Hi all,
I am fairly new to laying out large buildings and locating column lines. My employer is about to send me out to an amazon building layout and I was hoping to get some tips on setting control and just some general rules of thumb to ensure everything goes smoothly.
Thanks?ÿ?ÿ
Ensure that your primary controls are done properly and within specs.
There are no such thing as too much controls.
Always always, keep records (Who order the layout, when you layout, your computations, your layout points), be it hardcopy or softcopy or both. Always store them properly. You will thank yourself when the blame game starts.
Check your work after layout, especially when things that are square should be square.
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Set some control points far away, in case some sub goes on an unconscious mission destroying all your baseline points, and there's nothing left the next time you're on site.?ÿ?ÿ
That's some of the best advice this side or Rio-de-Janeiro, and on the other side.
Also, leaving a simple way to prove you did it right, can be essential.
Carry a whisk broom, and paint.
N
Set some control points far away, in case some sub goes on an unconscious mission destroying all your baseline points, and there's nothing left the next time you're on site.
I would say this is the most critical piece. Aside from that, make as many cross-ties and redundant measurements as possible. Run a network adjustment to get the best values, as well as error estimates so you have a good idea how tight that control really is and what you can realistically stake from it.
Properly performed resections are your friend on larger, complex sites.
Be careful laying out gridline intersections for really large buildings. Understand what the tolerances are and adjust your procedures accordingly.
Make sure you store all your stake points and back up your raw observation data. This can save your bacon. (We have had a few jobs recently where they sent some yahoo with a shiny new total station out to "check" our work; they can throw a major wrench into your project if you can't prove out your work.)
We have had a few jobs recently where they sent some yahoo with a shiny new total station out to "check" our work; they can throw a major wrench into your project if you can't prove out your work.)
Conversation circa 2013
Jack**s: Hey Jim this is Doofus McGee, I'm the field engineer for Ginormous Construction here at the Connecticut Avenue site and we just checked your grid control and a couple of the points are out by 0.003'
Me: **click**
Jack**s: Hey Jim this is Doofus McGee again, I think we got accidently cut off
Me: It wasn't an accident.?ÿ **click**
First, you need tight control that is outside of the immediate construction zone. Across the street works in urban areas.?ÿ Stable monuments. I use Bernsten brass plugs, mostly.?ÿ Redundant measurements and cross ties. Adjusted. Tight.
Collimate your gun and check/adjust all rod bubbles prior to layout.?ÿ?ÿ
Resect your instrument position off at least 3 of the control points, well spaced. Doubled angles and redundant rod orientations. Layout all your grid offsets from that same single instrument position and you will be fine.?ÿ ?ÿ ?ÿ?ÿ
As has been pointed out, there is no such thing as too much control.?ÿ Half of it's going to get mushed, dug up or parked over anyway.?ÿ
After that your task should be to communicate.?ÿ Find out how many sets of plans or drawings are on the sight and make damned sure they're all the same.?ÿ Depending on the type of construction architectural plans can sometimes be ambiguous about exterior dimensions (veneer) and foundation (concrete) dimensions.?ÿ Find out who is the "end user" of your stakes.?ÿ Talk with them. Verify, verify, verify. Make sure what you're staking is what they think it is.?ÿ
With all the equipment available nowadays accuracy is rarely a problem.?ÿ 99.99999% of the problems I've encountered on these sites was a communication problem.
"What we have here, is a failure to communicate..."
Most survey problems can be traced back there.
N
@rover83 You lost me at resection.?ÿ When your control is set out correctly and set to a restrained H & V net work, there should be any reason to have to resect.
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Except with resection you don't have to set up on an existing point. Set your tripod up anywhere, resect and you're off.
Exactly. You set your control well off-site where it stays safe, then set you instrument in whatever location is convenient for the days work. Slick.?ÿ
and watch out for last minute design changes where they only changed/overide text dimensions in CAD and leave the actual drawn design in the initial state - check your CAD before staking from dxf-files.
What about when walls go up and you don't have line of sight from the original control, or you would have to do a short legs and a long legs to see where you need to??ÿ
I only use resections as a last resort but sometimes it does make more sense. I haven't done any layout on high rises personally but I've been told that's all they do. Set stickers on nearby buildings so you can always resection to at least 3 or 4 points.?ÿ
Resections will also eliminate centering and measure-up errors at the instrument, and allow you to tighten up your station location far better than traversing into that point from existing control.
Many years ago when I didn't have tall buildings or existing targets around (and the office was too cheap to purchase targets), I used to set mag nails in power poles surrounding the site. This was in addition to our exterior control. It was a simple matter to set a tripod or two over ground points, then hit a couple of the mag nails too and dial in that instrument position.
I still encounter a lot of resistance to resecting, likely because of the continued myth that an angle + distance resection has the same weakness as an angles-only resection. Properly done, they'll save tons of time and make things a lot easier for the layout crew.
