It's 7 in the morning and I haven't had my three coffees and 4 fags yet but from what I can see he's designed the beams to act independently.
One of the problems with long beams is not so much excessive stress or deflection, but lateral buckling (ie they can tend to twist sideways before they
fail in other ways).
The only way to prevent this is by full- or partial restraint of the top flange. He's allowed for this on the inner beam because to an extent it restrained by the incoming beam, so will not be able to buckle sideways, but not so the outer beam. Strictly, there can be no criticism of his approach on a purely structural basis but it still gives excessively deep beams for a domestic setting where headroom is important.
One way round this problem is to have one wide- flange beam instead of two narrow-flange beams. In that position, I would have tried a 'column-section'. These are 'H'-shaped beams which are as wide as they are deep. Typically, that span and loading could be accommodated by a 254 x 254 beam. It would be heavier than two separate beams, but could be supplied in two or even three lengths and bolted together in position (though that adds to the cost).
Swings and roundabouts really, but in this case, I would have pointed out to the client the issues involved and let them decide - shallower (and prob. more expensive) beam; or deeper and more intrusive beam?
One of the problems with long beams is not so much excessive stress or deflection, but lateral buckling (ie they can tend to twist sideways before they
fail in other ways).
The only way to prevent this is by full- or partial restraint of the top flange. He's allowed for this on the inner beam because to an extent it restrained by the incoming beam, so will not be able to buckle sideways, but not so the outer beam. Strictly, there can be no criticism of his approach on a purely structural basis but it still gives excessively deep beams for a domestic setting where headroom is important.
One way round this problem is to have one wide- flange beam instead of two narrow-flange beams. In that position, I would have tried a 'column-section'. These are 'H'-shaped beams which are as wide as they are deep. Typically, that span and loading could be accommodated by a 254 x 254 beam. It would be heavier than two separate beams, but could be supplied in two or even three lengths and bolted together in position (though that adds to the cost).
Swings and roundabouts really, but in this case, I would have pointed out to the client the issues involved and let them decide - shallower (and prob. more expensive) beam; or deeper and more intrusive beam?
I will have a chat with my SE about the possibility of a single beam.
