Tubular Versus Non-Tubular Hot Spot Stress Methods

The hot spot stress (or strain) method has been used for fatigue design of pressure vessels and welded tubular connections since the late 1960s. Efforts are now underway to extend its use to non-tubular applications, such as bridge girders and ship hulls. The AWS Structural Welding subcommittee on design has a task group charged with harmonizing the tubular and non-tubular approaches to fatigue. Previous efforts have tended to focus on either one or the other, with associated choices of modeling methods and S-N curves. In both tubular and non-tubular fields, it has been particularly challenging to find a common method that deals with well-behaved (finite albeit high) stress concentrations as well as ones that tend towards singularities, e.g. the corners of box connections and nontubular gusset terminations. The conceptual advantage of explicit weld modeling, and the need to model the detail of interest in context rather than in isolation, are common to both. This paper will review these issues. At this point in time, pat answers cannot be guaranteed. The 2008 edition of AWS D1.1 is being targeted for incorporating consistent tubular and non-tubular fatigue criteria.