does anyone have any experience with keeping a highrise building core straight? this is going to be a 40 story building with Jacking formwork and my client has asked if we could look into devising a plan to ensure this goes up straight. The way i look at it after the 2nd floor i will have reached the limits of what i am comfortable doing with my total station. which only leaves 38 floors to figure out. It is not critical if this core is out 10-30mm or more at the top but whats important is that the error in every floor does not deviate 10mm for example creating a lean in the elevator core that could amplify to something much worse. My only thoughts right now are rigging a couple of GPS Receivers to the jacking formwork and taking readings every 2 weeks when the go up another floor. i feel the GPS should be able to keep me within 10mm all the way to the top. I have read about using wire and a bucket of oil at the base to determine this but after looking at the formwork system and the way it moves there is no way to get holes through it.
If you can get some good long sight lines at about 90 degrees and maybe 1000-2000 feet away assuming you can set up on top of the formwork and run a 3 or 4 point resection to tripods or fixed tilting prism mounts. That's my first thought but there are people on this site with a lot more knowledge about this subject than me.
or this
http://cenews.com/article/9843/standing-tall-with-very-good-posture
http://www.fig.net/pub/fig2006/papers/ts78/ts78_01_hayes_etal_0297.pdf
10 kilo Bob on wire. Hang into an oil bath to dampen. No way would I use optical for that height.
My 02...
:good: :good: :good:
That's still how they do it for some of the largest buildings. I don't think I'd want to rely on GPS either. I both love and trust GPS measurements and have gone through fairly rigorous procedures to get good results with it, but I wouldn't trust the GPS slop on something like this. That said, I never used a system like the one described in the article, nor have I worked on a building that tall.
On a somewhat related topic - what happens on the higher buildings as they go up when the sway of the building in the wind starts to have a noticeable effect? At any one point in time the upper floors of the building could be shifted one way or the other. Is an average measured?
You might want to search this site for discussions with Scott Zelenak about techniques used at the WTC.
See also [msg=162066]this thread[/msg].
It's a specialized job that calls for experience working with other experts before taking it on by yourself.
Not to question anyone's methodology but what would the issue with doing this optically with sufficiently long sightlines say 2-4 x height. Again not questioning just curious.
> Not to question anyone's methodology but what would the issue with doing this optically with sufficiently long sightlines say 2-4 x height. Again not questioning just curious.
An old party chief buddy of mine just yesterday was reminiscing of the days 30 years ago they would have to optically extend up fifty floors with offsets on the ground only fifty feet away because of tight busy downtown conditions. They did have to use a special 90 eyepiece attachment for the floors above the sixteenth, because eventually they could not crouch low enough to still see thru the scope.
By the way it is a good start that the OP knows his limitations. If he keeps reaching out here and elsewhere to his friends in the business he will be able to tackle this.
I know, because just this week I had some similar questions, and now I have a good plan of attack.
How close are they going to let you get to the core - either inside or out? I'd want to take a look at a zenith optical plumb. These things are designed to be able to eliminate errors and cross check your work. If you would be permitted to mount some instrument brackets either inside or outside you'd be able to reposition the instrument to the same location each time. But this would mean that you'd be working within a foot of the wall and that may not be permitted for safety considerations.
From a business perspective, are you familiar with the liability aspect/price of being wrong?
another thumb up.
Not first hand experience but, stories from the senior party chief I worked with in Atlanta circa mid-90s.
Seemed like it always involved the elevator shaft and I guess that's for obvious, plumb reasons. If it's true, and your wall thicknesses are known, you could set pretty tight control at each successive level.
My understanding was, they worked from a single/ multiple point(s) at the bottom of the shaft, repositioning the bob at the start of each new floor. So, I don't get how dampening oil would work, as it would be in the way of the ground control.
Sounds like a challenge. Good luck.
Brad:
I read your potential wall project with interest; although, I was a little late to the game to offer my thoughts (plenty of good ideas already posted).
Wondering what methods you are going to employ? Give us an update if you get the job.
If you can't devise a minimum of THREE methods to meet tolerance, you might want to subcontract.
"If you can't devise a minimum of THREE methods to meet tolerance, you might want to subcontract."
Great advice Scott. We've done several high rises in Chicago and plenty of Heavy Industry Engineering type surveys. We've traveled North America fixing surveying work started by Land Surveyors over their heads in a complex industrial project.
BTW we do VERY little boundary work.
Most states and professional licenses require you to work only in areas of your competence.
I've taken a few high rises up and I'm appalled at the guesswork by some on here.
This staement:
"10 kilo Bob on wire. Hang into an oil bath to dampen. No way would I use optical for that height."
Is something pulled out of a book, the fact that it was followed by several thumbs up is even more interesting/entertaining. I've never seen it done that way. In fact this is an old school procedure used to bring control down into a tunnel.
The new school way of maintaining plumb on larger buildings is GPS. But before GPS there were other methods.
To echo Mr. Richardson, "If you haven't done before why entertain it". The only reason my company offers this is because I've done it as an employee for someone else multiple times. Understanding, the process is the key and practice will always breed confidence.
I would expect a guy from New York to have experience in this area. I guarantee if there is a 'current' technique it is routinely employed there. What you may not realize is there is a big world out there where others have seen and done things different.
If the gentleman who started the thread took my few sentences and attempted to build a high rise it wouldn't be likely to work out well. On the other hand if he investigated he would likely find a host of people with experience in the technique and decide if it was useful or not.
While I would likely defer to someone currently employed and specializing in high rise construction, I wouldn't discount the valid experiences of others. I certainly wouldn't listen to someone who tried telling everyone that he knows the only way to get a job done.
We put laser plumbs on brackets, 1 in each diagonal opposite corner (2 in total for each internal "box").
You will need 2 small holes in each internal platform though. This has never been a problem although it is prudent to position the lasers mid way between the platform beams.
Looks like a PERI system. Is there a reason why you can't put holes in the internal platform?