Chapter 24: 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 made. This chapter first analyses the major sources of material and structural degradation: 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.

In spite of their relatively simple structural systems and well-defined supports, bridges suffer heavily from the effects of age, climate and, especially, traffic that often exceeds the codified limits. Their strength and durability depend on the type and quality of the constituent materials, structural design, construction and maintenance. This latter factor is the only one that can be influenced for existing structures. Maintenance, however, can be effective only in the light of adequate inspection, monitoring and assessment procedures, facilitating, if need be, an appropriate preventative action (Calgaro and Lacroix, 1997). This chapter will consider the main causes of damage, certain material and structural investigation methods and assessment procedures. Only concrete and steel bridge decks will be discussed.