UB or PFC? Steelwork Question

[Brad93]

Ive been asked to install some steelwork to replace an old wrough iron “lean-to” on the side of a barn. It’s rotten and not suitable for repair or re-cladding.

There’s is a concrete barn next door that they want to basically bring steel sections across to a wall about 7m away.

All the steel I can buy in ready cut, painted and drilled CE marked so that’s not an issue.

What I do need to know is do I use a UB or a PFC?

Do we have anyone on here involved in structural steel design?

The roof is about 5-10* degrees pitch, span about 7m, will have galvanised Perlins and fibre-cement profile 6 roof sheets to match the concrete barn.

I will draw a diagram, all measurements are estimated at the moment as we didn’t have any form of access or platforms onsite when we visited.

Nice job for us as we can do all the groundwork’s subsequently required too.

 

[Brad93]

@Welderpaul perhaps you could advise?

 

[Brad93]

Photo of what it looks like currently.

First drawing is what they have now.

Second drawing is what the guy wants.

 

[Welderpaul]

UB's are better than PFCs as a UB is symetrically stable. Under load a PFC wants to twist to one side - it is effectively a one sided UB.

I would guess at something like a 254*146 series of UB over that span. Its an easy calculation for an Engineer to do.

 

[Brad93]

UB's are better than PFCs as a UB is symetrically stable. Under load a PFC wants to twist to one side - it is effectively a one sided UB.

I would guess at something like a 254*146 series of UB over that span. Its an easy calculation for an Engineer to do.

Cheers mate. I’ve actually spent a few hours today looking at how the calculations are made.
Then came across an excellent document (although for Ireland but complied with EU regs) for agricultural buildings, in particular lean-tos!

Gives me all the specs for the beams, cross braces required, size of knee braces.

 

[CornishPete]

You may as well use beams as it'll be the same amount of work, and you'll be able to use smaller depth Vs PFC.
Size would depend on how many steels there are, and the calculations. It's not a small span so will be a decent size but the more steels the smaller they can be. I hope for your sake they're not 254*146 as they will take some manhandling! It took 3 of us to install one 6m long but it held up an entire roof so maybe yours will be smaller.

 

[Brad93]

The length of the barn is about 18m spread over three bays, so 6m a bay.

We should have a telehandler onsite. Gotta make a spreader for the beams yet.

 

[Hitch]

Crikey Brad, if thats a nice job, i'd hate to see one of your nasty ones


As Paul said, UB virtually every time, UB probably twists as easy if not easier than PFC given a specific twisting moment, but rafter beams are loaded evenly in most cases, and some amount of twist is restrained by the purlins too.
Are they just sat on the walls, no endplates welded on? UB deffinately works better in that instance.

Size wise...isnt part of 1090 to ensure any design is to a suitable standard...? No point buying in beams cut and drilled to 1090 if the design isnt...

 

[Revs1972]

As Paul says above, 254 x 146 UB should be man enough. Even though its agricultural, it still comes under ex class 1, so at the very minimum you should get some calcs done.
Trouble is most farmers dgaf about the rules, but itll be your butt in the dock if something happens. I usually stick a massive red disclaimer on my correspondance with a certain farmer who i know wouldnt get an engineer to confirm sizes and connections

 

[Revs1972]

Try explaining to a farmer who wants a copy of the building you are stood in, that it would not pass current regs as it would fail design checks . Thats fun

Building has been there best part of 50 years and is in pretty good nick

 

[Brad93]

I doubt the guy will want calculations done - one of them jobs “I don’t want to spend a lot of money”.

I’m just erecting it. He is ordering steel direct to his door & all materials.

I’ve heard a right range of prices quoted for structural calculations too!

Not sure on connections yet because I’ve not been up to the right level to assess whether the beam can rest on the concrete wall.

 

[Hitch]

Surely you just price them in... the job is £xxxx. To Design and Install, to current legislations/ requirements of EN1090.....

I suppose he gets it delivered to his yard, you glue it up there, and 1090 and its FPCs isnt an issue.