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Nanfang'ao bridge collapse Yilan Tiawan
2

Nanfang'ao bridge collapse Yilan Tiawan

RE: Nanfang'ao bridge collapse Yilan Tiawan

Yikes.

You can see one of the tendons fail where it connects to the arch. (from video above)





RE: Nanfang'ao bridge collapse Yilan Tiawan

Yep that tendon.. Pretty much right after that big truck blew by under it. Ohhh and looking again that truck doesn't make it onto the approach. That's one serious injury. Most the others were likely on that ship the bridge landed on.

I could see where that truck loaded the bridge as a rolling point load that set up a traveling wave that went both ways to the ends and rebounded meeting at the middle for a large over-stress. Perhaps if there'd been more traffic the reflections wouldn't have made it back intact or as single amplitude waves?

Could the truck have been overweight or overweight-speed?


It always bothers me when something like a bridge is made with lots of single point failures, no chance of saving the structure or even clearing it of potential victims.

Keith Cress
kcress - http://www.flaminsystems.com

RE: Nanfang'ao bridge collapse Yilan Tiawan

I am being told (by Chrome browser) that the video is private.

RE: Nanfang'ao bridge collapse Yilan Tiawan

The others snapped about 100ms after the first one.

Some idiots are yanking the vids. The last one Little put up is the best one anyway. I screen captured it if it all goes away.

Keith Cress
kcress - http://www.flaminsystems.com

RE: Nanfang'ao bridge collapse Yilan Tiawan

Wild Guess Flag -

I'll throw out a wild guess and say that some detail of the attachment may have allowed corrosion where it was tough to see and that, while the as-built brand new bridge could have survived the loss of any or even several tendons, that corrosion brought the margins down to where they were just barely able to hold the weight leaving the rest ready to domino.

RE: Nanfang'ao bridge collapse Yilan Tiawan

I heard there had just been a typhoon there prior to the collapse.

RE: Nanfang'ao bridge collapse Yilan Tiawan

Some of the cables seem to have broken at their tops, others at their bottoms.

RE: Nanfang'ao bridge collapse Yilan Tiawan

Top cable seems to go first - the lower ends are fairly dark so it's hard to see.

RE: Nanfang'ao bridge collapse Yilan Tiawan

(OP)
The protection of these cables from corrosion is apparently not a trivial matter. The marine exposure in this case would be an obvious consideration. As would the recent earthquake and typhoon of course.

I may be mis-remembering but corrosion was discovered in the cable stays of Tampa Bay's Sunshine Skyway in the mid-2000s. My recollection was that they determined that the chemical environment inside the protective polyethelene ducts around the cables caused corrosion of the stays as the ducts were being grouted during construction. This condition was especially bad near the top where the gasses accumulated as the ducts filled with grout. I wasn't able to find much on this when I went to look it up.

Edit:

Quote (Denial)

Some of the cables seem to have broken at their tops, others at their bottoms.

That reminds me of the first demonstration our instructor performed in high school physics. As a poor dumb farm boy I can still remember the exact moment like magic. A weight was hung from a piece of string and a piece of string hung from the bottom of the weight. If you quickly pulled the bottom string then the lower string would break. If you applied load firmly and gradually to the bottom string, the upper string would break. Not necessarily applicable here but it could be an interesting clue to point of origin that the first cable breaks under static load near the top and the others subsequently break under dynamic load near the bottom.

RE: Nanfang'ao bridge collapse Yilan Tiawan

The bridge cab;es all pass through an opening in the bottom of the arch, which does not appear to offer much in the means of access for inspection.

RE: Nanfang'ao bridge collapse Yilan Tiawan

The wikipedia say the bridge is a steel arch, but the photos of the broken ends look like concrete. Does anyone have any more specific info?

SF Charlie
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RE: Nanfang'ao bridge collapse Yilan Tiawan

JAE's second video shows the arch intact, after the collapse, so it's likely not to be concrete.

