We've been asked by a client to do some Tower crane plumb monitoring, but I've personally never had such a task....nobody in the company has either for that matter.
My question is; has anybody else ever had to do this on a project, and how was this process performed with acceptable results? Any advice or comments would be greatly appreciated on this subject matter.
I've done a fair amount of displacement monitoring for buildings with adjacent deep excavation as well as shoring walls.?ÿ We've found the most reliable method to be installing semi permanent prisms on the structure and measure them repeatedly from a stable location.?ÿ Depending on the duration of the monitoring you may want to include time/money for verification of your control point(s) to confirm?ÿthey have?ÿremained stable throughout.?ÿ In most cases my deliverable has been a simple .csv of NEZ values for the prisms.?ÿ They're looking for relative displacement so the basis of the coordinates is usually irrelevant.?ÿ Not a tower crane but the concept should apply.?ÿ Good luck, sounds fun!
I've done a fair amount of displacement monitoring for buildings with adjacent deep excavation as well as shoring walls.?ÿ We've found the most reliable method to be installing semi permanent prisms on the structure and measure them repeatedly from a stable location.?ÿ Depending on the duration of the monitoring you may want to include time/money for verification of your control point(s) to confirm?ÿthey have?ÿremained stable throughout.?ÿ In most cases my deliverable has been a simple .csv of NEZ values for the prisms.?ÿ They're looking for relative displacement so the basis of the coordinates is usually irrelevant.?ÿ Not a tower crane but the concept should apply.?ÿ Good luck, sounds fun!
When you do this, do you do all your measuring from one location, or do you use multiple setups for this?
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This site is pretty tight, so the farthest that we 'll be able to setup from the tower crane is somewhere around 200', and the height at its peak is around 140'. Not the best situation, but I'm sure others have experienced worse.
I was approached to do this once before but to get my insurance up to what they needed was going to cost more than having someone from across the state to come do it. So my advice is check your insurance before doing anything! Could be a very expensive endeavor if something goes astray!?ÿ
When you do this, do you do all your measuring from one location, or do you use multiple setups for this?
This site is pretty tight, so the farthest that we 'll be able to setup from the tower crane is somewhere around 200', and the height at its peak is around 140'. Not the best situation, but I'm sure others have experienced worse.
The last one was a temp shoring wall for a 90' deep building excavation.?ÿ The wall was in a C shape and the site conditions were super tight making it impossible to take repeated measurements from a stable position to all of the prisms from a single location.?ÿ I prefer to do them all from one setup when possible just because it makes the operation faster but in that case we had to do it from 2 setups.?ÿ As long as the same prisms are measured from the same place each time you've reduced that variable as much as you can.?ÿ Relative shift between measurements is the key.?ÿ
Are you in an urban environment??ÿ I did one where I was able to get on the 6th floor balcony of an adjacent high rise to take the measurements from.?ÿ That worked slick as I was outside of the active construction and high enough to get a great vantage.?ÿ They weren't allowed to start construction activities until 7 am so I got there at 6 am and was done and out before they even started warming up the diesels.?ÿ
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Are you in an urban environment?
Yes, it's in an urban development. A three story parking garage in the rear, three story buildings directly on each side, and a common walking area to the front with no access.
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What type of prism setup would you use on the top of the crane, and how many were sufficient for quality results?
This is what I used on the last building.
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The sticker reflectors might work great for your application though.?ÿ
It would seam like one at the top and one at the bottom of the crane would suffice to prove plumb.?ÿ Can you get on the roof of one of the adjacent buildings or the parking structure??ÿ The parking structure could be great if it has an open deck on top.?ÿ It seems like wind could be a big influence and if it is in operation with a load on.?ÿ Make sure the Client is aware of what external factors can/will influence your results and get the expectations set appropriately up front.
I have never observed any tower cranes but have done several communication towers over the course of their erection.?ÿ
My procedure involved reflectorless TS observations of key structural points from (usually) three control points that were geometrically equidistant from the actual base and shadowed their guy anchor geometry.?ÿ My agreement with the contractor was to only supply derived horizontal distances from the control points to his various points on the tower.?ÿ?ÿ?ÿI felt better about providing those numbers than attempting to determine "plumb" from an optical instrument that might introduce unknown error.?ÿ
I've 'plumbed' a lot of aerial transmission structures?ÿmerely by using the optics of an instrument, but most (if not all) of those were self supporting and under 100' in height.?ÿ ?ÿ
Mark,
Yes, I have?ÿdone plenty of this. Give me a call.
There is a much easier method than some have described here.
Lee - what is the easier method? We all want to know 🙂
Since you don't care where it is, only if it is leaning, do you need the complications of establishing prisms, reference points, preserving them, and precisely centering over them?
Paden's method seems simpler. What if you just use a few setups at approximate positions around it and shoot angles on high and low target points with both faces of a well-calibrated TS or theodolite?
How tall is it?
What is the allowed limit for out of plumb?
I vaguely recall seeing a spec of 1:400 leaning (top-bottom/height) for comm towers.?ÿ If that is in the ballpark, it isn't a super precision job like dam deformation.
I've been busy all week teaching contractors with Topcon LN-100 and Magnet Field. So no time to?ÿtype here, until now.
The most important part of the tower crane is the base. Sometimes the base (?ñ40' tall) will be set into 5' deep concrete. Much easier when they set anchor bolts with?ÿleveling plates or adjustment bolts to assist in plumpness?ÿof the first tower crane section. Others will just set the first section on a concrete pad and anchor bolts while using shims to plumb to the first section. Did one time in NJ, where the crew used circular?ÿsaw blades as shims under the crane section.
Using two theodolites?ÿperpendicular to the tower, aligning the edge with the vertical crosshair can easily plumb tower, as mentioned above. Lot's of walking for one surveyor.
Anyway, the procedure we use is a Reflectorless Total Station set perpendicular?ÿto one side of the tower about 100ft - 200ft away. Plumb left to right direction using vertical crosshairs. Plumb distances to/from tower?ÿusing non-prism?ÿmode. Use the instruments' on-screen display to measure horizontal?ÿdistance to the base of the tower section, then measure to the highest point on tower section. Give direction to operators to make adjustments.?ÿ Then for a final check perform the same procedure on a side of the tower crane perpendicular to your first setup. Most of the time this is all survey is called for. We hardly ever come back to check the top of the tower crane for plumpness. At that time is too late to make adjustments, so you'd better get it correct in the very first section.
For monitoring, we set permanent?ÿbase setups for the instrument and mount prisms on the crane tower. Use the Bernstein?ÿ180?ø prisms.
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Way to much liability. Regardless of what you do, as suggested by others, if it falls over the blame is on you.
Interesting link about tower cranes here:?ÿ?ÿ http://www.craneblogger.com/crane-resource-library/how-are-tower-cranes-built/
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Way to much liability. Regardless of what you do, as suggested by others, if it falls over the blame is on you.
Interesting link about tower cranes here:?ÿ?ÿ http://www.craneblogger.com/crane-resource-library/how-are-tower-cranes-built/
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I agree. To make troubles even worse, the monitoring?ÿspecs do not account?ÿfor weather conditions, L/1000. When the crane is in use it moves, and at times not in use, winds can make the top section of tall crane?ÿsway. To explain that you'll need to record the wind and weather conditions during every measurement.
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How tall is it?
What is the allowed limit for out of plumb?
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The Crane tower is 214' tall, and the allowable out of plumb limit is L/1000, or 0.21'.
