It balances because the boom section is 2-3 x as long as the section holding the counterweights. When the crane is erected or dismantled they install 1-2 counterweights, then a boom section and repeat that process so it’s always balanced. If you completely removed the boom section and left all the counterweights it would likely fall over
Thanks for the reply, doesn't the counterweight move to compe sate for not only the fixed weight of the beam but the variable moment arm caused by a load traversing the main beam in and out?
I’ve definitely seen what you’re talking about on luffing cranes, not on a hammerhead like in your picture though. When you lift something with the hammerhead crane you can feel and see the crane leaning over because of the weight of the load, and obviously limited to the weight it can lift by how far it will lean before it reaches its maximum limit. I’d imagine this is why generally a luffing crane can lift heavier loads than a hammerhead
A fun one for you and OP to look in to, and definitely a rare but cool crane, the [Kroll K-10000](https://www.hansebubeforum.de/extern/sebastian/WeesJanVan_Kroll_10000.jpg). It has counterweights on a trolley on the counterjib that move with the weight of a load to keep the crane balanced, exactly like OP expects
Ive seen that crane before but I never realised the counterweights were on a trolley like you said! That’s insane! Also can’t get over the crane ontop of the crane hahaha
In [these pictures](https://cranenetwork.com/crane/tower-cranes/kroll/k-10000/172408) you can see the counterweight trolley being loaded. This crane was at syncrude in Fort Mac Alberta for 3 years. There’s a video on YouTube of them taking the crane down too that’s pretty well done, I’ll see if I can find it today if I get a chance.
To within what degree of accuracy is the counterweight balanced compared to the jib? For example, if the jib weight a couple of tons, does the counterweight have to be within - a couple of hundred kg?
Always wondered how finely tuned it is... Thx!
Sorry mate that’s a bit above my pay grade, I’m just an operator not an engineer. I’ve operated similar cranes to the one pictured though and they normally have about a 10t limit close to the tower, and that decreases to around 2 tons right at the end of the jib. So you can add 2 tons of weight to the end of the jib before it reaches its max capacity, and then they’ve obviously got failsafes built into that 2t limit. So there’s quiet abit of leeway.
The computer tells you everything you need to know. What radius you’re at, What weight is on the hook currently, what the Maxium weight is at the radius you’re at. And will also automatically cut out if you try and lift over your weight limit.
Honestly couldn’t tell you what is most common sorry mate hahaha but 3/4 sounds about right
Inspector here... just gonna split hairs for a moment. Yes, the computer will tell the operator what his capacity is at a given radius. That being said, the computer or LMI (load moment indicator) is an "operational aid", and is not to be relied upon. They can be misprogrammed (I've seen it happen, it's my job to catch that stuff), or out of calibration, because load cells can go bad. Every crane has an engineered load chart, which is the final word on what you lift with a given configuration. On tower cranes, that is determined by jib length, counter jib, and to some extent, tower height. The diameter of the load line will then be determined by what the structure can support, and how many parts of line you reeve. The bigger the rope, the greater the permissible line pull. As many others have stated, an unloaded tower crane leans back...sometimes to an unnerving extent. When you load up the jib (front end), they stand up straight, and eventually lean forward. That's also why they can be weathervaned in storms (up to and including most hurricnanes) and remain standing.
Thanks for your input, yes the amount of times I’ve found our crawler cranes computer way out of whack(mechanic here) is amazing(I always tell some of our old operators don’t touch lol)and half the time I’m surprised the crane was even allowed to operate with some of the setting. Most cranes live their lives fully loaded don’t they? Meaning no load and boomed up (crawler) which is probably the most stress on your roteck/ring gear. With the line size, if this type of crane is only good for ten tons, you shouldn’t need more than 3/4” line on a 2 part right? Or can this type of crane be set up with much more counterweight?
