Tower Crane...Experience (Whoa!!)

I've worked much of my life in heavy construction. After college I progressively got into more technical fields, but my foundation has always been in "foundations" and structural steel.

Working in highrise heavy construction I'd seen many things. As a layout Engineer I'd walked the steel much like any iron worker. I'd always marveled at cranes, especially big ones. Many of the big cranes I'd worked with were big stick, ground based, cranes; Manitowoc 4500's or larger both on tracks and ring cranes. These cranes had giant counter-weights and several hundred feet of boom. They were delivered in pieces, and taken apart and sent back home in pieces. I'd seen all those, but one type of crane always fascinated me...a tower crane.

These cranes couldn't lift as much as the mighty Manitowocs, but they were WAY taller. The Manitowocs were mammoths, but the tower cranes were 30-40 stories taller...and they got taller as the buildings got taller. They were amazing.

As an engineer, one of the things which impressed me about tower cranes was how they could erect themselves, going higher and higher. This is where I focused first. How did they do that? Once you understand the process, it's not all that difficult to see how they work, but I wanted more.

I didn't know it then, but I soon learned tower crane operators are an odd breed. They start up long before the workday starts, and come down long after the workday is over. They don't hang out with the rest of the construction world, but keep to themselves mostly.

One day I actually met up with one of them, an operator. He was a pretty nice guy. We talked about all kinds of things. I asked him if he ever got afraid. He said "not really...it's just another day". He said lightning scared him (and others); he'd been hit many times. But the cranes are all grounded for just such things...but not everything works out as planned. He said he never worried about lightning after his first couple years or so, but his big fear was big wind and tornados. You see, those two things required the operators to evacuate and come down. If lightning struck the towers then...they'd be vulnerable. Hmmmm...seems pretty skeery to me!

Anyway, he offered to give me a tour of his crane. I had the OSHA certs for climbing, so I was good to go. The next day I showed up at O-dark-thirty and we started up. I always thought there must be an elevator, but there isn't. The way up is a half stair, half ladder, gig all the way to the top. This crane was up about 30 floors...it was a long hike up. The view was commanding; it was spectacular. We were 20 floors above anything. On this particular day the crane was lifting bunks of steel floor decking. The decking was 16' long and 4' wide, so even in the light morning breeze you could feel the wind taking the sheets and torqueing the crane around.

In the afternoon the wind started picking up. Nothing major, but just a light breeze. Now you could see the main riser of the crane actually moving around. The whole crane was flexing. The operator was bullet-proof, he could even anticipate the crane's movements as he swung materials into place down below. Then the clouds rolled in...

It was December in Minnesota, but the day had been very warm. As the sky darkened, and the sun set, it started to mist. The windshield wipers in the cab made it relatively easy for the operator to see the landing zones below (he had binoculars as well as radio comms). The radio was playing some silly song when all of a sudden some alarm went off. It was a buzzer. This guy didn't panic at all, but said "Well, that means we're out of tolerance for wind". By now it was dark. He disengaged the clutch on the swing gears and the crane boom swung around (about 270 degrees) away from the the wind. As the crane stabilized he casually gathered up his lunch box and weather gear. From there we headed out on the catwalk to the stairs. Then we started down.

The stair/ladder arrangement which had been a challenge going up had turned into something FAR different going down. The mist which had looked like rain in the cab had coated all the cold steel rungs with a thin layer of ice. The way the ladder was arranged you couldn't fall more the a floor (or that was the idea anyway). There was a steel landing where you had to turn around and go through a different hole to get to the next floor, but every thing was coated in pure ice. The protocol was one person would go down and get out of the way below, and then the next person would start down...over and over...30 times. On the way down we'd slip off the ladder and hang on for dear life as we smacked our shins into the steel rungs. Our hands would slip off and you'd have to grab anything you could to keep from falling.

I wasn't afraid of anything back then...and I was terrified. We did make it down finally, and when we got to the ground the operator, Jim, calmly asked me..."do you remember when you asked me if I was ever scared? ... THAT, was the scariest thing I think I've ever done right there!!"

It took me about 20 minutes to warm up in my truck; that, and to stop shaking from sheer terror!

So tower cranes? Yeah, they are really cool; I'm not sure I'd ever want to run one day in, day out, but I went there once. Maybe it was just a bad day, but I don't think I want to do that much ever again!!

a reply to: Flyingclaydisk

and some people climb them just for fun

Wow, that's a really cool story. Thanks for sharing. So, construction, huh? I've heard many stories, especially with high buildings and bridges, many people that get killed with 'super structures'. Because of the dangers. Also with people who work in renovation, 'ghost stories'. Some places pretty freaky, where the workers quit or don't want to go back. When our old house was being built in a subdivision, ambulances would come around often because of all the accidents, idk if anyone ever died, but many people in that subdivision would experience paranormal phenomenom.

