laminated ribs

[Erwinspiano@aol.com]

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Ron, Terry
    OK ....The laminated rib   compared to a solid rib .  Here's another 
point of view.
  Ok Now I,m confused.  If were only trying to  support only 400 to 600 lbs. 
of down bearing force as  Del inferred recently or whatever one calculates 
this to be,   then what's all the fuss about.  It's not that much of a load.   
I've never seen ribs sheer, break or explode under bearing.  I've seen  
compression crowned boards with fat crown & bearing after 40 , 50  , 60 years or more 
that sounded wonderful & the ribs still intact & of  course others that didn't.
.  The ribs do other things in these  boards like straighten out when the 
crown deflates but a stiff spruce  crowned rib with nice tight straight grain & a 
laminated rib in my mind  will do just about the same thing for as long as we 
want them to if designed to  handle the appropriate loads. And they will do 
it for a tremendously long time  reliably. I like the whole laminated rib thing 
& all & there pretty in a  techno sense too but
   I'm just throwing out the question is it  overkill?
  Flame suit on & feelin onry today
   Dale

>  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


 

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