Drill Stem Test Assemblies for Floating Vessels

ABSTRACT A major parameter needed in a bearing capacity analysis of floating sea ice sheets is the strength of ice in bending. Beam bending tests have been conducted by several investigators to determine the moment capacity of sea ice sheets. The present work describes analytically the behavior of sea ice beams at collapse. The bending strength of a beam is a function of the normal force in the beam. Because sea ice is very strong when compressed, the maximum moment capacity occurs when a normal compressive force is present. A failure analysis of sea ice beams should therefore include the bending moments and normal forces. The strength of ice beams in tension, compression, and bending are determined from beam and axial test data, and a failure criterion is elaborated which distinctly matches the strength properties in the three failure modes. The analysis of the failure of simply supported and fixed beams shows significant differences in behavior at collapse. Normal compressive forces develop in the fixed beams which increase the moment capacities of the beams but cause them to fail in an unstable manner. INTRODUCTION To effectively use the arctic ice cover as offshore drilling platforms, aircraft runways, and vehicle roadways, an accurate and reliable means must be developed for predicting the bearing capacity of the ice. Toward this end, the bending failure, which is then major cause of ice breakthrough, has been tasted using cantilever, simply supported, and fixed ice beams. These test have been conducted at rapid rates of loading (failure time of a few second) to make the ice behave like a brittle elastic material. The moment and the stress distribution in the beams have been conveniently determined by assuming that the ice beam are linearly elastic up to the point of failure. However, Peyton [1] measured sea ice stress-strain relation for slow rates of loading (failure time of few minutes) and found them to be nonlinear in tension and compression; this non-linearity suggests that the stress distribution is far from linear in ice beams. It is difficult to determine the stress distribution in ice beams at collapse because of the difference in strength and stiffness of ice between tension and compress, the varying applied stress rate through the thickness, and the varying degree of ductility of ice, It is therefore desirable to develop a method of analysis which does not depend on an ideal stress distribution in the beam. The analysis of the failure of sea ice beam require a failure criterion, which itself require a study of the strength properties of sea ice. Several investigators have conducted tests, to determine the strength of sea ice in tension, compression, and bending; a summary of their data is given by Dykins [3], and a method for determining the strength properties of sea ice sheets with arbitrary salinity and temperature profiles is given by Mohaghegh [4].