Suitable metal for flooring in an industrial lift + power - Physics Forums

Hi all, first post here.

I'm currently faced with an assignment in a class where we really haven't been taught anything and have to figure it out on our own. We've been asked to design an industrial lift system to raise approximately kg up 25 stories. I have done a lot of research and have been able to design a suitable platform frame with less than 3mm of deflection at maximum loading. I've also been able to calculate the required torque and kW rating of the motors I want to use. However, I am left with a few problems left to figure out and I'm not sure where to begin looking for solutions.

My frame is made from standard UK beam segments in a simple criss-cross pattern as below:


The assignment says:
"The floor needed to be constructed from the suitable expanded metal as per the given cage dimensions. The construction company would like the floor to be made of suitable light metal to keep the Material Cost to the minimum."

now, I could just slap a 200 mm steel plate across the frame and I'm sure that would be sufficient, but I honestly have NO idea how to begin to select a suitable material and thickness for this application. The most relevant teaching I've had was 2 years ago doing simply supported beam bending analysis, but this strikes me as a more complex type of calculation. Considering that it is a lift, I imagine that it should be able to take a "point load" of the maximum rated load of kg. This seems like the sort of thing a lightweight aluminium sheet might not be happy with. Can anyone suggest a way to calculate this?

also, the assignment gives us this:
"Power Supply Range : 370- 460 V,50 or 60 Hz,3 Phase
Rated power: kW ?
Power supply Fuse ?
Starting Current : 130 A
Power Consumption :65 kVA"

I've calculated that I would need about 17 kW with safety margin to lift this load with my design. I've never been asked to decide what fuse to use. Any pointers on that would be appreciated as well :)

Thanks in advance for any help you can offer!

-Chris

billy_joule said: The spec asks for expanded metal so you shouldn't use plate. If you do some googling on expanded metal you'll find load ratings tables etc which should help guide your selection.
Remember the lift must accelerate so you need to account for the dynamic loading - not just the static.

Thanks for that! I had no idea what "expanded metal" meant until i just googled it! It helps if you have a teacher who would explain these kinds of things! The guy teaching this module was in serious trouble last year and nearly costed my group our HNCs for not covering all the learning objectives for the CAD module, we were actually teaching HIM how to use the software... there are 6 of us in this group and I'm the only one so far who has produced anything for the assignment because I'm determined to prove my worth :)

Today we had a temp cover our class, we learned more in an hour than we had all semester!

also, he said the lift should move at 12 metres a minute, so in my calculations I assumed an "instantaneous" acceleration of 0.2 m/s force plus gravity just to be safe Well since the questions seems geared towards the frame side, there's a few important things to remember:
1) Even if you think it would be super simple to just throw a thick plate floor to lift stuff up, that plate itself will carry significant weight and will change your frame design (i.e. make it much heavier) and it will snowball into a gigantic motor and generally a messy situation. A 200 mm plate that big weights 20,000 kg by itself.

2) How spread out is your kg load? If you assume they will center the load and distribute it well across the floor, then you can use the span tables provided by expanded metal flooring providers. This will minimize the additional strain on your motor from the floor.

http://www.nilesexpandedmetals.com/nem/grating-load-tables.asp

3) Your scenario shows a working load of roughly 50 lbs/ft2 (250kg/m2), which is probably too low in the event that the client wishes to lift something compact but heavy (such as a pallet of bricks or a piece of machinery on a dolley). I would design your floor grating for 200psf (Kg/m2) minimum or a point load of lb (kg) at the center of the lift, whichever is worse.

Using that load table and assuming that you're only putting the grating on the beams shown, your span will be about 48". This means that even using the 7lb/sf grating, you're only going to achieve a working load of about 175lb/sf and that will cause a .25" deflection (6mm). You should add additional rows of beams to your frame as needed to make sure deflections stay low. This is especially important because the frame is going to deflect, too, not just the grating.

4) For the design of connections/welds/cables, be sure to use appropriate safety factors (look up applicable codes) and impact factors. Lifting cables are generally 3:1 or 5:1 safety factor on ultimate vs working strength, while impact factors due to moving load, uneven lifting, crane movement, etc. range from 1.05 to 1.6 in the extreme case of a sudden stop in the lifting trolley.

Let me know if there's anything else specific you don't understand (structurally). Hi, I have no idea what the spread of the load is, it isn't specified. I designed the frame to cope with a point load of kg at the farthest point from where it is connected to the rack and pinion rail because of this.

I've found an alternative material to expanded metal for the flooring that is relatively lightweight and wouldn't require additional supports, heavier than the expanded metal, but able to cope with a loading like this. I'll pitch it at the teacher tomorrow and see if he bites. Who knows, may get credit for thinking outside the box.

I really wish this design teacher would actually do something other than show a 15 min video of engineers at Dyson designing a vacuum cleaner and then tell us to go design a lift with no guidance. I've looked at some of the legislation regarding lifts but its a bit difficult to get your head around unless you already know something about lifts :)

If anything comes up, I'll update tomorrow. But, as it stands, I've done far more than anyone else in the group anyway, nobody even had a platform design as of last week. And nobody's given any instructions on how to calculate deflections and whatnot of a frame, we only know simply supported beam bending of a single linear beam. I used Autodesk Inventor's frame analysis to find my deflections. And not a single mention of how to go about choosing an appropriate motor, but I found that on my own and ran it by a different teacher who used to do this for a living and he said my calculations seem reasonable.

Thanks for the input!

Hello there.

I ripped up the carpet in our newly-bought home (one of two rooms in the house that were carpeted) to find two plates covering part of the board in one.

As you can see from the images, a previous owner had plans to finish the floors. Two colors were removed (light blue and brown) and the floors sanded. It looks like a trial of a brown stain was used, and then thought better of. This brown stain is similar to the hardwood in the rest of the house.

Close to this area is a small nailed-down metal covering, that when I pryed up, concealed a small mis-sized block that is rigidly in place.

My questions:

1. Any guesses as to why the previous re-modeler would abandon the project despite the great effort to remove two paint jobs already? Is it as simple as the trial stain not meeting their expectations? Is there a logistical concern that I have overlooked?

2. Do the metal plates have a purpose that I have not considered? Is it foolish to remove them and install a block that fits?

3. Does the quality of the wood look worth the effort to rescue? At this juncture I do not know if the brown paint on the second room floor is lead-based and so coupled with existing obstacles, I'm tempted to just lay a whole new install.

Many thanks.

John

https://preview.ibb.co/gxcHCp/.jpg
Floor with plate

https://preview.ibb.co/mNEKQ9/.jpg
Trial stain detail

https://preview.ibb.co/cWNTJU/.jpg
Second room painted brown -- note the attempt to sand the paint off, quickly called off

https://preview.ibb.co/gPUayU/.jpg
Plate pryed up