【转帖】concrete formslab floor layou

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concrete form/slab floor layout
i am creating a drawing and i need to dimension features to be incorporated into a concrete floor.  i need to provide dimensions so the items can be placed appropriately in the concrete forms before the cement is poured.  
what should i dimension from?  what should i use as  a datum? the edges of the slab? column lines?
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tcphoenix,
   what feature do you want your items located from?
   asme y14.5m-1994 allows for composite tolerances.  you have one tolerance to locate your hole pattern, and another to locate the holes within the pattern.  see figure 5-20.  this sounds like a good application for it.
   is asme y14.5m-1994 used in architechtural and structural drafting?
                         jhg
i am looking for what is practical for them in the field.
tcphoenix,
   define "practical for them in the field".  
   presumably, they need to measure something with a tape measure.  they need to be able to access whatever it is they are measuring from, and you need to open up the tolerances to something that can be done with a tape measure.
   composite tolerances are a strategy for calling up sloppy tolerances.  when i show a square pattern of holes and i believe they will be using a tape measure, i call up the diagonal dimension as well as the orthogonal ones.  consider calling up slots, rather than round holes.  
   this all depends on your requirements, and on the tools your fabricators have.  
                       jhg
check out the attached jpg.  what you will see is the footprint of my slab.  and to the lower right on the curved corner i have some holes that need to be properly dimensioned.  the important items are there relations to each other, the distance from the edge of the slab and they are also on a common radius.  
there are columns in the middle of the slab.  should we pull two column lines to make an interesting point that we can use as a datum, and then dimension the holes from that datum?  should we use the edges of the slab and give x an y coordinates away from each slab edge?
and when i say practical i am looking for input from the guys in the field who have to make the form.  
in the construction world is it obvious that column lines are used for measurements?  do they usually measure from the form edges?
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tcphoenix,
   which of your tolerances are more important.   when i suggested composite tolerances, i was assuming that the holes had to accurate relative to each other, and that the location of the pattern was less critical.  this is a good application for a cardboard template, especially if you have a large enough drafting board.  
   you need to review your requirements, then talk to your construction people and see what tools they have.  you need to know how accurately they can lay stuff out.  
   datums have to be real features.  the two straight edges and the radius all are potential datums.  it is acceptable even to use two of your holes as datums, but it all depends on what you need to do, and how your construction people are able to do it.  
   dimensioning and tolerancing is a language, not a procedure.  
                            jhg
tcphoenix: looking at your posts and jpg, i would ask if the radial pattern of holes are tied to a continuous integral component. if so, this dictates what between hole tolerances you need to hold.
i see 2 ways of dimensioning them. (1) locate the center of the bolt radius relative to the two large perpendicular edges of the slab, or the nearest column. show the bolt radius, and define the angular distgance between holes. this should be the most accurate. (2) layout accurate perpendicular x & y scribe lines near to and parallel to the large flat edges of the slab(can't trust squareness of the slab line). then locate each individual hole by x and y dimensions from these scribe lines.
this is basically structural work, and i would forget about any references to gd&t or asme y14.5. tape measure, straight edge, and string (or wire) and pencil compass layout work. composite tolerances are nice, but most likely inappropriate for this application.
this is coming from a gd&t guy, who also has done a lot on structural support work into concrete.  
since i have had to help build a couple of embassy suite hotels i will give you a small piece of advice. when building multi-level structures it is important to have a base layout. for example: when i set a hotel footprint i use the structure columns as my datums. i would establish the grid so that i can see all sides. i set grid points across the street in the sidewalks usually with a drill hole or a chisled "x". with the columns where they need to be create a grid, use intersecting lines to establish your datum control. everything else will be measured off of the control points. try it an see.
regards,
namdac