Arcos de Alconétar Viaduct (case study)

"The bridge over the Tajo river at Alcántara reservoir is formed by two twin 400 m long structures, each of which is an arch bridge 220 m span and 42.50 m rise. Each of the arches is formed by two box sections braced to each other.

The deck lays on a set of columns uniformly spaced over the whole length of the bridge (every 26 m). The columns are concrete in the approach spans and steel over the arches, rigidly connected to them. Each deck is a continuous composite steel-concrete structure (twin box girders) simply supported on the columns."

Object description

"The bridge over the Tajo river at Alcántara reservoir is formed by two twin 400 m long structures, each of which is an arch bridge 220 m span and 42.50 m rise. Each of the arches is formed by two box sections braced to each other.

The deck lays on a set of columns uniformly spaced over the whole length of the bridge (every 26 m).

The columns are concrete in the approach spans and steel over the arches, rigidly connected to them.

Each deck is a continuous composite steel-concrete structure (twin box girders) simply supported on the columns."

Civil engineering type
:
Road network Bridge
Year of construction
:
2006
Composed of materials
:
Location coordinates
:
39° 43' 10.00" N, 6° 24' 38.50" W
Country
:
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Object analysis

"During construction, the action of the wind triggered a resonant response in the structure in January 2006 (vortex shedding). The structure was just the freestanding arch (the columns had not yet been assembled).

The phenomenon produced considerable damage at intermediate sections of the arch. The movement was an antimetric vibration of the arch in its plane with a frequency of 0,70Hz (second mode).

A dynamic data acquisition system was installed and more than 2.600 wind events were recorded between February and June 2006. Aerodynamic deflectors were installed (see picture below).

They proved to be very effective in suppressing or reducing the formation of vortexes.

However, It was decided to keep the dynamic monitoring system with the bridge opens to traffic to survey the structural behavior under the wind action. The opportunity was taken to obtain information regarding joint movements and other environmental actions.

The total amount of sensors is 54 (thermometers, anemometers-vanes, accelerometers, and lasers for joint displacements)."

Case type
:
Research

Object state

The maximum vibration recorded since the deflectors were installed is 0.060g (± 37mm amplitude), caused by an average wind speed of 29km/h and associated with a frequency of 0.64Hz. That movement is 20 times less than that estimated in the structure before the installation of the deflectors.

Observed deterioration processes
:
Observed damage types
:
Performance indicators
:
Displacement, Dynamic response (acceleration/damping/frequencies), Other actions (wind/temperature/earthquake)

Images

Alconetar 1.png
Alconetar 2.jpeg
Alconetar 3.jpeg
Alconetar 4.jpeg
Alconetar 5.jpeg

Documents

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This case study was contributed by Silvia de la Orden of . Last edited by technical staff.