7.6m non load bearing ceiling span

[Liamr2021]

hi,
I'm building a new office in a warehouse, its roughly 7.6 x 7.6 which is open plan, its having a suspended ceiling fitted but I need to span ceiling joists to carry the suspended ceiling as there isn't anyway of attaching it to the warehouse roof.

Am I best using I beams to cover the span, or can I use an 8x2, over lapped by at least 2M and bolted together.

thanks

 

[Notch7]

Can’t you use one of the office walls to support it?

8 x 2 will only span about 4.5m

 

[tony1851]

IMO, 8x2 @ 400 centres would be OK for a false ceiling on that span. It would be carrying no live load, only the dead load of the ceiling tiles, which will be very low, plus the dead load of the beam itself.

An overlap of 2m would be ok, with plenty of coach screws (not bolts) in a staggered pattern. You'd need some noggins at third points along the span to stop sideways buckling.

Depending on the weight of the tiles, deflection could be up to 20mm, but that would hardly be noticeable on that span.

 

[Mr Chibs]

Out of curiosity, why coach screws in preference to bolts?

 

[freddiemercurystwin]

It's when the next tenant moves in and decides he wants to use the space over the top for storage the problems will start ....

 

[mrrusty]

No way of attaching? not even lindapters and suspension wires?

 

[phatboy]

Out of curiosity, why coach screws in preference to bolts?

I'd like to understand the same thing. A few years ago, our engineer advised joining joists with 3no M12 coach bolts, with dog tooth washers between, and 2mm flat square washers on the nut side, at 200mm centres, staggered heights on the timbers

 

[tony1851]

Out of curiosity, why coach screws in preference to bolts?

For similar diameters, coach screws have a higher maximum shear load than bolts. A bolted connection is also subject to 'slip', as the holes have to be slightly larger than the bolt for practical purposes.
But if you used toothed connectors between the members, a bolted connection can then be stronger.

 

[tony1851]

It's when the next tenant moves in and decides he wants to use the space over the top for storage the problems will start ....

But that's the next tenant's problem.............

 

[^woody^]

Building and fire regulations will apply to this new office, and the risk is very high to avoid it. In which case, the joists will need to be proved, not guessed.

 

[blup]

An overlap of 2m would be ok, with plenty of coach screws (not bolts) in a staggered pattern. You'd need some noggins at third points along the span to stop sideways buckling.

I can see how a staggered pattern of bolting draws the timber together but is bolting along the centre line not also permitted?

https://www.labc.co.uk/news/how-get-it-right-bolting-timbers-together-correctly?page=,1

Blup

 

[Chunkytfg]

I-Beams would likely span that distance and they normally will do the roof design for you too if you give them the size and loading requirements of it.

Add to that the current the timber prices and you might find it isn't much of a cost difference compared to normal timber.

 

[tony1851]

I can see how a staggered pattern of bolting draws the timber together but is bolting along the centre line not also permitted?

https://www.labc.co.uk/news/how-get-it-right-bolting-timbers-together-correctly?page=,1

Blup

Staggered bolting reduces the tendency of the timber to split, which it can do if the bolts are in a straight line and a little bit too close together. Staggering them enables you to get more bolts in a given length of overlap, while reducing the tendency to split.

 

[^woody^]

Staggered bolting reduces the tendency of the timber to split, which it can do if the bolts are in a straight line and a little bit too close together. Staggering them enables you to get more bolts in a given length of overlap, while reducing the tendency to split.

No, not spilt, cup. And is also better for load transfer between the two timbers and form a single beam.

 

[tony1851]

No, not spilt, cup. And is also better for load transfer between the two timbers and form a single beam.