laminated ribs

[Farrell]

>>>I'm with you on ease of crowning, accuracy and more uniform statistical 
>>>average MOE from batch to batch. But why would a laminated beam have a 
>>>higher average MOE than a similar solid beam?
>>>
>>>Terry Farrell
>>
>>
>>I'm not sure, but they seem to. I tested this once and recall finding that 
>>to be the case, but it's been a while so I might be mistaken. Memory 
>>leaks, and such.  Maybe it's time to do it again.
>>
>>Ron N
>
>
> No Ron you're not mistaken. Laminated beams have a higher MOE.

Let's see where this goes.

> Relative to a solid beam, the internal stresses which occur naturally in 
> the growing tree are largely dissipated when the individual layers are 
> joined back to form a whole.

Yes, I see that and agree.

> One only has to watch sawn strips warping all over the place as they come 
> off the saw to realise what must be going on inside the full piece prior 
> to resawing.

Amazing, isn't it? And a bit scary! But sure, I see that all the time.

> Think a tug-of-war analogy. With five strong people of nearly of equal 
> strength, at either end of a rope, it will only take a small addition plus 
> or minus to topple the balance in one direction. If those five strong 
> people were all working together holding a bar firm, for example, it would 
> take much more than a small force to move the bar.

True.

> Similarly, the various sectors of wood in a solid beam are not acting to 
> support a given load.

I'm not sure I understand that.

> Some will be trying to move with the load while other sectors will be 
> supporting it.

Yes, agreed. Some vectors may be supporting the load more than a neutral 
piece, while others will offer less than neutral support. So wouldn't that 
mean a net stress vector of zero? Just like with the laminated beam, if the 
solid beam is not bending on it's own (unloaded), the net strain is zero, 
and hence the net stress is zero. If a load is applied, seems to me the two 
types of equally dimensioned beams would have a similar ability to support, 
i.e. similar MOE.

> If a similarly dimensioned laminated beam was used to resist a load a much 
> higher proportion of the beam will be working to support the load. Hence 
> the higher MOE in the laminated beam. Hope that makes sense.

No, it doesn't. But that may just be me. Seems to me that if beams of the 
two types with no load will have a net strain of zero and thus should be 
able to support similar loads. I understand your point of the greater 
internal stresses in the solid beam, but if they cancel out (which them must 
if the solid beam is straight), there is no net stress and it will behave 
similar to the laminated beam. I suspect the solid beam might reach failure 
at a lighter load than the laminated beam, but I don't see why the strain in 
relation to stress would differ.

Care to try prying through my thick skull again? Or maybe I just need to 
take a few beams and apply some loads. I'll try to do that this weekend.

Terry Farrell

> Ron O.
> OVERS PIANOS - SYDNEY
>    Grand Piano Manufacturers