Assessment of U-type wrought iron railway bridges

A number of assessment codes and guides exist that take into account the particular details of old U-frame types and riveted wrought iron construction; however, a significant number of old bridges still have details that cause difficulty in reliable assessment or require very conservative assumptions, giving low assessed capacity. In this paper, an alternative assessment method using non-linear finite-element analysis of an old U-frame railway bridge is presented. By using the analysis results, some guidelines and recommendations are suggested that are considered to be useful for the assessment by the engineering community. However, this approach also has limitations, as it is reliant on assumptions that can be difficult to confirm without extensive field monitoring and experimental testing. The analysis results showed that main girders with non-code-compliant U frames do indeed benefit from a low but significant level of restraint to resist lateral torsional buckling and also that girders that are marginally non-compact based on codified assessment methods may actually have sufficient local stability to provide additional flexural capacity beyond the elastic moment capacity.