wich timber wood is better?
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hugo_inside
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wich timber wood is better?
Fir wood or Russian Pine??
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knightfly
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Not familiar with Russian pine - all my span calcs are done with #2 and better grade Douglas Fir - I have settings for Southern Pine (a US name, for southern US pine) - they show just a bit longer span capability than Douglas Fir.
To be safe, always take the WORST case though; no nasty surprises that way
Steve
To be safe, always take the WORST case though; no nasty surprises that way
Steve-
hugo_inside
- Senior Member
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- Joined: Wed Nov 03, 2004 3:58 am
- Location: Valencia, Spain
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knightfly
- Senior Member
- Posts: 6976
- Joined: Sun Mar 16, 2003 11:11 am
- Location: West Coast, USA
Sure; everything has a breaking point - where it just can't take any more stress, and something breaks. When this happens inside a building, people get hurt or killed. So there is a specification in building codes that attempts to prevent this.
Every kind of building material has different strengths and weaknesses; there are people whose only job is to TEST these weaknesses and catalog them, so SAFE buildings can be designed and built.
One of the things that are tested is the ability of framing lumber to support weight, and for any specific size and species (type of tree) there are published specifications as to how long a certain size and species of wood framing can stretch across two supports, and how much weight it can hold when SPANning that distance - so, if you have a 2x8 (35mm x 190mm) ceiling joist that's made of Douglas Fir, you can look up (in a span table) that size - the table shows how many pounds/kilos a structure using that size lumber can support for each square foot, and there are columns in the table for different spacing between the joists - under each column the maximum length for a certain loading will be different, depending on the spacing between the joists.
For example, the 2x8 mentioned above, when placed on 24 inch centers and loaded with a maximum (including its own weight) of 10 pounds per square foot, is safe up to 13.5 feet between supports (this is the SPAN)
I'm short on time so you'll need to convert to metric yourself; hopefully I explained the concept though... Steve
Every kind of building material has different strengths and weaknesses; there are people whose only job is to TEST these weaknesses and catalog them, so SAFE buildings can be designed and built.
One of the things that are tested is the ability of framing lumber to support weight, and for any specific size and species (type of tree) there are published specifications as to how long a certain size and species of wood framing can stretch across two supports, and how much weight it can hold when SPANning that distance - so, if you have a 2x8 (35mm x 190mm) ceiling joist that's made of Douglas Fir, you can look up (in a span table) that size - the table shows how many pounds/kilos a structure using that size lumber can support for each square foot, and there are columns in the table for different spacing between the joists - under each column the maximum length for a certain loading will be different, depending on the spacing between the joists.
For example, the 2x8 mentioned above, when placed on 24 inch centers and loaded with a maximum (including its own weight) of 10 pounds per square foot, is safe up to 13.5 feet between supports (this is the SPAN)
I'm short on time so you'll need to convert to metric yourself; hopefully I explained the concept though... Steve