3 metersHello! This was a tricky question. There are many factors it can depend on. A little kvist and some weight on the rule usually works better. (stämplat virke K)
A 120 mm wide board can withstand more pressure in that direction without buckling over a 3-meter length than it can in the 45 mm direction.
In general, you can use P = A x (permissible stress) as a guideline for how much it can withstand without considering buckling in either direction, especially not in the 45 mm direction. (P is the load and A is the area.)
If you nail together 2 pieces of 45x120, the area increases and the risk of buckling around the 45-direction (which now becomes 90 mm) is reduced. Therefore, it can withstand more than double the load without considering buckling.
The problem (to give you a concrete answer) is that there is no permissible stress in today's building codes (which existed before 1992). There is a characteristic strength value (constituting 95% of the empirically determined fracture strength for each wood grade) that must be reduced with partial coefficients for safety, location in the structure, etc., to an applicable permissible strength value. As your question is posed, information is missing about where the board will be placed in the house and which wood grade it refers to. Therefore, you need to ask a structural engineer about this.
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Byggaren
In general, you can use P = A x (permissible stress) as a guideline for how much it can withstand without considering buckling in either direction, especially not in the 45 mm direction. (P is the load and A is the area.)
If you nail together 2 pieces of 45x120, the area increases and the risk of buckling around the 45-direction (which now becomes 90 mm) is reduced. Therefore, it can withstand more than double the load without considering buckling.
The problem (to give you a concrete answer) is that there is no permissible stress in today's building codes (which existed before 1992). There is a characteristic strength value (constituting 95% of the empirically determined fracture strength for each wood grade) that must be reduced with partial coefficients for safety, location in the structure, etc., to an applicable permissible strength value. As your question is posed, information is missing about where the board will be placed in the house and which wood grade it refers to. Therefore, you need to ask a structural engineer about this.
_________________________
Byggaren