Assessment of Existing Bridges: The Swiss Experience of the Last Three Decades

Many of the existing reinforced and prestressed concrete infrastructures, such as bridges, subways or overpasses have reached or will reach, in this decade, half a century of existence, making it timely to assess their structural safety accounting for their state. It is desirable that the assessment of existing structures is carried out following a design philosophy by Levels-of-Approximation (LoA) as described in Model Code 2010. This design philosophy consists in starting with a lower LoA corresponding to simple and fast calculations with some safety margin (corresponding to an approach typically used in the design of new structures), refining in the following stages (higher LoAs) only the calculations associated with the governing structural verifications. This work aims at addressing the fundamental aspects of this methodology, based on the experience in Switzerland in the last three decades, discussing briefly the calculation methods that can be applied in higher LoA and that allow considering some reserves of structural resistances typically neglected for design of new structures.