The use of punched holes in bridge structures

Abstract

The use of punched holes in bridge structures in load-carrying members is not allowed unless the holes are sub-punched to a smaller diameter and then reamed to full size. Some owners allowed full size punched holes in cross frames and lateral bracing systems since these members were not designed to carry a calculated load. Three-dimensional analyses of bridges resulted in calculated forces in these members and the recognition that cross frames carry substantial forces, particularly in curved or skewed girder bridges. Consequently, punching of holes in these members was no longer allowed since they carried calculated design forces. A large experimental study was undertaken to evaluate the impact of punched holes upon the tensile capacity, bearing strength, block shear strength, and fatigue strength of members with punched holes. The study included the effect of plate thickness, hole size, punch clearance, and yield strength upon the strength and ductility of the plates. Recommended design values were developed that account for the lower strength exhibited by members with punched holes. In addition, due to the lower ductility of members with punched holes, they are not recommended for use in main load-carrying members.