BANANIERS VIADUCT - ALGERS

The viaduct crosses the East highway close to the Les Bananiers neighbourhood in the outskirts of Algers and, thanks to its structural layout constitutes a sign enhancing the entrance into the main city.

The preliminary project had an heavy aspect due to the use of precast prestressed concrete beams simply supported on the end retaining walls on two intermediate frames; this solution has been completely reviewed by designing a deck constituted by slender precast prestressed concrete beams bearing on the end retaining structure, on intermediate transverse beams supported by a four parallel systems of steel struts and ties anchored to the buttresses; a central wall constitutes the single intermediate support.

The beams were given continuity by the concrete deck slab, while a single joint is located over the intermediate support to allow for thermal and rheological deformations.

The steel structure has a layout resulting from two triangles with a common side constituted by the bearing mast leaning towards the middle and is composed of three prefabricated box section elements connected by in situ welding and of groups of bars with fork and pin anchors for the tie which supports the transverse beam.

The horizontal connection between the lower ends of the mast and of the rear tie is constituted by a reinforced concrete beam cast over a buttress longitudinal diaphragm; in the outer structures this beam is reinforced by an additional steel plate connected to the horizontal strut laying between the mast foot and the lower anchor of the bars.

The vertical component of the rear tie is balanced by post-tensioning cables embedded in the buttress longitudinal diaphragm.

In the structural scheme, quite easily intelligible, thanks to the different sectional shapes, the function of the elements is evident.

The viaduct has a total length of 80.50 m between the buttresses and a width of 27.40 m for locating two edge walk-ways, two double lane carriageways and a central double track for the programmed tramway line.

To balance the overturning moment due to the overhanging steel truss supporting the bridge, the buttresses are filled with granular material; the foundations are on piles.