Fatigue safety assessment of longitudinal and transverse reinforcements for concrete girder bridge designs

Highway concrete bridges are subjected to fatigue, with stress cycles from the traffic defining the fatigue lives of reinforcement and concrete. Most existing studies on fatigue reliability of bridges address bending, ignoring the fatigue effect on stirrups. This paper evaluates the service life and reliability indexes, from the fatigue point of view, of longitudinal and transverse reinforcements of several concrete girders (prestressed and reinforced) for new bridge designs. Traffic loads are considered as measured by a high-speed weigh-in-motion system at an important highway in Brazil. It is found that reliability indexes for longitudinal reinforcements tend to decrease with the increase of “span length/girder height” ratio and reliability indexes for stirrups tend to increase with the introduction of intermediate crossbeams. Safety levels of stirrups are usually found to be lower than those of longitudinal rebars and tendons, especially for reinforced girders. It is found that deterministic fatigue live estimates lower than 50 years correspond to unsatisfactory reliability indexes (probabilistic analysis).