OMG, that sounds terrifying! Glad you both made it down safely!!!!

a reply to: Flyingclaydisk
No thanks. I'm not that adventurous. So, did you pee yourself? I would have, just a little. Anywho, it's a good thing that you and your buddy Ward never got your hands on something like that.

Your story brought back memory's of one of my first large construction project. We were building a hospital and I was a young electrician at the time. The tower Crain broke down one summers day and someone had to climb it for trouble shooting, as the youngest jourman I was elected. It was a simple limit switch replacement, but I will never forget it.
Stars and flags my friend.

a reply to: Flyingclaydisk

I'm no good with heights. Those YouTube vids of people climbing towers & such give me the willies.

I am always amazed to watch one of those tower cranes go up (and down).

Fascinating story mate thanks

I'm assuming you have seen that famous video of the guy climbing the TV mast to repair it? Made my blood run cold. At the top..they could barely be called rungs yo climb up...looked more like screws poking out.

I got scared on the ladder today putting the Xmas lights up.

Awesome Story!!!

I Always wondered this about Tower Cranes.

Across the street from where I work they are building the Wilshire Grand Hotel. The tower will be 73 stories when finished. I like to go watch the construction on my lunch break and especially the tower cranes when they do heavy lifts. So one day I'm watching the tower cranes do their thing and a notion hit me. The main tower crane is on top of the Core of the building. Right now that's 64 floors. But the building will be 73. That tower crane is the highest crane attached to the building. So when they need to add to the height of the core, how the hell do you move the crane? Would't you need to take it down all together? And how? Disassemble it piece by piece? Lift off the crane with a jumbo helicopter? Use one of the lower shorter side tower cranes to lift the main crane on the top off? And once you do remove the crane to continue building the core. How do you get the new pieces of the core lifted up to the top to put them in place?

a reply to: BASSPLYR

So, there are a couple / three methods for removing a crane, but first to your first question about adding floors...

Most big tower cranes are self-erecting. If you look just below the top section of the crane, on the tower itself, you will see a larger section (sometimes they remove this for construction). This larger section serves as an exo-skeleton for the tower itself. It bridges / spans several entire segments of the tower. This is called a 'climbing frame', and it moves. To add a section, they unbolt the crane from the tower and the climbing frame lifts the entire crane up one full tower section. Then the tower crane picks up another tower section from the ground and it is inserted through the climbing frame onto the top most section of the tower. Then the climbing section sets the entire crane back down on the new tower section and it is all bolted together. This is assuming they only need one section. If they need more this process is just repeated for however high they need to go.

Side note: What I am describing here is the process for the really tall tower cranes, the ones which are far taller than a ground crane can reach. These are called climbing / self-erecting cranes. Smaller tower cranes are erected using ground cranes, and this process is much easier.

Disassembly works pretty much the same way with a couple variations. If the crane is external to the building core (which most, but not all, are), the disassembly part works the same as the erection process, but in reverse. The climbing frame lifts up the whole crane enough to unbolt the highest tower section. Once free, the highest tower section is removed through the climbing frame and lowered to the ground by the crane. The climbing section then moves down to the next section. This segment is removed and the climbing frame moves down again. This is repeated over and over until the crane is low enough to the ground to remove the gantry and counterweights with a ground crane. The rest is disassembled from the ground.

Sometimes (like in your case) the crane is not able to reach everything it needs to if it is external to the core of the building. In these cases the crane tower is actually inside the building core. The process for assembly works pretty much the same way as an external crane, but disassembly is quite a bit different (and yes, they are removed; they don't become part of the building). Because the crane can't go lower than the top of the building, they have to disassemble the gantry and counterweights at full height. They have specialized equipment using similar principles to do this. The gantry has a 'climbing' section, but it moves horizontally. Each piece is removed and brought back to the center where the tower is. Then they use special rigging davits to rotate the piece and lower it down an adjacent elevator core which is empty the full height of the building. They leave the framing out for two floors on the bottom of the building so these pieces can be removed once they get to the ground.

Once they take the gantry, the counterweights, the cab and the main swing and hoisting motors down, the work begins on dismantling the tower itself. They use a smaller climbing frame to do this. Each tower section is removed (similar to an external section) and lowered down the elevator hoistway to the ground. This process is repeated as the crane tower is disassembled inside the building. Each piece is brought outside once on the ground. Once the crane has been removed, the framing steel for the lower floors is bolted into place so the building can be finished.

And there you have it.

