laminated ribs

[Nichols]

Terry,
    In both beams, solid and laminated, the beam is a "system". When you 
add up the parts of the whole, bending stress and breaking strength vary at 
different values. The difference in variance changes dramatically with the 
overall difference between systems. A two-ply lamination will have very 
similar bending stress characteristics, but the breaking strength will be 
more different. As the number of plies increases, the variance changes, of 
course, but not as much. A dozen variables make it difficult to call it 
logarithmic, but it's basically a case of diminishing returns for bending 
compared to improved breaking values. If I recall correctly. It's 
been...... decades.

Guy



At 10:41 AM 2/17/2006 -0500, you wrote:
>>>>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
>
>
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