L frame design 5

[Luke91]

Hey, been asked to design members for this L frame as well as lifting lugs. Any tips greatly appreciated. Its to lift up to 2tons (2000Kg)
I have done a conservative design using just 1 L frame and applying a load at the worst case (between the two support bars to find the stress) Weld design and lug though i'm not to sure where to begin.

 

[Ussuri]

This may seem a silly question, but do you intend to lift items on the horizontal section of the 'L' Frame? You sketch suggests you plan to lift it using a 2 leg bridle attached to the vertical section of the 'L', if thats the case, it will not lift level because the CoG is offset from your lift points.

 

[HTURKAK]

One picture worths a thousand words ...

 

[Luke91]

Hey thanks for replies.
It is for lifting. To stop tilting could two more lugs be welded to the front. They would have to sit on the horizontal support spanning the L frames.
More so it’s not so much the lifting but some guidance on how to determine the sections needed for the loads and how to calculate the size of the weld for the moment in the joint

 

[BAretired]

Nothing welded to the front is going to decrease the tilt angle. If anything, it will increase.

The design of lifting devices is a specialized field. If you have not done it before, you would be best to seek the services of someone who has.

BA

 

[human909]

Begin by asking the people around you rather than random people on the internet.

If a client has asked you this I'd advise the client to look elsewhere. If a colleague engineer has asked you this then I'd be asking them for help.

Yes, Eng-Tips can be a great source of extremely good information. But if you don't grasp the basics this isn't the place the learn them. Furthermore advice given here could readily be misconstrued and result in a bad outcome. It is far better to say "I don't know" than to muddle on ahead.

I do wonder if this is a symptom of some younger generation of engineers, or just something always there. I currently have a new graduate hire. One of the most frustrating part of his approach is his innability to say "I don't know". I've certainly encouraged him and pushed him to ask questions to which he is slowly getting there. But other times he forges ahead with something that make no sense at all.

 

[dhengr]

Luke91:
I absolutely agree with what BA & Human909 said, and will add…, if you missed or don’t think it is important that the load C.G. will end up under the hook as soon as you start lifting, you’ve got bigger problems than the member sizes and stresses or the weld stresses. It is your responsibility to design the whole system to function well and safety for all the parties involved. Btw, the solution to your problem is to add a horiz. member (or frame) off the top of your back frame, to the left in your side view, so that you can pick, from this frame, over the C.G. of the entire lifting system. Given this thread so far, you should be asking these questions of your boss, so he can draw you sketches and explain what’s really going on. Also, he should know what you know and what you don’t know, so he can give you the proper guidance and keep you and the company out of trouble.

 

[Enable]

I do wonder if this is a symptom of some younger generation of engineers, or just something always there. I currently have a new graduate hire. One of the most frustrating part of his approach is his innability to say "I don't know". I've certainly encouraged him and pushed him to ask questions to which he is slowly getting there. But other times he forges ahead with something that make no sense at all.

It's everywhere and has always been there

 

[human909]

It's everywhere and has always been there

Good to know. I don't want to be one of those guys saying "younger generation" etc, etc...

I came into engineering belatedly after academic and career attempts down a different path. So I'm not 'young' anymore but I'm hardly what you'd call a seasoned engineer, my engineering career is just coming out of it's infancy. (Though I'm trying to make up for lost time.) I'm also have been in the category of an 'unmentored' engineer which in some ways is a scary thought! But it has also meant I have managed to carve my own path and create a structural division within a company that didn't know it needed one.

Back a little more onto topic any good professional needs to know their limit of their knowledge and abilities. Both can be improved either by self taught or mentoring, but when professionals try to run (or are asked to run) before they can walk or crawl it is not a good thing. Sometimes I scare myself with the variety things I've been designing in the last 3 years. Temporary works, complex lifting equipment, vacuum vessels, lots of strengthening work for deflagration events. I'm sure most of us can understand the position where some young engineers find themselves in positions outside their depth. But failing to grasp C.G. concepts and persisting to design lifting equipment is problematic to say the least...

 

[dik]

from your posts, you're doing OK... keep it up

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[dik]

Most lifting devices are C shaped and not L shaped

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[Luke91]

Hey all thanks for the input. I should have stated that under no circumstances am I designing this to be built or to get anyone else to use my knowledge to build this. This post was more for someone to point me in the right direction of steel analysis for this type of problem. This is for my own personal learning of different structures that is all.

 

[human909]

from your posts, you're doing OK... keep it up

Thanks. I have plenty of confidence/arrogance so I don't need too much patting on the back, but it is appreciated nevertheless. Besides posts about my personal career experience is essentially fishing for feedback. (good or bad) This forum has allowed me to explore and challenge my own understanding as I don't have any peers around me to do so.