Universal Beams Vs Parallel Flange Channel

[MonkeyHunter]

Hi,

I've had pans drawn up for an extension and it specifies PFC's bolted back to back. Just out of general interest, can some one point me in the direction of comparative span tables, or give me a rough run down on the strength differences? I am just curious as some time ago I had calcs done just for the knock through and the UB's specified then seem to be considerably bigger, than the PFC's now specified on the Extension plans.

I would just like to appreciate everything behind the design.

Cheers,
MonkeyHunter.

 

[Deluks]

A pair of PFC's will have a much thicker web than a single u-beam (rsj) of comparable size, so if the design is right then you can use a slightly less deep section, and can be easier to install. The trade off is cost, a single beam will be cheaper, less steel involved and less fabrication/bolts needed.

 

[MonkeyHunter]

Thanks Deluks,

The other UB specs were for 2 UB's to be bolted together. It would seem to me that the UB's would be much stronger than the PFC's, But I havent seen a PFC in the flesh as it were.

For reference we are talking about UB's 305x127x37 Vs PFC @200x90x30 either way bolted together with spacers the width of the cavity which is approx 50mm. Span is 4400mm.

 

[Deluks]

You mean the UB's were to be bolted together end to end?
I'd personally be happier with the PFC's but it doesn't matter what you use as long as it does the job and the engineer says yes.

I'd personally be happier with the PFC's, double webs spaced apart are as tough as old boots!

 

[MonkeyHunter]

You mean the UB's were to be bolted together end to end?

No in parallel, each under one cavity leaf. As you say the calcs have been done and im sure it will be ok, and if there are any issues the BCO will pick it up, but I was just looking for information as I like to fully understand everything I do, and am just interested in the strength differences of PFC's vs UB's