a contractor has recently asked me to do some grid layout on a rather large office tower.
foundation is a rectangle approximately 57.6m ( 189ft) x 92.9m ( 305ft)
8 grids north south and 12 grids east west
typically we would just set up on our control and radiate the gridline offsets in with my robitic TS. been doing this for years and never a complaint or issue from any contractors.
this specific contractor wants to be able to setup on any point, backsight any point on the same line and have it so his carpenters can turn 90 degrees easily to shoot accross the building. normally with a theodolite that the formwork subs use they can shoot across the excavation to the matching gridline on the other side so no angles need to be turned but due to how tight on space this site is and what kind of activities are going on they think i will only be able to layout the south and east sides.
my instinct is telling me this is a bad idea and it wont work out well for them. if you are on the east side set up on the middle gridline that would leave you with less than a 100' backsight and a 300' forsight.
in theory if my points were perfect this could work but i just cant see it being perfect as they want me to drill them into the asphalt/concrete and there is no way to adjust once installed. i know that radiating these points in could potentially increase there error.
i guess what im getting at is how can i layout these gridlines in a fashion that will leave the least amount of error?
my "idea" was to radiate the corner points in then setup on the lines and ensure everything is perfectly online with correct distances.
i am considering telling them that this is not a good idea and we need to figure out a solution to get all the gridlines marked.
thoughts??
He is wanting you to set up baselines for his crews to work from.
It is fine to guarantee the baselines for accuracy, just make it clear that you are not going to extend our liability and guarantee that his crews will do their staking correctly.
Some contractors have the idea that anyone with a builders transit can do stakeout for a construction site.
"Look out for number one and don't step in number two, Rodney Daingerfield"
I stake out buildings all the time in a similar manner. I prefer staking the column lines on some pre-determined offset, as opposed to setting foundation corners and/or anchor bolts.
One thing I always ask the job superintendent is to make sure of knowing is how smart his sub-contractors are. Amazing how it varies. Any carpenter who can't figure out a square is one I don't want to be involved with. When they start bringing in the steel, then it's time to cross your fingers and hope the architurkey plans are good, and the steel guys have the same set as you when you staked it. That also can vary.
Sounds like you are on the right path IMHO.
"typically we would just set up on our control and radiate the gridline offsets in with my robitic TS."
Wow - I can't imagine doing this!!
I've been wondering about this topic, since my recent acquisition of a robot, I'm curious about setting on grid lines and manually running the instrument. Is this what you're talking about Jim? Are you also a little concerned that running the Robot manually will introduce errors?
CT, fully understand the apprehension part of your concerns. I had them too, and wouldn't even resection for a while, until I got convinced. I've been robotic for about 20 yrs. What it does is eliminate centering errors, parralax in the scope from the Iman, sun glare, and even barking dogs & fast trucks to distract you. Robots are the way to go, and radial staking is just another way to do things.
Still have to check your diagonals though. Sometimes I'll set up to measure, sometimes just the old reliable steel tape. Depends.
It still is a 3 second gun, and keep your sights short and have good geometry with what you're doing. As I mentioned above, working with good qualified contractors is also critical. What really is the difference between turning a 90 or setting out a point at 45-31-22 for 300 ft.
Thanks Wayne.
We're still scratching our heads everynow and then when we happen to look through the scope, and the vertical angle cross hair is not dead center on the prism.
I'm still warming up to the Leica Robot. I'm sure over time I'll get more and more comfy. Luckily we havn't been asked to do any steel layout like this post since we took delivery of the new gun. If we are... i might bring to ole trusty topcon in the truck that day, if you know what I mean. 🙂
> I'm still warming up to the Leica Robot. I'm sure over time I'll get more and more comfy. Luckily we havn't been asked to do any steel layout like this post since we took delivery of the new gun. If we are... i might bring to ole trusty topcon in the truck that day, if you know what I mean. 🙂
Resections and 360 prisms:
Were sufficient to lay out the steel for this:
http://www.gim-international.com/issues/articles/id1562-Driving_Vertical_Towers.html
> "typically we would just set up on our control and radiate the gridline offsets in with my robitic TS."
>
> Wow - I can't imagine doing this!!
well...imagine it i guess.....i dont know what kind of construction your doing but i just cant see any other way around resections and radial staking on some of these construction sites. but i would like to learn if you have a better method which clearly you do.
my company has a massive profile of very large construction projects under its belt successfully so the "wow" comment is a bit insulting....its really not that bad....this is commercial construction not the nasa space shuttle
S,
"...how can I layout these gridlines in a fashion that will leave the least amount of error?"
Be prepared for frustration. Towers move, and floors expand and contract, over the course of a day and especially a season. And if they pour each floor in sections, nothing will match the control on the previous pour. Any errors in radiating points will be the least of your worries.
Dave
Drill a hole with a 1/4" bit, plug hole with 1/4" coiled fishing lead and cut with pruners, smash with hammer and place punch or tack. This will give you a little wiggle room to adjust your points as you run your QAQC. What you describe is pretty typical and doable, but there is some artistry to it.
Heard good things about Leica robots & know a couple guys who use them. A bit pricey for me but wish I wasn't in bed with Trimble.
Make sure on your supplier & service agreement because that IS a big deal, no matter which flavor you pick.
Have fun
