Peak Ice Force In Ice Crushing On Vertical Structure

Ice load is the dominant load of offshore structures in cold regions, and peak ice force must be considered firstly in structure's design in ice covered waters, i.e. the offshore structure have to be able to resist ice load and avoid being pushed over. In this paper the study of peak ice load on vertical structures is generalized, our monitoring on the two platforms JZ9-3 and JZ20-2 is introduced, which is used to be the first hand material for the study of peak ice load.The existed formula for calculating peak ice load on vertical structures is discussed and compared. The result according to these formulas is totally different, and sometimes the results are in different order of magnitude. There are many reasons for these differences, in which the main reason is the different viewpoint of failure mode in interaction between ice and vertical structures, i.e. non-simultaneous or simultaneous failure. Currently non-simultaneous failure mode is widely accepted, whereas simultaneous failure mode has not been verified in the field tests.According to field observations, the failure process of non-simultaneous mode is described. The peak ice load based on non-simultaneous mode is discussed, the correction coefficient of the formula based on non-simultaneous mode is between 0.4 and 0.7, even smaller.The condition in which simultaneous failure mode take place is very strict, it has not been verified in field tests, so the ice load calculated using simultaneous failure mode is high and can not be accepted widely. By field observation, we found that for slender and narrow structures, when quasi static vibration and steady state vibration happens in low ice velocity, ice failure is simultaneous, the peak ice load should be determined according to this mode. The correction coefficient of formula based on simultaneous mode is calculated using plastic limit analysis method, the result is between 2.97 and 1.15, which is much bigger than that of non-simultaneous mode. So for slender and narrow structures, the peak ice load calculated by non-simultaneous mode is dangerous and should be determined over again.