Bolting steel baseplates to concrete - Steel to concrete fixing

[Rick]

I will be bolting down a large number of 8mm thick Galvanised base
plates onto a reinforced concrete raft.
The plates are 300 x 300 and each fixed by 4 M16 anchor bolts - picture of thems at:

http://tinyurl.com/2qdjlj

The plates while pretty darn good, are not perfectly flat ... the welding on the upper faces (300 high T section in 8mm steel) plus in places the concrete may be a couple of mm out, although it is a good powerfloat finish.

We are only talking about slight rocking of the base plates, and the torquing each of the bolts to 100 lb ft will probably pull bases flat.

These are being used externally and will be subject to wet & full UK temp range. (hence the galv)
I have thought about spacing the plates up off the slab using 10mm packers, and then arranging a small formwork around the base plate, and pour in cementitious grout. (Cemgrout EF?)

The sequence I will follow then would be ..

Drill holes
Shim plates with 10mm steel spacers
Fine adjust to get plates plumb
Torque to 75% on finished setting
Create formwork, giving aprox 20mm all round base plate.
Pour cementitious grout
Let it set for specified time (24 hrs = 30 N/mm2)
Torque down bolts to final 100 lb ft

Does the above all sounds logical ?

The only issue I can think of .... the grout will be poured and will surround anchors & bolts threads .. when I then go to give final torque ... will the threads turn with no problem ? or conversely will turning them cause a problem.

Do I need to consider this ? .....pre-treat threads in any way ? or even perhaps look at full torquing down (onto shims) before grout is poured.


Thanks for any advice on this.

[Tony McC]

I'd not tighten after pouring the grout, Rick. If the grout is any good (I have a preference for LokSet) then the bolts won't turn. If they did move, it would probably be at the expense of the grout, by causing a crack or shattering it all.


Normally, I'd have threaded bar coming up and then have nuts on the top side of the plate which allows the plates to be removed at some futrure date without destroying the rest of the structure

[lutonlagerlout]

we use chemical fixings for most stuff like this now rick,what are the plates going to support?
i priced a job recently that had cones left in the concrete in polystyrene which once the concrete has cured you can form steel work out of it,then concrete the cone
cheers LLL

[bobhughes]

I would certainly have the nuts on top. How important is it to get the levels right - ie the posts vertical?

I was looking at a fence yesterday (2m high weld mesh on the side of a canal) supported by galvanised steel posts bolted to a brick base. There was some kind of gasket under the base plates and I guess that this would give a bit of leeway to get the posts vertical.

[seanandruby]

on a big job the bolts would be coned then the bottom nut and plate wrapped in denso. they would be hung in the reinforcing and concreted in situ. next day the bolts would be cracked with a few taps of a sledge ( on the nut not the thread ). any difference in height would have shims under the steelwork then grouted in. if you make a template out of ply and drill holes you shouldn't be far off. remember to fix all steel before grouting so you can fine tune with that trusty old sledge.

[Dave_L]

The cure-all - the big sledge!

[Tony McC]

We call it "The Persuader"

[seanandruby]

ah yes the "friendly persuader".

[Rick]

we use chemical fixings for most stuff like this now rick,what are the plates going to support?
i priced a job recently that had cones left in the concrete in polystyrene which once the concrete has cured you can form steel work out of it,then concrete the cone
cheers LLL

Thanks for the replies .. the base plates will be holding up the vertical 6x6 posts for my 'barn style' car port & garage.
So will be attached to some large Glulam beams and holding up the tiled roof.

I did look at using cones but was advised against it on my particular design of raft.
Structural Engineer advised to bolt down the plates using 125mm 16mm expanding sleeve anchors.

I have drilled the holes, and looks like I will use 10mm packers underneath, set bolts and fully tighten to spec (100Nm)
have made myself some formwork which gives a neat 10 degree sloped edge on all 4 sides, and is 20mm wider than base plate.
I have bought the pukker cementitious grout (Masterflow 928).. and will pour this in to flush with top surface of plates.

Only 2 issues now - how do I prevent it leaking out under formwork (it is liquid after all not concrete)- tempted to run a bead of silicone around the inner edge of formwork, and peel it off concrete after.
The 2nd bit is mixing the grout ... Tech sheet goes into detail that a high shear paddle mixer should be used or a non-colloidal mixer ... spiral mixers & whisks are forbidden as air entrainment is a no-no.
Maybe I just use my plaster mixer paddle in a drill on lowest speed and take time to mix.