ABSTRACT
This chapter presents the main degradation processes and typical defects of the original design. Establishing principles for the assessment and rehabilitation of existing structures is essential as repair and retrofitting require an approach that is substantially different from the design of new structures, and entail knowledge beyond the scope of design codes. In the case of corroded structural elements or steel bridges characterized by insufficient traffic load capacity, one of the most common retrofitting methods is the addition of steel cover plates to the existing structural elements. Managing authorities frequently ask for bridges to be widened, not only to extend the roadway and add supplementary traffic lanes, but also to obtain new cycle paths and footpaths raised above the roadway. Orthotropic steel decks, directly subjected to traffic loads in road bridges, are very sensitive to fatigue: in most cases, fatigue defects appear as fatigue cracks, which affect the top plates, longitudinal ribs and cross-beams of the deck.