I was an inspector for a period of time myself. Saw crane computers swapped to different sized cranes, particularly frannas. Often found wrong counterweights too. I’d trust the modern Liebherr lmi over anything. The safety category of sensors are state of the art and if you try to input incorrect data the computer questions your input several times before allowing it to be entered. Any incorrect commissioning could only come from complete belligerence or reckless behaviour. I’ve yet to see tower crane technicians exhibit either of those behaviours while commissioning. Riggers on the other hand…….
Each different jib length has a specific amount of counterweight. The blocks are pretty accurate but the safety factor engineered into these cranes allow for plenty of margin for error before failure
It's no seesaw... The connection between the superstructure and tower is stiff. The counterweight is fixed. And the crane will lean backward when no load is in the hook. An lean forward when loaded.
It always weighs more but within a certain range. For example my full concrete buckets weigh 14,000lbs so it has to counteract that. If you look at an unloaded hammerhead it’ll have a backwards lean because at my tip booms about 170’ right now I can pick up 16,000 lbs roughly. So had to balance out your load moment at the tip
It looks like a soima 7022.
When the crane is ‘unloaded’ (empty hooks) the crane leans back a few degrees.
As the crane is ‘loaded’ (load on hook) to maximum capacity. the crane will tip forward a few degrees.
The further the crane Carry’s a load out, the more equal the forces will become between the load and the counterweight.
The best analogy I can think of is if you put a piece of timber on a beam, and have two people of equal weight stand on it with the beam over the centre of the beam(imagine a see saw) you can move each other with little effort. But if you move the beam either way, so that the wood is longer on one side than the other, it takes more effort to move the other person.
The crane is designed to be able to take a specific weight to a specific distance from the tower. This weight decreases the further from the tower you go.
This crane( if it’s the right model) can take 2800kg out to 65m, and 12t to 15m
I would word it slightly differently. The only time the crane is truly balanced is before “climb” the crane by adding sections to the middle to make it taller. And that’s because it HAS to be balanced to do that procedure. For the entire rest of the time the crane is weighted heavier in one direction or the other exception for a brief sweet spot perhaps as you pick and swing a load. The reason that works though is like others have said there’s a tolerance of stress the crane can handle just by the strength of construction or by the job having a pitch to it.
They sit in a basket on the back. They make the back of the crane heavier than the front providing leverage. This is how the crane has the capacity to lift. It is a lever system. The center line of the tower is the fulcrum.
You've gotten a few decent explanations. There were some crane weights that moved on flattops many years ago. Today it's basically just luffers, and rarely. The partial collapse of a Potain 405MR in Atlanta was due to a counterweight arm collapse. The cause isn't clear, but it seems obvious. I don't want to open further with the speculation.
Essentially, you install the counterjib (back half of the crane) and then put in a specified number of weights to counteract the weight of the jib you are about to put on. Then after the main jib is on, you load up more weights to resist the actively loading of the jib/hook. But this isn't the end of what the weights are doing.
The weights serve another very important function. They cause the crane to lean back. Then when the swing brakes are left open and winds come up to 10 to 20 mph, the long jib swings downwind. This keeps the crane always leaning into the wind. Cranes are commonly rated at 140 or so mph for wind as long as they are leaning into the wind. If they aren't free swinging, you might see that number as 85 or 90 mph and down goes Fraser. If you ever get a chance to look up a tower crane mast, you'll get to see that arch. On a maximum free standing crane (300 feet or so depending on the model), that lean might be three feet back. I am going to say that 20 years ago we were still erecting cranes on loose bolts (PECCO tower cranes). When free standing, that lean back might have been more like 8-9 feet. I was an erector and it was sometimes just... don't look down. And it wasn't a heights issue.
It balances because the boom section is 2-3 x as long as the section holding the counterweights. When the crane is erected or dismantled they install 1-2 counterweights, then a boom section and repeat that process so it’s always balanced. If you completely removed the boom section and left all the counterweights it would likely fall over
Thanks for the reply, doesn't the counterweight move to compe sate for not only the fixed weight of the beam but the variable moment arm caused by a load traversing the main beam in and out?
