Plumbing of Steel Columns

[mac1992]

Recently arrived on a site in New Cumnock before the Christmas break, where, the week before, the engineer and external site foreman were unfortunately made redundant. As a 2nd year Site Engineer trainee (and having not worked under an engineer before), I was asked to take over to steady the ship until the Christmas break.
One of the tasks I am being asked to do however, is the plumbing of steel columns. I was just wondering what is the easiest/most accurate way of plumbing steel columns for a single-storey gymnasium.
A method that I thought of was to set-up using the total station and on each base plate of the column in the 4 corners mark off-set centre points (250 mm Northing and 250 mm Easting offset for instance)and then alter the co-ordinates of the local grid to suit the offset. Then, take a reading of the offset marks made on the columns to get a position of the column and line in the 4 corner columns. Then line the rest of the outer columns in using the 4 corner columns which are in the correct position (hopefully) using the theodolite, before lining the inner columns in using the outer columns, again using the theodolite.

 

[dik]

I'd be a bit concerned about 'not having worked under an engineer before' and not having one that you can confirm your methodology with.

Having said that, your method appears to be OK, except I'd likely pick two corners of the BP if you need that precision and you have to be careful that the BP is flat (machined?), with sheared edges, the distortion may not give you a plumb column (debris, mill scale, etc.), a half mm out at the base could reflect into 50mm or more at the top.

I've not been involved in the actual site measuring erection, but for plumbing they often use a steel cable and comealong to adjust and a normal level. I use a 4' mason's level with a magnetic strip glued on the one edge. Not scientific, but have checked it at 180 deg rotation to verify that the mag strip was parallel to the original face of the level edge.

Dik

 

[jgailla]

Another way is to use a laser level, which must be calibrated occasionally.
Measure off 6 inches or so and mark the slab. Place the laser on the mark and then measure off at the top.
Depending on the spec, you should be within about 1/4 or 1/2 inch of 6 inches.
Repeat in the other plane.

 

[Drumchaser]

mac


Been years, but we used a Theodolite. Utilizing the included optical piece (looks similiar to a 90 glass) that attaches to the site end of the barrel, and a person (on the beam) with engineers folding rule. Set up back far enough to site the column from the bottom to the top (no set up point needed) first plumbing along the side of the beam to get close, then using an offset and the rule adjusting the columns as needed. Of course you have to plumb from front and side of columns, similiar to the way concrete columns are plumbed before, during, and after concrete placement.
I am aware it seeems more prudent to set up on a control line/offset, but I am not convinced it is necessary.

This building was only 6 story, seemed to be very effective.