Fatigue Strength of Stiffener End Connections: A Comparative Study of Bulb Flats and Angle Bars

摘要

Stiffener end connections, particularly at side longitudinals, belong to fatigue critical details of ship structures. Fatigue cracks appeared some decades ago in tankers and, more recently, also in large container ships. These cracks occurred because cyclic global bending stresses and torsional moments in the hull girder as well as local stiffener bending were underestimated. This paper describes fatigue tests at stiffener end connections with bulb fiats and angle bars and focuses on the question how far bulb fiats are also prone to fatigue in view of the reduced eccentricity of the bulb compared to the flange of angle bars. Stress analyses were performed with the finite element method, applying nominal as well as structural hot-spot stress approaches to assess fatigue behaviour. The latter method was well suited to consider increased stresses caused by flange eccentricity, but it created problems in extrapolating stresses in bulb flats. A procedure for appropriate stress extrapolation is proposed. Finally, conclusions are drawn regarding a fatigue-resistant design for side longitudinals made of bulb flats and angle bars.