M.E. help needed: Optimum cantilever beam shape?

turtlevette said:
TheSkunkWorks said:
mrvette said:
72 FEET?? what in hell you building there, a bowling alley??? jeebus.....
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Yes, 72 FEET. You can click here to see a pic of it just before completion. Used a number of flitch-plate sandwich beams to save weight and several thou $ vs. I's.
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Are you a dentist? Looks like a dentist's office.
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Only as a hobby, but I'd best keep my day job, no? :bump:
buck-teeth.jpg
 
Well, the darker side said, would it be that a EE has to pull on his member to turn on the light upstairs?
 
kwplot34 said:
Yeah there are quite a few earth'n homes around here,all you can see of them is the roof sticking above the ground,except for the S.E side,you can see the front of the house,the rest of it is below ground.Cut's down on building cost you only have to put windows on one side of the home.
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And heating and cooling costs
 
Yellow73SB said:
kwplot34 said:
Yeah there are quite a few earth'n homes around here,all you can see of them is the roof sticking above the ground,except for the S.E side,you can see the front of the house,the rest of it is below ground.Cut's down on building cost you only have to put windows on one side of the home.
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And heating and cooling costs
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Yes it does cut down on heating and cooling bill,quite a bit from what i have been told.
 
turtlevette said:
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This Electrical Engineer is going to vote for the I beam.

for a given amount of material and conversely weight, the I beam can be made taller which resists momental force better.

better get out your text books and brush up.
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All my old engineering mechanics books are packed up for the move, so I'm out of luck here, but I got to thinking the other night. Is an I beam any better than a square tube? I was wondering, if you split the thickness of the center part of the I beam, and moved them out to the edges of the other two planes (making a square), would the cantilever performance be the same? I can understand the popularity of I beams as they are easier to manufacture than a square tube, but would there be a difference in performance? (I haven't had any caffeine this morning, so it might be a stupid question.) Just curious.
Thanks.
 
Or H beam. H beam is stronger in compression, I beam in extention. high rev motors generally use I beam rods.
 
69427 said:
turtlevette said:
..................................

This Electrical Engineer is going to vote for the I beam.

for a given amount of material and conversely weight, the I beam can be made taller which resists momental force better.

better get out your text books and brush up.
Click to expand...

All my old engineering mechanics books are packed up for the move, so I'm out of luck here, but I got to thinking the other night. Is an I beam any better than a square tube? I was wondering, if you split the thickness of the center part of the I beam, and moved them out to the edges of the other two planes (making a square), would the cantilever performance be the same? I can understand the popularity of I beams as they are easier to manufacture than a square tube, but would there be a difference in performance? (I haven't had any caffeine this morning, so it might be a stupid question.) Just curious.
Thanks.
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my first post here - and without a net!
from memory: the "I" beams you're describing are known more commonly as "wide-flange" shapes in structural speak. "I" beams have been replaced with "S" shapes that are typically used for some monorail applications.
the W shape is most efficient (lbs/ft) for typical structural static bending loads; getting the most mass farthest from the center of gravity (in the cross section) yields the greatest radius of gyration.
As the length of a W shape member increases, so does the likelyhood of failure due to buckling. this is why you'll see intermediate bracing - to reduce the unbraced length.
However, the torsional rigidity of a W shape is very limited. sometimes moment connected frames can get the job done, but within the selection of shapes, the square, round, or rectangular tube will outperform the W shape when torsion loads are present. the tradeoff is weight, but not if the W shape fails.
there is some discussion in the texts about compact vs non-compact shapes, but i can't remember details . . . these memories are all from the 80's; should verify
more details about the situation are needed to really help with specifics about the application.
hope that helps
 
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