Bridge Collapse in Dresden 1

[Retrograde]

The partial collapse of the Carola Bridge disrupted major traffic artery in Dresden and left the city without hot water.

A bridge carrying a tram line partially collapsed in the German city of Dresden. The Carola Bridge is one of the four bridges crossing the Elbe River.

The emergency closure of the 100-metre-long bridge resulted in severe disruption of the city's traffic, including the tram system and boat traffic. The bridge is a major travel route between Dresden's Old Town and New Town, and is used by motorists, pedestrians and cyclists.

https://www.euronews.com/my-europe/2024/09/12/major-bridge-partially-collapses-into-river-in-dresden

 

[3DDave]

The distress was plainly visible to people who did not understand what it meant. On top of that people are generally insensitive to gradual change. There's a bump; there has probably been a bump of some sort for as long as the riders have used it. Is it a bigger bump or is the rider more sensitive to it?

The nice thing about space based measurements is that an entire city can be measured at the same time and every measurement stored for quantitative comparison.

A different problem is when authorities ignore distress, like that on the Fern Hollow Bridge where the supporting columns had rotted through and the city was notified of the problem and, obvious from the temporary repair, also knew that a significant amount of the bridge had become rust flakes.

I think there are adverse incentives where the Feds will step up with funding, taking the burden of replacement and maintenance off the state and local budgets. Since members of state governments are almost 100% immune from legal judgments against them, why would they complicate their lives if the problem is self correcting?

 

[Sym P. le]

Using the information from the Casey Jones video, it appears something happened in Dec 2022 when there was a hard freeze (-11C) followed a week later by abnormal warmth (+17C). The displacement of the red line assumed an abnormal curve in the following weeks and then a steady trend of downward displacement until collapse. Maximum downward and upward displacement was recorded at approx. 60 mm just prior to collapse.

weatherspark.com

In the last video frame prior to collapse, downward deflection (left side of image) was obvious both north and south of the bridge support.

 

[simplebm]

I don't speak German but I was watching a video on this failure. The video showed post-tension ducts with what appeared
to be reinforcing bars instead of strands. See attachment. Does anyone have any knowledge of this?
[URL unfurl="true"]https://res.cloudinary.com/engineering-com/raw/upload/v1728328475/tips/Carola_Bridge_screen_shot_wkxurx.rtf[/url]

https://www.youtube.com/watch?v=hEff9ak4osM&t=429s

 

[Sym P. le]

The transcript can be copied and pasted into Google Translate. Here are some excerpts.

6:59. Here on this side the rod is in great shape and has no damage whatsoever. A few centimeters further on it has almost no cross-section. You can see here that this is called pitting corrosion. The rod is basically almost corroded away in one place.

That is also the dangerous thing about this form of corrosion. If you only open a small window, you can't really see it. If you open it here by accident, everything looks fine. 20 cm away it looks like this. That makes it very difficult to assess.

The material in question is Hennigsdorf prestressing steel, the western equiv. being Sigmar Oval steel. It is "very high-strength due to the tempering process."

They boast of their response efficiency, with 12 machines here within 6 hours and another the next morning.

Regarding the Hennigsdorf prestressing steel,

16:21. The Otto Mohr Laboratory at the TU Dresden is one of the most modern testing laboratories for the construction industry in Germany. Dr. Silke Scheerer and her team have been researching this special metal there for years. We have already taken a lot of samples in the lab, especially from old stocks, and we took samples from demolished buildings. Simply to generate more knowledge. In most cases we had very good strength values, very good elongation values, but not in every case. In other words, it has the potential to fail on the inside, but that is not the norm. The Carola Bridge is obviously an exception. The prestressing steel, which had been damaged by corrosion, failed without warning from one moment to the next.

Studies from 2023 indicated the condition of the structure was in keeping with its age but was in need of repair, as was planned.

 

[3DDave]

Are there acoustic methods to verify the condition of the rods? I would expect that an input impact would result in a sound transmission and that sound would not pass undisturbed if there was a reduced section; there should be a notable reflection from such a serious defect.

 

[simplebm]

Thank you Sym P.le. So I guess the Hennigsdorf prestessing steel,which is solid bars as opposed to wire strands, was used. It is hard
for me intuitively to understand why solid bars would be used instead of wire strands that are universally used for post tensioned concrete.
The strands stretch easily and are easily gaged to loads, whereas the solid bars would seem to be difficult to gage their effect. I guess it worked all these years, until now.

 

[3DDave]

Bars are easier to tension; they are more difficult to transport than coils of cable. Cable has complicated response to tension loading while bar is more predictable.

 

[IDS]

For anyone wanting a translation:

In the information section under the video, click on "more", then scroll down to the bottom and click "show transcript".
Right-click on the transcript and select "translate to English".
This will convert the transcript to English, and the subtitles will also be translated.

Doug Jenkins
Interactive Design Services

http://newtonexcelbach.wordpress.com/

 

[hokie66]

Whether cable or bars, the issue with this bridge was apparently corrosion. Does anyone know what was supposed to protect the reinforcement?

 

[Sym P. le]

I'm wondering why the samples being shown appear to have inadequate grout.

 

[hokie66]

Sym P. le,
Your question would assume bonded post-tensioning, with inadequate grouting. Do we know that, or was it an unbonded system, with inadequate protection?

 

[Sym P. le]

At 9:29 it appears the sample is unbonded and the duct is so tightly packed with steel that grout fill would be difficult to guarantee. At 9:43, the sample is only partially grouted.

No further details are offered so we'll just have to wait.

 

[hokie66]

'Unbonded' typically means without grout. So if that is the case, it would have required protection by other means.

 

[Ingenuity]

The tendons were bonded (grouted) tendons using HENNIGSDORF prestressing steel (oval-shaped tensioned wires) that have a history of stress corrosion cracking (SCC).

Voids in the grout (to bonded tendons) is still a problem today unless specially formulated grout and vacuum-assisted grouting techniques are used.

I would be interested to see the stressing anchorages and wedges used to these oval wire tendons.