Your estimate of hoist capacity?

[awl51]

I recently finished building a garage/workshop, and I'd like to have a ceiling chainfall hoist point to help get heavy items out of the pickup bed and onto the floor. I have a 24 foot span with IJoist 560 series, and the spot I've picked is about 8 feet along a 24 foot span of doubled IJoists (about 7 inches wide).

I anticipate a maximum 400-500 pound object being lifted, like my boxblade. I'm pretty certain that the IJoist itself will be able to handle this easily. My question is about how heavy to make the hoist frame itself. I'm thinking about bending some 1/4" by 1 1/2" plain steel stock (i.e., the max of my HF hand-operated parts bender) into an inverted "U", and then placing the base of the inverted "U" like a saddle over the tops of the IJoists. Where the legs of the inverted "U" extend below the bottom of the IJoists, I'd drill holes for an 8 inch long Grade 8, 1/2 inch bolt, and clip the chainfall onto that.

Does this framework sound like I'm in the ballpark? Of course, I'd pre-test any weight with the me+BIL test deadload (about 450 pounds) first -- but I'd prefer not to do this twice.

 

[SteelDust]

http://www.ilevel.com/literature/TJ-4000.pdf


There is a link to the I-joist literature that shows span tables and which each joist is capable of handling.

 

[hr3]

I would think that the "U" shape would dig in to the top 2+4 under load.. If you don't have a floor above the IJoists why don't you span the joists with a piece of heavy pipe or 6+6.. That way it spread the load out over several joists...and could be moved if you decided to move your pick point,,

 

[awl51]

Thanks for the replies.

HR3, just to clarify, I intend to form the corners of the "U" as square as possible, so that the horizontal part of the saddle lies flat against the top of the doubled Ijoist. And, yes, there is a floor above --- which is driving my choice of flat steel stock, rather than rod or pipe.

Steeldust - I've seen those tables, thanks - but wasn't sure how to translate them into point loads. When I+BIL stand at a point (nearabouts as we can manage) on top of the second floor above the intended hoist point, the deflection of the doubled Ijoists is negligible. So my primary concern is about the capacity of the bracket itself, I don't know how to determine its weight capacity.

 

[wedge40]

Doing this as an after thought is always a pain. My brother has a garage that he put together three 10' or 12' 2"x8" and ran them across (perpindicular) the ceiling joists. Not sure how he put the hook on them, but he said he's lifted the front of cars with it and so far no deflection at all.
In your case I would see about having a "hanger" made to hang the hoist from. That way you could spread the load out a little further, rather than just a point load. Something with basic welding skills could whip up in an hour or two.

Wedge

 

[jmc]

Awl51,

To your question: If you bend that metal sharply enough that the inside corners don't damage the beam, the severely stretched metal is a wild card for any stress calculation. Also, by using an 8 inch bolt, are you creating a span problem on the bolt? The way I interpreted your setup, you could use a shorter one.

Just some other misc. thoughts:

Point loads are a bad idea if your beam has the possibility of defects in it, as wood products tend to have. Murphy's law can stash the defect near where you end up applying the point load. This may be why the mfgr didn't rate on point loads.

Proper design technique dictates a factor of safety for a structure that is several times as strong as the maximum load it will ever see. For example, actual chain strength is about 4 (I think) times its rated strength. The higher the consequences of failure, the higher the safety factor. So just because it holds 450# a couple of times, doesn't mean it's safe. This isn't something that a bunch of lawyers came up with. People have found it cheaper to overbuild way before there were any lawyers.

Then think about unanticipated stresses. One that comes to mind is picking up a load that's off center a little and superimposes a sideload on a beam designed for pure vertical loads.

As the other posters suggested, with a little extra time and ingenuity, you can distribute the load along the beam length and, preferably, among several beams.

John

 

[yooperdave]

A few things to address:

1. Do not already have significant load on the joists if you are relying on them for your hoist support.

2. Provide solid blocking and/or strong backs to distribute the load to several adjacent joists.

3. Engineered wood products - such as I-series joist do NOT have large safety factors associated with them.

Good Luck,

Yooper Dave