How can the Nipigon Bridge be fixed?

[towerguy]

Any theories why the Nipigon Bridge failed?

I can only assume the steel cables contracted in the cold faster than the concrete contracted and that split the bridge.

How do you fix this bridge?

When the temperature gets warmer the steel cables will expand and the bridge will settle. What about next winter? Same situation again?

What temporary fix are they doing right now? Can the cables be adjusted for tension?

I assume they are relaxing the tension in the cables to bring the bridge back down but wouldn't that put more pressure on the structure?

And what about the other half of the bridge that hasn't started construction yet until the old bridge is completely torn down? That couldn't possibly use the same design could it? That would be insane.

[sonysnob]

Two lanes of traffic should be re-opened on the bridge by the end of the month:

http://www.mto.gov.on.ca/english/hig...es/index.shtml

[towerguy]

It's hard to believe that small Tie down system can outpull the upward pressure of all the steel cables hanging down from the tower. I guess they're banking on the warmer weather causing the steel cables to expand and exert less upward pull on the bridge deck which is what caused the deck to lift.

Can those steel cables be adjusted in strength?

What changes in design have to be incorporated in the twin that will be built right beside the current bridge?

[sonysnob]

Originally Posted by towerguy

It's hard to believe that small Tie down system can outpull the upward pressure of all the steel cables hanging down from the tower. I guess they're banking on the warmer weather causing the steel cables to expand and exert less upward pull on the bridge deck which is what caused the deck to lift.

Can those steel cables be adjusted in strength?

What changes in design have to be incorporated in the twin that will be built right beside the current bridge?

The cables contracting in the cold was quickly ruled out as the cause of the failure of the expansion joint. The cables were, and are still, properly tensioned. The anchor bolts at the western touch-down of the bridge were not up to the task. This alternative anchor system will be -- at least for the interim. They'll probably devise a more permanent repair in the future once they know exactly what caused the anchor bolts to snap.

[ScreamingViking]

Originally Posted by towerguy

It's hard to believe that small Tie down system can outpull the upward pressure of all the steel cables hanging down from the tower. I guess they're banking on the warmer weather causing the steel cables to expand and exert less upward pull on the bridge deck which is what caused the deck to lift.

Don't forget the cables are largely supporting the weight of the bridge. I really doubt the engineering behind this was not done properly, and I bet it in the end it will come down to a flaw in the materials that were delivered.

Still, while this bridge will be nice to look at, I don't understand NOT going with a simpler design, such as that which served the need for decades.

[towerguy]

so the Anchor bolts is the Expansion joint that was being yakked up by the media? I see expansion joints on bridges everywhere.

So I guess the cables did contract in the cold but the anchor bolts should have been strong enough to keep the bridge from lifting.

How does that tie down system under the bridge girder work?

[sonysnob]

Originally Posted by towerguy

so the Anchor bolts is the Expansion joint that was being yakked up by the media? I see expansion joints on bridges everywhere.

So I guess the cables did contract in the cold but the anchor bolts should have been strong enough to keep the bridge from lifting.

How does that tie down system under the bridge girder work?

The cables did not contract more than expected in the cold. The cables are, and have always been, properly tensioned.

The eastern span of the bridge is longer, therefore heavier than the western span of the bridge. The anchor bolts at the western edge of the bridge are designed to restrain the western, and lighter, bridge span to the western abutment. So in this case, the western bridge system is designed to hold the bridge down, not keep it up. Those bolts failed for reasons that are still unknown, which caused the lighter western span to uplift.

Following the expansion joint failure, the media very quickly surmised that the failure was related to the cables contracting in the cold weather. That was not accurate. If the cold weather was indeed a factor, it would have been because the steel bots that were used to restrain the western abutment were not manufactured properly causing them to become too brittle, and lose their tensile strength. But, that is is just one possibility of why the bolts failed. Until the laboratory analysis has been completed on the bolts, we won't know exactly what caused the bolts to shear.

[vid]

Cable stay bridges are the most common type of large bridge in cold climates. Vladivostok has two or the largest cable stay bridges in the world (including the largest) and a very similar (though slightly wetter) climate than Nipigon. Surgut, Russia has a massive cable stay bridge and their average annual temperature is -2°C. (Nipigon's is 3°C.) Deh Cho bridge in Northwest Territories is also a cable stay bridge.

The cables did exactly what they were supposed to do: when one side of the bridge failed, they prevented the road deck from falling down and killing people. No one was injured as a result of the bridge failure.

My theory on why they chose this design of bridge is because 1: Michael Gravelle has fought for this highway project during his 20+ years as MPP and it's the "crown jewel" of the project, and 2: Ontario doesn't have many bridges like this, so it is a way to say "Look, Ontario can build these too!" Except, well...

[towerguy]

There's 3 Cable Stayed bridges in Vancouver, the new Port Mann crossing, that one is huge, the Alex Fraser Bridge and the Golden Ears bridge. Are you sure the bridges in Vladivostok and Surgut are bigger than the new Port Mann in Vancouver? The new Port Mann is 10 lanes wide. So these bolts that failed, are these bolts in the expansion joint or in the anchors? I assume cause the anchors failed the expansion joint snapped.