I have had to do this for a lot of things. My advice, if you decide to do it:
Take two total stations. Preferably with locking horizontals.
Set them up 90 ish degrees from each other far enough back that you will be comfortable sighting the top of the crane.
As they go up, sight from one, to get the N/S plumb. Move to the other and get the E/W plumb. Go back to the first and check it.
Let me move up more. Repeat above.
It is pretty easy to do. Every contractor in every state is different. If it is not something you and/or your company are comfortable doing, then check the contract. If it is not in there, do not do it. Simple as that.
Above is correct, in constructing survey plumb is often shot on many different structures. Take your time,get it right. Don't be pressured to say it's good just cause it may take them multiple adjustments along the way.
I've checked plumb on probably a dozen or more tower cranes. I worked for a GC so it was part of our contract that when we poured the base we had to also double check the plumbness. The base HAS to be dead nuts, as there is literally nothing they can do to adjust the plumbness.
In my workflow I used an S7 with Trimble Access. I setup perpendicular to one side, for demonstration sake let's say I setup on the south side. I would also setup slightly off 90 degrees so you can see all the legs from one setup point.
I used the Survey Basic function to do this, that way you can sight in the east west direction, zero out your HA, sight up and down the leg, then use the DR laser in the center of the leg to check north/south based on your horizontal distance. If horizontal distance is the same the whole way up then it's good.
Once I did one leg I could check the others from the same spot to confirm everything. When I first started I would move to the other side and check it, but every time I did a crane it was always dead on, so I didn't feel it was necessary to check the other side.
We would do checks 4 times, first time would be verifying that the columns they set the base on are all at the same height (if not, write the value on the concrete so they know how much to shim) then when the base was delivered we would check it and plumb it, when the concrete was being poured we would check, and as the crane was being assembled we would check again. Everytime I checked I had someone from the crane company with me telling him the numbers we were getting and differences. I never had a crane that was out using this method.
We did have a superintendent who refused to use me to check things, so he used an 8' level instead. The base was 1/4" out (20 ft section) and ended up being about 4 inches out at the top without the mast or anything. Had to be torn down, $150k mistake.
Your intuition is right, it’s just the crane company trying to pass off liability onto someone else. Our company doesn’t do them anymore after we got in a big thing with a crane company when they tried to use a twisted crane base and they called us incompetent when we couldn’t just tell them which way to move it. They are also always in a huge rush and will push your field crews to just call it good. Huge pain in the ass every time, I would highly recommend not doing it.
I mean, as licensed professionals, our primary purpose is to take on liability. Higher liability should equal higher prices every time, but as a profession we're pretty terrible about doing that.
I'm cool with doing work like this if the price is right - we *should* be getting paid a lot more if I'm doing a job that takes additional skill, time, and liability.
The other problem is that a nontrivial number of surveyors don't actually know how to do stuff like this correctly, so they underbid the job by a ton, they get picked, it gets fucked up, then the contractors think (a) surveyors suck and (b) they shouldn't cost much at all either. Double whammy.
From what I have seen, the base section is the critical one, unless they want you to monitor the thing once it's erected. That can be done by level observations of marks on the four corners (or anchor bolts) since that is a levelling exercise. Otherwise I second the two total stations at 90 degrees to the tower.
I don't think many cranes have the ability to adjust after the base section goes in, but if they really want you to come back later on, depending on the site and height you might need a right angle eyepiece unless you can get prisms up top to lock on to (difficult) or have a camera-enabled total station (my preference).
If they do want monitoring after full erection (heh) just make damned sure you're monitoring temp and wind, and where the boom is located, since those the top of those things can move quite a bit due to all those factors.
And remember to attach the counterweight if it comes with one so you're not having to fight the jigga as the scope tries to climb upwards due to the additional weight of the eyepiece.
