Support work

[JDLDIY]

Well, once I've finished the rewire, which shouldn't be long now, the next job is to install an RSJ, where a supporting wall is removed. I'm planning the support side of the job at the moment - I want to have a really clear plan to avoid anything going wrong and to make sure the job goes smoothly.

On one side of the wall the upstairs floor joists run into the wall - these I plan to support separately from the wall with props. I will need to use noggins first to lock them together as at present there are none and the ceilings are down. I was going to support the wall itself with pairs of acros and needles (6"*8" timber), but see the hire shops have "strong boy" supports which the literature will have me believe do the job instead and using only 1 prop. I have a timber ground floor - joists of 8"*2", but the sub wall runs right under the line of the wall which will help.

The wall above the lintel is 1 storey high, it is an internal single leaf wall made from common brick and there is little other weight bearing on it.

So am I on the right lines? Anyone used strong boys before and would I be better off sticking to needles? The wall is 3m in length and I intended to use 4 pairs of props with needles or now 4 acros+sb's. The other thing is, when propping the ground floor from the sub-floor, what could I use? I know I could alternatively remove ground floor boards and run the acros to the sub floor but I'm not sure how flat and true it is. The upper floor joists are 8"*2", what size noggins should I use? I'm concerned that if I use 8" deep noggins and then put ceilings back up I'm inviting rot to set in where I have created little boxes with no air movement.

OK, sorry for the long post, many thanks for any advice on this one, I've done loads of DIY, joinery, electrics, plumbing, roofing etc in the past but this is quite a big job and I want to get it right first time!

JD

 

[JerryD]

Before you do anything, have you had a design on the steelwork or are you just going to 'bung in an rsj'? (i.e. have you got Building Regs approval for this?)

What is the steel going to sit on at the ends?

You'll need minimum of 3 acrows and 3 Strongboys for a 3m opening.

Support the ceiling by using a spreader of some sort (timber, often a clean scaffold board) which is supported on separate acrows, every 1200mm or so.

Very important: get the steel in position on the floor before setting up the acrows, you may not be able to get it in afterwards!

Joist noggins can be 2" smaller than the actual joist, so in your case 6".

How are you going to lift the steel beam? I could weigh a lot. You'll need to 'have a plan' of how you're going to tackle this bit of the job.

You'll need at least a couple of extra acrows to finally support the steel when it is in place, prior to final supports being done. If you can, lay a mortar bed on top of the steel beam just before finally acrowing it into place.

The steel will need fire protection.

 

[JDLDIY]

JerryD - many thanks, well here goes:

Before you do anything, have you had a design on the steelwork or are you just going to 'bung in an rsj'? (i.e. have you got Building Regs approval for this?)

Yes I have and it is sitting in my back yard. It is a bit non-standard, being a piece of 8"*8" with the top plate cut down to 4". It is the correct weight of steel etc to do the job and yes I will have full building control approval.

What is the steel going to sit on at the ends?

I had intended to support the ends on padstones, dense concrete but would be grateful for any advice on this aspect/what to use. The padstones will sit on the inner leaf of an exterior cavity wall and onto the top of an inner wall at the other end. I appreciate that the more I can spread the load with bigger padstones the better.

You'll need minimum of 3 acrows and 3 Strongboys for a 3m opening.

Support the ceiling by using a spreader of some sort (timber, often a clean scaffold board) which is supported on separate acrows, every 1200mm or so

Great, that is more or less along the lines I was thinking.

Very important: get the steel in position on the floor before setting up the acrows, you may not be able to get it in afterwards!

Yeah, funnily enough I thought of that, but if I use strong boys the access with the steel will be easier because I can do all my support work on one side leaving the other free for access to the space to install the steel.

How are you going to lift the steel beam? I could weigh a lot. You'll need to 'have a plan' of how you're going to tackle this bit of the job.

