Land Surveyor Forum

Replies

• 

  MARK GREGORY HILL March 3, 2011 at 12:26am

  Well I don't believe this can merely be "explained" with words (experience is the best teacher). In my part of the United States the building surveyor is typically called a field engineer and doesn't have to be a licensed surveyor. I never had a superintedant wait on me to lay out a wall or column. Concrete has been ordered and is scheduled to come at a certain time and you will be ready or you won't work there any more. As LSU Justin mentioned you have to be very descriptive with your problem to get any results. A drawing or sketch might help. Every building is unique unless there are typical buildings within the same complex. There are different ways the structure is designed and built and different methods employed depending on the design, type and material of the structure. Structural steel verses poured in place concrete or even a combination of the two might be one example of this. Try "laying out" a building with a curved side or many curved sides or even reversed curve sides or when the curve radius changes on upper floors or there are cantilevered floors on a curve. Weee doggies. (Not sure I spelled cantilever correctly). The utmost important thing is that the building ends up being plumb. Poured in place concrete can be a little forgiving when it comes to accuracy but prefabbed steel or concrete is not. The elevator contractor will let you know how well you did when the building is "topped out" or the structure is complete and he hangs his piano wire in the shaft with a concrete block attached at the bottom. The ultimate plumb bob! As others have explained you have to set up base lines on the ground with points relative to the grid or column lines. Sometimes you have to offset. Sometimes the lines need to be extended out far enough to be able to see through the instrument eyepiece when aligning the control to the upper floors. Sometimes there is not enough room for this to work (example: a high rise building in the middle of a populated city). A 90 degree eyepiece may have to be used. A good quality laser that can be used vertically may be implemented also, once the control has been established on the ground although I do not believe they are accurate enough when the building is over 12 stories. I have seen it done with a plumb bob and drilling holes through the floor at each column on a short 8 story building. The wind is the biggest enemy when attempting to use a plumb bob. I've seen a "jig" or tool built with a plumb bob inside a clear plastic tube but I've never seen a 2000 foot long clear plastic tube. I heard a "horror story" where the "field engineer" converted inches to hundredths of a foot incorrectly by using 12.66 of a foot for 12 feet 8 inches. I didn't make much difference when the error was in only one floor but when that error got multiplied times 50 floors it grew to be near a 4 inch error. The best tool for plumbing (I truly believe) is a high quality, properly calibrated theodolite (i.e. a wild T-2). Like I said every building design and site condition is a different situation and will require it's own unique method or technique to establish control but the preliminary procedure is normally generic. Establish good control on the ground, offset this control out away from all the construction activity and protect it with your life. I personally believe GPS is not good enough for the precision and accuracy required for a high rise building and of course will only work on the top of the building and not near the building or under any of the floors. I hope some of this info will help.
  • 

    Michael Alan Sanchez > MARK GREGORY HILL March 12, 2011 at 8:10pm

    Well said, I would add the pendulum effect of a rotatting earth on a plumb bob, I have seen large bolts used in a bucket of oil.  We use a 90 degree eyepiece to double plumb the elevator separately, on the highest floor, then using it as the backsight, bring the line down to the bottom.
• 

  Arnel M. Domag February 27, 2011 at 6:04am

  To my opinion, using conventional methods always pose a threat to the reliability of your output. Let us always remember that the basics of surveying thought us about figure strength. Taking very steep measurement lines from short baselines will surely provide very weak figure strength. I think you have three choices to take: 1. employ state-of-the-art monitoring system 2. widen up your work space for a wider and longer base lines, and 3. device your own offset prism assembly.

  In making your own offset prism assembly, I am thinking of a two-line-intersection-offset method for better result. Using this approach, you need to shop mill two rod lengths to your specification and install two prisms for each rod (a total of 4 prisms). Taking shots to the 4 prisms will intesect to the point of interest. Hope this helps.
• 

  zafarnawaz February 27, 2011 at 4:46am

  Michael Alan Sanchez      thank u its help me lot
  
• 

  zafarnawaz February 22, 2011 at 4:52am

  akram shahid the prob is how i can take a shot while my rodman on 40th floor ......so i should have a point there on the 40th floor and that is my question how to make first two points to start my job there on 40th floor and so on ...
• 

  zafarnawaz February 22, 2011 at 3:08am

  Mr Michael Thanks for UR all effort to help me  before to go action I am going to repeat what I got ur explanation

  Step by step

  1 -setup building grid line create offset points away from building .

  2- On the offset points   setup instruments and mark vertically on the columns .

  3-by using plumbs transfer to the higher floors and these marks use a reference and take offset from theses and mark grid line ….

