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Impact Analysis

Impact Analysis

Impact Analysis

(OP)
I am looking at calculating the impact force of a large container (say 4 tonnes) being lowered by a crane at a slow speed (1m/min) onto a flat plate supported by concrete. To ensure the position is correct the plate is fitted with vertical guides with 30 deg tapered face to guide to container into position. The guides are relatively very stiff which when used the equating energy method is giving very large impact loads. So I was wondering if anybody could provide details of alternative methods / advice for dealing with such a situation. Ie the initial impact load of a container being lower by a crane at constant velocity onto an angled surface which is used to ensure to correct final position of the container. Thanks.


RE: Impact Analysis

One solution is to reduce the speed of lowering the container.

BA

RE: Impact Analysis

I think one of the better methods of figuring impact force (IMHO) is the method/formulas in Blodgett's 'Design of Welded Structures' that takes into account stiffness. (See Section 2.8.)

With the info you give, my first try would probably be one of the impulse-momentum equations. I.e. F= mv/Δt. (Where m=mass of object, V=velocity at impact, and Δt= impact time.) The problem with that method is (as you alluded to): you can get some pretty high numbers. It's hard to know what the duration of impact will be. (It can range from as high as 300 ms to as low as 0.1 ms. On rare occasion even be shorter than that 0.1.)

So the stiffness method is a good sanity check.



RE: Impact Analysis

Pgbuxton:
They do this thousands of times a day at container terminals, loading and unloading facilities. And, for the most part, they do not harm the containers or the conc. slab on which they are resting. What lowering speed do those cranes operate at? 4 tonnes is not a particularly heavy container. What components do you expect to be harmed by this lowering process? Take a look at the std. container corner bearing and load securement hardware for the shape and size of your own 30̊ vertical guides. For that matter take a look at the std. design of commercial containers used in transportation today. They may offer you some design ideas and construction components.

RE: Impact Analysis

If you have guides, can they be secured to a 'base plate' that distributes the load as well as adding stiff coil springs to the base plate to minimise the loading on the slab... also steel fibre reinforced concrete is almost prescribed for impact loading.

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