Baltimore Bridge Collision and Collapse

[Capt. Eric]

Anything less than 3-4 times the ship's beam is going to be a problem. Not to say they can't fit some good fenders at the current spacing, but they can't go less than 500-600 feet clear. Even that might give them some pause. We have a project currently running where a barge is being taken through an opening 1.5 times the beam. That took two tugs tied up hard to the barge and a lot of simulator time to make it work.

If there's any more restriction to the channel than what's there at present, the pilots will need a say.

Regardless, I'm sure the pilots will be asked for their opinion. Doesn't mean anyone will listen to it, but they'll be able to comment I'm sure.

Clearance. Oh boy. That's a whole different subject. But I can tell you that a ship doesn't need much, if push comes to shove (literally). In the mid 90's I worked on a tanker (about 660ft long) that shuttled fuel from Texas to the north east. (There's that Jones Act again!) In Boston we'd discharge to 3 docks in East Boston up the Chelsea Creek. One of the 3 bridges we passed under was a draw bridge, on a bend. I think we had about 4 feet on either side. Also had to be within a certain narrow window of draft (maybe about 6 feet?). Too deep and we go aground. Too shallow and we're too high and hit the draw bridge (it didn't quite go straight up). Of course we did this with 4 tugs. Two guided us up to the last moment, and 2 went ahead and "caught" the bow after it came out. Timing was everything! I've also been through the Panama Canal locks (old ones) with as little as 1.5feet on either side. Some interesting hydrodynamic forces come into play there. That's another story for another time.

Point being, wide openings are great, but not essential. My guess is that from now on, tugs will be required alongside until the ships pass that bridge. Many ports have that requirement at certain points. Slows the ship down a little, and costs more to keep the tug with you, but I think we'll see that happen, unless the new bridge span is well beyond the channel limits.

 

[wsume99]

Learned something new today. According to this article construction companies are required to have a safety boat in the water whenever workers are over or near water. Looks like there was not one present at the time of the collapse. This seems to be a rule that is often not followed or enforced but given the outcome here this infraction may not be overlooked.

 

[boatgeek]

Learned something new today. According to this article construction companies are required to have a safety boat in the water whenever workers are over or near water. Looks like there was not one present at the time of the collapse. This seems to be a rule that is often not followed or enforced but given the outcome here this infraction may not be overlooked.

I went down a little rabbit hole on this one. The AP article above cites an OSHA ruling that more or less says that the skiff is required whenever people are working above water. The footnote quotes another ruling that goes into a little more detail about when a skiff is considered to be available. That makes it pretty clear that there should be a skiff in or near the water, with an operator on duty at all times.

The AP article quotes lawyers saying that a skiff would have heard the ship's mayday calls and coordinated with the bridge crews. However, the OSHA guidance doesn't require that the boat be manned, just that the operator is on hand. Nor does the boat's engine or radios have to be running, just that it needs to be ready to go. It's also entirely possible that there was a skiff on site, and it happened to get taken out by the falling bridge. So I think that the journalists and lawyers are reaching a bit. We don't really know whether a boat would have helped or not, or even if one was present. We do know from previous lawsuits that the construction company used skiffs on other bridge jobs.

If the construction company didn't have a skiff on site, I'm sure they'll be fined.

 

[cls]

That makes it pretty clear that there should be a skiff in or near the water, with an operator on duty at all times.

I'm not volunteering for the job of being the guy in the John boat when the bridge is falling down on top of me from 180 feet up.

 

[Greg Furtman]

I will never set foot on a cruise ship. Giant petri dishes.

Yup. I hate crowds. The last think I would do is be on a large cruise ship.

 

[bjphoenix]

Not sure the span needs to be wider, MV Dali was 158 feet across the beam, the center span was something like 1200', thats 500' approximately of clearance on either side of the ship. If Dali had been transiting the span sideways then there would have been very little clearance (Dali is 948ft long roughly). This was an accident....so lets make something bigger just because even if its not needed. On the other hand I can see changing the design from a Continous Truss (what the bridge was) to a two pier cable stayed span so that in the event a pier was hit only half the span would have been lost, and possibly fewer lives. These ships are large but when working as they should they are also surprisingly maneuverable for their size.

