Structural question 3

[Grawschbags]

Hi folks,

I'm new to the forum. I previously worked in the defence industry as a mechanical engineer. I have recently made the switch to a smaller engineering firm who deal with tanks and structures.

Now, my memories a bit rusty and I need a quick solution to a problem I haven't come across since my uni days. Hopefully you can help.

I am designing a structure that is to support a 60m^3 storage tank, that when full could weigh up to 90 tonnes.

This cylindrical tank is to be supported by 4 legs (with additional cross members) equally spaced around the tank diameter.

It has been proposed that the legs of the tank be made from 180X180X8mm square hollow section, mild steel.

The height of these legs will be roughly 4m tall, with the tank sitting on top.

The cross sectional area of the beams is 54.4cm^2, and the moment of inertia is 2661cm^4.

Could one of you kind people please confirm if these sections are man enough to do the job?

Thanks for your time/help.

G.

 

[EricaB]

bgstructuralengineering.com is a great website full of useful information about structural design. Check it out and it may give you some basics on structures and practical application knowledge beyond what google can teach you.

 

[izax1]

Just remeber when you (or any other for that matter) do your design that there is no such thing as a perfectly straight column, and it never had been. Unless anyone can tell me how to make one. And then you still have to explain: How straight is prefectly staight.

We live in an imperfect world, or else we would not have a job. And remenber the world is non-linear and dynamic, not linear and static.

 

[dhengr]

Grawschbags:

Then, maybe you should develop a more direct working relationship with that Structural Engineer, if he is willing, and he should be your mentor on the structural parts of these jobs. That way you will become more adept at putting together a design package, on your end, of your parts and components, which he can finally do his structural design around, without a lot of back and forth hassle. I say ‘if he is willing’ because on the one hand he may not want to give up his bread-and-butter (work) to you, for your edification alone, and he certainly may have some reservations about just signing-off on your work; but if your company has a long working relationship with him, and he gets a fair amount of work from you, he should welcome your knowing what he needs to finish his part of the job efficiently. And, you stand to learn a lot from this professional exchange and interaction. You probably will never be able to sign-off on the structural parts of the job, but you can become proficient at preliminary sizing and anticipating what he wants and needs. Thus, your prelim. details, connections, arrangements, number of legs per tank, bracing needs, etc. won’t have to be completely redone when the Structural Engineer gets his hands on it. And, there is a lot more of value to you and your company by taking this approach to your learning the ropes, than the exchange of a few formulas which has taken place here. You have just touched on a few of the many structural considerations on this design, so far.

You should approach him early on in the job, with a schematic of what your company or client wants to do, so he can tell you about how he would structure that configuration of tanks or whatever, maybe no final sizes at this stage. That way you don’t get too far into your design process, and arrangement of your components, without his having some very important input, you do want the thing to keep standing under all the loads, after all. Take full advantage of that 40+ year guy while he is still around, he may not be a P.E., but many of those guys have a wealth of knowledge to pass on if you are a willing learner, and show enough interest. He may not know all of the engineering fine points, but more often than not he will keep you out of trouble by just saying ‘something just doesn’t look or feel right about what you are showing at that detail.’ He’s a valuable mentor too. Finally, take some old plans, drawings, specs. and details home and study them, and ask questions, you will see how your company’s various components fit together under various conditions, and how that Structural Engineer handles the structuring under each of these conditions. This will be a real service to your company over and above just ‘producing technical drawings and documents.’

 

[Grawschbags]

Thank dhengr for your input. It's much appreciated.