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Setting Good Control For Large Building Layout
Posted by BeerLegJohnson on August 24, 2021 at 11:59 pmHi 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
dmyhill replied 2 years, 7 months ago 18 Members · 47 Replies- 47 Replies
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.
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.
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
- Posted by: @jph
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.)
“…people will come to love their oppression, to adore the technologies that undo their capacities to think.” -Neil Postman - Posted by: @rover83
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. **click**
First, you need tight control that is outside of the immediate construction zone. Across the street works in urban areas. Stable monuments. I use Bernsten brass plugs, mostly. Redundant measurements and cross ties. Adjusted. Tight.
Collimate your gun and check/adjust all rod bubbles prior to layout.
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.
As has been pointed out, there is no such thing as too much control. Half of it’s going to get mushed, dug up or parked over anyway.
After that your task should be to communicate. Find out how many sets of plans or drawings are on the sight and make damned sure they’re all the same. Depending on the type of construction architectural plans can sometimes be ambiguous about exterior dimensions (veneer) and foundation (concrete) dimensions. Find out who is the “end user” of your stakes. Talk with them. Verify, verify, verify. Make sure what you’re staking is what they think it is.
With all the equipment available nowadays accuracy is rarely a problem. 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. 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.
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.
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.
@mark-mayer
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?
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.
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.
“…people will come to love their oppression, to adore the technologies that undo their capacities to think.” -Neil PostmanAgreed. Also get them to send you a change order, by email or with a transmittal form. That way you don’t have to search through the plans to see what’s actually changed. It’s easy to miss something that no one has mentioned or called out
And this is why cloud/website-based project management software is awesome for any commercial construction project. Everyone from the construction PM down to the smallest sub can track RFIs, DCs, change orders, etc. I still have multi-million dollar projects where email is the only method of communication and I get dropped from email lists all…the…time.
In my experience the biggest hurdle to employing such software is ensuring that all the individuals with access are tech-savvy enough to use it…
“…people will come to love their oppression, to adore the technologies that undo their capacities to think.” -Neil PostmanResection is a very routine part of my work. I no longer bother with setting control points within the construction zone. They are just going to be promptly destroyed as soon as I turn my back on them anyway. The positions so established are excellent – probably better than any I can twist in off a single occupation and backsight. So doing propagates any error in the 2 control points, whereas resection interpolates a best fit position relative to as many controls as I care to include- and facilitates identifying and rehabilitating (or tossing out) any that have been messed up.
As far as what happens after walls go up – the need for further layout is not so great at that point anyway, so it’s not often that big of a worry. But when there is a need I can still usually work out the necessary sight lines – if you have sufficient controls. If not, there is always the option of falling back on twisting in a control, or of using previously set offsets as control.
@350rocketmike Why as a last resort?
Mathematically, angle & distance resect is as strong a solution for a set up point as a traversed solution. Far stronger than a stubbed in point. Multi-point resect, 3 or 4 and more provides a very robust set up point solution.
Anticipating walls or other obstructions is part of the art of resectioning. Be there before that walls are placed to get the needed control set. (Walls or dirt stockpiles, or a crane, or jobsite office trailers or a frickin’ 12 foot stack of hay bales that won’t be used ’til next spring…)
I used to say that resections were great as long as I did them. Very powerful tool, very easy to abuse. It is so obvious, yet so hard to put into words, just what makes good resection geometry. I saw a lot of field crews screw them up. Typically by using the bare minimum of 2 controls which were too close together and/or not sufficiently “tight”.
@norman-oklahoma
Last resort only because my boss feels the same as some on here do about resections. I figure if I only use them when it is clearly the better option than whatever my alternative is..and then do several checks to prove it was good…then he won’t complain about it.
I set up as close to the middle of where I’m working as possible and shoot points in several directions. If I only have 2 points I make sure they’re 90 degrees apart.
Originally I only used them to find control points buried in the snow or under dirt or for staking for excavation (0.100m tolerance for those). That gave me the chance to see how well they worked on multiple occasions before actually using one for anything that needed to be very accurate.
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