Yes you are right and as this piece of steel is heavier than some (I intend to fit the first floor joists into it and rest them on the bottom leaf) it will take at least 5-6 people to lift it comfortably. I was then going to look at having some form of scaffold step in place so that we can step up, I'll need to then use acros to support the weight as well.

The steel will need fire protection.

Yes, this is something the building inspector has alluded to but the one bit I've got no clue about. For one thing why is it necessary? The timber will have burnt to hell long before the steel surely? How do I go about fire protection of the steel?

Thanks, really useful advice.

JD

 

[JerryD]

Padstones will have been designed by whoever did the steelwork calculation. If an inner wall is being used as support, how do you know this has a foundation? It may just be a block partition built off the slab?

Lifting the steel into place is more than just having a load of guys round for the day. You will not be able to lift is straight from to floor and then place it some 7 feet above the floor onto the padstones. You can use a pair of TALL builders trestles. Get the steel onto the trestles and then carefully raise one trestle up a notch. The go to the other end and do the same. Keep repeating this until the steel is at a height suitable for just 'sliding' across into position. The advantage of the trestles is that you can have a rest as often as needed. Safety is paramount when doing this type of work.

It may be sensible to temporarily stabilise the trestles by fixing them to something (even to the Acrows), as tall trestles with a heavy steel beam on them tend to wobble alarmingly! I'm sure HSE would have a heart attack if they saw this!

Fireproofing the steel can be done in many ways. The most common is to encase it in two layers of 12.5mm plasterboard (with staggered joints) and all plastered in afterwards. Wedge timbers into the steelweb and fix the plasterboard to that. However, I see that you intend to fit the joists onto the bottom web, so this means the steel will mostly be enclosed within the floor space. Boxing in the part showing below the ceiling is still required however.

If (for instance) the steel beam was to be TOTALLY enclosed within the floor space (i.e. a level ceiling with no beam visible at all) then fireproofing is achieved by just a standard ceiling.

Fireproofing steel is needed because the steel would become hot and soft during a big fire. A 'soft' steel beam will collapse and bring down all walls etc above it which rely on it for support. The timber joists would be long gone of course, but the idea is to minimise structural damage which steel collapse would cause.

 

[Thermo]

On the subject of fire protection, the rsj will go before the timber. the rsj will become warped by the heat fairly quickly in a fire and become structuarly sound. timber on the other hand will char over its surface. once it has done this there is very little fuel on the timber for the fire to burn, the charring effectivley seals the timber and protects it and will take a long time to burn through.

Thermo

 

[oilman]

I agree the RSJ is likely to fail before the wood, but I have not looked into how structural timber is affected in a buildings fire. In a wood fire the wood is heated up and then tars and gases which form the wood are driven off and burnt, despite the charring on the surface. Is something different happening in buildings fires?

 

[JDLDIY]

If an inner wall is being used as support, how do you know this has a foundation? It may just be a block partition built off the slab?

The part of the inner wall concerned used to support part of the weight of the wall that has been removed and also a brick built boiler chimney which has been totally removed. The inner wall is made of brick, not block and reaches down past the slab, ie the slab comes up above the lowest brick seen under the floor. How would you check this out further though?

Lifting the steel into place is more than just having a load of guys round for the day. You will not be able to lift is straight from to floor and then place it some 7 feet above the floor onto the padstones. You can use a pair of TALL builders trestles. Get the steel onto the trestles and then carefully raise one trestle up a notch. The go to the other end and do the same. Keep repeating this until the steel is at a height suitable for just 'sliding' across into position.

I hadn't thought of using trestles and was intending to use a piece of scaffold, in a stepped form. I think I'll still erect some form of scaffold to get decent access to the level at which the beam is to be inserted, but then having the trestles to either side to take the weight of the steel and anchor the whole lot together with the acrows.
It still strikes me that the better way to go with regard to the props is the traditional method using needles, surely that would be more stable? Also with needles I can make sure that they are clear of the level at which the top of the steel will sit if you know what I mean. Strong boys will by design be sitting at that level and therefore be in the way won't they?

