Optimum design for fatigue strength improvement of spot-welded T-type bus window pillar member

The body structure of a bus is generally assembled by using various spot welded box members. Window pillar member is ordinarily built up by T-type member. It has been shown that T-type member has problems such as high stress concentrations, low fatigue strength and low structural rigidity on spot welding nugget. In this study, a new approach to optimize the design of the bus window pillar member concern with stress concentration on spot welding nugget was proposed based on optimization technique, finite element method. To describe the shape of the gusset connecting the vertical and horizontal members of the T-type window pillar member, B-spline was adopted and this curve was optimized to have minimum weight satisfying strength constraints. It was found that the new approach could effectively improve fatigue durability and structural rigidity.