Cracking walls after RSJ installed

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Hi all,

I know it’s extremely hard to tell just from a description and I will upload photos once I get home but hoping someone can help me out.

I am currently having a rear single story pitched roof extension and knock through done.

I am opening up the rear dining room into the new extension to have an open plan kitchen dinner.

After the builder has installed the steel RSJ (5 meters long) into the external wall with 500m concrete pad stones 2 cracks in the room above have appeared. One is above the door and is approx 300mm from the top of the doorframe to the ceiling and the other is where the internal wall meets the external wall and runs top to bottom. Both cracks are approx 1mm wide.

The builder has told me that this is just settlement after the acro’s have been removed and there is nothing to worry about, however as this is my sons room I am concerned it may be dangerous.

Should I expect some sort of settling in the rooms above the RSJ?

Thanks
Mark
 
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On a 5m span, there will inevitably be some slight movement above as the load is transferred from the props to the steel. 1mm does not seem much considering the span. Is the wall which runs into the outr wall supported by a beam?
The time to worry would be if cracks appeared in the supporting wall(s) below.
 
Thanks for your reply Tony.

Yes there is a bean supporting the wall which runs into the outer wall which is currently being supported by 2 acro's as the new steel hasn't arrived yet.

Once this new steel is in I will fill\paint the cracks and monitor for any more movement.

Mark
 
There should be no settlement after props are removed or not.

If there is, its because the builder has not packed the joint between the beam and the wall enough

Assuming the beam is sufficient then the wall should not move any further. However, the builder would be responsible for making good this damage as he has caused it
 
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Once the props are removed and the load transferred to the beam, the beam will inevitably deflect under the load of the brickwork, floor and roof above.
On a 5m beam, this deflection (which is unavoidable) will be a few mm. This will impart some tension in the brickwork above, which may cause cracking.
Usually the cracking is not serious and is hidden by the plaster.

If anyone can find a steel beam which will not deflect when loaded, they will have made a discovery which dwarfs the invention of the wheel.
 
The permissible deflection of a designed beam should be such that damage to finishes are avoided. And definitely no cracking to walls

i.e. if it deflects so much that it cracks finishes and walls, then the beam is inadequate .... or the builder is
 
The permissible deflection of a designed beam should be such that damage to finishes are avoided. And definitely no cracking to walls

i.e. if it deflects so much that it cracks finishes and walls, then the beam is inadequate .... or the builder is

You are quite correct in this.
However, the problem is that in steelwork design, the deflection which must be allowed for is usually only that caused by the live load.
When a new building is going up, the deflection caused by the load of the structure on the beam above is already 'built in' (ie allowed for). The only additional deflection will be that caused by the live loads and it will be these which may damage finishes if excessive..
When putting a beam in a breakthrough in an existing building, it will deflect under the weight of the structure and this deflection may - or may not - cause cracking above.
This is why it can be problematic, as the possibility of cracking will depend partly on the stiffness of the beam (known) and partly on the strength /condition of the brickwork (unknown).
 
However, the problem is that in steelwork design, the deflection which must be allowed for is usually only that caused by the live load.

It's limit state design - all loads

BS5950 and BS EN 1990 gives permissible deflection limits depending on the span

Any deflection within this limit will not cause cracking because it is so small

Any deflection outside these limits will cause cracking in certain places which will be indicative of deflection movement - ie no cracking to a solid panel directly above the beam.

It is very, very common, that builders over tighten the props and lift the panel and then it drops again when the props are removed. If the cracking is located in the prop location or centrally, then it's an installation issue

It really is simple ... " if it deflects so much that it cracks finishes and walls, then the beam is inadequate .... or the builder is"
 
I thought he was praising the builder when he said 'cracking walls'. :mrgreen:
 
However, the problem is that in steelwork design, the deflection which must be allowed for is usually only that caused by the live load.

It's limit state design - all loads

BS5950 and BS EN 1990 gives permissible deflection limits depending on the span

Any deflection within this limit will not cause cracking because it is so small

Deflection is a serviceability limit state and BS 5950 gives limits of deflection for unfactored IMPOSED loads (typically span/360). This is purely to stop cracking of finishes if the beam is overloaded in use.

In new-build, the deflection caused by the load of the structure on the beam (DEAD load) is not usually allowed for because any bend caused by this will be covered over by the finishing trades.

This can not apply when sticking a beam into an existing structure because the load of the structure will cause it to bend immediately, regardless of any additional bend caused by imposed loading.

It is this initial deflection which is problematic and if excessive can cause cracking in the brickwork above. Whether or not this happens depends on how much the beam initially deflects, and the state of the existing brickwork above.
It really is quite simple.
 
Do you actually design beams, and know what you are on about?

The whole point of a deflection check, to make sure that the beam does not deflect so as to crack finishes. Nothing else, its just for that.

A worst case figure is used, ie both live and dead loads

So your argument seems to be that all beams will deflect all finishes can be expected to crack and everyone can expect cracking to plaster with every single beam put in to houses up and down the land? But if we are lucky, and purely by chance sometimes plaster wont crack and that's a bonus?
 
And do they all crack the plaster?

Yes, and not only that, there are usually fissures in the brickwork big enough to get one's fist through.
What's more, windows jam and the double glazing cracks; and bedroom floors slope down towards the beam.
But I warn the clients that these niggly little problems are only to be expected and that a bit of Polyfilla here and there and a few books under the end of the bed are all that is necessary.
It's because of this that I continue to get all my calculation work through recommends.
My clients obviously appreciate the skill and care of my design work :LOL:
 

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