How do you do it??ÿ The thread about the advisability of setting up on a plywood porch brought this to mind again.?ÿ On really big jobs and multi-floor jobs ( over a few hundred feet in height) how do you keep your information sufficiently accurate?
How do you get locked down so that you know you aren't moving??ÿ How do you lock down the target to know whether or not it is where it is supposed to be.......today.........vs weeks from now or weeks ago.
Expansion and contraction of building products
Wind load sideways
Settling, for lack of a better word, describing the impact of massive dead load on positions lower
Angle of the dangle or?ÿ how much does a long cantilevered beam hang downward relative to where it is to be attached to another member
Shaded side of structure versus sunlight side on high insolation days
Vibration due to various sources.
Allowable tolerances
Potential twisting due to moving center of gravity
?ÿ
My lack of understanding about these very questions keep me far away from those projects. ?ÿI too, am curious to see the answers and responses.
Scott Z had some great posts about this. As I understood it, someone, maybe Leica, created software to provide real time corrections by GPS for targets set on adjacent towers. And lots of resectioning.
A few things to say about the original questions Mr. Cow poised, from my perspective on doing a few high rises.
My experience includes:
one at 10 stories
one at 9 stories (A parking garage. Is a parking garage a "high rise"?
three at 14 stories
one at 16 stories
one at 18 stories
one at 22 stories
one at 8 stories
for or five at 6 and 7 stories.
a few more at 4 and 5 stories.
A 4 story that had something like 40 feet between floors. (billion dollar+ chip fab)
Many more at 2 to four stories that I don't consider high rises.
These are just from my own company. The prior company I worked for did dozens and dozens of them so I gained valuable insight from the "institutional knowlege" from there.
I don't know everything, but I do a little about this stuff.
Firstly, the presumption is you have good control established. Then, corollary to that is the presumption that once you have the building "out of the ground", that is, you're starting to work floor 2 and above, the building is situated correctly.
Building movement isn't much of a consideration until floor 5 or so.
But, above that, buildings move. Fact of life.
The question becomes, how do you deal with this fact. Answer: Minimize the impact and analyze what's important.
To minimize impact:
Bring control to the floor you're working on early in the day, before the sun heats up the building to minimize movement. That control is for the current floor only, and maybe for today only.
What's important:
The differential between floors, that is, columns have to stack up on top of each other for concrete structure buildings, and slab edges need to align. AND the inside of elevator core better be plumb. Elevators have a hard time with angled walls.
Regarding what we call "crush" or what Mr. Cow calls settling: again what's important is floor to floor. So you pull your elevation benchmarks up from the previous floor. Using a tape. Let's say the difference in floor heights is 12 feet on a 14 story building, and let's say you have 1/16 inch crush for each floor. (The art is the lower floors experience it more than the upper floors.) This results in 7/8th inch total crush. Now, elevation difference between floor 1 and the roof should be 168 feet. Measurement from ground floor to roof might give a distance of 167.93. Is that significant? Well, you're difference in floor height is, nominally 12.00 feet, is 11.995 feet. I'd argue (and win the argument) that it is not significant.
Regarding Allowable tolerances: prove me wrong. Like all people, I make mistakes. I'll check and double or triple check to see if I'm wrong. If I am, I acknowledge it and correct it. If I not wrong, and someone thinks I am, prove it.
Closing point for now: don't make a problem where there isn't one. Some things aren't a survey issue.
Line and grade. That's what we're obligated to provide. (And arcs and circles sometimes but not as common.) I'll give you a benchmark and a grid so you can get your cant. beam in the right position, or measure it to tell you where it is. Otherwise not the typical layout surveyors issue.
This took way too long to ponder and type. I didn't check for grammar and spelling arrows 😉 Lots of other stuff to add, but maybe another time.
?ÿ"prove me wrong" scenario.
The foreman for the concrete column form work told me my column layout wasn't right because when he cut a square out in the deck form of the current floor based on my layout, the square didn't align with the top of the column rising from the floor directly below. My response was, "well, you didn't build the column below right". He says "prove it. We just build it directly on the one below it."
I keep this photo stored on my phone. Zoom in if you can. You can see the columns are NOT built directly on top of each other.
?ÿProved it.
Hell Yeah you did!
