Ontario Cable Stay Bridge Failure

[Brad805]

Some engineers in Spain are going to have an interesting few days of review/discussion ahead of them. 2' of movement seems to suggest something was fundamental was missed. It is posted in the failure section too, but it would be interesting to hear some comments from people that design cable stay bridges.

Link to news story:

http://www.cbc.ca/news/canada/thunder-bay/nipigon-river-bridge-closed-transcanada-1.3397831

 

[boo1]

looks cold
thermal movement?

 

[racookpe1978]

Looks like thermal movement "shortened" the longest cables on the ends, which lifted the (somewhat flexible) ends of the bridge platform up (off of the static bridge end platform).

Did the other end lift up as well?

At this end, there seems to be one platform segment that did not move up. A different support piece spanning a gap between the dirt-supported roadway and the first cable-suspended roadway section?

 

[Brad805]

I believe the other end lifted as well. I agree it seems to be cable shrinkage, but that seems a fundamental consideration if you open the bridge code and look at the degree days where your structure is being built. Much of Canada is very cold in the winter.

 

[DETstru]

Thermal issues seem pretty plausible, especially since the bridge was just built.

The article claims a "gust of wind" but I find that very unlikely.

 

[LittleInch]

This is a curious design and construct though. See

http://www.enl-tbay.com/NipigonBridge/plans-drawings.html

It looks like one side is longer than the other and the final design is to have three towers and cable systems, but they opened one half while they demolish the old bridge to make way for the second half.

This picture looks like they have just weighted it down with a lot of concrete to get it back in place....

http://topoflakesuperior.ca/north-superior-news/nipigon-river-bridge-is-closed-in-both-directions/

scroll down to the 4th photo

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

 

[bridgebuster]

In a cable stayed bridge Unequal spans = potential for uplift under certain loading conditions. The photo caption said "mechanical failure" I wonder if the tiedowns failed.

 

[Brad805]

Would this would be the start of the tiedowns?

 

[rb1957]

Littleinch's links were good. yes, the span are slightly different in length, but the cable system looks symmetric.

Looking at the stack on concrete, I wonder if one cable system and bridge deck gave out (allowing them to jury rig something to get the other side of the bridge open ?

I'd be surprised if thermal expansion/contraction wasn't considered in the design. It can't be a surprise that it gets cold in Canada in winter !



another day in paradise, or is paradise one day closer ?

 

[boo1]

Update – 18:33EST – Thunder Bay Superior North MPP Michael Gravelle reports that he is being informed that the bolts that connected the bridge have broken.

http://www.netnewsledger.com/2016/01/10/nipigon-bridge-heaves-cold-weather-impact/

 

[boo1]

http://www.enl-tbay.com/NipigonBridge/plans-drawings.html

 

[Brad805]

Now how to relieve the cable stress to replace/add bolts unless mother nature is helpful.

edit: The MoT had some spare blocks to re-open.

http://www.cbc.ca/news/canada/thunder-bay/nipigon-bridge-transcanada-update-1.3398207

 

[boo1]

pictures LittleInch linked show they tried to load the bridge with barriers

 

[KootK]

What does it mean for a pile supported cable-stayed bridge to "heave"? And which bolts? Darn lay people.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[racookpe1978]

Well now, as a temporary measure you see, ya load down one end of the bridge with weights until the deck is level with the roadway, but leave a lane open. Load up the traffic on that end, then drive the traffic over the bridge to the far end (goinguphill just a little bit obviously) that lowers down the far end, and you clamp that fat end down until the traffic drives off. Then you release the far end, it goes up, the near end goes down, and you repeat. Now, if traffic had to go both ways, you just alternate ends: one high, one low, then swap until the weather warms up and both end cables expand far enough.

Ought to work, right? 8<)

 

[Ingenuity]

Brittle fracture of the pre-loaded vertical hold-downs on the shorter span end, resulting in abrupt uplift then downward crashing of the deck superstructure end onto the abutment?

Some eyewitness accounts report that the end of the bridge abruptly uplift then crashed downward, reported like a buffet/burst of wind.

From Link

"As we turned [onto the highway], we saw the whole bridge — a kind of big gust of wind came underneath it and blew it up and then it came back down," she said, adding it shifted by about half a metre.

"We watched two pickup trucks come flying over. … They didn't see us, didn't hear my horn honking, and they flew over and smashed their front ends down on the cement."

There is a photo that I saw (but cannot now locate) that shows some acute deflection in the subject span adjacent to the abutment.

 

[Ingenuity]

Deflected span after failure and BEFORE kentledge:

Same span AFTER install of concrete barrier kentledge:

 

[bowlingdanish]

What's the load path in a cable stayed bridge? For uneven spans, is the central pier designed to cantilever in bending due to more tension on one side? Maybe the central pier wasn't stiff enough so the all the load was transferred through the abutment opposite abutment in uplift. But I don't know anything about how cable bridges work.

 

[LittleInch]

I'm wondering if the fact that the bridge is only half built had anything to do with it. The complete design is three sets of cables and two double lane decks so presumably the middle set are twice as big to hold the central piece and two decks, but they have opened the bridge with only one half built while they demolish the old bridge on the south side.

There must be some sort of differential loading / response here and maybe they didn't analyse the single deck operation quite as much as the whole bridge?

I'm pretty sure it is the "short" side which has jumped up, which tends to show that the uplift force has not been well anchored down.

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

 

[DETstru]

I'm not a bridge guy, just wondering how thermal effects are typically handled in cable-stay bridges.

So in an unrestrained condition, when the cables shorten due to lower temperatures the bridge deck would go up (most notably at the ends), correct?
Were the bolts that "broke" used to hold the deck at the same elevation as the rest of the roadway as the cables shrank? Essentially taking care of thermal effects by increased stress in the cables and bolts?