RHS steel over 7m bi-fold

24 May 2019
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United Kingdom
Have a largish single story rear extension in progress with a 7m opening for bifold doors.
SE has specified 300x200x10 RHS steel with welded bottom plate for a soldier brick course. Small parapet built off steel which also supports 8x2 timbers for 4.5m deep flat roof finished with asphalt.
The above steel is bloody expensive and just wondering why an RHS section has been specified. Any feedback welcome, best, Ernesto.
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"300x200x10 RHS steel with welded bottom plate"

Just supporting a roof? absolutely bonkers...
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That's a very chunky bit of steel, it would be interesting to see his calcs. Bifolds don't like beam deflection, what is the spec for your bifolds (ie how much sag can the track tolerate before the doors jam). Sounds as if SE has gone for a beam that would not deflect if you parked a tank on the roof.....EDIT a Sherman tank, not a water tank :)

ANY beam of that length with a 10mm plate welded to the bottom is going to require mechanical lifting.
Yes - that goes without saying - and an I-section is likely to be a lot cheaper than a box section. Also easier to fix things such as curtain rails on timber noggins, rather than drilling through 10mm steel.
Having said that, closed box sections are better at resisting twist than open sections - so maybe that is the governing factor for the SE?
Depends on what the load is on the plate supporting the outer skin.
So to clarify he has asked for 600mm bearing on each side, the steel is therefore 8.2m

I had wondered if he had concerns of twisting as well as deflection hence box section and not normal I beam.

There is little in the way brickwork above steel, maybe 8 or 9 courses with a coping just enough to hide flat roof/lanterns and allow for flashing details within.

We are looking at using a mini tracked crane with hydraulic arm for the installation which apparently requires minimal manpower, that should be interesting !!
How big is the crane? Where is the beam located in terms of lorry v's final location? Are there any trees or uneven ground?

Gotta post a vid.(y)

Theres lots online about these relatively new mini tracked cranes called Hooka. A lot of guys make a living out of buying one and offering their services to the industry, the same way guys do with a digger. Was quoted 550+VAT for the day to offload all steels from lorry and installation of two large steels at 800KG each. The guy said I only need one other guy on site as there is no manual handling of steels whatsoever.... Well I'll give it a go :)
I've hoofed many a tonne bag of gear about with a 3 tonner and even with a 1.5 tonner. Something that is 8m long though is different gravy.

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