Haifax-Dartmouth Bridge Commission

[OldDartmouthMark]

Originally Posted by ns_kid

We're still likely years away, given that changes to the road network and toll plazas will have to be completed.

I would imagine the changes to the network would happen after the payment method has changed, as the toll booths and extra lanes needed to facilitate the slowdowns caused by them, would need to be functioning right up until the system changes over.

Just a guess, but I imagine they could funnel traffic as required temporarily with portable concrete barriers after the changeover, while construction happens outside the barriers.

But yes, either way, this is great news... if and when it happens.

[OldDartmouthMark]

Given the tragedy that unfolded in Baltimore yesterday, I'm hoping that Halifax's bridges, current and future, have sufficient barriers to prevent some of these large container ships from coming into contact with the supports.

Any thoughts?

[Dmajackson]

I had goosebumps yesterday driving over the bridges but what calmed me down was a few facts;

- Our bridges have rock islands around the piers to slow or stop any wayward ships (Baltimore did not)
- Tugboats are required in the Narrows
- HHB is alerted to all container ship traffic and monitors every passage from a spot that they could quickly close the bridge.
- Baltimore's port is busier than ours and only some of our ships go under the bridges. It took 47 years to happen there. Our lower chances would be longer than the lifespan of the bridges.

It's not impossible but it is extremely low chance that this will ever happen in Halifax.

Besides the superstitious person in me believes the literal burying of the hatchet will protect us.

[Dartguard]

Originally Posted by OldDartmouthMark

Given the tragedy that unfolded in Baltimore yesterday, I'm hoping that Halifax's bridges, current and future, have sufficient barriers to prevent some of these large container ships from coming into contact with the supports.

Any thoughts?

I keep an eye on a blog called Shipfax. Mac has watched over the ins and outs in Halifax Harbour for decades. He wrote a very comprehensive note on our situation yesterday. It seems the Halifax explosion has instilled a safety culture here in Nova Scotia.

[Nouvellecosse]

Not only the rock islands, but also only one of the two towers on each bridge is actually in the harbour with the towers on the Halifax side actually being on land (or with MacKay, in the shallow water steps from land). So theoretically having 50% fewer vulnerability points would reduce the risk by 50%. Plus our spans are longer meaning there's more room between the supports. The FKS bridge had a main span of 366m while ours are 426m and 441m respectively. One of MacD's towers is about 20m inland but that still gives both around 50-60m more horizontal clearance which means a greater margin or error.

[OldDartmouthMark]

Originally Posted by Dartguard

I keep an eye on a blog called Shipfax. Mac has watched over the ins and outs in Halifax Harbour for decades. He wrote a very comprehensive note on our situation yesterday. It seems the Halifax explosion has instilled a safety culture here in Nova Scotia.

Thanks for that. A very interesting read.

Sounds like Halifax has robust safety measures in place to help prevent a similar disaster from happening, though still possible, as he sums up:

So the simple answer to the question "Could it happen here?" is a conditional yes. There are many safeguards in place, likely to be strengthened now, so the likelihood of it happening here is slight and probably even less so as time goes on due to a heightened awareness of the dangers.

https://shipfax.blogspot.com/

A couple of thoughts I had:
1) I was aware of the rock islands, but wonder whether they are large enough in diameter to prevent contact from the bow or stern of a large ship, given the overhang on a number of them, plus the possibility of displacement of rocks combined with deformation of the ship's hull as momentum pushes it towards the bridge support columns.

2) Bridge construction: I think most people were surprised at how quickly the Key bridge in Baltimore collapsed into the harbour. I know I was, but with each agonizing sequence played over and over again on the news channels (how many times can we watch those poor construction workers die?), it became clear that the integrity of the truss construction of the bridge was completely dependent upon both support points being intact. I can't say for sure, but I imagine the bridge deck on Halifax's suspension bridges would be more difficult to bring down completely due to their method of support and the nature of suspension bridge configuration.

Anyhow, thanks to all for posting your thoughts on the situation. I was curious as how others in the area were processing this.

[Saul Goode]

Originally Posted by OldDartmouthMark

I was aware of the rock islands, but wonder whether they are large enough in diameter to prevent contact from the bow or stern of a large ship, given the overhang on a number of them

That's much less a concern than you might imagine. Virtually all large commercial vessels have bulbous bows below the waterline which would strike the stone pier before the prow could make contact with any of the bridge structure.

[OldDartmouthMark]

Originally Posted by Saul Goode

That's much less a concern than you might imagine. Virtually all large commercial vessels have bulbous bows below the waterline which would strike the stone pier before the prow could make contact with the bridge any of the structure.

Thanks, I had a feeling that you might know the answer to this.

I will now be able to relax a little more whenever I am driving over the bridge and see one of these behemoths passing underneath!

It perplexes me a little that Baltimore didn't have similar protections in place.