If (for instance) the steel beam was to be TOTALLY enclosed within the floor space (i.e. a level ceiling with no beam visible at all) then fireproofing is achieved by just a standard ceiling.

Yes the steel beam is to be totally enclosed in the ceiling, it is 8" deep and so are the joists, so the whole lot is designed to end up flush. It would be no bother to enclose the sides of the steel in plasterboard before putting up the ceiling boards, do you think that would be necessary? I will be checking that with the Building Inspector as well.

On the subject of fire protection, the rsj will go before the timber. the rsj will become warped by the heat fairly quickly in a fire and become structuarly sound. timber on the other hand will char over its surface. once it has done this there is very little fuel on the timber for the fire to burn, the charring effectivley seals the timber and protects it and will take a long time to burn through

I take it you meant 'unsound'? I never would have thought it - steel failing before the wood but of course it makes sense, thanks.

In a wood fire the wood is heated up and then tars and gases which form the wood are driven off and burnt, despite the charring on the surface

Not with you here Oilman, can you put that past me again?

 

[JerryD]

The only GUARANTEED way to establish if a wall has a foundation is to dig a test hole.

Now that we know that the steel being totally enclosed within the joist space, how are you going to prop the wall above? (regardless of whether using needles or Strongboys). You will have to prop it through the floorboards. In other words the props will have to go through the upstairs floor to pick up the brickwork which will have to be supported on the course that is to sit on the steel beam. Some flooring will have to be removed upstairs. Are you aware of this?

Strongboys won't "be in the way" of the steel beam as they are very thin at the edge where they support the wall. The steel will have to have a bed of strong mortar applied to the top of it before screwing it up on the acrows that last inch or two. This mortar bed gives that tolerance to pick up all the bricks in the wall not matter how uneven they are and in addition allows the Strongboys to be pulled out next day. They may need a wiggle but they will come out.

As far as I am aware the steel beam needs no fireproofing if it is within a floor space with a standard plastered ceiling below. If your building inspector says different I would be interested to hear.

If the steel is to be enclosed in the joist space then the end bearing of one end will have to be larger (temporarily) to allow the steel to slide in one end enough to clear the bearing wall at the other. Does this make sense. In other words if you have (say) a 3500mm beam and a 3200 opening (with 150mm bearing each end) then the gap above the padstones needs to be 3650 minimum (i.e. one bearing 300 long rather than 150). If this doesn't make sense I'll do a sketch and post it here.

Just to put you in the picture of how we do steel installation, we use two very helpful gadgets. We own a Genie Lift which is a hand operated forklift. It is quite small and goes through doorways and will lift about 350kg up to 24 feet in height! These can be hired and are extremely useful. The other thing we use is what's known in the automotive trade as a 'transmission jack'. We've had extended rams made so we can lift beams from 5' in height to over 12' in height. This is hydraulic and again is very useful. We use the Genie Lift on ground floor beams and the Jack on first and second floor beams (as it's easier to carry up the stairs!).

Rather than get loads of 'mates' round (unless they are reasonably skilled in construction) I would suggest the Genie Lift hire. Having load of unskilled people for a potentially dangerous job is very risky, everyone will be doing their bit but it needs a co-ordinated effort with one man in charge. Just my 2 cents worth...........

 

[JDLDIY]

Now that we know that the steel being totally enclosed within the joist space, how are you going to prop the wall above? (regardless of whether using needles or Strongboys). You will have to prop it through the floorboards.

Yes that was something I was always aware of. It's just par for the course and the whole house is an ongoing project so disruption is something we have become accustomed to!

In other words the props will have to go through the upstairs floor to pick up the brickwork which will have to be supported on the course that is to sit on the steel beam

I may be reading that bit wrong, do you mean I should be inserting the support above the lowest remaining course of bricks? If so what's to stop some or all of the lowest course falling away?

As far as I am aware the steel beam needs no fireproofing if it is within a floor space with a standard plastered ceiling below. If your building inspector says different I would be interested to hear.

