Using an RHS to support trusses?

[seconb]

Hi all,

A question here, a client wishes to remove a load bearing wall in a bungalow and needs a beam designed to support the trusses which spanned onto this wall. I have designed a 356x171x51UB which is 171 wide and therefore cannot be supported on the 102 wide wall and requires two new piers to be built. Obviously, the client won't be so keen on this solution and I have calculated that a 300x100x6.3 RHS would work, my question is does anyone see any issues with using a box section in this scenario, I cannot think of any but don't remember ever seeing this anywhere either.

Thanks for any help,
Connor

 

[SteynvW]

Are the walls masonry?
Are you sure the single skin wall is load bearing for the roof truss?

 

[milkshakelake]

Since the strength and deflection is passing, I don't see any issue. It's just different support and truss connection details. Something about the sizes seems off, like the deeper wide flange member should be much stronger than a shallower tube section, but I'm not too familiar with the notation. The reason you haven't seen more tube sections as beams is because their moment of inertia is lower so it's generally not economically viable; they're more the exception than the rule.

 

[seconb]

Hi, thanks for the replies.
@SteynvW I believe so yes.
@milkshakelake Yes I agree with you it seems odd, the I beam fails in buckling as I have considered the beam unrestrained so I thought I'd try a Rectangular beam to see if the size was reasonable and thats what the numbers seem to say.

 

[GeorgeTheCivilEngineer]

Seems like quite a large beam for only a .... 4m span? I'd have expected something more like a 203UB.

You can use steel which is wider than the wall below, so long as you account for the increase stresses due to the reduced bearing area. This can be done by elongating the bearing on the in line wall. Clearly not an issue on the perpendicular padstone.

In general terms, though, a RHS would be fine in this scenario.

Last thought - have you considered the impact of removing the buttressing wall on the 8.5m long exterior wall? Both for lateral resistance of the exterior wall and crack control.

 

[seconb]

Hi @GeorgeTheCivilEngineer,

Thanks for the reply, I get the span to be approx 5.9m from the attached drawing, I did not know about using a wider beam on a narrower wall though, is there anywhere I can read up on that?

As for the buttressing, am I correct in thinking no buttressing is required if the wall is less than 9m in length and 3.5m in height? Assumed from table 3 of building regs document A.