I'm not real knowledgeable of the details of their channel but if the bridge support piers are farther from the sides of the channel it would be easier to build up rock barriers around the bridge supports, a ship with larger draft couldn't make it to the bridge support without running aground.

 

[jderimig]

How about piers on the shore? Or instead of dophins, put the earth just inside of the piers with a wider span. The earth seems to do a good job of stopping a ship.

 

[boatgeek]

How about piers on the shore? Or instead of dophins, put the earth just inside of the piers with a wider span. The earth seems to do a good job of stopping a ship.

More span = more strength required of the bridge to hold up traffic = heavier bridge = more strength needed to hold up the bridge itself... Not to mention that you would need to rebuild the bridge pier foundations, adding time and money. It's all in the tradeoffs.

 

[NTP2]

More span = more strength required of the bridge to hold up traffic = heavier bridge = more strength needed to hold up the bridge itself... Not to mention that you would need to rebuild the bridge pier foundations, adding time and money. It's all in the tradeoffs.

The rocket equation but for bridges…

 

[boatgeek]

The rocket equation but for bridges…

That's a pretty good analogy. Unlike rockets, though, bridges aren't subject to the tyranny of the rocket equation. If rockets are North Korea, bridges are more like Switzerland. Highly ordered, don't step too far out of line, but you do get some creativity within the limits.

 

[Peartree]

That's a pretty good analogy. Unlike rockets, though, bridges aren't subject to the tyranny of the rocket equation. If rockets are North Korea, bridges are more like Switzerland. Highly ordered, don't step too far out of line, but you do get some creativity within the limits.

But it is subject to the tyranny of "strength of materials." That's usually what limits the span of everything from backyard decks to building interior supports to bridges. Engineers and architects can get really creative but still can't exceed the strength of the materials that they're building with.

 

[bjphoenix]

But it is subject to the tyranny of "strength of materials." That's usually what limits the span of everything from backyard decks to building interior supports to bridges. Engineers and architects can get really creative but still can't exceed the strength of the materials that they're building with.

I might have said "tyranny of gravity". So does Chaos.

 

[cwbullet]

I might have said "tyranny of gravity".

Gravity definitely always wins.

 

[bjphoenix]

The engineering question I have is "Why all four of the concrete legs of the bridge support broke at the same height above the pier base?"

I haven't gotten a good look at the supports but what I've seen shows 4 columns in pairs, each pair of columns leans together so they push against each other at the top. My understanding is the deck of the ship hit the 2 columns on the ship side, maybe halfway up the columns, and broke them. Those 2 columns would have broken at the point of impact and at the base. Once those 2 were broken then the weight of the bridge acting on the other 2 columns would have caused them to break at the bottom also.
Reinforced concrete elements might look nice and monolithic like a big block of plastic but the strength relies on the reinforcing within and the reinforcing can vary at different places in the concrete. Not only can the size and quantity of bars change, the way that the bars splice can also affect the strength at some locations. I've read that the columns supporting the bridge were hollow which throws in another variable- the hollow interior might have stopped at the base near where the columns broke.

 

[Tech 68]

Obviously a coincidence...

 

[Sooner Boomer]

That one's not Boeing's fault...

 

[boatgeek]

Obviously a coincidence...

Not doubting that it happened, but the only news stories about this are (a) not on gCaptain, and (b) quoting this tweet. I would love to see a story from another source.

 

[Sooner Boomer]

Not doubting that it happened, but the only news stories about this are (a) not on gCaptain, and (b) quoting this tweet. I would love to see a story from another source.

https://nypost.com/2024/04/07/us-ne...dge-days-after-baltimore-key-bridge-disaster/

 

[boatgeek]

https://nypost.com/2024/04/07/us-ne...dge-days-after-baltimore-key-bridge-disaster/

It's weird that gCaptain doesn't have anything up on the story yet since they apparently broke the news. The story has filtered out to more news organizations, but all are basically on the same template as the Post article linked above. The Post and other published stories say that the initial three escort tugs were enough to keep the ship under control until its propulsion power was restored, and don't mention the extra three tugs that the tweet above discusses.

Worth mentioning that the escort tugs did their job and kept the ship in the channel.

