4.2 - Fatigue Strength Investigations of Connections between Primary Ship Structural Components

Abstract

Primary structural components in ships are usually built-up I-beams with deep webs and flanges formed either by flat bars or by water-tight stiffened plating of the ship hull, decks or bulkheads. Typical examples are stiffened decks with large T-shaped girders beneath the decks or the floors and girders of the double bottom. Highly stressed are often the end connections between horizontal and vertical members which can be designed in different ways. One way is to apply large triangular or curved brackets which additionally support the connection. An alternative is offered by widening the depth of the component towards the connection with knuckled flange or plating. A further alternative particularly for ro/ro ships is a simple intersection of the I-beams which is well-known from steel structures. The different alternatives are discussed in the paper. As all designs contain fatigue-critical details, several numerical and experimental investigations have been carried out in the past, which are reviewed. Recent investigations on the third alternative, i.e. simple intersections of I-beams, are described in more detail. The stress analysis was performed with an extensive finite element model using the structural hot-spot stress approach for the assessment of the critical weld toes. The fatigue tests with large-scale models showed a fatigue behaviour which differed from the numerical assessment. Possible reasons for the discrepancies are discussed and conclusions are drawn.