure interaction has become of more serious concern to engineers. The dynamic behaviors of structures in ice have been investigated from various viewpoints. Peyton1), Neil1 2), Michel et al. 3) and Lipsett et al. 4) reported that ice itself had certain failure characteristics irrespective of the properties of structures. According to the study by Peyton, the ice breaks with a certain failure frequency of about 1 Hz. Neill and Michel et al. reported that the ice tended to break into pieces of finite length - 20 50% of the ice thickness - and that the frequency of the ice force could be determined by the finite length and the moving velocity of the ice sheet. Määttänen 5),6),7) noted that the strength of the ice decreased as the load rate increased. He reported that the self excited vibration of the structure occurred due to negative damping in the ice-structure system, resulting from the decrease of the strength. He also indicated, based on his model tests, that the larger mass the structure has and the more flexible it is, the more easily the self-excited vibration occurs. Matlock et al. 8) proposed a mechanical analysis model. In the model, the structure was represented by a spring-mass-damping system with one degree of freedom and the ice was replaced by a succession of elastic brittle elements. The model had an advantage in its simplicity, but it did not take the dependency of the ice force on the strain rate into consideration. Toyama et al.9) proposed a mathematical model for the prediction of a structure's response based on the results of their field model experiments. According to the mathematical model, maximum response displacement of the structure increases with the moving velocity of the ice until it reaches a critical vel'ocity beyond which Self-excited vibration disappears. In our study, intensive model tests have been carried out mainly for clarifying effects of both natural frequencies of structures and strain rates of ice on the ice-structure interaction.