Fixing diagonal timber braces to concrete stumps?

When dealing with fixing diagonal timber bracing to concrete stumps does anyone have any better ideas than either:
[list=a][*]U bolts (either from a trailer manufacturer or made out of 12mm all-thread rod); or[*]drilling into each stump and using a chemical set bolt.[/list=a]
Given the stumps will only be about 100x100mm and are fairly hard concrete I’m not keen on drilling any further than 1/3 into them if using the chemset option.

Either way I’ll check out the timber braces so the bolts will only be holding the timber in place. I’m amazed that none of my framing info makes reference to fixing bracing to concrete stumps?

Do you want to brace the stumps because of the height of the stump? or are you trying to brace a wall to the stumps?

I'll be running bracing from the first row of stumps across the front of the house (elevation 1.8m) to the third row back (elevation 0.5m), so it is due to the height of the first and second row of stumps.

Eastie,
no help to you at all I know, but all the older places that I've seen with consrete stumps have bolts cast into them for bracing and tie down. If they're only 100 x 100 I'd be looking at sandwiching a plate either side with 4 bolts and having one of the plated large enough to bolt the timber to also. A couple of short steel dowels or bolts through the plates located in holes in the piers to prevent movement would ensure everything was keyed into place. A simpler method might be to use threaded rod U bolts as per your plan but with the addition of a short stud welded onto them and fixed to the concrete.

Mick

I'd have real concerns with 100 square concrete columns. Just doesn't sound right and you'd be wanting to brace them in both directions to keep lateral deflection to zero I think?

Perhaps it would be worth asking the question of an engineer for the sake of safety. (There I go again!)

I'd be cautious about drilling into them at all, and reckon either the plate or U bolt will work, but don't forget to pack (halve?) and bolt the crossover point of the braces as well.

Concrete stumps are usually precast these days (around here anyway) with holes in strategic locations so they can be through-bolted. In the "olden" days some guys had steel shutters with holes through which they inserted threaded rod before pouring.

Cheers,

P

G'day Eastie,

Somewhere in the dim, dark recesses of my mind I seem to recall that brackets for that purpose used to be available. I suggest you ring a stump manufacturer like Copes for example rather than a supplier.

In the event that they are no longer available, or never existed, (its been a number of years since I had to put stumps in) I think your U-bolt idea has the most merit. As you probably know, stumps withstand a lot of force in compression, but can be rather delicate if you start 'playing' with them by drilling and then inserting bolts or anchors.

HTH,

Drilling holes in 100 X 100 , doesn't sit at all well with me.

I like Micks idea of the two plates, it gives an opportunity to really clamp onto the stumps, not just around them as a U boly will. The slightest movement with a U bolt could allow the whole setup to become "sloppy" rendering the whole bracing idea useless.

I have developed a macabre fascination for these 100 x 100 stumps I'm afraid.....

Eastie, when you said the stumps "will be about 100 x 100" does that mean they don't exist yet?

I am assuming they are holding up a house, if you were to tell me they were for your pigeon loft I'd sleep easier!

The only concrete stumps approaching that size that I have been able to find tonight on the net are 100 X 150 Fence Posts.

Standard stumps are 200 x 200 reinforced with four 10mm bars, and abouve about 2.4 metres the size of the reinforcing goes up. Or you could use steel.....

If the stumps are already there, why is the building still standing, and why do you need bracing? If on the other hand you haven't built them yet, why not be a good chap and build them of sufficient size to hold it up, so I don't have to worry about your well being any more?

With a bit of deft engineering, a larger column set deeper into the ground may not need any bracing either.

Cheers;

the sleepless BitingMidge!

Like the bitingmidge I too am intrigued with your 100x100 concrete posts. I’ve never seen house stumps that small before. Has there been some new advance in concrete technology? Please post some info so I can get some sleep.

If you havent got the stumps yet the manufacturers used to make bigger ones that could be 1800 high without bracing.

U bolts directly holding timber braces are not a real good idea as they can loosen up over time as the timber shrinks. If u bolts hold a metal plate to which the braces are bolted they wont loosen up and slide up or down the stump.

why not just ask the building inspector which way he would prefer that you fix the braces to the stumps.

Biting Midge, I appreciate your concerns –however 100x100 or 125x125 are most common (at least down here) with 100sq being used up to 1.8m and 125sq being used from 1.9m to 3m. Certainly the larger ones have at least four rods of 10mm bar or Y12 but the smaller ones cut back on this. Believe it or not there is also a mob whose structural engineer has created a new stressing and pouring method and subsequently rated their 100sq stumps to 2.4m at standard spacings. Whether they stand the test of time I don’t know and I certainly don’t plan to be the test case.

Other questions – no the stumps are not in yet – they will be replacing the red gum posts currently keeping my floor off the dirt. Larger columns may not need bracing, but it’s easier and totally acceptable to go with conventional sized stumps and cross brace them in the same manner that wall frames are braced (at least according to the Vic. timber framing manual).

As far as asking the surveyor goes he will flob it off to the engineer who will then want detailed plans, make a couple of calculations and then confirm the original bracing should be re-instated, perhaps with the highest corner cross braced on both faces to prevent raking on the north – south axis despite the predominant wind loadings being east/west (plus I've asked the surveyor at work and he recons what I've come up with is satisfactory)

Mick – unless I can dig up anything better I think I’ll go with the U bolts and plates – great idea.

Thanks all for the ideas/comments, you've certainly made me think :D

So Eastie when are the old red gum stumps going to appear on the buy, swap n' sell forum?

Firstly I’ll have a good look at them and then put them aside where they will sit until I realise that I’ll never get around to doing anything with them. Shortly after that I’ll fire up the chainsaw and they’ll be added to the firewood pile. So if you would like to get to them either before or after they go on the free firewood pile let me know (still about 4 ton there for the taking).

Mark

Eastie,

As you say, the timber framing manual has nothing to say on the subject. Maybe we should not expect it to. Concrete stumps are really a latterday addition to the traditional use of timber and maybe don't sit too well in a manual geared to timber framing.

Avoid drilling the stumps, the risk of spalling is very real and would render the fixing totally useless and weaken the stumps.

In my opinion referring a problem like this to an engineer is not necessary. As a building surveyor I think good common sense is the way to approach the fixings for the braces. Look at the potential directions for movement and make provisions for it.

I too like Mick's plate and u bolts.

As a flatlander I also like the potential space under the house. Are you intending to make use of it, or do you already have a wine cellar?

I'd ask the question why concrete.

up here in the land of the house on stumps steel is very popular.

100 x100 steel with a bolting flange on top.

much easier to handle easy to fix to.

Ive seen houses with 20' high stumps fo 100mm steel. theres one particularly uggly modern design down the road from one of my current jobs.

great for replacements too.

dig your old stump out bolt the stump to the bearer & fill the hole with concrete.

the smart blokes give the props a few extra mm to account for settling.