tips for site-plumbing up with laser plumb ups

[pierref]

does anyone have any ideas on which is the best instrument for the job?? Im going up +_40 m for residential block of flats with 3mm tolerance in edges due to cladding being underdesigned.. (yeah i know its probably bullshit, but hey, thats what our contract specifies.)
also, anyone ever use it to plumb up lift shafts and what method>>???

 

[KRSServices]

Are you looking for an istrument that will verify the vertical alignment of walls? Or are you looking for horizontal elevation? KRS Services

http://www.krs-services.com

 

[mikejoe]

If you cannot get a satisfactory set-up location as to not over-run your vertical circle on a conventional theodolite, buy or rent a right angle eyepiece for the instrument that you plan on using making sure your plate level is perpendicular to gravity. In the past we have had to use jig transits ( which are .001" tolerance) to check plumbness on a 25 story hotel under construction, I'm sure that was like shooting a chicken with a bazooka, but it allowed for tolerance errors. Also when taking the measurements, you wave the scales as you would rock the rod on level shots as to get the smallest reading when perpendicular to your line of sight. Optical engineering in Marrietta should have all of the equipment you need to accomplish this job, and yes the tolerances are B.S.

 

[pierref]

krs, i m looking to verify vertical allignment of shafts to make sure it maintains a even plumbness all the way up the building. i have used the edm before on jobs, and the chippies use plumbbobs, but still get it wrong some times. this job doesnt allow for it, any ideas??

 

[mikejoe]

hey, at least it's worth a try, no plumb line will stay stable enough at that distance, it needs to be done optically.

 

[carlorom]

Hi,
There are optical plummets available which will do the job - See typical surveying instruments websites such as LEICA, Optron, Sokkia etc. Alternatively a LASER can be used as a plumbline reference - This yields a visual line which cabn also accurately be measured with a special sensor.Be aware that the side of buildings can heat the air differentially thus causing turbulence in the air and affecting the line of sight. An alternative is to measure - set out the "same" point (in X,Y) on each floor with a theodolite / total station. This can be done very accurately provided you can see "down" on the building (say from an nearby block) as long as the vertical angles are not too steep.
I have also used some mining survey techniques to do this with double checks across the building - A technique known as Weisbach triangles is useful.
Good luck.

 

[minerbill]

Optical methods would probobly be best if you can stand off from the building, but if the work is in the interior, (shafts and such) a heavy plumb suspended on a thin wire and then damped by placing it in a bucket of oil should give satisfactory results.

 

[nhyankee2]

Try the olde mason's trick. Get the heaviest bob you can find and suspend it so it and about a foot of its string is submerged in water. A 5 gal (20 L) bucket should do just fine! The friction of the water will hold the bob and its line steady in all but the most windy day. The trick is to take the mean of the largest and smallest measurement. It will only take a second or two per reading and it is cheaper than all the optics i've seen.