Square section steel tube specifications

According to my handy reference book, square hollow section (SHS) steel tube is manufactured to BS4848:Part 2 (1991) and the 75x75 you are thinking of is actually 76.2 x 76.2mm (i.e. 3" x 3") and comes in the choice of 3.2,

You might consider that you could use acrow props to achieve the same result, so have a look at the rating tables for those and see how your instinct is holding up ;-)

Of course you should refer the issue to a structuaral engineer (who IME will just come and have a look and tell you what you need off the top of his head - not a pencil, slide rule, calculator or reference book in sight).

HTH

I have been thinking a handy reference book is the thing to get.

Acrow props are not an option for aesthetic reasons.

David

Sorry, I didn't mean to suggest that you use acrow props; I meant to say that an acrow prop will take several times more load than your estimated load and has a comparable cross-sectional area to your proposed SHS...

Smudger

Something about that size is used to support a mezzanine floor in a building I work in. Assuming a normal sort of roof they'd probably be several times oversized.

A quick play with SuperBeam applying only a downward axial load of 250kg gives you a 50x50x3 SHS hollow section. This is the smallest and thinnest standard square hollow section it supports. It also suggests a 48.3 x 3 CHS (I'm guessing this is a cylindrical hollow section), which is also the smallest it deals in.

With the 50x50x3 SHS, it seems to be happy up to 42kN, equivalent to 4.2 tonnes.

Remember, I am not a structural engineer and am probably using the software completely incorrectly. For the real result, backup by a guarantee and a greater amount of competence, consult a structural engineer.

Christian.