 

[Capt. Eric]

It's weird that gCaptain doesn't have anything up on the story yet since they apparently broke the news. The story has filtered out to more news organizations, but all are basically on the same template as the Post article linked above. The Post and other published stories say that the initial three escort tugs were enough to keep the ship under control until its propulsion power was restored, and don't mention the extra three tugs that the tweet above discusses.

Worth mentioning that the escort tugs did their job and kept the ship in the channel.

Not newsworthy. No death or destruction. No spectacular video. Tugs, pilots, and crew did their jobs.
Nothing to see here. Move along.

 

[teepot]

Ah, but it was a Chinese ship. Probably bent on sabotage but the tugs stopped it.

 

[NTP2]

Ah, but it was a Chinese ship. Probably bent on sabotage but the tugs stopped it.

 

[Greg Furtman]

Just posted.

 

[Marc_G]

I'm a Baltimoron, living for a few decades elsewhere. I flew back for a college reunion on Friday. Approach path to BWI followed the river/bay right past the bridge site, so I got to see it from a good vantage with my own eyes. All I can say is "wow." There's something more visceral when you see it up close for real.

 

[teepot]

I was looking at You Tube and found this. New pictures of the Dali. And Navy Sonar images. There are some pictures of the bridge before the accident. A question for you engineers. The way the bridge sits on the supports doesn't look very solid. I'm sure there is a reason for this. But I can't think of why. Also some of the video shows the bridge pillars and they are hollow. Why? After the diver goes into the water there is video of the visibility. Or lack there of. In the stills I took you can see the You Tube channel info. It is worth a look. There are two videos I watched. The Dolphins are visible in a couple of pictures. Why only one and why are they so far from the bridge. The ones I've seen are sets of three before the pylon and a lot closer. The guy doing the video said the channel was 50' deep and the Dali had a 49' draft. How does that work together?

 

[NTP2]

I was looking at You Tube and found this. New pictures of the Dali. And Navy Sonar images. There are some pictures of the bridge before the accident. A question for you engineers. The way the bridge sits on the supports doesn't look very solid. I'm sure there is a reason for this. But I can't think of why. Also some of the video shows the bridge pillars and they are hollow. Why? View attachment 639753View attachment 639754View attachment 639755View attachment 639756View attachment 639757View attachment 639758View attachment 639759View attachment 639760After the diver goes into the water there is video of the visibility. Or lack there of. In the stills I took you can see the You Tube channel info. It is worth a look. There are two videos I watched. The Dolphins are visible in a couple of pictures. Why only one and why are they so far from the bridge. The ones I've seen are sets of three before the pylon and a lot closer. The guy doing the video said the channel was 50' deep and the Dali had a 49' draft. How does that work together?

I think I can answer the sitting question, it’s probably because a lot of stuff is stronger when under compression (force top and bottom), imagine trying to smush a steel plate versus trying to snap it.

 

[Greg Furtman]

Here's the video that the above pics are from.

 

[Tractionengines]

The way the bridge sits on the supports doesn't look very solid. I'm sure there is a reason for this. But I can't think of why.

Expansion and contraction with temperature change, and load changes. Almost all bridges, or bridge sections, are fixed rigid at one end. The other end is on a roller, slip plate, hinge (of some type), etc. A "rigid" bridge will quickly fail from internal stresses. Bridges NEED to have some "flex" in them to allow stresses to spread out evenly and not concentrate.

Also some of the video shows the bridge pillars and they are hollow. Why?

Most strength in pillars/columns is in the wall. A hollow column is stronger than a solid column, because of how stress concentration, and load disperses around it.

 

[boatgeek]

A question for you engineers. The way the bridge sits on the supports doesn't look very solid. I'm sure there is a reason for this. But I can't think of why. Also some of the video shows the bridge pillars and they are hollow. Why?

Material savings. You don't put material in that you don't need because all of that costs money. The connection between the steel bridge above and the concrete pillar below is literally a hinge. You do that to keep from putting torques and moments that you didn't expect into the column structure below and the bridge structure above. It probably has a very hard steel pin connecting the top and bottom. The steel side is just pinned through the two heavy side plates on the structure above. The concrete side needs a bigger pyramid because concrete isn't as strong as steel and you need to bolt the plate down instead of welding the side plates directly to the structure above.



