How to calculate weight of wooden joists.

15 Aug 2023
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For an exam assignment I have to calculate an entire construction in wood, for this I need to know what the weight (in kN/m³) of joists is.

In my assignment I use I-joist of 90mm wide and 360mm high.

I've already seen all kinds of things and all kinds of different numbers (in the technical data sheets) and found nothing in kN / m³...

You can find it from very simple materials, PUR and OSB in kN/m³ immediately, but I-joist apparently not.

Can someone help me? :)
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IIRC a newton is about 1/10 of a kg, so a kilonewton would be about 100kg. Metres cubed is just the three dimensions multiplied together.

Good luck

Depends what type of I beam you picked- the solid ones or open lattice.
If its the solids then easy life- yiu just need to determine the volume (and thus the weight) of timber and OSB in a metre then apply that number to all the I beam in the scheme.
found nothing in kN / m³

List of Density of diffrent types of wood here (in kg/m³):

I believe Most UK joists are Pine, so likley to be one of these:
Pine, radiata480 kg/m³
Pine, Scots510 kg/m³
Pine, white350 - 500 kg/m³
Pine, yellow420 kg/m³
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Weight is measured in kg, not kN - which is for force/load.

So be clear what you have been asked to do or are attempting to do. Be careful not to mix up the two, that can be catastrophic!

For example, a 350mm deep engineered joist, with a OSB web is either approx 4.5 or 5.5 kg/m run depending on the loading required - ie for greater loads or spans the web or flange timber would be thicker, so the weight greater. For specific joists, only the manufacturer can provide specific details

For these types of questions, you would not normally calculate and add up individual materials, rather you would typically work out component values such as a floor comprising of ceiling, joists, decking and services. Likewise for walls and roofs.

Also remember to work out component weight/load (dead), imposed load (live) (furniture, people etc) and any snow or wind loading. And add the relevant factors to the calculated figures depending on what standard you are using - BS, EN.
Thank you all! With all this information I can further continue with my school assignment :)
So where he is "a newton is about 1/10 of a kg" just as it is everywhere else on Earth.

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