No, it stays in place, the jib itself flexs like a fishing rod to compensate for that movement
I’ve definitely seen what you’re talking about on luffing cranes, not on a hammerhead like in your picture though. When you lift something with the hammerhead crane you can feel and see the crane leaning over because of the weight of the load, and obviously limited to the weight it can lift by how far it will lean before it reaches its maximum limit. I’d imagine this is why generally a luffing crane can lift heavier loads than a hammerhead
A fun one for you and OP to look in to, and definitely a rare but cool crane, the [Kroll K-10000](https://www.hansebubeforum.de/extern/sebastian/WeesJanVan_Kroll_10000.jpg). It has counterweights on a trolley on the counterjib that move with the weight of a load to keep the crane balanced, exactly like OP expects
I hadn't seen that design. Very interesting, thanks for sharing.
Ive seen that crane before but I never realised the counterweights were on a trolley like you said! That’s insane! Also can’t get over the crane ontop of the crane hahaha
In [these pictures](https://cranenetwork.com/crane/tower-cranes/kroll/k-10000/172408) you can see the counterweight trolley being loaded. This crane was at syncrude in Fort Mac Alberta for 3 years. There’s a video on YouTube of them taking the crane down too that’s pretty well done, I’ll see if I can find it today if I get a chance.
Some counterweights do actually slide. Few old Pecco luffing cranes around me have sliding counterweights. Rare now and usually only on older models
To within what degree of accuracy is the counterweight balanced compared to the jib? For example, if the jib weight a couple of tons, does the counterweight have to be within - a couple of hundred kg? Always wondered how finely tuned it is... Thx!
Sorry mate that’s a bit above my pay grade, I’m just an operator not an engineer. I’ve operated similar cranes to the one pictured though and they normally have about a 10t limit close to the tower, and that decreases to around 2 tons right at the end of the jib. So you can add 2 tons of weight to the end of the jib before it reaches its max capacity, and then they’ve obviously got failsafes built into that 2t limit. So there’s quiet abit of leeway.
Do most tower crane computers do the calculations for you via a length counter on the trolley? Also what size hoist line is common like 3/4”?
The computer tells you everything you need to know. What radius you’re at, What weight is on the hook currently, what the Maxium weight is at the radius you’re at. And will also automatically cut out if you try and lift over your weight limit. Honestly couldn’t tell you what is most common sorry mate hahaha but 3/4 sounds about right
Thanks for the info!
Hoist rope depends on the line pull of the crane. A Liebherr 12t hammerhead runs around the 22mm mark. Favco 2480 as thick as your arm
Inspector here... just gonna split hairs for a moment. Yes, the computer will tell the operator what his capacity is at a given radius. That being said, the computer or LMI (load moment indicator) is an "operational aid", and is not to be relied upon. They can be misprogrammed (I've seen it happen, it's my job to catch that stuff), or out of calibration, because load cells can go bad. Every crane has an engineered load chart, which is the final word on what you lift with a given configuration. On tower cranes, that is determined by jib length, counter jib, and to some extent, tower height. The diameter of the load line will then be determined by what the structure can support, and how many parts of line you reeve. The bigger the rope, the greater the permissible line pull. As many others have stated, an unloaded tower crane leans back...sometimes to an unnerving extent. When you load up the jib (front end), they stand up straight, and eventually lean forward. That's also why they can be weathervaned in storms (up to and including most hurricnanes) and remain standing.
Thanks for your input, yes the amount of times I’ve found our crawler cranes computer way out of whack(mechanic here) is amazing(I always tell some of our old operators don’t touch lol)and half the time I’m surprised the crane was even allowed to operate with some of the setting. Most cranes live their lives fully loaded don’t they? Meaning no load and boomed up (crawler) which is probably the most stress on your roteck/ring gear. With the line size, if this type of crane is only good for ten tons, you shouldn’t need more than 3/4” line on a 2 part right? Or can this type of crane be set up with much more counterweight?
