Steel Lifting Frame/Spreader Frame Design Help

[psychedomination]

Hi there,

I recently started working at a structural engineering company, having finished university about a month ago(fresh graduate). I have been tasked with designing a cross braced 4 sling lifting frame/spreader frame to pick up freight containers filled with hazardous waste, which would prevent the containers from buckling in on themselves (the containers are heavily corroded at the top). I am still very inexperienced when it comes to steel design, so am wondering if anyone out there is willing to help me. I have already given a fair attempt as far as analysis is concerned. I followed the British standard 2573 which have rules for steel used in crane design. I have attached an image of what I am trying to achieve along with the calculations that I have done so far. It seems that smaller UKC beams will pass the conditions in the calculations also but they have a much higher slenderness ratio due to the much smaller radius of gyration in the y-y plane(not sure if this would make them sub-optimal or not, would love to hear opinions on this). I have only done the calculations for the long beams and am guessing I will need to do the exact same calculations for the shorter members carrying less compressive loads. I am also unsure of how to determine which beams to use for the cross bracing members. Should I use the same I beams used for the Cy long beams? I would love it if someone could take a look at my calcs so far and give me an opinion on areas where I am possibly incorrect in my theory and areas where I am not providing the optimal solution. I am also now considering how I will connect the 4 members together to make a frame. I have absolutely no knowledge of connection design so any help in choosing a simple design solution for this would be a great help.

Image of what I am trying to design :

http://files.engineering.com/getfil...3-32ed-434d-8be9-7cbfe37203b3&file=synch4.jpg

Design calculations :

http://files.engineering.com/getfil...86f&file=LiftingBeamCalculations305UKC118.pdf

 

[dhengr]

Psychedomination:
You have to be brave enough (smart and confident enough) to tell your boss you need help, and need a mentor. He should not expect you to do this problem, one month out of the Uni., without any help. And, he should want you to learn and do well, and he should want to know what you do and don’t know, so he can keep you (the company) out of trouble. You should sit with him/her and discuss the general analysis and design of this lifting frame, look at and study existing examples; and then really discuss and review the details and how this thing gets fabricated and used, and how these dictate your design. Being in the USA, I would look at the AISC Steel Manual and the ASME BTH-1-2008, or later, Std. That is ASME, “Design of Below-the-Hook Lifting Devices.” You should be able to find these on the internet. Obviously, your Engineering Mechanics, Strength of Materials, Theory of Elasticity, Welding, Machine Design text books, etc. are important, and you better use them, partly on your own time, to show that you want to learn, and become productive. Whichever codes and stds. you use, the laws of physics don’t really change, nor does Statics and Strength of Materials, nor does good common sense and good, sound engineering judgement. So, most of the better codes and stds. will arrive at about the same acceptable solution. It’s dumb people and bad judgement which come up with the inferior solutions or failures.

However the container is loaded, its C.G. will always end up directly under the hook, so all four slings may not have exactly the same tension. And, if one of the slings is a bit long, or should break, or a container corner fail, you don’t want to drop the container. So, this frame should still work with only three slings in place, sort of an ultimate or emergency condition. Look at your detail (FBD, free body diagram) of the forces and moments on the corner of one of the WF beams, your calcs. pg. 2: you would like the three force vectors to meet at the neutral axis of the beam, this will minimize the moments on the joint and members. You do this with the design/shape of the corner lifting plates, a nice, direct load path. You do not want lifting plates bent out of plane by the lifting operation, so they should be oriented in line with the slings. WF shapes are not nearly as efficient for this application as pipes or HSS (tube) shapes, becuase of their improved stability as compression members. Certainly, WF shapes can be used, but they have a weak orientation which you must deal with. Welding and good clean detailing are very important for this type of equipment because of the abuse they take in the field. Good, clean direct load paths are very important; hook, sling, clevis, corner lifting plate, to load attachment. Don’t chase them (the loads) around, you either lose them (forget them) or concentrate them at some nasty detail or weld condition.

Good Luck

 

[desertfox]

Hi

try this link
thread404-290250

see my post with attachment dated 28 jan

“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein

 

[oldestguy]

For an application like this you have to visualize all the negatives that may come about and then add more safety factor. For instance, what is the expected life of this unit? Will it be exposed to acidic conditions? Will it be subject to abuse, such as dropped from some possible height or shoved by a dozer or snow plow to push it aside with other units. I'd guess these possible abuses may far overweigh any loads it will carry. How about cracked welds, will they be readily observed?

 

[rb1957]

for me the sketch on pg 2 doesn't account for the fitting between the beam and the cable; ie Cy would be even further from the NA.

It sounds like you want something like the attachment ?





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