Dan Maloney
Hello everyone, welcome to the Hack Chat! I'm Dan, I'll be moderating today along with Dusan as we welcome Andy Oliver. We're going to be talking about Heavy Engineering, which I'm really looking forward to. Hi Andy, are you online yet?
OK, maybe he's running late or logged in somewhere else. Hold on a sec while I see what I can do...
Oh my that was dicey. I made it!
Hey, welcome -- no worries!
Was trying (and failing) to log in on my phone to let everyone know... but here I am on a real computer.
And before we get started, I just want to note the fact that Andy is the first Hack Chat guest I've ever booked through filling out the host form! I've gotten plenty of responses there, but they've been -- err, crackpots I guess is the right way to put it.
Glad to help.
I feel like the Cessna pilot with 100 hrs sitting in briefing room for sr71 sled jockeys
Andy was the first with a real idea and some cool stuff to talk about. So maybe you can start us off with a little about yourself?
Sure. I'm an electrical engineer at a firm that, among other things, designs and inspects movable bridges.
"Drawbridges," though some movable bridge engineers get picky about that term (not me)
I studied electronics but ended up in this job. Like always, college is nothing like real life, but useful none the less
I can see why, really -- there was a railway bridge in the middle of the Connecticut River that pivoted on a central axle. But people still called it a drawbridge
Instead of electronics, we do controls (but not fancy stuff like you learn in university), electric power distribution (on the site), big motors, lighting, and some other randomness
Yep. That's technically a swing bridge
We have vertical lifts (tower drive and span drive), bascules (from the French for seesaw), pontoon bridges (several in Washington state because of the DEEEEEP fjords there... you can't get a foundation big enough to reach the bottom)...
So it seems like there wouldn't be a huge market for movable bridges, at least for building new ones. But I'd imagine there's a lot of work in repairs and upgrades, right?
That covers the main types. Occasionally we get tangled up in movable roof work and locks on waterways
That's about right. They get replaced after about 100 years or so in most cases.
And it costs a lot to build a new bridge... hundreds of millions for a fancy pants one
So they keep them going with repairs
That said, just between Florida and Louisiana there are about 200 movable bridges among all the owners (state, local agencies, railroads especially).
FL and LA are about tied for the most movables and probably have more than half of the country's inventory if I'd have to guess
Really? I'd have been an order of magnitude low if you'd asked me to guess.
Yeah, where I live in South Florida, the Florida DOT district that covers a handful of counties near me has 37 or so movable bridges.
That's more than most other agencies, but we still... Back in the 50s after WW2 the barrier islands here underwent a great deal of growth quickly.
So they had to build a bunch of bridges fast to keep up with population growth as people came back from war, had kids, used the GI bill to get educations and jobs, etc.
I wondered if there are any participants here that have such a bridge on their commute and curse it every morning.
I guess Lars was one of them ;-)
Hahhah
Also, since many of us are engineers, I might talk about the curious way these things are often controlled
And see if we get more questions
Not me, at least now here in Idaho. But back when I lived in CT, there were plenty of bridges like that.
Almost all movable bridges have control systems to prevent the bridge tender from doing something out of order, like opening the bridge while the warning gates are up.
Most seemed to be permanently stuck up
Yeah, it's often because maintenance is expensive and difficult that they find themselves out of order.
In FL here they are on major thoroughfares so they usually are not out of operation for more than a few hours... but that's a lot if you need to get somewhere
So about the controls, the have some sort of control system to keep track of those things. They monitor inputs and allow the tender's commands through based on basic Boolean operations.
what's the 'have you unplugged it plugged it back in' of bridge maintenance?
Good question
It's probably literally the same thing
hah, makes sense
In some cases a bridge will not "seat" for whatever reason and refuses to come down the last few inches.
Most tenders don't bat an eyelash and open the bridge again and close it. And 90% of the time it works. Like power cycling.
then 10% of the time you gotta call the tug pilot to... nudge it?
The reason is often because the motion control on these things is a little dumb (let's call it simple), so if for some reason the tender stops the bridge while it's in slow speed... maybe a boat tried to sneak through... we often don't have the momentum to quite get the bridge down to click the limit switch saying it's fully closed.
For the 10%....
Get on the end and jump up and down
The equivalent of that is manually releasing the brakes if it's an electro-mechanical bridge.
hah yeah... what's the 'persuasion bar' of bridge maintenance?
They are typically balanced to close themselves, at least when nearly closed, so you can often just release the brakes by hand and it will close... if it's well enough lubricated
Limit switches -- I'd imagine those would have to be much, much different than the usual microswitches we'd see.
Persuasion bar reminds me... one government client who is known to have VERY old fashioned control systems (like 1960's Westinghouse or GE style systems) says that they want their control systems designed so you only need a hammer for maintenance
Needless to say that means no Arduino or even a PLC
thats a design I can get behind
so all electro-mechanical?
Yeah, limit switches for us are pretty big, though we do specify rotary cam limit switches that have switches inside not unlike the typical microswitch
Electro-mechanical in terms of relays only. Even the motor speed controls (if an electro-mechanical bridge as opposed to hydraulic) will use relays to switch resistance in the secondary of a wound rotor motor.