P.S. On a side note; the 'climbing frame' is only strong enough to lift sections of the crane itself. So, when sections are being added or taken away, the crane is not lifting construction materials. In engineering-speak, the rotational "moment" would buckle the climbing frame if they tried to lift heavy items far away from the tower without the crane attached to the tower itself. The tower, in turn, gets its strength from being both counterweighted and by being attached to the building itself at various intervals.

Oh, and one other thing...helicopters are rarely (if ever) used to assemble or disassemble these cranes. The flight dynamics to assume one of these loads at altitude creates dangers which far outweigh the benefits of attempting it. It's all done manually with hard work and ingenuity. Helicopters are used in construction quite often, but just not for this task generally. Because of the way the cranes come apart there's no good way for a helicopter to take on the load before a section is cut free. And this would mean a sudden load on the helicopter which could cause all kinds of bad things to happen. I imagine they could maybe use them for taking counterweights off and the like though.

a reply to: Flyingclaydisk

THANK YOU!

it all makes so much sense now. on Monday I'm going to look at the construction site for the Wilshire grand differently now that I know a bit about how the climbing frame works.

never thought to think of the roof crane that's "sits" on top of the core is actually not "sitting on top" of the core but running down the inside of one of the elevator shafts of the core similar to the tower cranes mounted to the side of the building.

speaking of which. I've noticed they, every 10 floors or so, bolt the tower cranes to the side of the building. are they also bolting the center tower crane that's running up the elevator shaft to the inside of Said shaft similar to the exterior tower cranes? or do they have a way to wedge it in the shaft and not require bolting it directly to the building? if they do indeed bolt it to the inside of the shaft can you tell which shaft they used if you were the elevator repairman by noticing tell tale pock marks in tge shaft cement wall where the bolts used to be?

a reply to: BASSPLYR

No, they're just anchoring the tower off to the building structural steel. The ties do not go all the way back to the tower itself.

However, that said, there are considerations in the building steel design to take these lateral loads into consideration. In other words, the crane which erects the building is actually part of the building design itself.

edit...oh, I misread your question. External cranes are attached to the building steel. Internal cranes are also attached to the building steel. Elevator hoistways are not always concrete; some of them are framed. So attaching to the steel in these arrangements is relatively straight forward. If concrete, the tower will still anchor to the building steel through a block-out left in the concrete. And yes, you would be able to see these afterwards (if you were inside the elevator shaft.). They fill them in afterwards for fire reasons, but you would see the block outs.

They generally do not tie the tower to the concrete itself. The reason for this is because concrete's greatest strength is resisting 'compressive' loads. Concrete's weakness is in tension. Lateral loads represent tension, which is why there is structural steel to resist these lateral loads. Therefore there's no real advantage tying to the concrete when the concrete is already using the steel to resist lateral forces.

I should add one further thing...

Some buildings (particularly in the far East) do not employ structural steel in the classical sense. They are concrete structures which utilize reinforcing steel (rebar) to give the concrete lateral stability. In these cases the crane tower would be bolted to the concrete.

Just thought I would clarify this permutation.

a reply to: BASSPLYR

BTW...here is a picture of a climbing frame in action...

very cool. now that you mention it i think i have seen block outs on the building when i watch the contruction.

im going to pay more attention to the core on monday and see if i can spot other little details to ask you about that spark my curiosity.

in regards to differences sometimes between using classical steel frames and reinforced concrete for the core. what are the trade offs? why pick one over the other.

finally the Wilshire grand appears to have a massive concrete and rebar core from what i can tell. I watch the tower cranes lift prefabricated 15 x 30 foot "walls" of rebar to the roof and attache them to the core. it looks like they then back fill the rebar walls with concrete. is this indicative of the reinforced concrete core construction or classical steel?

a reply to: BASSPLYR

It's a little bit hard to tell from your description. The term "core" has a specific meaning in construction, and this is different from 'the whole building being structural concrete'. One type of construction has a structural concrete 'core' surrounded by a structural steel building (meaning the majority of the building is steel, and just the main core is concrete). Another type is a structural concrete building where the whole structure is predominantly concrete (i.e. floors, columns, major interior walls and exterior). The other type of commercial building is one which is predominantly structural steel (i.e. columns, beams, etc). This type may not even have a concrete core at all, but rather all steel.

From your description it sounds like the building you are looking at is more concrete than steel, so it may be a structural concrete building.

The walls of rebar you are looking at are "tied" on the ground to save cost and risk. They are then hoisted up into place and tied to the existing rebar. From there two more walls are lifted and placed on either side of the rebar forming a sandwich of sorts; these are made of wood and called "forms". Concrete is then pumped in between these forms and allowed to cure. Once cured, the forms are 'stripped' away from the concrete and prepared for re-use. Rebar sticks out of the top and sides of the concrete. This process is repeated forming the walls, all stitched together with the rebar.

The reason for choosing concrete over steel is cost and resource availability.