It would seem to me that the cables would have to have been grossly under-designed if, even accounting for corrosion, the remaining cables couldn't support the weight after the fire cable failed as evidenced by the near simultaneous failure of the next 4 cables to snap.

image from other article shows weld seams and tearing of the structure


TTFN (ta ta for now)
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RE: Nanfang'ao bridge collapse Yilan Tiawan

Wow! Obviously a "Bridge Too Far"!

Probably will develop into a big coverup...

Mike McCann, PE, SE (WA, HI)


RE: Nanfang'ao bridge collapse Yilan Tiawan

Least what's left seems fairly intact. Especially the arch, so I'd think if failure initiated there as videos suggest it would be fairly easy to establish initial cause.

RE: Nanfang'ao bridge collapse Yilan Tiawan

(OP)
Since the arch is steel then I'm guessing their must be a hatch and an internal passage for inspection and maintenance of the stay anchors. That would have to be there for the original installation I think. There is even a ladder in the @IRstuff photo but I suppose that could just be for changing the light bulbs.

RE: Nanfang'ao bridge collapse Yilan Tiawan

The arch itself is intact, but it came adrift from the wishbones. In addition to the hangers and their attachments, the joint at the arch and wishbone should be investigated. Probably the connections to the abutment as well.

RE: Nanfang'ao bridge collapse Yilan Tiawan

While bridges as I understand it are often designed for the removal of a cable or missing a cable to ensure some level of robustness exists against say traffic taking out one of the hangers. I wonder in these assessments if the dynamic effects of instant removal of the hanger is accounted for in these types of analysis, time history or similar? I'd imagine for example you'd see significantly higher forces as the structure finds the new state of equilibrium. Any bridge guys have any experience in what might be considered best practice?

It would be interesting to see details of how the hangers/strands/tendons were anchored, it almost looks like they 'pulled through' whatever detail was provided setting off a domino effect of overloading all the other end anchorages. If you look at the photos, the one that initially went only has a few loose strands hanging from the top anchorage suggesting it possibly failed inside the arch box girder member

RE: Nanfang'ao bridge collapse Yilan Tiawan

One would hope that the design process accounts for things like cables breaking; I might have expected the design to accommodate half of the cables breaking because of, say, small plane collision, or some-such.

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert! https://www.youtube.com/watch?v=BKorP55Aqvg
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RE: Nanfang'ao bridge collapse Yilan Tiawan

Looks to me that the bridge deck falling pulled out the moorings of the arch; otherwise, the arch might have even stayed put. You can see the arch flex as the deck pulls the moorings, and arch, inward, and then relax when the load is removed. That arch itself appears to have had more than sufficient design margin.

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert! https://www.youtube.com/watch?v=BKorP55Aqvg
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RE: Nanfang'ao bridge collapse Yilan Tiawan

The bridge failed at approximately 10% or less of the design LL - just single typical fuel truck, which is rather difficult to overload. The design should account for a minimum one hanger failure, so the culprit will be likely corrosion of the hangers, or more likely fatigue cracking of the cable due to fluttering and over stiffened connectors at the terminals. Recent hurricane could be the last straw. Fatigue damage to the gusset plates connecting the hangers to the structure is fairly common and was observed on several bridges before. Typical bridge inspection should pick it up, or just notice visible fluttering of the hangers, and investigate further.
With the advance of the computers and design software, anybody could design a bridge - the biggest challenge unfortunately is in the details.

RE: Nanfang'ao bridge collapse Yilan Tiawan

That's a good point about the fuel truck wiktor -- unlikely to be over design weight.

As in many parts of the world, Asia is not immune to the push for faster, flashier designs relying on software output and without a lot of engineering oversight. So I wouldn't be surprised by a root cause that combined poor detailing for access/inspection/maintenance and poor execution of that inspection/maintenance program.

----
just call me Lo.

