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Originally posted by 1KIKI:

I read an interesting article about the foibles of steel-reinforced concrete: to wit, concrete is porous and transmits moisture, and rebar rusts, and when it rusts, it expands. So, in general, steel-reinforced concrete has a shelf-life beyond which it needs to be torn down and rebuilt.

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Originally posted by 1KIKI:
Death Toll Approaches 40 in Collapse of Cable-Stayed Bridge in Italy

Modern technology has not come up with answers except high-tech, expensive, and diligent monitoring. And all that does is hopefully prevent unexpected failure - so that at least you might see it coming.

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As of the collapse of the bridge, only pillar 11 had been internally inspected in the 1990s, showing severed and oxidized strands. About 30% of the tendons had corroded away.
On pillar 9 (the site of the collapse) they could identify only four global modes (of vibration), and the deformations of two of these identified modes were not fully compliant. Modal frequencies were more than 10% different, specifically on the southern stays. As little as a 2% shift could represent severe damage.
It has been reported that the southern stays (the bridge suspensions that run diagonally from the towers to the road bed) gave way explosively due to corrosion and damage.
In July 2019, a video showing the fall of the bridge was made public. It originated from the nearby Ferrometal company cameras, showing that both southern stays and locally attached road sections at pillar no. 9 started dropping virtually simultaneously. From the movement of the top cross-beam, it appears the tension cables of the south-eastern stay gave way.

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Originally posted by 1KIKI:
The problem is that there is no effective way to repair the stays, beyond external supports and patches.

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