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How Do I Design And Calculate The Stress Of My C-Channel

03/27/2014 12:29 AM

I have a weight of 6,000kg to be lifted by a c-channel (6mmT x 65mmH x 125mmW) with length of 2m. As I calculated, the c-channel weight will be 22kg. The c-channel yield strength=248MPa, Ultimate tensile strength=841MPa. The c-channel then is lifted by a crane of 10,000kg using sling (T1 and T2 with weight 3,000kg each).

This might be a stupid statement/question. With a 22kg of c-channel, it is so sure cannot lift the 6,000kg. That means, I have to design a c-channel of 6,000kg?

However, how do I calculate the stress of the c-channel of how much it can withstand? Will it bend? Will it break?

Any suggestions is highly recommended.

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#1

Re: How do I design and calculate the stress of my c-channel

03/27/2014 12:42 AM
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#2

Re: How do I design and calculate the stress of my c-channel

03/27/2014 1:09 AM

Master, if your reasoning was correct your slings would have to weigh at least 3000 kg in order to lift the 6000 kg weight.

Logically the C Channel has to be designed for the set load and not having the same weight. If it was you would need a crane for 12000 kg lift.

You need to design a channel FOR 6000 kg load.

Look at your vectors and forces and I am sure you can come up with some ideas how to calculate the loads on your channel!

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#3

Re: How do I design and calculate the stress of my c-channel

03/27/2014 5:19 AM

Your assumption is WRONG: in the cable the loads are NOT 3000 BUT 6000! You neglected the angular effect of the 30°

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#4
In reply to #3

Re: How do I design and calculate the stress of my c-channel

03/27/2014 7:28 AM

Yes, and the compression force in the C-channel = 6000*cos 30° = 5200 kg = 51000 N. The C-channel has to take that, also taking buckling into account. (that's for the OP, not for you )

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#11
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Re: How do I design and calculate the stress of my c-channel

03/28/2014 7:49 AM

My thoughts exactly. I voted/rated your post good.

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#5

Re: How do I design and calculate the stress of my c-channel

03/27/2014 8:31 AM

The channel has to take the axial load, plus the bending moment from the eccentricity of the connections.

The channel is one of the worst shapes for this job.

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#6

Re: How Do I Design And Calculate The Stress Of My C-Channel

03/27/2014 9:42 AM

Please do not try to do this yourself. You don't know how.

Simply call a metals supplier and ask their engineer, or hire an engineer to SELECT, not design, a channel for you.

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#7

Re: How Do I Design And Calculate The Stress Of My C-Channel

03/27/2014 1:06 PM

Kudos for knowing your limitations but filling in what you do not know by asking a public forum is wrong. On the other hand, we do clearly explain your assumption and we could then correct those assumptions. So you do have the potential to eventually get it right but not now.

Safely moving things with a crane requires proper training and certification. Your two dimensional drawing does not take at all into account that we exist in a three dimensional world. The mass of all parts including the spreader bar and the lifting base must be included in the analysis. There is also no identification of the center of mass of any part, let alone the entire body to be lifted.

Oh, since when is kilograms a unit of force? With the sparse information provided, I calculate that each strap will be under tension of 60.8 N to just be in stasis. The lifting acceleration will add additional loads.

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#8

Re: How Do I Design And Calculate The Stress Of My C-Channel

03/27/2014 8:02 PM

Stop. Pick up the phone and discuss the lift with several crane hire companies, who will be pleased to quote to carry out the lift using tested and certified lifting equipment, including the correct spreader beam for the job.

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#9
In reply to #8

Re: How Do I Design And Calculate The Stress Of My C-Channel

03/27/2014 11:50 PM

Exactly!

It's a spreader, and unless that load is a 6T 2 dimensional object then you will need at least 2 of them and they will need to be spread as well.

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#16
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Re: How Do I Design And Calculate The Stress Of My C-Channel

03/31/2014 6:58 AM

Quite. The drawing shows a 6000kg object held up by only two lifting points. Unless it is infinitesimably thin, and therefore unknowingly dense, it will only be metastable as drawn and the slightest breath of wind will cause it to flip over. Also, the tensile stresses in the members between the spreader beam and the hook point are incorrect.

One hopes that all other CR4 readers are standing well back when the lift begins...

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#10

Re: How Do I Design And Calculate The Stress Of My C-Channel

03/28/2014 7:07 AM

Why you want to use 'C' Channel?. There are many alternatives readily available in market:-

1. Link Chain sling with 4 legs and 'O' ring at top.

2. Wire Rope Sling.

3. Nylon Web slings.

4. Lifting Beams. etc.

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#12

Re: How Do I Design And Calculate The Stress Of My C-Channel

03/28/2014 9:14 AM

A simple job for a structural engineer, if you aren't one, get one.

allowable stress= Mc/I + TR/J + P/A

for lifting devices I use a factor of safety of 5:1

Rather than risk injuring(or worse) anyone, hire a consultant to design your spreader beam, or leave it to the crane rental company who will be doing the lift. They usually have quite a selection of spreader beams in their arsenal to choose from and good ones have engineers or technical people on staff who can do the calc's for you. If you aren't hiring an outside crane, refer to my first sentence.

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#13
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Re: How Do I Design And Calculate The Stress Of My C-Channel

03/28/2014 9:16 AM

And I forget that the same goes for calculating deflections, etc., of the structural section the will be used.

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#14

Re: How Do I Design And Calculate The Stress Of My C-Channel

03/28/2014 3:43 PM

No one called student on this one?

This is somewhere in Strength of Materials, late in Statics.

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#15
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Re: How Do I Design And Calculate The Stress Of My C-Channel

03/28/2014 9:31 PM

It might fit somewhere in the student distribution.

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