Deterioration, investigation, monitoring and assessment

With age, aggressive environment and steadily increasing traffic, bridge decks wear out their strength and durability, especially where design, construction or maintenance errors are committed. This chapter first analyses the major sources of material and structural degradation: mainly concrete deterioration, steel corrosion, excessive magnitude or repetition of applied stresses or strains, temperature level, fluctuation and non-linear diffusion. The principal types of cracks and weakened areas are shown and commented on. For material and structural appraisal, numerous powerful methods are presented, ranging from simply conventional to highly advanced, selected for each case after a thorough desk study and a detailed visual inspection. The last presented method illustrates the feasibility of permanent monitoring and active control of structural safety, approaching the performance of smart systems. Finally, the residual strength evaluation procedures are outlined for a potentially distressed bridge. They involve a well-prepared semi-probabilistic recalculation process, based on site investigation results and on the concepts of serviceability and ultimate limit states.