RE: Nanfang'ao bridge collapse Yilan Tiawan

Sad to see such a disaster happen in my homeland Taiwan..., there are 4 found died and still 2 remained unfounded until now. R.I.P. for the victims.

The authorities said the formal report of this collapse will be published in 6 months the soonest. Some local news reveal that the bridge had been detected with some tendon rusting in 2016, but seems not been repaired properly after that. The root issue still in investigating.

RE: Nanfang'ao bridge collapse Yilan Tiawan

Quote (Agent666)

Dynamic effects of instant removal

A simple, reasonably accurate and usually slightly conservative, way to get a value for this is to assume 100% overshoot. This approach results in
    Ppeak = 2*Pstatic2 - Pstatic1

You raise a good point, and the breaking of the first cable would seem to be a classic case of a sudden (but impact-free) additional load on the neighbouring cables.

RE: Nanfang'ao bridge collapse Yilan Tiawan

Yeah, could be simple progressive collapse. All of them struggling, and then one lets go....

RE: Nanfang'ao bridge collapse Yilan Tiawan

Interesting how the cables on the left seem to fail at the top and cables on the right fail at the bottom with one exception. I wonder if there was already a failed cable or two, only one cable seems to show tension release, wouldn't one expect at least the 2nd failed cable to show some sign of spring back.

RE: Nanfang'ao bridge collapse Yilan Tiawan

Almost like the failure of the center cable allowed a pin to develop at the center of the deck, or lost vertical support at the pin location.

This implies to me that the cables were not properly tensioned, or some had relaxed over time, putting more stress on the cable that failed.

Mike McCann, PE, SE (WA, HI)


RE: Nanfang'ao bridge collapse Yilan Tiawan

(OP)
Hokie's point about inspecting the wishbone connections could also be relevant to the uniformity of tension in the cables. Any change in the shape of the arch might cause tension to concentrate at the ends or the middle strands.

From reports so far, it is looking like the main culprit will be corrosion that was flagged but not addressed.

Again, for inertial reasons, it would not be too surprising if the initial cable failure occurred at the top under near-static conditions and subsequent cable failures occurred at the bottom under dynamic conditions.

RE: Nanfang'ao bridge collapse Yilan Tiawan

There are a few reports going around saying that inspections had found corrosion, but nothing much was being done.

Interestingly it also seems to be used for a light attraction. Weight is probably negligible, but the action of attaching these and then taking them down might cause damage and flexing. There is a bunch of junction boxes at the base of all the cables which indicates use on more than one occasion.

There is also no protection against vehicle impact and again a few reports saying vehicles had run into the cable supports.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

RE: Nanfang'ao bridge collapse Yilan Tiawan

Corrosion seems likely. The curb looks like a good spot for water to pool - I don't see any drainage systems, only some caulking around the cable sleeves.


RE: Nanfang'ao bridge collapse Yilan Tiawan

Interesting view here in looking at the right most exposed cable connection of four small bolts with plate stiffeners.

Seems pretty light considering the possible tension forces involved...

The whole design with a centrally supported superstructure seems highly susceptive to torsional forces from wind and traffic loads, as with the Tacoma Narrows failure, although that failure was solely due to harmonically induced constant speed wind.

Mike McCann, PE, SE (WA, HI)


RE: Nanfang'ao bridge collapse Yilan Tiawan

That's got to just be a light pole, no? I think the red ones are the cables.

RE: Nanfang'ao bridge collapse Yilan Tiawan

You are probably right...

Mike McCann, PE, SE (WA, HI)


RE: Nanfang'ao bridge collapse Yilan Tiawan

This is a pretty good shot of the bridge just before the deck hits the water. The cables on the right look the individual strands snapped from the extra load during the drop, but did not snap like the ones on the left. Interestingly, it looks like the cables are not wound, but simply wrapped with the red stuff.



TTFN (ta ta for now)
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RE: Nanfang'ao bridge collapse Yilan Tiawan

Quote (IRstuff)

Interestingly, it looks like the cables are not wound, but simply wrapped with the red stuff.

