Stress calculations for longitudinal hull members fatigue assessment

Abstract

Simple formulae for calculating stress ranges in longitudinal ship hull members, exceeded with an assumed probability, are proposed. The stress ranges can be applied to fatigue life assessment. The assessment is based on approximation of long term stress range distribution by the Weibull’s distribution and S-N curves application. The total stress range is calculated in the form of sum of global and local components, multiplied by partial stress range coefficients. The global stresses are caused by general bending in vertical and horizontal planes. The local stresses result from bending of stiffeners or plating. Approximate values of the partial stress coefficients were found on the basis of long term stress distribution direct calculations, performed for 6 ships. Approximate values of dynamic stress cycle numbers that occur during ship lifetime and coefficients defining the Weibull’s distributions were also found.