Wall mounted crane design 1

[KieranSean]

Hi all, i really need some guidance. I am new to this game having been employed just a little over a year.

Our company has decided to take on work to design and supply hand operated wall mounted cranes.

I'm struggling to get started with sizing the beam (see attached pic). Can anyone tell what method i should be using?

Cheers

Kieran

 

[PetroSynergy]

Are you referring to the horizontal I-beam you are trying to size?

BTW, kudos on the nice conceptual design, most people scribble on computer paper and hastily scan and upload it. Hard to decipher.

 

[KieranSean]

Yes the horizontal I beam. Is it the case that i decide on the safety factor i would like to use, then using the beam stress equation work back to obtain the correct beam properties.

after looking into the design a little more, i have become extremely worried about the fixing situation.

how can i determine that i am using the correct number of fixing bolts?

 

[CastMetal]

Choosing a safety factor then working backwards is a good idea.

When the load on each joint is determined you can find the tensile and or shear stresses the bolts will be subjected to. Using a slightly larger factor of safety for the load on the bolts u can calculate an appropriate number specific to each joint.

And there are always FEA programs to double check yourself.

 

[KieranSean]

This is where i really am strugging now, if i ignore the gussets top and bottom and treat it as a simple cantilevered beam, how do i go about finding the stresses the bolts will be subject to.

sorry if i sound like a simpleton but this is quite new to me.

 

[PetroSynergy]

Keep in mind, you cannot use the entire length(in the formula) if you are trying to look at it as a cantilever pole. Does this make sense? It's hard to convey through text.

Also keep in mind wind loads, and ice loads(if applicable).

Assuming you will be using a winch for the vertical lifting, it is not a static load. This is especially important when you are moving around 622kg.

Once you have figured out the conditions of the dynamic loads+ any other aplicable conditions(dynamic+wind...etc), you can truely calculate the max stresses the bolts need to handle, and can design accordingly.

 

[dhengr]

Kieran88:
The best guidance I can give you is that you should be talking with your boss about this problem. He should know what you don’t know about this topic and problem, so as to keep you and the company from making serious errors and out of trouble with whoever would use this crane. This is not a trivial problem or project, and sizing of the beam may be the least significant part of the problem. He/she should find you a mentor or advisor, maybe him/herself, who can sit with you and do sketches, and have back and forth discussions about the critical aspects of this design project. And you, on your own accord, should invest in some text books on Strength of Materials and Statics and simple Structures to make yourself smart enough to tackle a problem like this. No good ever comes from pretending you know what you are doing on this kind of project, when you so obviously don’t. Do not try to fool your boss about what you know, by coming here for answers or worse yet, partial answers, and then presenting them as your own, when you don’t have some idea if they are right or wrong, or have considered all the important aspects of the design problem.

A few questions for you... Why not make the upper diag. member a tension member, then the beam won’t be a cantilever? What kinds of bolts, what kind of wall, is the wall strong enough to hold this crane? Might not the beam be two channels back to back, then the tip sheave and the sheave near the wall and the lifting cable can be between the channels and out-of-the-way, and down the wall to a winch? Should this crane pivot at the wall so as to store against the wall when not in use? Should you provide a vertical steel member at the wall for all of your parts to be fixed to, and then bolt this whole system to the wall as a unit?

We all need help as we start out, so don’t be embarrassed about that. Don’t call yourself an engineer if you are not. And, don’t B.S. your boss about what you can do, unless you can do. And, even then, there will still be questions about the finer points of the design, or best parts suppliers, grades of materials, etc.

 

[boo1]

Establish work cycle, load safety factor (~125%), external loading (wind, snow), impact factors, conduct a reaction force calculations. Check bending, buckling, and deflection.

CMAA standards state that the maximum stress in a main beam must be less than 1/5 of the ultimate strength of the steel. The maximum deflection must be less than 1/600 of the length of the crane (CMAA Standard 74 Section 3).

It appears your beam to wall connection does not povide much rigidity in the Z direction.

Get a senior engineer to mentor you and a registered engineer to sign off on the design and calcs....

Cheers
Boo1

 

[KieranSean]

Thankyou dhengr for your comments. I must state that in no way am i pretending to be an engineer or B.S.ing my boss about me being capable of designing such equipment.