  My question is does it workable for 50 story building …..becouse there are lot of obsticals like scaffolding curve of building and safety (as going to edge of building for using plumbs)
  • 

    Michael Alan Sanchez > zafarnawaz February 26, 2011 at 7:52pm

    So far I only been on 40 story, so far so good, but I believe these methods were developed in NYC which went much higher, one important item I forgot to mention, always when taking up a line, check to the line on the floor below and do not, I repeat, do not set points more then 0.02 off the previous mark.
• 

  Akram Shahid February 22, 2011 at 2:36am

  hi Dear

  As You Work On ground You can Shift Your Point On Any Height Remember Only height(Z) Will Be Change/Increase But The N&E Will be Remain As On Ground
• 

  Michael Alan Sanchez February 21, 2011 at 9:16pm

  Presuming a rectangular building for the sake of simplicity, set up an "envelope" around the building on convenient offsets to the exterior grid lines, something that is consistant and hopefully on a clear working surface, like a sidewalk.After you set out the corners of the envelope rectangle as best you can, then check the diagonals (they should be equal +/- .015.  Then begin laying out the grid lines you have agreed in your contract to provide for the floors, usually every normal bay, I don't usually do fractional grid lines, as these sometimes change floor to floor.  Anyway for sure you will lay out the perimeter grid lines and other important ones like the elevator shafts, escalators, staircases etc.  Assuming (a bad word in high rise) that this is a normal (what's "normal"? Yes I know, trying to make this brief) job, you will layout Row's A-P, and Columns 1-15 .  What I like to do is make a stationing plan for the grid lines, starting  a the corner being 1+00. You can lay out using a mini-prism close to the ground, shoot the end station and if within a hundreth, then play with your ppm's untill you hit flat (I call this "proration by PPM's") then   set all the intermediate stations (grid lines) this can also be done with a steel chain if you can find a 200 footer incremented thruout, you can pull to the end station and holding the weight on the spring balance, set the rest of them, if the tempreture remains constant. Whatever you do, finally measure station to station and double check all dimentions against Plans.  Now having completed the entire envelope, set up on one side and sighting the same grid line on the other side double back the line to away from the contruction site, accross the street, on adjacent buildings (oh I forgot get a 90 degree verticle sight eye adapter for your gun) after doing all the grid lines like this (before all the scaffolding and other impediments get in your way, like the columns) you can now at any time measure to a convenient offset on both side of the building to sight thru the building.  You will now "stack" the grid lines on the steel columns, punch a mark for centerline of column, by holding a sight at 90 degrees with the same offset as the instrument set up on the convenient offset (ususlly 2') , level the plate level and sight the offset line on the other side of the building, I get a folding ruler and place a plastic target on the 1' and mark the 3' with a red pencil. The instrument man then reverses the gun, relevels the plate level, sights the sight on the other side of the building and plumbs up the line a second time, these should be within .01 (maybe more up higher) the guy on the floor in question splits the two marks.  This is repeated thruout the project, usually early in the morning when the steel has normalized (it leans away from the sun as that side expands) also be careful if the crane is attached to the building frame picks a load, as the building can lean. Lets say you have done every third bay this way on the perimimeter, you can chain in the ones inbetween,  using a  column clamp you clamp to the column, and has a slot with a frog to screw down the instrument, set it up on the same offset and sight the offset on the same floor on the other side that you also stacked, now set the line inbetween do this everwhere grids are needed both N-S and E-W ,   When the decking has been tacked welded down you can mark the decking, and when the concrete has been poured (wait until the floor above is cured) you can set final gridlines basically the same way, you might be able to use a tripod now.  Concerning elevations, I like to use the HI of the level set 4' above FF on the bottome floor before pour and  5' above after, set the crosshairs of the level exactly on that Height you wish to mark and have the rodman walk around a mark columns, these will settle over time, but that is just the way it is , so get them in agreement early, then set up every once in a while and eliminate the ones that are going bad. To stack the benches you need to set a least three near elevator shafts or edge of the north side of building (the south side will creep over time as the steel expands and contracts so stay away from those areas exposed to the sun.

   

  Take you steel chain and hold it down from the floor you wish an elevation from and stack the three bm's you have desided to use (some use a spring balance, but a firm pull should do, as long as you let the chain normalize to the temperature of the column), check the bottom ones once in a while during construction try hold them the best you can, but when up on the upteenth floor use the two best to set the elevations you need, basically using the same proceedure to getting the cross hairs on 4' above FF and scanning them over to all the other columns they are needed, you will need the column clamp to do that before the floors are poured. Remember the building and the chain will expand and contract exactly the same so let the chain normalize both for vertical and horizantal applications.

   

  There are many applications where the total station will be of value to set out, but remember that once the grid lines are set on the ground they are no longer at exactly 90 degrees, so verify everything against stacked gridlines (not to mention the building constantly moving) These proceedures apply to a steel structure, precast has a whole 'nother set of proceedures.

   

  Every day take time to thank the Lord for your work and pray for the safety of the job, and you will do just fine.

   

   

   

  God Bless you, in the year of our Lord 2011! 
  • 

    Kweku Danquah > Michael Alan Sanchez March 30, 2016 at 12:10pm

    Thank you very much