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16th July 2016




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Cantilever formula
Hello, gents!
i am new here, and i am looking for a formula to solve a calculation for a cantilever.
Please see attached!
A solution would be much appreciated!
Would be possible to solve this in Robot from Autodesk?
Last edited by pride2iceman; 16th July 2016 at 02:19 PM.

16th July 2016




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W X P / T X 3
W = weight
P = projection
T= Tailing length
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18th July 2016




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Quote:
Originally Posted by philliosmaximus
W X P / T X 3
W = weight
P = projection
T= Tailing length

Can you explain more ? I didnt get where the 3 comes from?

18th July 2016




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Safety factor. Some people use a factor of 4.

18th July 2016




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Quote:
Originally Posted by lmk
Safety factor. Some people use a factor of 4.

Thanks for the answer

18th July 2016




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Your welcome.

19th July 2016




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Quote:
Originally Posted by pride2iceman
Hello, gents!
i am new here, and i am looking for a formula to solve a calculation for a cantilever.
Please see attached!
A solution would be much appreciated!
Would be possible to solve this in Robot from Autodesk?

Some considerable time ago I created a simple spread sheet for cantilevers PM me a mail ID if you think it would be of use
Alan

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19th July 2016




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Just to interfere here. Be careful with the 3 times and 4 times safety factors chaps.
Work out what the force f is under the applied loading including the self weight of the beam and then decide how you are resisting it. If you were using kentledge, every 1 kg that you add to the kentledge increases the load on the edge of the slab by 1 kg. If you need 1500 kg as in this case to balance the cantilever and that is what you put on it, the load on the edge of the slab is 25 kN (plus self weight). If you multiply the 1500 kg by 4 and put 6000 kg, the load on the slab edge increases to 70 kN which it might not be able to carry.
If you punch off the slab above you are limited by the weight of the slab above to how much force you can apply but assuming there is sufficient weight the load on the slab edge from the beam will only be enough to balance things ie 25 kN.
If you anchor down to the bottom slab, the same thing applies. Here, though, you have a fixing that you may want to over specify to give you confidence that it won't pull out. 15 kN might require 2 no 7.5 kN fixings but you could put a greater number in to give a better safety factor than normal to allow for bad workmanship. On suspended loads a factor of safety of 3 is considered normal (see EN13155) so may be right here but this is the factor between the failure load and, in this case, the working load of 15 kN. A fixing rated at 7.5 kN safe working load already has a factor of safety on its failure load and may not fail until a load of 23 kN is applied to it giving you a factor of safety of 3.
Using serviceability analysis, I would work out the actual load without factoring and then use engineering judgement to decide the type & capacity of the means of resisting it, taking account of the whole situation.
Using ultimate analysis, I would vary load and material factors to suit the situation.
If I was working on site and I saw some anchors that I hadn't put in stopping me toppling off the building with the cantilever, I would probably put a couple of props off the structure above to be sure, to be sure!

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Thank you, gents!

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[QUOTE=TG6;366400]Just to interfere here. Be careful with the 3 times and 4 times safety factors chaps.
Work out what the force f is under the applied loading including the self weight of the beam and then decide how you are resisting it. If you were using kentledge, every 1 kg that you add to the kentledge increases the load on the edge of the slab by 1 kg. If you need 1500 kg as in this case to balance the cantilever and that is what you put on it, the load on the edge of the slab is 25 kN (plus self weight). If you multiply the 1500 kg by 4 and put 6000 kg, the load on the slab edge increases to 70 kN which it might not be able to carry.
If you punch off the slab above you are limited by the weight of the slab above to how much force you can apply but assuming there is sufficient weight the load on the slab edge from the beam will only be enough to balance things ie 25 kN.
If you anchor down to the bottom slab, the same thing applies. Here, though, you have a fixing that you may want to over specify to give you confidence that it won't pull out. 15 kN might require 2 no 7.5 kN fixings but you could put a greater number in to give a better safety factor than normal to allow for bad workmanship. On suspended loads a factor of safety of 3 is considered normal (see EN13155) so may be right here but this is the factor between the failure load and, in this case, the working load of 15 kN. A fixing rated at 7.5 kN safe working load already has a factor of safety on its failure load and may not fail until a load of 23 kN is applied to it giving you a factor of safety of 3.
Using serviceability analysis, I would work out the actual load without factoring and then use engineering judgement to decide the type & capacity of the means of resisting it, taking account of the whole situation.
Using ultimate analysis, I would vary load and material factors to suit the situation.
If I was working on site and I saw some anchors that I hadn't put in stopping me toppling off the building with the cantilever, I would probably put a couple of props off the structure above to be sure, to be sure![/QUOTE
I was talking about pure kentledge as opposed to using anchors. I assume the safety factor of 3 is still relevant there?



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