Flitch beam bolt spacings

[messimagician]

What are the typical spacings of the coach bolts used for flitch beams? The timber is 75x145 with steel measuring 10x140

I was looking at a friend's report which says to use M12 bolts staggered 36mm off center line but further down the report it says must be 48mm from ends and edges of the timber. 4x coach bolt size

If bolts are staggered 48mm from edges then it certainly won't be 36mm from center of the beam.

It also says 2 bolts at each end 50mm from inner edge of support. Each bearing is 100mm but obviously M12 bolts will leave 38mm to edge of timber less than 48mm specified.

The beam spans 3m which breaks up a 6m span for domestic floor.


Which are the most important measurements when it comes to fixing the the bolts because it seems impossible to please every dimension

 

[Dereekoo]

Any forces that are passed from the steel to the wood will be most at the extreme edges so to lessen the chance of any problems occurring at the outer edges of the wood I would say the 48mm is the more important but in reality it probably makes sod all difference

 

[Deleted member 292770]

must be 48mm

must be at least 48mm ?

 

[Deleted member 292770]

It also says 2 bolts at each end 50mm from inner edge of support. Each bearing is 100mm but obviously M12 bolts will leave 38mm to edge of timber less than 48mm specified.

50mm from INNER edge leaves 138mm from the end .......
more than ‘at least’ 48mm.

 

[tony1851]

For that span and loading, 3 timber joists screwed together to make a built-up beam should have sufficed. Surely one extra length of 75 x 145 would be cheaper and easier than a steel plate and associated drilling and bolting and getting everything lined up?

 

[Deleted member 292770]

For that span and loading, 3 timber joists screwed together to make a built-up beam should have sufficed. Surely one extra length of 75 x 145 would be cheaper and easier than a steel plate and associated drilling and bolting and getting everything lined up?

won’t be that much in it now . given timber prices.

 

[messimagician]

Well I took it as the 50mm from inner edge of support meant it was directly in middle of bearing. 100mm bearing would leave 44mm to end of timber

 

[messimagician]

For that span and loading, 3 timber joists screwed together to make a built-up beam should have sufficed. Surely one extra length of 75 x 145 would be cheaper and easier than a steel plate and associated drilling and bolting and getting everything lined up?

This beam is 3 x 75x145 with 2x 10mm steel plates. It's for 1.5kN floor. Is it seriously over spec?

 

[tony1851]

This beam is 3 x 75x145 with 2x 10mm steel plates. It's for 1.5kN floor. Is it seriously over spec?

Considering the floor area supported by the beam (9m²?) IMO that beam is considerably over-designed.

The weight of steel you have in the two plates themselves is almost identical to the weight of a 152 x 152 x 23 steel beam, which would be far more than adequate for your span and loading (assuming you are only supporting a floor, and not a floor + partition).

I don't know how the cost of steel beams compares with the cost of plate kg-to-kg, but installing a steel beam on its own would be far less hassle than trying to bolt 5 sections together (which would be far heavier). The bottom flange of the beam would be wide enough to support the joists from each side. Just a bit of cutting and notching to ensure you have a flush ceiling.

 

[^woody^]

Bolts at 1/3 and 2/3 depth, and within 100mm of the wall face

 

[tony1851]

Bolts at 1/3 and 2/3 depth, and within 100mm of the wall face

Had the SE specified a beam, which would be perfectly satisfactory, there wouldn't be any problem faffing about with bolts and spacings.
Anyway, as the steel would be taking most of the bending stress, the bolt spacing in the timber would not be that critical.

 

[^woody^]

Had the SE specified a beam, which would be perfectly satisfactory, there wouldn't be any problem faffing about with bolts and spacings.
Anyway, as the steel would be taking most of the bending stress, the bolt spacing in the timber would not be that critical.

Has the OP explained why an SE would go straight to a flitched beam not UB? There most be some reason.

 

[tony1851]

Has the OP explained why an SE would go straight to a flitched beam not UB? There most be some reason.

Not that we're aware of?

Maybe the SE likes designing flitched beams?

Maybe he feels he can charge more for one than just specifying a boring steel I-beam?

Maybe he likes designing beams which are wider than they are deep?

But two 10mm steel plates with three 7" x 3"s...... just...........Wow!

 

[^woody^]

When an engineer is asked to design a beam, a flitched beam is not ever the first type that comes to mind, so there must be a reason it was selected in the first place and that may well be the reason a UB was not suitable.

 

[tony1851]

Obviously we don't see the bigger picture, but from my own experience I've rarely come across situations where a 3m steel beam isn't practical.