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Weight calculation for Floor Joists

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OwenRS

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Hi All,

Got a mezanine floor that was put in approx 20 years ago.

Section of Joists are 9" x 2" and they span a distance of 16'. One end sits on top of the external walls and the other side is notched into the I girder making the end only 7" x 2". The centres are 16" and they are braised at regular intervals.

Is there a quick way to calculate what weight this will support as we kind of keep on taking things upstairs but never bring them down? got lots of stacks of timber etc along with half of the unwanted items from the garden shed.

Thanks in advance
 

9fingers

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My experience of loading calcs comes from some time ago when putting another floor on my bungalow.

I've long lost the data I used but I do recall having to reduce a joist span to 14 feet to allow 8 x 2 joists and they were on 16" spacing so your 16' on 9 x 2 (even with reduced ends) sounds like it would have met the building regs in the 80's when I did my calcs.

We can possibly assume that the steel was calculated on the same basis ie to meet domestic regs

At that time I recall working out that the loading capacity required by the regs was about 2-1/2 people per square metre. Now this is not very exact but I reckon you could put 200kg/sq metre with confidence.

The other figure that sticks in my mind from then is that the permitted deflection under load for wood was 1/360th of the length and 1/300th for steel (or just maybe the other way round??)
So if you made an accurate measurement unloaded (vertical stick?) and used that to compare deflection as you load the floor, start getting worried if it moves by more than 1/2".

Perhaps a little vague but a starting point at least.

hth

Bob
 

RogerBoyle

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Forgot to add
this is the modern day acceptable limits but 15 - 20 years ago things were different and its probably been built correctly
and followed the then current regs ( even so I wouldn't like to trust a 7*2 just personal preference)
could you not slide in additional joists if required or have any doubt about it

Roger
 

9fingers

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Excellent link Roger- bookmarked for future needs.

It even supports my memorised details above. 0.5kN dead load and 1.5kN imposed load is the same as my 200kg/sqm total.

In terms of what that means in real loads, 200kg of wood is over 2Cu M so you could cover the floor with wood 2metres high and still be within spec. :shock:

Bob
 

OwenRS

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Hi again,

Thanks for your help guys. Wish my father had of thought about this when he put the floor in 20 odd years ago. We've been putting new items up there all the while for the pass 20 years or so. We've got racking up there with timber on, which are sitting on large wooden feet to spread the load etc and also pallets of timber but its only now we are questioning how many ton we have up there.

Nothing has exactly sagged or moved but we are loosing floor area / space up there and want to potentially go upwards on the stacks adding more weight. The majority of the heavy items are either around the edge or straight down the middle of the upstairs which is directly above the steel I gurder.
 

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