Comparison of Fatigue Resistance of Various Longitudinal Weld Joints

Abstract

Abstract Various types of one-sided and two-sided longitudinal weld joints were madein the web/flange connection of large-scale HSLA-80 I-section beams. Fatigueexperiments were conducted on 78 beams. As expected, there is a decrease in thefatigue strength of the one-sided welds relative to the standard double filletweld. Among the one-sided welds, the differences in the fatigue strength wereslight. The findings show that existing design rules for longitudinal filletwelds in bridges can be used for ships. The data provide a rational basis forthe selection of longitudinal weld joints, fit-up tolerances, and NDErequirements. Introduction The Navy is considering advanced (unidirectional) double-hull surfacecombatant ships. A simplified schematic of the advanced double-hull crosssection is contrasted with a conventional stiffened-panel hull cross section inFigure 1. The multiple load paths (redundancy) and improved stiffness inherentin a double-hull design offer potentially improved strength relative toconventional stiffened-panel hull construction [1]. The double-hull design mayhelp contain damage from leaking due to fatigue cracks. A cracking element ofthe double-hull framing system transfers load to adjacent members more easilythan stiffened-panel construction, reducing the probability of catastrophicfailure. These ships are also likely to be fabricated from modern high-strengthlow-alloy (HSLA) steels which offer increased strength and toughness relativeto conventional ship steels. The unidirectional double hull concept has also been proposed for commercialtankers [2,3]. Concern for the environment has led the Oil Pollution Act of1990, which requires that new oil tankers over 5000 tons built for use in U.S.waters have double hulls [4]. The International Maritime Organization hasrequested that member countries also require these tankers to have double hulls[5]. In commercial tankers and bulk carriers fabricated from high-strengthsteel, fatigue cracking has become a serious problem. For example, betweenJanuary 1990 and September 1991, 36 bulk carriers suffered severe structuralcasualties due to corrosion and fatigue causing the loss of 21 ships and 250lives [6].