Sir,i have some issues to ask about getting started for building layout such foundation and gridline offset,which method advisable and accurate to use in 300m x 108m building by coordinates method or angle/chaining method.thank you sir i realy need ur advise.thank u
This Content Originally Published by a land surveyor to Land Surveyors United Network
Are you talking about "Design" grid or "As-staked" grid reference points?
If the later then you already have design grid points and you are looking for field procedure here are some...
Grid Ref. best practice plan
1) Have a tight Survey Control network that surrounds the building site (Primary Control Horizontal & Vertical). Preferably far enough away from proposed building to use on all floors.
2) Work at night or Early morning to reduce error issues related to temperature change, vibrations and line of site.
3) Preform resection using at least 3 points from primary control and set grid reference points on each floor that can be checked for “stacking”.
4) Check “stacking “ from ground level to make sure grid reference points match on each floor.
5) Set grid reference points on each floor & check Distances between them with 100’ steel tape.
6) If setting TBM’s on each floor then clamp steel tape on column on 3rd floor and then measure up from TBM on ground level, marking elevations on column at each floor. Repeat this step clamping tape on upper level then measuring up from lower level. * If this is not possible then make sure to tilt prisms to correct angle to carry “Trig” elevations to each floor.
7) Always check instrument to make sure it has not gotten out of level and check your Backsight.
thank you sir for the information,i prefer coordinates.now for coordinates method i will set my building in positive Y positive X GRIDLINE,using cadd first gridline X as N-20000 and gridline Y E-20000 from those coordinates each gridline subtract or addition method on what dimension shows on plan,
i have installed 8 numbers of BM around building project site closed and fixed,so i can do the resection method in any area as long as BM is visual and clear sight for backsite.
ok sir,highly apreaciated.thank u
Rey, your question has a few key phrases:
Your equipment is a theodolite and chain.
Create coordinates for any method you choose.
-300m x 108m building
This is a large footprint.
-foundation and gridline offset
This is a good approach when using a theodolite and chain.
I would create a baseline, 10 or 20 meters away from the building (or wherever practical), parallel with the longest building dimension, and chain in the points for grid-line.
I would then create baselines for the other three sides, turning only 90 degree angles (and sets of direct/reverse observations, of course), and make sure you tie-in/adjust to your original baseline before marking your grid-line points for these additional baselines.
Don't worry about offsets yet.
Depending on MANY factors about the job I do not know, you are now prepared to layout foundations.
Grid-line works well for foundations because there is little or no vertical work obstructing your line of sight.
The great thing about this type of control is you can backsight the grid on the other side of the building to furnish the workers reference lines without turning any angles, or chaining, as you can set up on the perpendicular baseline and perform the same action.
And, with baselines, offsets are very easy to install. Just use a ruler.
Need a quick 1 meter offset?
Measure and mark it on your occupy baseline, and on the backsight baseline on the other side of the building, set up and go. This measure and mark routine does not require great angular precision. If you have to turn a 90, buck in on your baseline.
You get fast at this.
Also, when line of sight permits, "bucking in" can be done almost anywhere on site if you have boxed in the building with baselines properly. Better than two-point resection in many cases.
When vertical or elevated work will obstruct your line of sight across the building, establish practical offsets, such as one meter.
A theodolite and chain makes baseline/control work difficult by comparison to a total station, but once you complete your baselines, it is not so bad.
But if any of you try to lay a hand on my robot....grrrrrr!!!
Co-ordinate method is the best suited for this kind of jobs. Steps.
1. Run a traverse around the site and do the correction based on bowditch rule.
2. plot the points and superimpose the proposed building and extract the co-ordinated of the required corners, center of columns etc.
3. stake these points at site.
A Murali babu
A Murali babu
Thank you A Murali babu..
Good day My Dear Colleague Surveyor and My Dear Murali Babu,
Just an opinion
From my knowledge " BOWDITCH " method is not suitable with building and grid line.
It is because of this method is adjusting both of the angle and the Distance, which means GRID LINE is a fix distance where we cannot adjust distance in the traverse STN to STN .
Distance is fix, what we ( shoot ) got is what we get, No adjustment in that, but angle adjustment is a YES.. Do the True Bearing Adjustment, Normal steps M+/- Correction and C+/- Correction as per Traversing result should close to 1:80000 or more. But still we get a little bit of an error here and there when we apply the Working Coordinates, where our coordinates runs around 3 mm to 7 mm, X or Y, even more depends on closing, But that not means we have to use Bowditch Method, there is other way to adjust those error...
For Me Bowditch rule only can be use in Road or Rail works, which had the alignment,
It is because the Traverse that been made is an open travers From 1 known STN to another Known that already been set up using GPS,
Just an Opinion from my knowledge, please do to Correct me if i am wrong
But for the one who had problem with what i am saying about the "A little Here and There Error" after traverse adjustment been made, still this +/- 3 to 15 mm or more in X or Y,
can e-mail to me email@example.com their Traverse Booking/sheets, Close or an open one, and ill adjust it for you and send it back for your checking again, if agree with the result and wanted to learn ill be happy to teach the lesson
Just an opinion...
I agree with you partially. The only way to correct open traverse or closed traverse is to give the correction for both angle and distance. If not done the errors creep into, due to several reasons like, local attraction, errors in the instrument, prism constants etc.. so it is better we close the mis-closure before doing any survey. regarding to road and rail surveys, it is mostly open traverse, maybe with known co-ordinates fixed by GPS or any other method. We do the open traverse and then close them with bowditch rule. In a closed traverse as we are discussing for the grid line, I have done several projects in the same lines as explained by me and have achieved accepatable results.In most of the cased i have achieved accuracy of more than 10000. In case you need the calculations and correction excel templates please visit our website www.esurveying.net. here you can download free templates for both open and closed traverse.
A Murali babu