On the column side, the strength of a column basically goes up linearly by cross section area (varies by outside diameter squared minus inside diameter squared) and also linearly by the radius of gyration (varies by the square root of OD squared minus ID squared, call it approximately linearly with OD). That means that you can get a lot of gains in column strength by increasing the OD. At some point, the cost of adding another form to make a hollow column is less than the cost of the concrete to fill that volume. Once you get to that point, it's worth making the column hollow.

As you can probably guess, it's a little more complex than this, but this gives you the basics. Also, everything that @Tractionengines said. Once you start looking for hinges and rollers, you'll see them everywhere on bridges.

The Dolphins are visible in a couple of pictures. Why only one and why are they so far from the bridge. The ones I've seen are sets of three before the pylon and a lot closer.

I see two basic sets of dolphins. One set is the big diamond-shaped ones that support the power wires, though these are big enough to stretch the definition of a dolphin. There's another set of smaller, round dolphins closer to the bridge. Most likely the location of both sets was related to what was relatively easy to build while not stopping traffic on the bridge. Incidentally, this street view picture has a car carrier going out with two tugs nearby. If the tugs were actually escorting the ship, they'd be much, much closer, like 1-2 tugboat lengths.

The guy doing the video said the channel was 50' deep and the Dali had a 49' draft. How does that work together?

Usually the channels are dredged to a minimum depth and the actual depth will be somewhat more. The depth is also 50 feet below mean lower low water (long term average of the lower of the two low tides per day). The actual water level was probably somewhat above MLLW, and would depend on the tide. Even so, you can't go too fast with that little clearance under the keel or Bernoulli will suck the ship on to the bottom. @Capt. Eric can add more info about this effect, also called squat.

 

[Capt. Eric]

Usually the channels are dredged to a minimum depth and the actual depth will be somewhat more. The depth is also 50 feet below mean lower low water (long term average of the lower of the two low tides per day). The actual water level was probably somewhat above MLLW, and would depend on the tide. Even so, you can't go too fast with that little clearance under the keel or Bernoulli will suck the ship on to the bottom. @Capt. Eric can add more info about this effect, also called squat.

You're right on the money. MLLW is what's marked on the chart. Add tide level to that. Pilots will also typically know where the high and low spots are in a channel. The speeds they move a ship at are dependent on several factors. Size of the ship, width and depth of a channel, clearance below the ship, work going on nearby, proximity to banks, traffic, and so on. 30 years ago when I was starting out, few of us worried about squat. When a ship is moving through shallow water (relative to it's draft) and especially in a narrow channel, the water needs to be pushed aside. That movement of water is actually enough to cause a lower pressure area and the ship settles down into that area a bit. That's called "squat." The effect can be several feet under the right circumstances, but it's usually more like a foot or so. Usually not a problem if you have the clearance under keel. Way back when, we would look at our wake and see if there was a lot of mud and debris being kicked up behind us. It would actually smell fishy sometimes, so we called it "smelling the bottom." In the last couple of decades there has been growing awareness and requirements to ensure a minimum under keel clearance to allow for squat. This is now typically accounted for, and noted, in passage plans in and out of port.

Having said all that, sometimes you gotta push those limits a little. Not giving specifics, but I have moved ships drawing close to 40ft over shallow spots with less than a foot under. You go slow, almost drifting across. And that would be for only short distances of a few yards. A pilot will usually tell you if you can make it or not, and I would very much take their advice. Working in third world ports, even pilots don't always know what's down there, so sometimes you get a surprise. Sometimes you learn it's better than you thought and you file that away for the future. Sometimes it's less than you thought and you're glad you were moving slow. They talk about ship handling and navigation as being an art, not a science. Making those choices are (partly) where the "art" comes in. Sadly, that is less prevalent today, and that's a shame. I have seen a reduction in the abilities of seamen over the years because no one is allowed to use their judgement, experience, and "art" in operations. It's become a "dumbing down" of the industry I'm afraid. It might sound like playing by the numbers is better, and sometimes it may be. But life at sea is often gray, not black and white, so having experience in working off the plan when things go differently than you expected better enables you to handle real emergencies, and even better - see them developing and avoid them becoming emergencies. A checklist doesn't replace experience and competence, but some people think it does.

Sorry, didn't mean to get on my soap box there. Please return to your regularly schedule programming.