Bridge Collapse Genoa - Informed Engineering Perspectives

[jim hardy]

It's a few meg pdf file, and in Italian, but has interesting pictures during construction.
Those stay attachments were added sometime after 1968.
Which doesn't really mean a thing .

The stays themselves are encased in concrete that's why they're square. . I don't know what provisions there were for inspection.
There are in that document @nsaspook linked some pictures of them before the concrete cover was put on.

Hey - @ worked first time ! Something has changed !

 

[DrClaude]

A recent newspaper article points to poor maintenance as the probable cause for the collapse:
https://www.theguardian.com/cities/...lapse-and-the-end-of-an-italian-national-myth

 

[alantheastronomer]

This might not have anything to do with the bridge collapse, but I noticed that in cases where old rebar is newly exposed that the rebar is severely rusted out. How would this affect the material's ability to handle stress? How does rebar rust while it's encased in concrete? Does it occur while the concrete is curing? Now that there are coatings to prevent corrosion shouldn't rebar be treated before being used?

 

[Tom.G]

If the old concrete is near salt water there is a chemical reaction between the chloride and the concrete. I don't recall the exact details, someone else here may be able to correct any errors, but here goes.

The chloride reaction weakens the concrete and makes it more hygroscopic. When the absorbed moisture reaches the rebar, it rusts. Since rust has approximately 13 times the volume of the steel, the expansion cracks the concrete, letting in more moisture.

Several years ago I lived in a building where this was happening. The individual concrete stair steps on a steel framework were cracking. The building was built on a concrete deck over underground parking which had the same problem, chunks of concrete were falling off the deck into the parking garage. I moved, the building is still there, so far.

Another example is the Gerald Desmond Bridge in Long Beach, Calif. It is being replaced for the same reason. The temporary "fix" for the bridge was to put steel nets under it to catch the concrete before it fell on the ships entering the port.

There is now an additive for concrete that supposedly avoids that chemical reaction, but it isn't always used; especially for imported products like concrete steps.

Cheers,
Tom

 

[Baluncore]

Since rust has approximately 13 times the volume of the steel, the expansion cracks the concrete, letting in more moisture.

Get with the times. Basalt rebar is stronger than steel, weighs less, and does not rust.
https://basalt-rebar.com/

 

[jim hardy]

I always liked this photo

one bridge tries to push itself together
the other tries to pull itself apart

Both succeeded.

I question the value system of anyone who advocates cheap construction and expensive maintenance.

 

[Tom.G]

Baluncore said https://www.physicsforums.com/threa...ering-perspectives.953337/page-2#post-6141799

Get with the times. Basalt rebar is stronger than steel, weighs less, and does not rust.
https://basalt-rebar.com/
. . . . . . . . . .
An alternate product. Thanks, I learned something new.

The website says the stuff is a natural-fiberglass reinforced polymer but stronger than the fiberglass version.

 

[berkeman]

one bridge tries to push itself together
the other tries to pull itself apart

Both succeeded.

Which is which Jim? Sorry, I'm dense sometimes...

 

[jim hardy]

Which is which Jim? Sorry, I'm dense sometimes.

not at allthe one in compression is still standing . Think Arch.

The one in tension fell down. Think Truss.