cantilever system extended 8 ft past a ledge
cantilever system extended 8 ft past a ledge
(OP)
at my job we were wanting to do a cantilever system and we wanted to extend 200lbs out approximately 8ft.. i know every foot it extends the heavier and heavier it will become.. i was wondering at 8 ft how heavy will it seem? i calculated about 1400lbs.. would anyone know what the weight will be?





RE: cantilever system extended 8 ft past a ledge
But it still weighs only 200 lbs. This is Statics 101 - are you a student??
RE: cantilever system extended 8 ft past a ledge
Are you comfortable with statics & strength of materials?
RE: cantilever system extended 8 ft past a ledge
im reading about the strength of materials and statics from machinery's handbook. I wanted to use 4"x4"x1/4" tubing to extend the 200lbs. The formulas they had in the book were throwing me off. Since i had to find moment of inertia and the elastic modulus
RE: cantilever system extended 8 ft past a ledge
Just knowing the moment is just the begining of the design process.
TTFN
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RE: cantilever system extended 8 ft past a ledge
google "bending stresses" ... you should find an expression My/I
M = your moment, 1600 ft.lbs = 1600*12 in.lbs
y = extreme fiber distance (from the neutral axis) = 2"
I = 2nd moment of area of your cross-section (or moment of inertia) = (4^4-3.5^4)/12 = 8.8in4
stress = (1600*12)*2/8.8 = 4400 psi ... very small
RE: cantilever system extended 8 ft past a ledge
RE: cantilever system extended 8 ft past a ledge
Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask
RE: cantilever system extended 8 ft past a ledge
RE: cantilever system extended 8 ft past a ledge
RE: cantilever system extended 8 ft past a ledge
RE: cantilever system extended 8 ft past a ledge
sizeable compared to the 200 lbs load ...
M = 200*8+120*4 = 1600*480 = 2080 ft.lbs ... 25% increase ...
stress goes to <6000 psi ... still very small
RE: cantilever system extended 8 ft past a ledge
First, they may require the design to be done, or at least checked/approved, by a suitably qualified individual, such as a PE in the appropriate specialization.
Second, there may be rules relating to safety factors/margins, load cases (static V dynamic V what happens in an earthquake...) and other design aspects you need to consider.
Third, even if you can safely size the beam, sizing/designing it's connection to whatever structure it's mounted on may be another matter.
I can testify to this first hand, a few years back I mounted a punch bag to a brick wall via the appropriate bracket for its size, I think I even chose to mount it on a buttress part of the wall thinking it would be more rigid etc. Sadly I hadn't taken into account the strength of the wall, or rather the bonding of the individual bricks via the mortar - especially on the top course.
Low and behold about the second or third time I used it I managed to punch it off the wall, or more accurately I suppose I managed to punch the top brick the bracket was mounted on out of the wall. I'd like to think it was due to my immense power and high work rate etc. but I'm pretty sure it was because I didn't adequately allow for the loads on the top unbound brick.
So, it may be worth contracting an appropriate professional who should be familiar with all the relevant codes etc. to at least give what ever you come up with a once over.
That, or at least make it stout out of things you know about and check your/your companies liability insurance to see if you're covered.
Good luck.
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