steel beam bowing

[RonnyRaygun]

Not withstanding the buckling note, thats interesting as I did a quick check using the Blue Book and depending what roof span and loads were taken there seemed to be a possibility that it could suffice. As a matter of interest what loading did you take for the span.

You mean for a 254x102x22 UB?

I took half of a 3.5m span (guess) at 0.80kN/m2 Dead and 0.75 Live (for the roof), and 0.9m of cavity wall, on a 7.5m span
Based on that, the deflection of the 254x102x22 beam under dead and live load is 44,5mm. Live load deflection is within limits of span / 360, but 44.5mm combined seems a bit excessive??

The buckling resistance moment is 11.7kNm while the actual bending moment is 63.7kNm. Fully restrained (which it isn't) the capacity of the beam is 91.9kNm.

I'm not actually sure the beam has been designed at all, but maybe the "engineer" checked it as fully restrained and for live load deflection only...

 

[^woody^]

The joists would only be coming in from the one side so the risk would be that the top flange would buckle outwards.

Maybe from rafters with a lateral force, but not from flat roof joists with vertical loading only

But if anything, surely they would buckle inwards as that where the load is

 

[tony1851]

will speak with structural tomorrow beam is UB254x102x22 with an 8mm welded bottom plate looks like the plate that is rotating only a beam has no flex really dont want too add a mid point post if i can help it. just measure ed of beam and looks like builders have installed correct beam.

A 254 x 102 x 22 on that span is absolutely bonkers - first class fail/bottom of the class.
The twist downwards on the plate is due to excessive torsion on the beam; open-section beams are not inherently good at resisting torsion effects - as jks says, hollow sections are better.
As a very minimum if using an I-beam, and subject to checks, you'd be looking at a 254 x 146 or even a 305 x 165.
The deflection will get worse once the roof is on and with 6" of snow on top.
Can you post the calcs, we could do with a laugh after the Truss debacle.

PS, just notice a "900 parapet of blockwork" - this gets worse. There was a thread on here a few years ago in which an SE specified a beam spanning over wide bifolds with a parapet, checked it for live load deflection = OK as presumably <span/360 but forgot to check for dead load deflection and the doors were all ready to go in. Don't know what happened but presumably the insurers got a phone call.

 

[RonnyRaygun]

Maybe from rafters with a lateral force, but not from flat roof joists with vertical loading only

Buckling occurs because of compression in the top flange, not because of lateral loads. When the top flange reaches its compressive limit it'll buckle.

I'd assume it'll buckle in the nominally weaker direction and more likely away from the applied load, not towards it.

 

[tony1851]

Buckling occurs because of compression in the top flange, not because of lateral loads. When the top flange reaches its compressive limit it'll buckle.

I'd assume it'll buckle in the nominally weaker direction and more likely away from the applied load, not towards it.

Yes, for that beam, the ratio Le/ry is about 360 (even if we take the effective length as only the actual length instead of x1.2) which is way beyond the maximum 250 in the tables.
Once the parapet is up and the roof on, the top flange will buckle outwards - the bottom plate won't give much restraint.

 

[showtime247]

thanks for comments see attached calcs

 

[RonnyRaygun]

As I suspected...

He's taken full lateral restraint

and taken live load deflection only

Put him back on photocopying duties until he learns what he's doing

 

[catlad]

Yes the joists would tie into the beam and stop sideways/ buckling movement?

There is four course of blockwork above the beam so I can't see how that could be achieved.

 

[catlad]

This idea of massive openings and massive bi-fold doors is a fad! my advice is bring it in a meter either side, the room will work better as you will have space to put your sofa ect. and not just a large glass wall where you can't put anything, remember bi-folds are only good for a quarter the year!

 

[jks7492]

As I suspected...

He's taken full lateral restraint
View attachment 283576

and taken live load deflection only
View attachment 283577

Put him back on photocopying duties until he learns what he's doing

Rubbish in, rubbish out!
No point using software if you don’t understand any of the principles behind it…

 

[kingandy2nd]

Let’s hope the guy/firm have professional indemnity insurance…sounds like there’s going to be a claim coming

 

[Notch7]

Wow, the OP has got some fantastic technical advice on this thread.

Luckily the remedial work at this stage won’t be too much….the builder should redo the appalling blockwork gratis.


If the job had got fully completed the SEs PI would’ve got a hammering

 

[Dereekoo]

Luckily the remedial work at this stage won’t be too much….the builder should redo the appalling blockwork gratis.

Notwithstanding that the blocks have been quarter bonded (does this affect the final strength?) I assume the blocks will be rendered so why is there a need for rebuilding?

 

[Dereekoo]

There is four course of blockwork above the beam so I can't see how that could be achieved.

Thats very true (although SE calc seems to be working on a 300mm high parapet?,) my mistake (Bouy)

 

[George_engineer]

As I suspected...

He's taken full lateral restraint
View attachment 283576

and taken live load deflection only
View attachment 283577

Put him back on photocopying duties until he learns what he's doing

I think you're being a bit pessimistic. Fig 3.15 of SCI P360 would suggest a series of joists can provide lateral restraint. And 2.5% of compression forces should be able to be held by joist hangers. (if the joists are parallel then red alert)

Bigger issue for me here is use of an open section for torsion resistance, wall returns instead of posts (not very impressed with the padstone/wall calc) and lack of dead load deflection. Oh and its not galvanised on.