I'm in a situation where i am still in study whilst working full time, the company i work for has no senior design engineer to consult with or guide me, my boss isn't capable either.

I have explained to my seniors that i am not capable of such things yet and am uncomfortable even attempting to design such equipment. The worst part of it is, the sales man says jump, we're forced to say how high!

Where do i seek guidance?? Is there extra training courses i can take to improve my knowledge in this type of design??

 

[RockEngineer]

When I look at your sketch, the first question I have is where and how are forces resolved to the support structure. I assume you are trying to put some type of wire rope drum and hoisting motor on the vertical member. Once you know how and where you are attaching the crane and have the external forces, you can break it down to analyze the individual members by following your forces through.

Eventually you will need a PE who is familiar with lifting equipment design requirements to approve the design. I would never recommend buying a piece of lifting equipment without the design approved by a knowledgeable PE. There is too much risk involved.

 

[chicopee]

The drawing that you are showing is really badly designed for such light load crane jib since the supported end is overly built. I would remove the lower diagonal member and extend the upper one further out. The load line should be riding a sheave, mounted on the upright, of a diameter several times that of the load line to minimize sever bending. This sheave can be made to slide sideway to minimize the fleet angle at the hand operated winch. In addition the conditions set by OSHA regulation should be met and and the entire design and calculations documented for possible review by an OSHA inspector..
The structural analysis involved is not complicated if anyone in your shop has knowledge of statics, strength of material and machine design. As shown the horizontal member is primarily under compression, therefore, axial and bending stresses have to be considered but include some eccentric loading and some torsion if the load line is riding in a grooved sheave at the end of the horizontal beam.
Of course, other aspects of design mentioned above such as anchoring the crane jib should be evaluated.

 

[pgpada]

You could advice a machine design book (Shigley maybe) and then you can find all the answers and formulas that you would want to.

 

[hokie66]

Kieran,
As dhengr said, this is too much to expect of you at this stage. If you have no mentor, you can't do it. Simple as that. What intrigues me is why a company such as yours would even try to do this, as there are lots of folks already supplying these type jib cranes, and they have many years head start on you. They are pretty much off the shelf items. Salesmen, they give me the s...ts.

 

[KENAT]

You're in GB?

I'd take a look at the relevant British Standard(s) (your local library may be able to help if you don't have an account/access from work) and any additional requirements from 'elf & safety' or other legislation.

I believe there are legislated load factors for lifting equipment. It may vary by type of equipment etc. but I've seen situations where the factor was something like 8!

Making this thing safe may be less of a concern than making it safe & cost effective. You'll almost certainly have to proof load it to well above the max working load which mitigates serious safety concerns - so long as you're careful when doing the test.

Oh, and if in the UK you wont need a PE (Professional Engineer) to sign off on it. You may need a Chartered Engineer but probably not. You may need to get it CE certified though.

(If you don't state where you're from on this site it tends to get assumed you're in the US.)

Posting guidelines faq731-376

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(probably not aimed specifically at you)
What is Engineering anyway: faq1088-1484​

 

[KENAT]

forum507 may have some relevant threads too.

Posting guidelines faq731-376

http://eng-tips.com/market.cfm?

(probably not aimed specifically at you)
What is Engineering anyway: faq1088-1484​

 

[racookpe1978]

After applying ALL of the above "lessons learned" in the design of the crane members and bolts and gussets ... you MUST remember to analyze the resulting load on the wall: Pull (out from the wall), twist (from unsymmetrical loads/forces), shear (down), and acceleration (and stopping/deceleration!) loads must be transferred to the wall, the columns and baseplates/foundations of the wall.

This (also!) is not trivial, and, if not done correctly, can either make your "solution" too expensive and will ruin your company and cost you your project, or will fail and cause injuries, deaths, structural failure of the building. Which will also ruin your company and cost you your project.

 

[PeterStock]

Also remember you are not (I presume) doing the installation. Be sure your instructions for installation are understandable and provide for determining that the wall can handle the load.

Peter Stockhausen
Senior Design Analyst (Checker)
Infotech Aerospace Services

http://www.infotechpr.net