Development of an optimum design technique for the bus window pillar member

Abstract

Abstract

The body structure of a bus is generally assembled by using various spot-welded box members. The window pillar member is ordinarily built up with a T-type member. This is a very important member connecting the upper and lower structures of the bus body. However, it has been known that the T-type member has some problems such as high stress concentration, low fatigue strength and low structural rigidity. Because these problems cause degeneration of the performance and the durability of the bus body, there is a need to improve them. In this study, a new approach for optimum design of the bus window pillar member was investigated. Stress distribution and fatigue strength were estimated through finite element analysis and experiment. To optimize the shape of the outer gusset connecting the vertical and horizontal members of the T-type window pillar member, a B-spline was applied. To verify the results, stress analyses on the spot welding points, which were fatigue crack initiation points, were performed. It was found that the new approach could effectively alleviate stress concentration at the spot welding point and the outer gusset and improve structural rigidity. In particular, the new bus window pillar member designed through optimization has the following characteristics: (a) the configuration of the structure is very simple; (b) the fabrication process is not complicated in comparison with the current model.