I was the Instrument person or rodman on these jobs, and learned the things you're preaching. I was always uneasy with the amount of supports both wood 4x4 and metal screw jacks that remained in their bizarre forests of structural neccessity for months and months, waiting for the concrete to finish curing all the while as we kept on visiting to continue layout and checks.?ÿ We did several 3-5 story buildings, and when we brought the bigger one ( finished at 15 or 20 stories,i moved into a boundary crew so didnt get to top out) out of the hole and then up to the eighth floor, after the pool and parking garage had cured to 95% we were done, then they carried the rest to the top with Column clamped TS work. I was trying to understand how they could just continue without our survey services, but we were off the site and never came back. I guess our work stood up to their requirements, and the building is still standing proud and occupied.?ÿ
Thanks for sharing, your description unfolded all the awesome memories of the overflowing crappers, when flown overhead cascaded human excrement everywhere sending the rebar monkeys, and other workers scrambling to safety anywhere they could find it from the brown effluent rain. Was one of the galvanizing experiences on why i didnt like construction survey work.?ÿ
It is a great money stream as long as you're always on the top of the game, the risk of being sloppy is not worth the disaster that can unfold. We did lots, and we didnt have any big mistakes i was aware of, but that's just ignorance on my part.
?ÿ
?ÿ
One of the reasons why I hate and don't do construction work is the difficulty in dealing with engineers and foremen. I try to to get accuracies to the nearest mm and when they do their forms they use a retractable tape and use a blunt pencil tip that is 2-3 mm thick. Sometimes I wonder why exert extra efforts to check on the layout. Civil engineers and surveyors have different understandings of accuracies. Ours is theoretical and the other is real life situations. I say ours is theoretical because for us, all traverse must close; level loops must close; to within mm if possible. But when you construct that fence or road or building, those mm closures cannot be followed because the walls are +10cm thick, the cement cannot be poured to the nearest mm.?ÿ
In construction survey, all you can do is minimize those errors by making sure that your controls are in a safe location with minimal traffic to disturb them and as Tim said, can they prove that it was your error??ÿ
They built the Empire State Building before any of that stuff?ÿ
?ÿ
Plumb, measure up along the columns, stack the grid, from what I understand that is how they did it back in the day.
Tim describes it well. It is a whole different world from boundary or residential construction. I believe it should require the oversight of a PLS with a certification (that doesn't exist).
This is compounded by the lack of competent technicians that are available from the union. (At least around here.) You can get more training in layout on a highrise from the carpenter's union than you can from the operating engineers.
Our goal was the same....layout to the nearest 0.005
They'll never be able to build it that tight.
They can try to prove we weren't that close, but they have to go find someone willing to slow the whole project down to do so.?ÿ I was lucky, the company that hired me had a long history of solid work and was always getting tons of repeat biz from the bigger construction companies.?ÿ?ÿ
Another note on high rise survey method. The vertical optical plummet site is your best friend when transferring horizontal control points onto different floors. I did not use the elevator space. Too dangerous. I requested before construction started that they leave several holes (minimum of 5 each floor/15 cm diameter)?ÿ near the edges when they are pouring each floor. The holes need not be perfectly aligned as long as you can see straight to the 1st floor level where your main control points are located. Get some lighting equipment to shine on those control point markers on the ground. You then place your equipment and prism on a tripod over the holes. Once centered, those positions are the same as those on the ground floor. Transfer elevations using TS from another set of control points located as far away from the building as possible. There is an equipment that would allow you to measure electronically in the vertical position but I have never used it. Cost was prohibitive I was told at that time. But today you could build one yourself using a laser meter and a frame to make sure that it was pointed vertical during measurements.
?ÿ
?ÿ
Funny thing.?ÿ That was part of the design of 5 different buildings we did work in. Maybe the survey and engineering groups had been talking.?ÿ ???? ?????ÿ
It's not for everyone, but there is definitely a niche and a career to be had and successfully in high rise construction Surveying.
Back around 1988 a client brought out his plumb bob to show us. It was huge, must have weighed 20 pounds. He said they used for building hi-rise buildings in his day. I believe he said they suspended it into a bucket of water, to reduce sway from the wind.
@dmyhill?ÿ Nah... I disagree that PLS should oversee, even with an added endorsement. Buildings get built very well now without that.
Many, if not most, PLS's, in my experience, don't have the aptitude to do this type of work. For example, living with constant ambiguity and your plan for the day is very likely going to change.
Me: pretty good at construction surveying. Average joe at PLS'ing.
I've had success with using holes, we call it the "sleeve method" in my world. Using sleeves gives a different set of advantages/disadvantages, with the disadvantages generally being overcome-able.
Major disadvantage is the sleeve positions aren't shown on the plans. Eight floors up on one of my projects I arrive to find no holes. Oops. They forgot to install the sleeves prior to pouring the concrete floor. When asked, the new foreman said "it wasn't on the plans!"
What should have taken me 2 hours to do the work I was intending to to ending up taking 3 days because I had to re-establish control that I never would have needed if the sleeve had been installed.
Not all that much of added cost for surveying, but 3 day delay in schedule had major cost impact. Cranes, and deliveries, and concrete schedule all impacted.
I can go with your argument, but I do think that some sort of certification should be required for oversight on projects of a certain size. Note that I said PLS WITH an additional cert.
I actually think that there should be two flavors of surveyor: Land Surveyor and Construction Surveyor. They would have overlap, but Construction would include heavy civil.
