Lessons Learned in the Design and Erection of Box Girder Bridges from the West Gate

The West Gate Bridge, intended to span the Yarra River in Australia, collapsed during its third year of construction in 1970. Investigation into the project revealed numerous issues in the bridge's design and construction. The West Gate Bridge is one of a number of box girder bridges built during the mid 2 0 th century, and was one of four to fail in a three year period. An overview of the design and erection issues is presented, particularly those dealing with thin elements in compression. A comparison of moments and stresses resulting from the use of concrete blocks and jacks to reduce the camber difference encountered on span 10-11 shows that the latter method would have been preferable. The failure of three other box girder bridges between 1969 and 1971, and the required strengthening of dozens of others, reveal the lack of understanding of the slender compressive elements present in such structures. A brief literature review presents the buckling and deformation modes found in stiffened plates under compressive loading, showing the development of understanding of these systems from papers written or published in 1997, 2001, 2004 and 2006 over three decades after the West Gate collapse. Criteria by AASHTO and by B. H. Choi and C. H. Yoo for the minimum moment of inertia of longitudinal and transverse stiffeners of box girders are presented. The resulting values are compared to the moment of inertia of sections used to strengthen the West Gate Bridge after the collapse of a similar bridge. This comparison shows that the requirements are quite sensitive to scale and can provide inconsistent requirements for stiffness. Thus, there is currently a lack of guidance and regulation from codes for the design of wider single-cell box girders. The complex and non-linear nature of the slender elements in compression used in box girders does not allow the extrapolation of simpler rules developed for the design of smaller bridges. Despite the complex behavior of box girders, they offer a number of advantages and further research is needed to improve their analysis, design, construction, repair and maintenance. Thesis Supervisor: Jerome J. Connor Title: Professor of Civil and Environmental Engineering