Towards cost optimal design and maintenance of steel structures under stray current interference

Steel is a cost-effective and durable building material. Corrosion is one of the major degradation mechanisms of steel structures, also for underground structures like sheet pile walls. Traction currents leaking into the ground (called stray currents here) and interfering with the structure can cause increased corrosion rates, and wall thickness loss. At the moment the limited quantitative and qualitative information on this phenomenon hinders objective assessment of its consequences for the durability of underground steel structures. In this paper the development of a method to calculate cost optimal maintenance schemes for steel sheet pile structures under stray current interference from DC traction systems, in the design phase is presented. To come to such schemes the following procedure can be followed. First an analysis of the design options and possible maintenance, repair, inspection and preventive measures must be made. Also the risks of possible failure are to be assessed and the associated costs quantified. From this analysis several design options and associated maintenance schemes are postulated, in specific scenarios. Next a service life design of the structure for each scenario is made, based on a desired reference period (e.g. 100 years) and a desired reliability that the structure will not fail in this period. This delivers detailed designs and specified maintenance plans, on which costs estimates can be based. Next the Life Cycle Cost (LCC) of these scenarios is calculated. For every scenario an equal service life which is reached with the same probability is obtained. Therefore a well-founded objective choice between different scenarios can be made, based on the associated risks, costs, and e.g. need for maintenance