Well he is of pretty much the same opinion, although he says it wouldn't hurt to encase the sides with plasterboard before fitting up the ceiling plasterboard. It's no bother so I might as well do that. When I've gotten to that stage I'll be happy enough to do anything!

If the steel is to be enclosed in the joist space then the end bearing of one end will have to be larger (temporarily) to allow the steel to slide in one end enough to clear the bearing wall at the other. Does this make sense. In other words if you have (say) a 3500mm beam and a 3200 opening (with 150mm bearing each end) then the gap above the padstones needs to be 3650 minimum (i.e. one bearing 300 long rather than 150). If this doesn't make sense I'll do a sketch and post it here

Yes it does make sense.The inner wall side has some excess end bearing, although I'm yet to get up there and do the exact measurements. If not then I will have to consider other options, ie the outside wall! Thing is, as the beam is to be fitted over the joists, the whole thing is going to have to go up to the correct level and inserted into the wall adjacent to it's final resting place before being slid over, if you know what I mean. I may end up supporting brickwork on the side walls as well with acrows and strong boys!
Genie Lifts!! What a brilliant tip! That is very appealing I must say, too many "experts" can be a pain in the a**e. Looking at HSS' site they have them, but sounds like you might be suggesting a bigger version? I can't grab a link from their site but if you go to their main page http://www.hss.com/Fae.asp?sysTemplate=wsHomePage.htm&resetToGroup=YES and then type genie lifts into the main search box you can see them. Same sort of thing? The tallest one (code No 70105) quotes a S.W.L (safe working load I presume)of 159kg, which is just enough to lift my 152 kg steel. Thing is will my floor take the strain? It is 8"*2" joists, with a sub wall running underneath where the wall is to be supported. If I should support it (which I probably would) What's the easiest way to do it?

Thanks again

JD

 

[JerryD]

I may be reading that bit wrong, do you mean I should be inserting the support above the lowest remaining course of bricks? If so what's to stop some or all of the lowest course falling away?

No, you must support UNDER the bottom course of bricks, in other words the course that is to sit on the steel is the one to support. You may find that some bricks will still fall away from the underside of the supported opening (between the Strongboys), wear a hard hat and be aware of the risks!

Genie Lifts!! What a brilliant tip! That is very appealing I must say, too many "experts" can be a pain in the a**e. Looking at HSS' site they have them, but sounds like you might be suggesting a bigger version? I can't grab a link from their site but if you go to their main page http://www.hss.com/Fae.asp?sysTemplate=wsHomePage.htm&resetToGroup=YES and then type genie lifts into the main search box you can see them. Same sort of thing? The tallest one (code No 70105) quotes a S.W.L (safe working load I presume)of 159kg, which is just enough to lift my 152 kg steel

That Genie Lift is not the one I was thinking of, it's too small really. You really need HSS Item number 70107 which is a Genie Superlift Advantage. That's what we have (ours is an older version but exactly the same technology). This will be lifting well within its capacity and these bigger Genies are much more stable than the little ones.

Thing is will my floor take the strain? It is 8"*2" joists, with a sub wall running underneath where the wall is to be supported. If I should support it (which I probably would) What's the easiest way to do it?

The floor will be well strong enough but it MUST be smooth and level. We always lay a clean 8' x 4' sheet of 18mm ply on the floor for the Genie to run on. You have to position the ply so that when the Genie runs forward to place the beam on the padstones, the front wheels of the Genie are still on the ply. Consider all this when positioning all your Acrows, you may need 4 now as the central one (if you only have 3) will be smack bang in the way!

Another tip - the forks of the Genie can be fitted either way up, it is ESSENTIAL (for your particular job) that the forks are fitted with the forks ABOVE the fork mounting, not below it.

By mounting the forks ABOVE the mounting it means the forks are the highest part of the machine when the lifting starts to rise above the boom. Do it the other way and the boom will hit the ceiling before the steel is high enough!

