Aug 15, 2018

A 50-year-old cable-stayed concrete bridge, one of the first of its type in Europe, collapsed August 14 in the Italian city of Genoa. Early reports say that multiple fatalities occurred when the bridge fell during a heavy storm.

Image taken August 14 showing collapse of a portion of the Polcevera viaduct in Genoa, Italy.
 

The bridge — which carried the A10 motorway across a river, railroad tracks and numerous structures — was built between 1963 and 1967 by the Italian Society for Water Pipelines. It was designed by Italian engineer Riccardo Morandi.

The Polcevera viaduct had a length of 1,102 m (3,615 ft), a height of 45 m (148 ft) on the road level and three reinforced concrete piers that rose 90 m (300 ft) in height. The maximum span was 210 m (690 ft).

Image of the viaduct prior to its partial collapse.
 

Local news reports said that the bridge was under repair. The country's transport minister said that the bridge had shown "signs of problems" in the past.

Major repairs were made to the bridge between 1992 and 1994 after inspections showed that concrete stays had degraded, particularly around a bridge element known as pylon 11. A general restoration project was taken on, including structurally reinforcing the concrete stays of pylon 11.

The cause of the bridge's collapse remains under investigation, and there was no indication as to whether the 25-year-old repairs were a factor.

The repairs added both long and short cables for each concrete stay. The long cables were located along the vertical faces of the concrete stays and were linked to them by means of steel ties that were fixed on the top of the pylon to steel caps. They were also fixed under the bottom of the transverse beam to steel plates.

Image of the viaduct prior to its partial collapse.
 

The short cables were located on the sub-horizontal faces of the concrete stays and were fixed to the lower parts of the concrete stays by way of steel checks.

A report compares the long cables to the main tendons of the concrete stays and the short ones to the secondary tendons.

In the repair design, the short cables also had the temporary function to bear all the load of the bridge as the old strands were cut away. More permanently, they helped to regulate the stress level in the concrete stays.

The replacement stay cables were made with unbonded strand encased in an high-density polyethylene duct. Their design allowed for them to be checked, tension regulated and replaced either altogether or strand by strand.

Part of a Morandi-designed bridge in Venezuela, which was built using a similar design to the one in Genoa, collapsed in 1964 after being hit by a ship.

 

Reference:
https://insights.globalspec.com/article/9596/fatal-italian-bridge-collapse-is-under-investigation

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Keywords: Italian Bridge Collapse Construction

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