Concrete Column Formwork
Column Formwork - Column shuttering.
On the right we have a shot of concrete formwork for a column.
Just behind it we see a column that is completed, with it's cranked
starter bars sticking out of the top, ready to connect to the next
stage, the suspended floor slab.The finished column would have been
left in it's concrete formwork for a day or so, then stripped and
the clear plastic immediately wrapped around it to stop it drying
out too quickly. This is known as curing the concrete.More on
concrete curing here.The footings are poured in the ground, and
starter bars will be coming out of the footing, and the column
rebar steel will be fixed the them.The carpenter makes up two pairs
of formwork shutters or forms, and nails them in place around the
rebar steel.He has already shot pieces of timber onto the footing
concrete to allow him to locate the concrete formwork in the
correct place. You can see one at the bottom left of the close up
photo.He then bangs in 75mm nails to hold up the column clamps
until he has them assembled and just nipped up. The photo shows the
column clamps which come in different lengths. A clamp set consists
of four lengths of 75 x 8 steel with a hook on one end and
overlapping slots in the other end, to take the steel wedges that
do the work.
Column Formwork - Acrow metal column clamps
You can see that the clamps are positioned alternately up the
column, So that the wedging force changes direction with each
clamp. If they were fixed all the same way, there would be a
tendency to put a twist in the column.The props used are the
industry norm "Acrow" type props. Which come in varying lengths.The
props have large and small holes at the top and bottom for
connecting to other fittings, and nailing the props to sole plates,
at the bottom and bearers etc. at the top. Steel props like these
were designed for concrete formwork, but have found there way into
many other applications because of their versatility.back to
topWindows In Deep FormsThere is a requirement in the standards for
concrete formwork and concrete codes, that mixed concrete should
not be allowed to fall freely over a certain distance. The reason
for this is that the concrete ingredients tend to segregate when
they fall.The columns in this picture would have had to have a
removable window in the forms, say half way up, that is used to
fill the lower half of the form, then the window is put back in
place and usually wedged, then the rest is filled.It is not often
done these days , because of the use of concrete pumps that allow
the last section of the delivery pipe to be lowered into the column
and brought slowly out, as the concrete rises. Also the mix of the
concrete is designed differently for pump use.The same thing
applies to walls of course. I can remember putting windows half way
up some walls that were tapered, thinner at the top. The pump
delivery pipe did not have enough room, because of the reo steel,
to get down the inside of the form without a risk of getting it
stuck.If you are doing small slow pours, say mixing on site, in
high forms, use windows. Apart from the segregation issue, the
concrete as it falls from the top sticks to the sides of the form
and rebar, and can have already taken on it's initial set before
you add the rest. This later gives a flaky surface to the finished
concrete.Setting Up A Column Form
Column formwork - Another method on larger columns, using tie
bolts. The horizontal pieces in this case are steel "C" sections
that have plates welded across the gap to stiffen them. Once again,
notice how close together the bottom supports are
Shoot down timbers (Ramset gun) to position form accurately over
the footing. The photo on the right shows them. Clip on plastic bar
chairs to the reo/rebar, to maintain the correct concrete cover to
the steel. (I have sometimes used a length of the correct thickness
of timber on each side, that is drawn out of the wet concrete as it
is poured) Tack the four shutters together, roughly plumb. Probably
at this stage the guy that did the job on the right, checked for
square at the top, and put a through bolt diagonally across to pull
it slightly. Fix the clamps lightly Put a prop on each side and
plumb up. Plumbing up a column like the ones in the photo may be OK
with a spirit level because the timber thicknesses etc all look
consistent, but I have always used a string line and plumb bob.
Nail a bit of scrap timber to the top and hang the line off it.
Measure back to the ply, top and bottom. My first spirit level that
I ever owned (a Stabila) was designed so that I could put it down
the inside face of a column or wall form, and read it from above.
They don't seem to make them like that these days. Tighten up the
column clamps checking for twist as you go. Check again for plumb.
It is always a good idea to stand back and look at the column in
relation to the others columns or walls nearby. See this page for a
better explanation ofplumbing up columns by eye.back to topLow Tech
Concrete Formwork For Columns
Column Formwork - Timber yoke used as a column clamp
Column Formwork - Timber yoke. The bolts clamp the shutters
together one way, and the wedges the other way.
Here is a method that was used before steel column clamps came
on the scene. At least where I was. It is easy to make up a few
sets of of these.You may say why bother showing something that is
obsolete? Well plenty parts of the world still work with home made
stuff, and I say "good on em". More to the point though, this
method can be used for one off column or larger boxes. It can even
be used around a one off beam where no other formwork is needed on
the job.Left is a sketch of the wedges from the side. The wedges
are put as close to the ends of the bolts as possible, otherwise
the bolts could bend under pressure.Note! Clamping the forms
together can push the forms intoo farif you do not lay out the ply
and battens as detailed. There must always be a firm edge to push
up to. (desirable with most formwork actually).
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