Fatigue and Fracture Behaviour of Long Term Operated Bridge Materials and Components

This book chapter intends to provide a fatigue database for some representative materials of old Portuguese metallic bridges (Eiffel, Luiz I, Fao, Pinhao and Trezoi). Puddle irons and structural steels are covered, depending of construction year of the bridge. Besides the base materials, also S–N fatigue data of riveted joints made of original rivets or new rivets are presented, but in any case using original plates. As regards the materials characterization, S–N fatigue data obtained using smooth specimens is presented; also, fatigue crack propagation data obtained using CT specimens is presented. The monotonic tensile properties are also characterized as well as the microstructures. S–N fatigue data for riveted joints was also presented and compared with existing literature data, including existing design curves. This comparison shows some data falling below the design S–N curves that corroborates the presence of cracks originated by the prior operation of the bridge or material degradation. Regarding the strain-life behaviour of the materials investigated, the number of transition reversals decreases with increasing age of the materials. Only the material from the Trezoi bridge shows a transition life typical of low carbon steels. The fatigue crack propagation tests showed that Paris law gives a good description of the fatigue crack growth data with an exponent always greater than 3. The C coefficient was in same range of that recommended in literature for modern construction steels.