Shell footbridges over the river Manzanares

Madrid

Structural typology: Bridges
Completed: September, 2010
Owner: Ayuntamiento de Madrid
Construction: MRIO Arquitectos y Acciona Infraestructuras
Scope: Detail Design and Site Supervision

These are twin footbridges which are to be found located in the urban area of the River Manzanares, between the Praga Bridge and the so-called Southern road Network. More specifically, the abutment on the West Bank pertaining to the Footbridge Km202+121.6 is to be found located between the streets San Graciano and Eugenio Caxes whilst the Footbridge Km202+402.0 is located between the streets Eugenio Caxes and San Zacarías.

The span between supports is 43.5m whilst the total length is 49.10m.

The Project consists of a reinforced concrete arch with a lower steel deck, offering a maximum rise of 7.70m. The deck is suspended from two rows of 8.1mm diameter hangers spaced every 0.60m on each side of the deck.

The transversal cross-section of the arch forms a vault with varying dimensions. The thickness varies from the central span to the supports as well as transversally from the longitudinal centre to the edge of the shell. The minimum thickness is 0.15m at the centre of the span and the longitudinal axis and the maximum thickness is 0.57m is at the arch supports at the joint with the deck.

The deck is composed of two 0.25m deep longitudinal beams and transversal beams which are placed every 2.40m, upon which a 0.10m thick reinforced concrete slab is cast. The width of the deck varies according to the arch projection, hence the minimum is 4.50m in the span centre and the maximum is 8.40m at the abutments.

The foundation solution differs for the abutments, be they on the right bank (West) or on the left bank (East).

In the case of the abutments on the West bank, the structures are supported upon foundation beams which spread the load over the existing tunnel walls of the underground area of the M-30 ring road. The rest of the abutment is composed of a closed reinforced concrete box which is filled with expanded clay pellets so as not to exceed the admissible load permitted upon the tunnel roof slab.

In the case of the abutments on East bank and taking advantage of the fact that there is more space between the Banks of the River Manzanares and the tunnel walls, a deep foundation solution was opted for, employing 6 micropiles.

CONSTRUCTION PROCESS:

Due to the fact that both Footbridges/Shells are the same, it was decided to construct them employing prefabricated reinforced concrete elements and joining them with welded steel plates in-situ. Each shell was composed of 6 sections and therefore 3 different moulds were needed.

To follow is a summary of the footbridge construction process, once the arch pieces had been manufactured:

1. Execution of micro-piles and abutments.

2. Execution of a temporary peninsula over the river and foundations of the auxiliary structure.

3. Assembly of the first level of the formwork and execution of the steel deck.

4. Execution of the deck slab.

5. Placement of the second level of formwork for the arch assembly.

6. Placement of the segments for the concrete Shell.

7. Placement of hangers.

8. Removal of second level of formwork and loading of hangers.

9. Removal of first level of formwork and temporary peninsulas.

10. Finishes.






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