PFC's - how to install

[ryme64]

There is no way that a 152x89 will support the walls. A 203 x102 minimum on outer skin and possibly a 203X133X30 on inner skin.

No doubt that damn yank will be along soon to tell me I am wrong.

 

[icornish]

Thanks Ryme64...
Back to the PFC question... Would they be installed as a C or as a U or inverted U to support the walls?

Sorry for all the questions - want to ensure it is done right.

 

[ryme64]

As C's Back to back to form an I. Bolted together with spacers, the length depending on your cavity width. I.E. Each channel sitting directly below each skin.
Be aware that when you come to fit them, that they are not as stable as a beam. once they are bolted together there is no problem with stability.

 

[RonnyRaygun]

There is no way that a 152x89 will support the walls. A 203 x102 minimum on outer skin and possibly a 203X133X30 on inner skin.

No doubt that damn yank will be along soon to tell me I am wrong.

No, agree completely, minimum 203x133x30 inner leaf, or 200x90 as suggested by engineer.
A pair of 203x102s would work if connected in such a way as to force them to have to work in combination.

 

[designinsteel]

I was reading this and saw that there was no answer to why a structural engineer specifies PFCs, and how they should be connected. How they connect is critical so I want to clear it up in case others read what has been advised. I'm not saying what you guys are saying is wrong, but you need to know the following also.

If you use 2 x PFC (i.e. C-sections) you can get better buckling resistance out of the beam if they are combined back to back with a given space between. This only works if the engineer specifies how they are to be fixed together. According to the steel construction institute documentation this would need to be by short PFC sections used as spacers or similar -- normal spacers will not work. The spacers need to act to stop the beams twisting relative to each other.

Other than that, a pair of UBs will usually be cheaper.

 

[tony1851]

I was reading this and saw that there was no answer to why a structural engineer specifies PFCs, and how they should be connected. How they connect is critical so I want to clear it up in case others read what has been advised. I'm not saying what you guys are saying is wrong, but you need to know the following also.

If you use 2 x PFC (i.e. C-sections) you can get better buckling resistance out of the beam if they are combined back to back with a given space between. This only works if the engineer specifies how they are to be fixed together. According to the steel construction institute documentation this would need to be by short PFC sections used as spacers or similar -- normal spacers will not work. The spacers need to act to stop the beams twisting relative to each other.

Other than that, a pair of UBs will usually be cheaper.

Agree with the points here regarding connecting beams together. The BS code specifically advises against this. Quite what builders expect to achieve by using bits of 12mm threaded bar and pieces of tube at 900 centres to connect 2 I-beams is anybody's guess - it's been likened to 'two drunks trying to prop each other up'.
Either the I-beams should work on their own, or as you say get two big PFCs back-to-back with designed connections.
https://www.labc.co.uk/news/beware-don’t-just-bolt-your-beams