Land Surveyor

Scale Factor in Tower

My company(Consultant) transferred me to a new project a 4 TOWERS consisting of 34 floors and linked in pairs from the top. The piles and shoring system works were carried out by 95%. When reviewing the Control Points of the project, I found that they used the Scale Factor in the implementation.

Note that

* Dimensions of the building are 100 * 100 meters.

* Tolerance is 7 cm in pile.  
the question
- Is it possible to complete the building with a Scale Factor?

- Or any one have another solution?

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Replies

  • Land Surveyor

    That's really annoying to say the least because they stretch all the coordinates by applying a scale factor. The trouble I faced in Riyadh for the CMA tower project was the same. The surveyors use UTM system (from Municipality) to do the preliminary survey. Based on that survey the designers placed the building and axes etc, ... Now when they started setting out the project, the question was "scale factor" or not ? Of course not and this is not because the coordinates are in UTM that you have to apply the 0,9996 scale factor for setting out. On the contrary, you need to start with the minimum datum (1 point E,N,h, and an orientation) and keep all the measurements "scale free" otherwise comparing distances will lead to disaster. Ok the distances are not long and the scale factor applied my mistake will not lead to serious problem but it adds biases and we, surveyors, don't like systematic errors and biases. So the answer is clear : no scale factor for setting out. What to do when you face that situation ? That's a lot of work to re-define a proper datum and to understand what has been poised and what is saved ... Any help on that ? Please don't hesitate to contact us.

  • Land Surveyor

    Good thread and some nice comments here. Apart from the 1st reply!

  • Land Surveyor
    More information would be nice but I think I understand your question with the info you have provided. Keep in mind that I am in the United States and therefore do not us the Metric System typically. That being said, I believe your question is in regards to the actual established survey control of the project. If there is a scale factor noted on the control sheet from the engineering plan set then I would imagine that the original design survey was done using GPS on a State Plane Coordinate System that was scaled to ground coordinates. When you get to the field and are occupying a control point you will need to use the published scale factor in order to check into your other control points. Once you have checked into the other control and everything is working as it should, the first thing I would do is shoot the existing piles and bolt patterns. If something isn’t right between the control you are using and the proposed design plans of the building you will see it then and there. If the pilings are positioned as they should be and your control is checking accurately, you should be good to go. Keep in mind that now that the pilings are laid out, they basically control more so than the project control points (so long as the civil engineer and the architect agree that they are ok with the position of the existing piling). Sorry if I haven’t helped or if you already knew everything I stated, I was trying to answer your questions without a complete understanding of the situation you are facing.
    • Land Surveyor

      Dear Anthony Whitlock

      I agree with you in all what you said, and we already coordinated with civil and architectural to correct this matter after studying the relationship between the piles and the foundation of the building but the project is currently suspended for other reasons, so after correction i will raise what happened. 
      I like to thanking and appreciate you, you have an open mind to deal with any problems and this is came from your experience.

      thanks& best regards 

  • First of all, you don't need a scale factor in a building stake out because the architectural dimensions are as they are. If they used a gps in coordinating the controls , then a scale factor of 1-0.99 can be used in correcting distances, but not the building. Thank you.
    • Land Surveyor

      Dear Kweku Danquah 

      the Scale Factor which used in the project is 0.999666,  it is impossible to complete the building with Scale Factor, and i will correct and after correction i will raise what i did.

      i appreciate you for  your reply 

      Mohamed

  • Mohamad,

    A bit more information would be useful - 1) when you say a scale factor was used on the control points, are you referring to the general site survey?  2) When you say 95% do you mean that the piling and shoring work is 95% complete?

    With out this information I will say the following - A scale factor is used mostly in larger area or route surveys - think a couple of kilometers or miles.  Once you get to a building layout condition revert back to a scale factor of 1.00000 - remember architects only think in square, level and plumb (I know..don't start)  I've never applied a scale factor to a building before. And I am only speaking about normal conditions - nothing like Burj Khalifa or Ping An towers.

    On the tolerance vs. the size of the building, consider this - a 100.00 meter length must be established with a tolerance of +/- 7 cm or 0.07 meters at each end. So your +/- or long and short for the 100 meters is 14 cm or 1 part in 1428.  Normal survey scale factors come into play in the 1 part in 10000 and higher ranges.  So your construction tolerances seems far greater ( read "looser" here ) than any survey related scale factor that you might have on your control points.

    Hope this helps and Good Luck,

    Kevin

    • Land Surveyor

      Dear Kevin D. Allen

      1) when you say a scale factor was used on the control points, are you referring to the general site survey? yes 

      2) When you say 95% do you mean that the piling and shoring work is 95% complete? yes and i completed up to 100%  by the same sequence, and thin the correction will be at the whole site.

      With out this information I will say the following - A scale factor is used mostly in larger area or route surveys  - think a couple of kilometers or miles.  Once you get to a building layout condition revert back to a scale factor of 1.00000 - remember architects only think in square, level and plumb (I know..don't start)  I've never applied a scale factor to a building before. And I am only speaking about normal conditions - nothing like Burj Khalifa or Ping An towers.

      ( In accordance with US specifications, the Scale Factor should be eliminated in areas less than 250000 square meter, my project area 18500 m sq) and I know it is impossible to complete the building with Scale Factor, and this issue need to coordinate with the Arch. and Civil. 

      On the tolerance vs. the size of the building, consider this - a 100.00 meter length must be established with a tolerance of +/- 7 cm or 0.07 meters (sorry the +/- 7 cm tolerance in pilling only not in the whole of building) . So your +/- or long and short for the 100 meters is 14 cm or 1 part in 1428. (the Scale Factor which used is 0.999666 which mean the variance in 100.00 m distance will be 0.0334 m)  Normal survey scale factors come into play in the 1 part in 10000 and higher ranges.  So your construction tolerances seems far greater ( read "looser" here ) than any survey related scale factor that you might have on your control points.

      I offer you my sincere greetings and thank you for your patience in responding and for the excellent information you mentioned.
      I met this problem and I liked to share it with all.
      After i processed it I will mention here everything that has been done, and i like any advise from any one.

      Mohamed

    • Land Surveyor

      Kev,

      Easy there? On me?

      I know nothing of your background; nor you, mine.

      A wee fair tiny bit of my surveying – background, that is –  is that I have done virtually every bit (type/discipline/genre … pick your flavor) of surveying around this planet for nearly three decades.

      I have far, far, far too often witnessed – firsthand – the absolute incompetence and sheer inability of *surveyors* from India, Pakistan, Afghanistan, Sri Lanka, etc. They are wholly incapable of surveying anything. They exist in the business solely by nepotism – quite typically in its purest form of being religion-based.

      Harsh? Without doubt.

      As harsh they are, my words as equally true.

      Every bit of sincere,

      Kevin Singer

      • Land Surveyor

        Dear Kevin Singer 

        i have 14 years experience 9 as a consultant.
        you get the main point who did this issue is Pakistan surveyors ( consultant and contractor) and this first time to me to meet them, most of the data requested from them they brought it  wrong.

         

        thanks for your reply. 

        Mohamed

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