Actually OSB is fairly homogenous, and is used in large scale, where the 
defects are accounted for in the allowable stresses. Plywood has 
different allowable loading parallel and perpendicular to the grain of 
the face ply. And all these formulas apply only in the linear zone and 
less than the elastic limit (after deformation, the piece returns to 
it's original shape when the load is removed), and all safe loading is 
in this area.

I can't caution enough, as a registered structural engineer though, 85% 
of structural failures are details, connections, etc. , NOT the main 
member (beam or column). Think Holiday Inn Kansas City where a small 
connection killed and severely injured many; The I-35 bridge in 
Minneapolis where a plate failed, and this isn't just big structures. 
Compared to the entire structure, the cost of a competent engineer is 
inexpensive, and may save money by recommending more economical material.

Lee Jones wrote:
>> You have a beam that is ( theoretically )  x long, y wide &
>> z thick.  Weight is applied perpendicular to the xz plane.
>> Beam is supported at both ends of the length.  What happens
>> if you compare it to a beam of the same material x long, 2y
>> wide and z thick ?
>>     
>
> As I recall, weight capacity is essentially based on length
> (x) and thickness (z).  As Z increases, resistance to bending
> stress goes way up (non-linear).  While strength is only
> directly related to width (y) -- i.e. a linear factor.
>
> Besides the high-tech, on-line sources, the US Department of
> Agriculture has some excellent publications, available through
> the US Government Printing Office (GPO), on wood framing and
> basic structural strength.  They're aimed not at the structural
> engineer but the farmer who needs to construct a building that
> isn't going to collapse while in use.
>
>   
>> For example: If you have a beam made of 7/16 inch OSB that is
>> 21 feet long and 8 inches wide.
>> How much stronger will a similar beam be if it is 16 inches wide ?
>>     
>
> I think it's a simple factor of 2 stronger.  OSB (Oriented
> Strand Board) may not follow the rules of a solid wood beam
> due to it being chunks of wood glued together (non-linearity
> at joints where adjacent pieces meet).
>
> 						Lee Jones
>
>   
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