Thought this might be a good question for Breaktime, I usually am on the Knots side.
I need to build a beam to support up to 700 pounds hung from a chain in the middle of a six foot span.
Anyone know of a good online source for finding the beam strength of common wood construction materials? Thinking of maybe even laminating ply or making a box beam of sorts.
This is basically a wooden gantry crane for pulling an engine if you’re wondering the application.
Thanks,
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Replies
google "built up beams"
or look at page 133-140 of "Elements of strength of materials", Timeshenko and Young, Van Nostram, 1964. (my old college text).
junk:
Thanks to you I dusted off my Timoshenko. Not everyone keeps that edition handy. It was not a best seller.
"Elements of strength of materials", Timeshenko and Young, Van Nostram, 1964. (my old college text).
Mine, too. And purchased in the first year of its publication.
From the JLC Structure & Framing Book
fb=M/S fb is the max stress tolerable by the material (use 1000 psi for Hem Fir)
M is the Moment for your case its 700 lb x span/2
S is the section modulus 13. 1 for a 2x 8 , 7.6 for a 2x6
so for 2 2x6s it would be M=700 x 72/2= 12600 fb=12600/(15.2)=828 psi
So you are safe with 2 2x6. I'd use 3 to be safer (knots or bad lumber) or 2 2x8s
Thanks, really appreciate the help.Would have taken me a while to research and apply the equation.
Wow!
I would never have thouight of trying to do math on something that small and light weight. I would have just thrown a 6x6 up there, oriented the grain and hung the pulley.
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Me too. If it bent or bowed or broke, I'd beef it up.
blue"...
keep looking for customers who want to hire YOU.. all the rest are looking for commodities.. are you a commodity ?... if you get sucked into "free estimates" and "soliciting bids"... then you are a commodity... if your operation is set up to compete as a commodity, then have at it..... but be prepared to keep your margins low and your overhead high...."
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dont you guys just all do p l over 4 or w l squared over 8 equals sigma b h squared over 6 in your heads first for rectangualr solids ?
That's just plain irresponsible. Suppose it came down and you weren't wearing a hard hat? or had tennis shoes on? or shorts? Where would you be then huh? No math indeed!
Head is already damaged as you can plainly see, and I never wear tennies or shorts outside my bedroom
Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!