RSJ Steel Beam over window

[23vc]

I don’t think any lintel/beam of the height that fits above the window would be anywhere near big enough to carry the steel, so you can assume it’s wrong unless the cantilever thing is true. Dim window fitter failed to notice they were smashing out an opening directly below a couple of steels maybe?

Doubt they go back as far as the 80s but worth doing a search on your local building control applications page just incase there’s any details on there submitted at the time

 

[tony1851]

If your plan drawing is to scale as regards the supported and unsupported lengths, the load at the end of the cantilevered part may well be zero.?

 

[DR007]

I don’t think any lintel/beam of the height that fits above the window would be anywhere near big enough to carry the steel, so you can assume it’s wrong unless the cantilever thing is true. Dim window fitter failed to notice they were smashing out an opening directly below a couple of steels maybe?

Doubt they go back as far as the 80s but worth doing a search on your local building control applications page just incase there’s any details on there submitted at the time

Just checked the councils planning portal and the application was in fact granted in 1985, "ERECTION OF A TWO STOREY EXTENSION TO SIDE OF
DWELLINGHOUSE." Unfortunately there are no documents or attachments showing plans.

I suspect your right about the fitter. It appears no consideration was made for the beams and according to the seller he has passed.
On purchase there was no paperwork provided for any of the windows and there is no building control history other than the extension.

If the lintel isn't upto the job and the structure is now considered to be cantilevered it may explain the cracks on the garage/hallway wall.

If your plan drawing is to scale as regards the supported and unsupported lengths, the load at the end of the cantilevered part may well be zero.?

Its only a quick excel mock up, not to scale.
Supported length - garage/hallway wall to the far end of garage is about 2.4m.
Unsupported length - window to garage/hallway wall is about 1.2m.
Are you suggesting that the 1.2m overhang carrying about a 2.4m tall stack of inner/outer skin blocks should not be an issue? How can the load be zero in this case? For info, the single skin wall is constructed from 150mm wide lightweight breezeblocks.

 

[DR007]

As a cantilever, surely you'd be needing to stop the RSJ moving up at the garage end? Wouldn't a column (pointlessly) stop it from moving down?

Just re-read your comment and I think I understand your angle now.
The column or support would not be at the garage end but rather where I believe most of the load is, which is at the shared wall between the garage/hallway, this is the point at which there will be an overhang/cantilever. I was suggesting that rather than knock the existing wall, the support could be positioned against the wall but on the garage side so as to minimise disruption.

 

[tony1851]

Are you suggesting that the 1.2m overhang carrying about a 2.4m tall stack of inner/outer skin blocks should not be an issue? How can the load be zero in this case? For info, the single skin wall is constructed from 150mm wide lightweight breezeblocks.

I know it seems counter-intuitive but the weight on the cantilevered part will not bear down on the window as much as it might appear. This is because the weight on the longer span causes the 2.4m part to deflect downwards. This causes an upward 'hogging' moment over garage/hall wall, which in turn tends to lift the 1.2m part up at the end, so reducing the load on the end support.

Attached is a 'back-of-envelope' calculation showing the effect in numbers, which any SEs about will recognize. (This is just a simplification assuming the beam is only carrying wall and not floors or roof or incoming beams etc).

If we assume the wall weighs 10kN per m (approx 1 ton per m) then you would think the load at the window end (where the arrow is) would be (10 x 1.2)/2 = 6kN, but in fact the 'uplift' will reduce it to 1.4kN

(PS if there are cracks on the garage/hall wall, that is because that wall will be carrying the majority of the total load across the whole beam and maybe the padstone wasn't big enough, particularly with the wall being low-strength areated concrete?).

 

[DR007]

Wow many thanks for your efforts on the analysis, I remember doing similar truss calculations at uni.
In my case the wall built on the beams do also support the extension roof and concrete tiles but not the floor.

The photo of the beam in the garage shows that the wall doesn't have any pad stones but 1-2 courses of brick! Its the same across all 3 walls.

I intend to get in touch with a structural engineer/surveyor after the holidays and can't say i've been through this before.
Are there any tips to look out for when employing an engineer and likewise the tradesmen who will carry out the work?