Probability based modelling and assessment of an existing post-tensioned concrete slab bridge

This paper presents the application of probabilistic techniques to the load capacity assessment of a post-tensioned concrete slab bridge which was built in 1959 outside Copenhagen. The bridge failed to demonstrate the required capacity following a deterministic assessment and as such was deemed to require repair or replacement. Following the Danish Roads Directorates stated policy of performing probabilistic assessment, where deemed beneficial, prior to repairing or replacing, the structure was probabilistically assessed according to the newly developed Danish guideline for Reliability Based Classification of the Load Carrying Capacity of Existing Bridges. The paper presents the techniques employed in modelling the critical limit state, as well as the statistical techniques employed in modelling loads, resistance and associated uncertainties. Ultimately, the structure was shown to have sufficient load carrying capacity and as such the scenario of expensive repairs or replacement was avoided, with significant financial benefits to the bridge owner.