Bridge 3D Survey

3D survey and structural deformation analysis of Axios river bridge at Northern Greece

Purpose

Close to the city of Thessaloniki, in Northern Greece, the Patras – Athens – Thessaloniki – Evzoni (P.A.TH.E.) Motorway, which is the main from South to North road transport axis of Greece, crosses the Axios river, one of the largest of the wider Balkan area. The crossing occurs with two long bridges, each carrying one carriageway. The southern bridge was constructed first about 40 years ago, while the northern one is much newer.

The southern bridge is 780 m long with 25 spans, built from armed concrete and has begun to show noticeable damages through time. The Greek Ministry of Environment, Planning and Public works assigned a project to check the bridges efficiency. Within the frame of this project, a complete 3D survey and deformation analysis was required.

Project tasks

  • Establishment of geodetic network (GGRS’87).
  • TLS survey with Optech ILRIS3D:
    • 6 scanning positions (from newest bridge)
    • Average resolution 2-3 cm
    • Georeferencing: 6 scanning stations, 12 circular (d:50 cm) targets, additional “natural” control points
  • Conventional survey for remaining details (southern side).
  • Basic processing of TLS data and other measurements.
  • 3D features collection (deck geometry, piers, road level, etc).
  • Geometric evaluation and deformation analysis.

 

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Results – Conclusions

To better evaluate the 3D deformations of the bridge components, the results were presented as a longitudinal section of all examined deck edges, as well as angular measurements for each pier along the 3 axis, to demonstrate possible pier rotation. The evaluation showed insignificant rotations for the piers, but surprisingly revealed considerable subsidence of all piers, except those which were founded in the river’s bottom. Different type of foundation was identified as the most possible cause for this problem. Corrective actions are being studied to prevent further damage and deformation of the bridge’s structure.

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