What Size Aluminum Angle for 200-Pound Load on Attic Hoist?

[RetSysEng]

TL;DR Summary

Aluminum Angle Deflection calculation for 48" x 36" platform sizing

Hello Everyone,

I'm a retired systems engineer from the aerospace industry, while working part of my job was to come up with concepts and then have great mechanical engineers implement them. Now that I'm retired I have to do both parts for myself. I'm designing a storage hoist to get heavy things into my attic. I've found online beam deflection calculators I've used for the steel rectangle tubing and steel round tubing portions of my design but I'm unable to find any calculators for aluminum angle deflection.

My load platform will be a 48" x 36" 6061 aluminum angle four sided frame with two aluminum angle 36" cross members at 18" spacing. I would like to use 1" x 1" x 1/8" 6061 angle for the entire thing to keep both weight and cost down but I'm concerned that maybe to light and may need to upsize to the 3/16" or 1/4" thickness or even move to 1 1/4" x 1 1/4" or 1 1/2" x 1 1/2" size angle in a 1/8", 3/16" or 1/4" thickness.

I'm designing for a 200 pound, uniformly distributed load across the 48" x 36" platform. Can anyone point me to any free online aluminum angle deflection calculators or provide me with insight or guidance on the best choice size of aluminum angle to use in selecting one of the sizes, 1" x 1", 1 1/4" x 1 1/4" or the 1 1/2" x 1 1/2", in one of the thicknesses, 1/8", 3/16" or 1/4" ?

Your help and insight is greatly appreciated!

 

[AZFIREBALL]

Will this 48X36 rectangle structure have a bottom plate of some sort? How will it be hosted?
The attach points will be the most important consideration.
BTW - 48/3=16.

 

[RetSysEng]

Thank you for the reply.

Will this 48X36 rectangle structure have a bottom plate of some sort?
Yes, it will have a 1/2" plywood top deck.

How will it be hosted?
It will have cables attached at the four corners of the platform that go up to the hoist assembly.

 

[AZFIREBALL]

Do you plan on raisers at the corner attach points?
Also, do have room for a 'backbone/strongback/wiffletree' beam above the the structure/load being hosted?

 

[anorlunda]

Be careful in this thread regarding safety problems. We routinely reject threads asking for help on structure design, and refer the OP to building codes and structural engineers.

In this case, with 200 pounds you are marginally into the unsafe zone. It could kill if it falls on someone's head. So, let's keep the thread open, but be careful to emphasize safety above all else.

I might be wrong, and perhaps this lift does need a permit, or insurance company approval. If so, please say so.

 

[RetSysEng]

Hi anorlunda,

I completely understand about the safety aspects, coming from the world of aircraft systems design, believe me that is foremost in my mind. I've already done all my structural calculations for the ceiling joists and had my builder double up the ceiling joists when the house was framed in the garage attic storage area. This is my second home where I've done the same thing, the first one I purchased a commercial attic lift but for this home, now that I'm retired, I have time to design my own. Regarding weight, the 200 pounds is for the design load calculations only which includes my built-in 50% safety margin. The most weight the lift will probably ever see is maybe 100 pounds at the outside, Christmas boxes, tools, etc.

I've also been my own owner/builder/general contractor for two homes so the permit and insurance issues go without saying. So as a disclaimer to anyone reading this post in the future that is a non-engineer, that does not know what is required to do this type of job, please hire a professional for the design and installation when it comes to anything requiring modification of your home's structure.

 

[RetSysEng]

Hi AZFIREBALL,

Do you plan on raisers at the corner attach points?
The "raisers" will be eye bolts directly into the aluminum angle corners with the cables attached to the these four eyebolts.

Also, do have room for a 'backbone/strongback/wiffletree' beam above the the structure/load being hosted?
The backbone attic frame will be three sided, constructed with 1 5/8" x 1 5/8" Unistrut framing. The electric hoist motor with have a 48" shaft supported on either corner of the 48" side of the frame with the cables coming off the shaft down to two corners of the platform. The two 36" sides of the frame will have pulley's routing the cables from the motor shaft down to the other two corners of the platform.