Assessment of flat deck metallic plates – yield line and membrane analysis

A large number of metallic riveted bridges have been constructed using flat plates to form the deck of the structure. When assessed using traditional elastic methods these plates are routinely found to be under capacity for the application of the prescribed load even though they show zero signs of distress. This paper considers the use of alternative methods of assessment, namely yield line and membrane analysis, utilising the beneficial effects of plastic methods of analysis where appropriate to enhance the assessed capacity of these failing plates. The analytical formulation of both methods is presented considering the effects of the plate aspect ratio, support conditions, the presence of stiffeners, plate thicknesses and rivet sizes. By comparing the reassessed capacities of the plates obtained through the refined methods with the original assessed capacities it is shown that the former offer considerable enhancements in assessed capacity ranging between a factor of 1.3 to 7.