PSI - Issue 75

Bruno Depale et al. / Procedia Structural Integrity 75 (2025) 254–261 Bruno Depale/ Structural Integrity Procedia (2025)

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Among the railway bridges, those with a riveted design represent a large percentile of them, especially for the oldest ones built in the XIX th century and the first half of the XX th century. The evaluation of their fatigue strength has been subject to many articles. Recently, an Italian paper (Milone et al., 2024) illustrated the fatigue assessment of an Italian riveted railway bridge, mentioning previous works and comparing their results with normative ones based on Eurocode EN 1993-1-9. This paper presents a Residual Life Assessment (RLA) of the old Long Bien Bridge in Hanoi, a typical riveted design of a railway bridge of the end of the XIX th century. 2. Case study: Long Bien Bridge (LBB) 2.1. History and structure of Long Bien Bridge It is a steel railway bridge which construction started in September 1898, designed and constructed by the French firm Daydé & Pillé. It was inaugurated in February 1902 and originally called Paul Doumer Bridge, connecting Hanoi with Haiphong, the main port city in northern Indochina. According to the original design drawings, the length of the bridge is 2,290 meters above the river and 896 meters of stone access ramps. Its 19 spans are supported by 20 pillars 40 meters high (including abutments, see Fig. 1). At the time of its completion, it was once the second longest bridge in the world (just after the Brooklyn Bridge which spans the East River in the United States). Originally, it was only a single-track railway bridge in the middle, but two side paths were added in 1924, nowadays only used for motorcycles and bicycles (about 2.6 meters wide) and for pedestrians (about 0.4 meters wide).

Fig. 1. Long Bien Bridge, general arrangement drawing (extract, 1897).

It was heavily bombed during Vietnam War due to its critical position, 14 times from 1967 to 1972. 1,500 meters of the bridge were affected, knocking down nine spans and severely damaging four pillars. Since the war of Vietnam, many general overhauls took place: additional pillars were built and destroyed spans were replaced by Russian or Chinese beams. The chosen design of the original bridge is the cantilever one, allowing for longer and lighter spans. The longest span is 106,2 m long, and the shortest one is 75 m long. Its lattice steel framework is mainly composed of specific cross-sections, the compression steel members are on top of the bridge and tension chords are on the bottom, supporting the rail track (see Fig. 2.), wind bracing being used to connect left and right truss systems and the distance between two adjacent truss joints is 4.75 m. The connections are riveted type. 2.2. Current condition of Long Bien Bridge The 123 years old Hanoi’s iconic Long Bien Bridge suffers from significant structural deterioration. Various structural elements of the bridge, particularly the French-era iron beams, have corroded and weakened over time. For the most critically damaged spans, immediate reinforcement is required. Additionally, several wind braces have suffered severe rusting and material loss, while wooden suspension bearings have rotted. A few temporary steel supports have corroded to the point of losing their function, necessitating urgent repairs. Similar diagnostic is given for the roadway sections on either side of LBB. The corrosion process results in a reduction in the real cross-section and increases the stress ranges due to railway