The stays are possibly multiple 'single-strand' stays: multiple, 7-wire individual strands (6 wires around a straight king wire), inside a external (RED colored) HDPE sheath. Today this would be probably done with multiple single-strands however, each one individually corrosion protected (i.e. greased and sheathed monostrands, individually stressed and replaceable), making up a stay group, inside a external sheath.

EDIT: added 'multiple' to define that the stay is NOT a singular strand, but a multiple of single strands.

RE: Nanfang'ao bridge collapse Yilan Tiawan

izzotsai (Structural)
We are sad to hear of the lost of lives. We can only hope that lessons will be learned and future lives saved.

SF Charlie
Eng-Tips.com Forum Policies

RE: Nanfang'ao bridge collapse Yilan Tiawan

Probably not related to the failure, but I found it interesting that bwing08's picture shows no traffic barrier to the middle to protect the tendons against any traffic collisions, the kerb is sort of good for nothing in this respect.

RE: Nanfang'ao bridge collapse Yilan Tiawan

I get that the stays are multiple strands of single or multi-strand cables; I just used to seeing them wound, as I think that gives them more uniform and repeatable strength.

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert! https://www.youtube.com/watch?v=BKorP55Aqvg
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RE: Nanfang'ao bridge collapse Yilan Tiawan

Quote (IRstuff)

I just used to seeing them wound, as I think that gives them more uniform and repeatable strength.

Suspension spans typically have their main cables 'compacted' (compression wound) - not common for cable-stayed bridges.

RE: Nanfang'ao bridge collapse Yilan Tiawan

Ingenuity,

So which would you call this one? It is/was an arch, but the hangers perform a similar function to those in a suspension bridge.

RE: Nanfang'ao bridge collapse Yilan Tiawan

hokie66: Vertical hangers to suspension bridges seldom are compacted (wound) - usually only the main suspension cables. I think these cables to the 'hangers' of the arch were detailed like stays. I may be wrong - but the photos I reviewed show no signs of compaction.

Single strands stays (and/or hangers) make replacement easy (relative term!). I am aware of one 300 m (1000 ft) long stay that was damaged by a barge and replaced strand-by-strand using small, light weight equipment.

RE: Nanfang'ao bridge collapse Yilan Tiawan

(OP)
Wires are wound into strands and strands can be wound into rope. There are many options including straight bars, but from the photos we have so far it looks like each hangar consisted of several strands or ropes in an HDPE duct. I also don't see any signs that the strands or ropes were wound or compacted together but I think this is pretty common for hangars. One reason is that compaction and field winding can have negative effects on creep.

Edit: Ahhh, Ingenuity and IRstuff already said most of this. Creep issues and ease of maintenance are the two reasons why the hangars might not be wound.

RE: Nanfang'ao bridge collapse Yilan Tiawan

It seems a concrete-filled steel tube arch bridge.
I guess it fell by fatigue or corrosion of cables , but that's a guess!

RE: Nanfang'ao bridge collapse Yilan Tiawan

I am in a photography group as a hobby and one of the other members uploaded these iages and gave permission for me to show them here.

So they are copyrighted to Kang Lin.



RE: Nanfang'ao bridge collapse Yilan Tiawan

When it failed it almost looked to me like the two legs of the Y were slotted inside the main arch Y piece and just seam welded on but the main connection was internal by simple gravity / weight of the bridge.

Some construction photos or drawings of how those cables were connected inside the arch would shed a lot of light.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

RE: Nanfang'ao bridge collapse Yilan Tiawan

The y-joint may look rusty because of the truck fire.

RE: Nanfang'ao bridge collapse Yilan Tiawan

Oxidation in a fire does that. Most burned cars I've seen look like they have 50 years of rust the day after. As for being roughened it may be a weld joint that was torn apart.

In the Google maps images there weren't rust streaks like normally happens with long term corrosion.

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