So when you are setting up the Genie, the forks can fit in one of two ways - if you have it so that the forks can virtually touch the floor, then you have them the WRONG way up. If you have the forks correctly fitted (for this particular job) then the lowest the forks will go is about 2 feet from the floor. Therefore you have to get the steel beam at least 2' off the floor to be able to pick it up with the Genie, we use a small stack of blocks for this purpose.

The Genie must be dead center under the steel. We always clamp the steel beam to the forks as we lift, just to be on the safe side. With these Genie lifts you can stop at any time, the handle doesn't spin backwards and drop the steel!! You just stop winding and the steel stays there, suspended quite safely.

If you have to manoeuvre the Genie when the steel is high in the air, it is safer to lever it forwards (or backwards) right at the bottom by the wheels, using a piece of timber as a lever. This means you are not trying to push it over which could happen if you pushed it from a higher position.

I would still recommend hiring a pair of TALL builders trestles, you may need to put the steel onto them at a high level and then re-position the Genie to get a better angle of attack. It is helpful to have as much gear on site to cover every eventuality.

 

[JDLDIY]

Resurrecting an old thread here, trying to get closer to doing this job in the new year but still in the planning stage.

If the steel is to be enclosed in the joist space then the end bearing of one end will have to be larger (temporarily) to allow the steel to slide in one end enough to clear the bearing wall at the other. Does this make sense. In other words if you have (say) a 3500mm beam and a 3200 opening (with 150mm bearing each end) then the gap above the padstones needs to be 3650 minimum (i.e. one bearing 300 long rather than 150). If this doesn't make sense I'll do a sketch and post it here

Absolutely. Having had a look at the layout involved, the only way to gain this excess end-bearing looks like it will be to remove some bricks from the exterior leaf of the exterior wall and "poke" the steel through to the outside before straightening it up to slide into the end-bearing space at the other end. Is this a fairly standard situation? What about the structural implications of this? I'm thinking that by removing say 10" square brickwork from the exterior and interior leafs of a cavity wall I shouldn't cause too much of a weak spot just to get the job done?

Cheers

JD

 

[JerryD]

That's a perfectly acceptable way to do it, quite common too.

Just minimise the damage to the face brickwork, this makes it easier to make good later.

 

[JDLDIY]

Thanks JerryD. Luckily for me the face bricks to remove will at a level which is to be rendered in due course, so no problems there. As a general guide, how much brickwork can be removed from a wall before support props are needed? Just wondered what pro's would go by as a rule of thumb?
JD

 

[JerryD]

I would go no more than 900mm wide without support, preferably 750mm max. It all depends how 'solid' the brickwork is.

 

[JennyC]

Sorry to bump an old topic but I am trying to install an RSJ / UB and I am pretty much in exactly the same situation as the original poster.

A structural engineer has designed our steel for us. Although we told him we wanted to remove our wall completely with no piers if possible, his intial design left in 500mm piers on each side, which was totally pointless as it was essentially leaving in almost 1/3 of the existing wall length.

So we asked him to redesign, but whether we can have a "no pier" design depends on the depth of the existing foundations, and he has said we will have to dig a test hole to find this out. My question is, what is the best way to go about digging a test hole?

One will be outside (to discover the depth of the foundation to the external wall), but the other wall that the steel will rest on is internal, and we have concrete floors. Is the situation safe to use a heavy duty concrete breaker to break up some of the ground slab? We've tried our mini-breaker and it has taken an eternity to get about 30mm down. I was just worried about the vibrations from a heavier duty version causing cracking elsewhere? Also, how far away from the internal wall should we start digging the hole, as assuming we will find strip foundations, I don't want to break too much of the foundation itself away if we can help it and am not sure if I will be able to tell what it slab and what is foundation?

My final question is, if we find the internal wall is just built straight off the slab with no foundation, what options do we have if we want a pierless design? Can we create some sort of foundation under the area of the wall on which we want to place the steel or will this be ridiculously expensive?

Thanks in advance for any help or advice anyone can give.