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Author: Subject: Anyone know about using rebar to strengthen a brick column?
John P

posted on 24/7/17 at 11:13 AM Reply With Quote
Anyone know about using rebar to strengthen a brick column?

I’m building a raised deck on the back of our bungalow which will be supported on four brick columns each 1 ½ bricks across which means there will be a hollow down the centre around 100 mm square.

The columns will be around 1.8 metres high so to provide lateral strength I plan to fill the 100 mm square hollow with reinforced concrete after the column is complete. (I know there are alternative ways of supporting the deck but really want to go with brickwork).

In the foundation I am setting some rebar which will stand up above the foundation by around 200 mm or so.

I would prefer not to fix the long lengths of upright rebar before building the columns as I feel they will get in the way when doing the brickwork so do they actually need to be fixed to the ones projecting from the foundation or would the 200 mm overlap be OK? I am hoping to simply build the column then put in say two lengths of rebar and pour concrete into the void.

Is this OK.

John.

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r1_pete

posted on 24/7/17 at 11:31 AM Reply With Quote
Are you tieing the deck to the house to help prevent lateral movement? If not the rebar ought to be tied to the footing bar, if you are tieing in then the columns will only be under compression stress so rebar is not really neccessary.
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stevebubs

posted on 24/7/17 at 12:09 PM Reply With Quote
Can you put a former in the middle of the foundations and create a void to be filled later and allow a greater overlap...?

No idea if this is a better idea...but a thought....

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John P

posted on 24/7/17 at 12:56 PM Reply With Quote
It will be tied back but only over a short length at each end as there's a narrow "post box" slit window in the way (which just allows some light into an under floor void) plus some cantilever supports for a bay window / patio door which will eventually lead onto the deck.

Of the overall length of 4.4 metres only around 600 mm at either end can be tied back but obviously this will give some lateral support.

I have seen rebar being used on major industrial builds and it looks as though the upright bars are only wired to those projecting from the foundation which I was assuming was to keep them in place rather than for strength.

I guess I could pour the foundation pad with say a 100 square recess in the centre so the bars could run down into this but it would make the positioning of the pads very critical as the bricks could easily end up overhanging the recess slightly.

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r1_pete

posted on 24/7/17 at 03:19 PM Reply With Quote
If its tied to the house at each end, and you put a diagonal support under the deck joists, you'll have no lateral movement. So I wouldnt go over engineering the rebar, as you suggest drop a couple in each pillar and pour concrete in.
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MikeR
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posted on 24/7/17 at 03:35 PM Reply With Quote
I'm not an engineer but.... Why not sink a 2.4m concrete fence post and build bricks around that. I know it's not quite what you want but it sounds ideal to my non building brain and ready made.
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rachaeljf

posted on 24/7/17 at 04:30 PM Reply With Quote
A structural rebar overlap has to be 40 x the bar diameter. Eurocode 6 gives the rules for reinforced brickwork. You really should get your deck and supporting columns designed by a structural engineer.

Even if the deck is braced to the house, the slenderness (ratio of height/thickness and the end support conditions) of the columns is what matters for their resistance to buckling under vertical load.

For me, I would prefer to use galvanised 100x100x 3 or 4 mm square hollow section steel columns, bolted top and bottom. Then I would build the (non-structural) brickwork around them.

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John P

posted on 24/7/17 at 05:54 PM Reply With Quote
Thanks for all the comments.

I have a design guide from the timber decking association and according to this I could use 140 x 140 minimum timber for the columns so I'm very confident the brick construction will be OK in compression and buckling. My main concern was that any small lateral movement could cause cracks between the bricks but I'm now fairly happy to go ahead and tie the deck in at both ends and include a diagonal brace under the joists as per the suggestion from r1_pete.

I will then fill the brick columns with concrete after they are completed and fit two lengths of rebar in each. I'l also have a somewhat greater length of rebar in the foundation so that at least I'm close to the 40 x bar diameter mentioned by rachaeljf.

Thanks for all the help.

John.

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