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Overpass railway bridge in Al Faw grand port
A large concrete arch bridge overtakes the very large marshalling yard and provides an iconic landmark for the Iraqi grand port.
Project: Al Faw grand port – overpass railway bridge.
Location: Al-Faw, Iraq.
Client: Iraqi Minister of Transportation.
Cost of total Works: 38,000,000 € (Cost assessed for the arch bridge and approach viaducts).
Services: Master Plan.
Technital has been engaged in the study of one of the greatest container port in the world. The Engineering Consultancy Services for the New Al Faw Port includes also the design of an internal road network of 60 km, where the main road axis crossing the wide marshalling area (20 tracks) is hinged by a remarkable arch bridge.
Architectural considerations play an important role to offer a landmark for this region. The parabolic shape enables the bridge to emerge from the surrounding operative site while the double inclined arches provide a strong sense of stability.
Following the development of possible alternatives that matching the set requirements, through a comparative analysis made by the assessment of the main functional attributes, the optimal solution has been identified for the long-span bridge. The chosen structure is a tied-arch bridge, where the horizontal forces are transmitted directly from the arch to the deck, which acts as a bottom chord. Two inclined arch ribs, joined at the crown section, suspend the deck through two sets of hangers.
The overpass consists of the arch bridge having an outstanding span 226 m long, two short side spans of 17 m and two access viaducts spanning typically 38 m.
The main advantage of this kind of structure is the strong reduction of the horizontal forces transmitted to the foundations (poor soil). The vertical loads acting on the deck, deriving from own weight, permanent loads and live loads, are transmitted to the arch through the suspension rods (hangers) placed at a distance of about 6 meters.
The arch bridge is made partly of reinforced concrete and partly of prestressed concrete; the deck is isolated by means of friction anti-seismic devices. The chosen structure can ensure high durability over time, despite extremely severe conditions of the site (closeness to the sea, sand). To ensure this, some measures should be taken into account, like use of a high-performance concrete for the entire structure, adequate concrete cover, good protection for deck hangers and post-tensioned cables.
One of the most important challenges is surely related to the construction of the arch ribs, because the temporary support structure has to be strong enough, not much deformable and its cost should be as low as possible. Among various available technologies, the most suitable seems to be the one using steel tubes injected with concrete, also known as CSFT (concrete filled steel tubes).