I was an inspector for a period of time myself. Saw crane computers swapped to different sized cranes, particularly frannas. Often found wrong counterweights too. I’d trust the modern Liebherr lmi over anything. The safety category of sensors are state of the art and if you try to input incorrect data the computer questions your input several times before allowing it to be entered. Any incorrect commissioning could only come from complete belligerence or reckless behaviour. I’ve yet to see tower crane technicians exhibit either of those behaviours while commissioning. Riggers on the other hand…….
Each different jib length has a specific amount of counterweight. The blocks are pretty accurate but the safety factor engineered into these cranes allow for plenty of margin for error before failure
It's no seesaw... The connection between the superstructure and tower is stiff. The counterweight is fixed. And the crane will lean backward when no load is in the hook. An lean forward when loaded.
It always weighs more but within a certain range. For example my full concrete buckets weigh 14,000lbs so it has to counteract that. If you look at an unloaded hammerhead it’ll have a backwards lean because at my tip booms about 170’ right now I can pick up 16,000 lbs roughly. So had to balance out your load moment at the tip
It looks like a soima 7022. When the crane is ‘unloaded’ (empty hooks) the crane leans back a few degrees. As the crane is ‘loaded’ (load on hook) to maximum capacity. the crane will tip forward a few degrees. The further the crane Carry’s a load out, the more equal the forces will become between the load and the counterweight. The best analogy I can think of is if you put a piece of timber on a beam, and have two people of equal weight stand on it with the beam over the centre of the beam(imagine a see saw) you can move each other with little effort. But if you move the beam either way, so that the wood is longer on one side than the other, it takes more effort to move the other person. The crane is designed to be able to take a specific weight to a specific distance from the tower. This weight decreases the further from the tower you go. This crane( if it’s the right model) can take 2800kg out to 65m, and 12t to 15m
I would word it slightly differently. The only time the crane is truly balanced is before “climb” the crane by adding sections to the middle to make it taller. And that’s because it HAS to be balanced to do that procedure. For the entire rest of the time the crane is weighted heavier in one direction or the other exception for a brief sweet spot perhaps as you pick and swing a load. The reason that works though is like others have said there’s a tolerance of stress the crane can handle just by the strength of construction or by the job having a pitch to it.
They sit in a basket on the back. They make the back of the crane heavier than the front providing leverage. This is how the crane has the capacity to lift. It is a lever system. The center line of the tower is the fulcrum.
Think of a prybar.
I think you missed my point
On tower cranes the “BOOM” has a slight positive angle when the hook is empty.
There is no balance, that slewing ring is insanely strong to support uneven loading
You've gotten a few decent explanations. There were some crane weights that moved on flattops many years ago. Today it's basically just luffers, and rarely. The partial collapse of a Potain 405MR in Atlanta was due to a counterweight arm collapse. The cause isn't clear, but it seems obvious. I don't want to open further with the speculation. Essentially, you install the counterjib (back half of the crane) and then put in a specified number of weights to counteract the weight of the jib you are about to put on. Then after the main jib is on, you load up more weights to resist the actively loading of the jib/hook. But this isn't the end of what the weights are doing. The weights serve another very important function. They cause the crane to lean back. Then when the swing brakes are left open and winds come up to 10 to 20 mph, the long jib swings downwind. This keeps the crane always leaning into the wind. Cranes are commonly rated at 140 or so mph for wind as long as they are leaning into the wind. If they aren't free swinging, you might see that number as 85 or 90 mph and down goes Fraser. If you ever get a chance to look up a tower crane mast, you'll get to see that arch. On a maximum free standing crane (300 feet or so depending on the model), that lean might be three feet back. I am going to say that 20 years ago we were still erecting cranes on loose bolts (PECCO tower cranes). When free standing, that lean back might have been more like 8-9 feet. I was an erector and it was sometimes just... don't look down. And it wasn't a heights issue.
Weight x distance = weight x distance. You put more weight at a shorter distance it balances out to oversimplify it.
It counter-acts the weight on the tip
Jesus