Installing steel beams advice

[^woody^]

No,it's a common sense thing.

Architects specify bolting beams with spacers, but don't know why; builders put them in, but don't know why; building inspectors usually ask for them, but can't say why. Even some SEs include them, without thinking it through.

Bolting the webs together with a tubes and a few lengths of M12 bar from B&Q does not help the beams 'work together'. It also does not help them to share load equally and so equalize deflection.

BS 5950 (the design code for steelwork) states that bolting beams together in an attempt to provide mutual support is not allowed.

I wonder why timber is bolted together to form a stronger beam or when doubling up rafters?

Can the world just lay these timbers side by side in future on the basis of this revelation?

Should I sell my shares in the bolt and washer industry? Looks like it's going to crash.

 

[tony1851]

I wonder why timber is bolted together to form a stronger beam or when doubling up rafters?

Can the world just lay these timbers side by side in future on the basis of this revelation?

Should I sell my shares in the bolt and washer industry? Looks like it's going to crash.

Timber as a structural material is used in a different way than steel.
Timber code (BS 5268) specifically allows two or more timbers to be bolted/nailed/screwed together to make a compound beam; it even allows for an increase in strength if two identical timbers are fixed together.
If two identical-size timber beams are properly fixed together in accordance with details apecified in the Code, they will act as one beam.

But to try to bolt two steel I-beams together through the webs and expect them to work as one is a fool's errand. There is no way bolts could be tightened sufficiently to stop the webs moving relative to the ends of the tubes.

(You can, however, make a compound steel beam by bolting/welding two channels back-to-back --> ][ to make one 'I' beam, but that is a different proposition than trying to connect 2 'I' beams through the webs; don't sell your shares just yet)

 

[^woody^]

Nuts. Never mind bolts.

 

[Dereekoo]

Nuts. Never mind bolts.

Can the world just lay these timbers side by side in future on the basis of this revelation?

I wonder why timber is bolted together to form a stronger beam or when doubling up rafters?

Can the world just lay these timbers side by side in future on the basis of this revelation?

Interestingly the allowable design stresses in floor joists that are laid side by side ( albeit with a 400 space) can be increased by 10% over that of a single floor joist acting alone.

 

[Dereekoo]

,

 

[^woody^]

Interestingly the allowable design stresses in floor joists that are laid side by side ( albeit with a 400 space) can be increased by 10% over that of a single floor joist acting alone.

We can just use a single joist around stair openings from now on then and save a few quid. And no other double beams required to trim to either.

 

[tony1851]

We can just use a single joist around stair openings from now on then and save a few quid. And no other double beams required to trim to either.

Not really. He was referring to floor-joist systems, where a number of floor joists run parallel to each other but spaced apart equally. In that case, the Code permits a 10% increase in allowable stress over that allowed for a single joist, as there is load-sharing, eg by the boarding and noggins.

Trimmer joists around stairwells are acting individually and usually carry higher loads (particularly point loads) so in most cases need doubling up.

 

[^woody^]

He was referring to floor-joist systems, where a number of floor joists run parallel to each other but spaced apart equally. In that case, the Code permits a 10% increase in allowable stress over that allowed for a single joist, as there is load-sharing, eg by the boarding and noggins.

If I may be so bold .... that's complete poppycock.

A "floor joist system"? You mean a timber floor.

And this "10% more" than a single joist, baloney. When do you have a single joist on its own just there on its own?

It's factually correct, but worded to sound grander and sound like it's profound, when it's just common sense.

But above all, what you are describing is actually a load-sharing situation that .... wait for it.... comes about when two components are mechanically joined together to transfer loads between them and share loads. Does that sound familiar?

 

[^woody^]

Trimmer joists around stairwells are acting individually and usually carry higher loads (particularly point loads) so in most cases need doubling up.

2. And this doubling up to take these increased loads .... why are the joists fixed together if fixings don't transfer loads between the two? Does that sound familiar?

 

[SpaceWorm]

2 identical timber sections sat next to each other but not connected wil have double the capacity of a single joist yes (obviously). The degree of connection between the sections is specified to ensure the new section acts compositely. The increase in allowable stress is due to the reduced slenderness of the new section, which can only be achieved with adequate connection ensured.

Tiny spacer tubes or threaded bar are just that - spacers, they cannot transfer vertical load between adjacent I sections because they are too long and flexible (again obviously).

 

[Dereekoo]

It's factually correctQUOTE]
What more can one ask

worded to sound grander and sound like it's profound, QUOTE]

Multiple joists can be designed to take 10% more load than a single joist. Profound and grand? You live a very complicated life Woody

Its just common sense.
/QUOTE]
Is it? Use more joists and each one becomes stronger

And Happy Easter Woody

 

[noseall]

Tiny spacer tubes or threaded bar are just that - spacers, they cannot transfer vertical load between adjacent I sections because they are too long and flexible (again obviously).

..And I think that is where Woody completely misses the point. No doubt hell come up with some grand analogy with timbers and solid bridging or some such that is not at all like steels and crappy spacer tubes.

 

[tony1851]

If I may be so bold .... that's complete poppycock.

A "floor joist system"? You mean a timber floor.

And this "10% more" than a single joist, baloney. When do you have a single joist on its own just there on its own?

It's factually correct, but worded to sound grander and sound like it's profound, when it's just common sense.

But above all, what you are describing is actually a load-sharing situation that .... wait for it.... comes about when two components are mechanically joined together to transfer loads between them and share loads. Does that sound familiar?

When two timber joists are bolted together, the frictional force between them holds them together.

Conversely, if you try to bolt two 'I'-beams together via 2" tubes pressing against each web, there is hardly any frictional force between the tube and the webs. So if one beam is more heavily-loaded, that beam will deflect more.

Trying to bolt two 'I' beams together with spacer tubes has been likened to two drunks trying to prop each other up.

Will someone take the spade out of Woody's hands please

 

[stuart45]

Trying to bolt two 'I' beams together with spacer tubes has been likened to two drunks trying to prop each other up.

Two drunks holding each other up actually works quite well, but the calcs are too complex to put on here. Same as 2 drunks can understand every word they say to each other, whereas someone sober can't make any sense of it.

 

[davidmiller]

I didnt realise you were still chatting on here.
Anyway the engineers spec is M16 g8.8 bolts on 10mm end plates.