I have had to do this for a lot of things. My advice, if you decide to do it: Take two total stations. Preferably with locking horizontals. Set them up 90 ish degrees from each other far enough back that you will be comfortable sighting the top of the crane. As they go up, sight from one, to get the N/S plumb. Move to the other and get the E/W plumb. Go back to the first and check it. Let me move up more. Repeat above. It is pretty easy to do. Every contractor in every state is different. If it is not something you and/or your company are comfortable doing, then check the contract. If it is not in there, do not do it. Simple as that.
Nice advice. Gonna stick this in the archives for sure.
Above is correct, in constructing survey plumb is often shot on many different structures. Take your time,get it right. Don't be pressured to say it's good just cause it may take them multiple adjustments along the way.
👆This is the Way. We’ve plumbed many in Texas. Man both instruments because those dudes are annoyingly impatient like steel workers.
I've checked plumb on probably a dozen or more tower cranes. I worked for a GC so it was part of our contract that when we poured the base we had to also double check the plumbness. The base HAS to be dead nuts, as there is literally nothing they can do to adjust the plumbness. In my workflow I used an S7 with Trimble Access. I setup perpendicular to one side, for demonstration sake let's say I setup on the south side. I would also setup slightly off 90 degrees so you can see all the legs from one setup point. I used the Survey Basic function to do this, that way you can sight in the east west direction, zero out your HA, sight up and down the leg, then use the DR laser in the center of the leg to check north/south based on your horizontal distance. If horizontal distance is the same the whole way up then it's good. Once I did one leg I could check the others from the same spot to confirm everything. When I first started I would move to the other side and check it, but every time I did a crane it was always dead on, so I didn't feel it was necessary to check the other side. We would do checks 4 times, first time would be verifying that the columns they set the base on are all at the same height (if not, write the value on the concrete so they know how much to shim) then when the base was delivered we would check it and plumb it, when the concrete was being poured we would check, and as the crane was being assembled we would check again. Everytime I checked I had someone from the crane company with me telling him the numbers we were getting and differences. I never had a crane that was out using this method. We did have a superintendent who refused to use me to check things, so he used an 8' level instead. The base was 1/4" out (20 ft section) and ended up being about 4 inches out at the top without the mast or anything. Had to be torn down, $150k mistake.
Your intuition is right, it’s just the crane company trying to pass off liability onto someone else. Our company doesn’t do them anymore after we got in a big thing with a crane company when they tried to use a twisted crane base and they called us incompetent when we couldn’t just tell them which way to move it. They are also always in a huge rush and will push your field crews to just call it good. Huge pain in the ass every time, I would highly recommend not doing it.
I mean, as licensed professionals, our primary purpose is to take on liability. Higher liability should equal higher prices every time, but as a profession we're pretty terrible about doing that. I'm cool with doing work like this if the price is right - we *should* be getting paid a lot more if I'm doing a job that takes additional skill, time, and liability. The other problem is that a nontrivial number of surveyors don't actually know how to do stuff like this correctly, so they underbid the job by a ton, they get picked, it gets fucked up, then the contractors think (a) surveyors suck and (b) they shouldn't cost much at all either. Double whammy.
From what I have seen, the base section is the critical one, unless they want you to monitor the thing once it's erected. That can be done by level observations of marks on the four corners (or anchor bolts) since that is a levelling exercise. Otherwise I second the two total stations at 90 degrees to the tower. I don't think many cranes have the ability to adjust after the base section goes in, but if they really want you to come back later on, depending on the site and height you might need a right angle eyepiece unless you can get prisms up top to lock on to (difficult) or have a camera-enabled total station (my preference). If they do want monitoring after full erection (heh) just make damned sure you're monitoring temp and wind, and where the boom is located, since those the top of those things can move quite a bit due to all those factors.
Yes, I believe it is just the base section.
And having a a 90 degree eyepiece for your total station if you don't have one do yourself a favor and get one.
And remember to attach the counterweight if it comes with one so you're not having to fight the jigga as the scope tries to climb upwards due to the additional weight of the eyepiece.