Timers, even, are often not electronic if they can manage. It's hard to find them anymore, but they'd prefer the oil-filled dashpot style of timing relay
To be honest, I think I prefer that kind of thing as well after seeing the way some agencies maintain these things
They keep them safe, but not necessarily operational if that makes sense
We draw up our control systems in relay logic: https://en.wikipedia.org/wiki/Relay_logic
I was going to say that this seems like the kind of thing a PLC would be used for. Is that true, or are the control electronics more of a bespoke thing?
Depending on the client, that might be built in literal relays and switches (and often machine tool relays the size of... half a shoebox maybe?)
Exactly. Many clients will use PLCs
So I, and my peers, do not design our own control systems. What we do is honestly so simple it's almost entirely representable in relay logic... even advanced functionality like remote operation
By "design" I mean designing the electronics.
It's more like we specify as opposed to design, and we will design the relay based control circuit and the power distribution... but when it's PLCs it can become a black box that the Contractor designs based on the requirements.
... that last part sometimes makes me wonder what exactly I'll be doing in the future.
And again, I shouldn't have said that the contractor "designs" but rather "integrates" a system of stuff they buy
Yeah, but it's knowing which stuff works and plays well together that's the trick, I'd guess.
Yes, and even then that's often a system integrator's job. Contracts and clients are different, but the industry may be moving more toward the engineers providing specifications and minimal design plans. There are lots of other requirements for the engineer to keep track of, like codes and standards and owner preferences.
Unfortunately that's all the boring stuff and not the programming or problem solving. We'll see where it goes.
does lateral winds impact a balanced bridge in operation. ie weather events causing motivational failure?
Sooo, in the US our design code is from AASHTO, the Association of American State Highway Transportation Officials, and they actually cover that in the code
A bascule bridge is especially subject to wind load... the whole thing being an enormous sail. And here in Florida we get hurricanes.
So there is a load they design the machinery to be able to withstand a certain wind load without breaking gear teeth and things like that.
It also needs to be able to operate under certain wind loads
SO you must have to work closely with the mechanical/structural engineers to make sure your stuff isn't going to break their stuff
In the case of a bascule (seesaw type), wind loads are the controlling loads but also don't occur in normal operation. So we have to test the motors to verify that they can operate under the design loads
However the whole system cannot be tested
Yes, my boss always says we're all "movable bridge engineers" instead of structural, mechanical, or electrical
Usually it roughly goes that the structural designs the bridge, then the mechanical engineers design machinery that can make it move, and then the electrical engineers provide enough juice to make that happen
i have been on the golden gate bridgeb
But as you can imagine, if machinery doesn't fit, they need to get the structural engineers to make more space... and in some cases that has spillover effects that lead to everything going up a size
It can be a real pain, but it helps to keep everyone involved and hopefully keeping tabs on each other to make sure we're not overdoing something unnecessarily
sorry only have one hand. ... golden gate bridge during wind event as they closed the traffic off.
Fortunately most movable bridges are pretty low to the water so wind tends to not be a problem for traffic.
They do leave them closed in high winds, but the crossings stay open for cars.
awh thank you.
This website has information on 3,166 movable bridges in the US: https://bridgehunter.com/category/tag/movable/
I believe that includes previous bridges that no longer exist, but still, there are a bunch.
Ah yes, it includes a bunch of old bridges. But anyway, there are apparently bridge hobbyists like rail fans and the people that watch airplanes land and take off.
Honestly, there are weirder things to be interested in. Anything big that moves at least rates a second look for me.
There are a couple Hackaday articles on relay logic including a Nixie clock (they beat me to it): https://hackaday.com/2021/08/09/relay-logic-nixie-tube-clock-checks-all-the-boxes/
https://hackaday.com/2020/10/23/relay-computer-consumes-six-years-and-4-5-suitcases/
Relay Computer Consumes Six Years And 4.5 Suitcases
If you thought your home-brew project was taking a long time, [Jeroen Brinkman]'s MERCIA Relay Computer project probably has you beat. He began working on this impressive computer back in 2014, and has been at it ever since.
Yeah, it's my job but when you think about a million pounds of steel lifting straight up 60 feet... I guess that's not a small feat.
Makes me think -- what's the biggest thing humans have ever moved? Aside from carriers and supertankers -- those are too easy ;-)
But it's just engineering and math. You just add a couple zeros but F still equals m*a
I kinda feel like it would be something like the crawler transporter for the Apollo program
That is an interesting question. I don't know.
that's gotta be up there
Stadium roofs are pretty enormous... but probably not that heavy
CHICAGO CORROSION GROUP WARREN BRAND
The World's Largest Movable Structure You've Probably Never Heard About - Chicago Corrosion Group
"It is the mark of a truly intelligent person to be moved by statistics," George Bernard Shaw So let's start with the numbers: Weight: 40,000 tons. Roughly the weight of 3 Eiffel Towers, 107 fully loaded 747s or the USS Missouri battleship. Height: 590 feet tall.
Read this on Chicago Corrosion Group
TIL
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