Strength of Steel Box-Girder Bridges

The research on steel box girders in the United Kingdom which followed the recent bridge disasters is reviewed. The feature special to box girders rather than plate girders is the wider use of thin stiffened plate in the former. Because of this many of the design procedures developed for plate girders are not directly applicable to box girders. Among the aspects examined are the role of imperfections in reducing the strength of compression flanges, the difficulties in applying available tension field theories to box-girder web design, and the stress systems and other parameters affecting the design of load-bearing diaphragms. The key points of the research results which helped form the basis of the Merrison Design Rules are presented. These rules, which are based on limit state design philosophy, are the most comprehensive available to date for box-girder design. Those areas needing further investigation are also identified.