[Saul Goode]

Originally Posted by OldDartmouthMark

I will now be able to relax a little more whenever I am driving over the bridge and see one of these behemoths passing underneath!

It perplexes me a little that Baltimore didn't have similar protections in place.

It may ease your mind a bit more to know that any large ship approaching either of the bridges in Halifax Harbor would be accompanied closely by at least one tug (or more, depending on the size of the ship) which could quickly re-direct the vessel (or at least try to) if allision were imminent. I don't know USCG or Baltimore port regulations, but the two tugs which had been with Dali after she cast off had left her and were returning to port as she approached the Key Bridge, too far away to be of much help.

Nonetheless, there are lots of variables involved in such things, and it's hard to say whether Halifax's bridges could withstand impact of their stone barricades by a, say, 100,000+ ton mass moving at, say, 5 knots. It's not (thankfully) as if they've actually been tested...

[Keith P.]

Originally Posted by OldDartmouthMark

2) Bridge construction: I think most people were surprised at how quickly the Key bridge in Baltimore collapsed into the harbour. I know I was, but with each agonizing sequence played over and over again on the news channels (how many times can we watch those poor construction workers die?), it became clear that the integrity of the truss construction of the bridge was completely dependent upon both support points being intact. I can't say for sure, but I imagine the bridge deck on Halifax's suspension bridges would be more difficult to bring down completely due to their method of support and the nature of suspension bridge configuration.

The Key bridge despite being built in the '70s was an unusual and now obsolete design called a continuous truss. It was what is called "fracture critical" in the loads are carried through the entire structure and it has no redundancy should a single part fail - thus why it is called "fracture critical". We can see the sad results of that in this case. It was quite shocking how quickly the entire structure failed. Suspension bridges like those in Halifax are not immune to failure but would typically not have the sudden result we saw here. Plus as Saul noted the tugs that are employed here every time a large ship passes under our bridges were only used in Baltimore to get the ships off the dock and then peeled away, another unfortunate choice.

I learned this from watching the impressive Jennifer Homendy, head of the NTSB, whose press appearances are posted on YouTube. She indicated that there are a number of such bridges still in service in the US. Also there you will find "B-roll" footage posted by the NTSB on their YT channel of what they found after they arrived. Worth a watch.

[OldDartmouthMark]

Thanks Keith, that's very interesting. I'll check out the videos that you suggest.

[OldDartmouthMark]

A crack was found in one of the trusses on the MacKay (presumably a fatigue crack?). While to me this seems like evidence that it's time to move forward with the bridge's replacement, the article below mentions that they are considering a re-decking project similar to the 'big lift' that was done on the Macdonald? Perhaps it might be necessary to extend the life of the bridge sufficiently until a replacement can happen, given that I don't think there's even a solid plan in place yet.

Emergency repair on MacKay Bridge highlights further work to be done in coming years

Emergency repairs shut down part of the MacKay Bridge in Halifax after a crack was detected in a steel truss.

The issue was discovered Wednesday night by a painting crew. Halifax Harbour Bridges(opens in a new tab) (HHB) says the engineering team was alerted, at which time a partial closure took place in order to get repairs done.

The bridge commission says the crack was smaller than two centimetres in length. No other cracks were found, and it says there was no threat to safety.

Wright says a lot of the work in recent years have been focused on the MacDonald Bridge – mostly notably the ‘Big Lift.’

That project began in 2015 and saw all 46 deck segments replaced over roughly two years.

It’s now something being considered for the MacKay.

“We refer to that as a major rehabilitation project, and we`re evaluating the feasibility of doing the rehabilitation similar to what we`ve done on the MacDonald Bridge,” said Wright. “Although, this particular bridge, the MacKay, was built substantially different. It was built very economically back in the seventies, but we need to do our homework and see if it`s possible.”

[IanWatson]

I don't think a "big lift" for the MacKay would be intended as a holdover until the bridge could be replaced; it would be in lieu of replacement. The evaluation they're doing right now is to determine if it would be better to replace entirely or to do a "big lift".

[OldDartmouthMark]

Originally Posted by IanWatson

I don't think a "big lift" for the MacKay would be intended as a holdover until the bridge could be replaced; it would be in lieu of replacement. The evaluation they're doing right now is to determine if it would be better to replace entirely or to do a "big lift".

That would make sense, though I thought it was previously reported that the bridge was built to minimum standards back in the day, which would be below standard for today. Thus any plans for increased capacity or adding transit-only lanes (LRT?) wouldn't be possible.

Unless they make it a proverbial George Washington's axe, and eventually replace everything piece by piece until it meets any new requirements that are decided upon.

[Haliguy]

I don't think a big lift type project like they did on the MacDonald would be feasible, especially since they will have to replace all the cabling for the suspension as the current suspension would not support new decking. I think replacing the bridge with much larger cable-stayed bridge with 6 lanes, active transportation lanes, and maybe even an LRT line makes a lot of sense. This is especially true if they don't plan on building a third bridge.