Adding bearers to increase spanning capability

Hi Folks

I live in a typical Canberra 'ex-Govie' which is constructed on a sloping block with the garage underneath and on one end of the house. The houe is of brick veneer construction with frames and truces and none of the internal walls are load-bearing.

Apart from the garage area, the floor area is constructed on brick piers spaced at about 1500mm intervals, and about 1500mm between rows of piers. The piers are spanned by 100x70 hardwood bearers. The joists are at approx 450mm intervals.

There is a fair amount of headroom underneath the floor and the previous owner concreted the area to make a sort of cellar.

The problem is I'd like to make more use of the open space under the house, but face the problem of removing piers whilst ensuring that the floor is adequately supported.

Specifically, I would like to replace or bolster the bearer between three piers and then remove the middle one. This would be repeated for the neighbouring rows of piers.

I have looked at span tables for steel bearers and hispan wooden bearers and have found that I would need to use 150mm bearers. The problem that I would end up with some bearers of 100mm (existing ones) and some of 150mm. This creates a bit of a problem in stallation because the some piers would have to be reduced by 50mm and others would also have to be modified to support both 100mm and 150mm piers (at the overlap betweent the two types).

My question is: would it be possible, instead of replacing the 100mm bearers, to bolt one or more 100mm hardwood bearers to the existing bearer, and so meet the support standards for a 3000mm span between piers? My hope is to minimise any trimming to the existing piers.

I appreciate any advice?

Gooseman

Whilst I'm not an engineer and any structural work should be approved by one to be safe but I can tell you what I did at my place.

My house is similar in that we have a sloping block and the front of the house is level and the back is a story high. To make more room for my workshop over the years I excavated more and more and replaced stumps with stronger bearers.

Do a search for the pictures of my workshop and you will notice that the back part covers two spans of over 3 metres. I bolted 2 additional 100*75mm bearers (one on each side), doubled the end stumps to take the additional load and then removed the middle stumps. Incidently these bearers support a load bearing wall.

The way I did it is to bolt the new bearers onto the old at either end and then use a prop and car jack to jack up the old centre bearer about 10mm in the middle of the span. Then drill and bolt the bearers together at about 400mm spacing before removing the jack. This is because the new bearers will sag about 10mm when the centre stumps are removed and therefore the floor will remain level.

I did the first one about 25 years ago with the assistance of a structural engineer and have never looked back or had any problems.

Provided that you are careful, use 1/2 " threaded rods (cheaper than bolts), and oversized washers and you beef up the stumps on either end to take the extra load you should have no problems.


Peter.

Peter.

Looking at OneSteel's span tables a 100x50 Parallel Flange Channel (C section)
will do what you need.
Slide it straight in next to existing bearer and add a few bolts, piece of cake :)

Gents

My grateful thanks!

I was thinking about the piers and how the remaining one would support the extra load.
Looks like it will be worth while getting an engineers assessment of my idea.

Gooseman

The other way you may be able to achieve the result you want and achieve bigger spans is to use a 2 UB (I shaped beam) and fit them up to 10mm below the floor boards. In this way you get the joist and bearer space to utilise in the size of the UB's. The beares are cut and the beam is slid sideways against the end of the cut bearers (both sides) thus supporting the bearer then replace the cut away section by slotting new section of bearers into the space between the two UB beams.

My steel guy reckons he had done this type of job on a number of occasions with great results.

You might want to discuss this sort of approach with your engineer

Cheers

Hi Sturdee,

What did you end up doing to beef up your outer pier supports ?

Cheers mate
Tom

Quote:

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Originally Posted by tcns

Hi Sturdee,

What did you end up doing to beef up your outer pier supports ?

Cheers mate
Tom

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The original stumps are 100*100 redgum against which I bolted and nailed two 100*50mm treated pine, one on either side making them 200*100mm which then supports three 70*100mm.

I also cross braced the 2 stumps in the middle of the total span amd against the work bench and the end stumps with the workbench onto a further set of stumps, outside the workshop, to stop any movement. The bracing is not in the way as they form support for the work benches.

Peter.

Quote:

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Originally Posted by Sturdee

The original stumps are 100*100 redgum against which I bolted and nailed two 100*50mm treated pine, one on either side making them 200*100mm which then supports three 70*100mm.

I also cross braced the 2 stumps in the middle of the total span amd against the work bench and the end stumps with the workbench onto a further set of stumps, outside the workshop, to stop any movement. The bracing is not in the way as they form support for the work benches.

Peter.

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Did you increase the size of the soleplates?

Quote:

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Originally Posted by echnidna

Did you increase the size of the soleplates?

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No, but the sole plates are 300*300mm which seems to be adequate. This work was done about 4 years ago and there has been no movement whatsoever.

It is also interesting to note that out of the 4 stumps removed only 2 were actually supporting anything as the other 2 were no longer supporting the floor beams. Now all the remaining stumps are as they should be.:D


Peter.