PSI - Issue 57

Jacques BERTHELLEMY et al. / Procedia Structural Integrity 57 (2024) 872–903 J. Berthellemy / Structural Integrity Procedia 00 (2023) 000 – 000

899

Fig. 47 : Cross section of the Nevers bridge ensuring sustainability by reducing fatigue risks

6.2 How to ensure the same « Box girder beam » performance with « Double I-beam »

Double I-beam bridges require more complicated features to achieve the same result. It is, of course, possible to apply corrosion protection to all horizontal surfaces of the lower longitudinal and transverse I -beams. However, the use of an inclined plate forming a triangular box on the lower flange of the I-girder has many advantages, so that it is often used for painted bridges [27], because it also: • helps resisting impacts for overpass bridges, • prevents pedestrians or animals from advancing on the lower flange, • avoids buckling of the web and improves the transfer of shear forces, stiffens the bottom flange with a non-deformable triangular box. Some references can be found in [27] and [37] for the use of a box at the bottom flange. Recent studies by the Chinese University of Tongji [38] even suggest that a box may also be of economical interest for the upper flange. However, painting the horizontal surfaces of main and cross girders is probably the least cost effective method of avoiding the fatigue problems caused by weathering steels, either at the design stage of a double I-girder bridge or during its maintenance. As the Scyotte Bridge carries a full motorway deck with a reduced redundant cross-section of only two I-girders, this is probably the best option for this bridge to achieve a sustainable fatigue prevention.