I have a shelf that is about 4 feet long 2 feet wide and 1 1/2 inch thick. I would like to place an item on it that weighs about 90 pounds. I want to know if it will hold that and I don't know how to calculate it.
How to calculate the weight capacity of a shelf
shelving
Related Solutions
Heavy duty shelf brackets - supposed support 1000lbs (450kg !)
Shelf construction
If the shelf has its front open edge positioned such that at each four feet the cable would go up to a separate roof truss than I think that you have a workable system. Make sure that your 2x3's under the outer shelf edges are placed to that the nominal "3" inch dimension is vertical.
Hardware
Note that the lowest cost eyebolts, known as the "bent type eye bolt" are generally not recommended for lift and continuous tension applications. For this application it may be suggested to search out the drop forged type eye bolts as shown on the right below. These will cost more but they are actually specified for "lift" type applications.
If you do use the bent type, orient them so that the split end of the eye is up, as show above. Definitely use through-bolts rather than any type of screw-in eye.
I would use 5/16" diameter eye bolts or larger.
Connection points
Put the upper end of the cable through a threaded eye bolt that goes all the way through the side of the rafter truss and is secured in the far side with a washer and nut. Avoid the use of a screw eye type fastener. The eye bolt should be attached to the upper rafter part of the truss instead of the lower cross tie. When drilling the hole for the eye bolt position it in the upper part of the rafter as opposed to the lower portion.
Put the bottom end of the cable through an eye bolt that is long enough to go through the shelf material and the 2x3 and secure on the bottom with a washer and a nut.
Note that the orientation of the cable clamps is important, and it is always advisable to use two cable clamps for securing the cable.
Cable sizing
The size of cable is really dependent on the amount of load that you expect for the shelf. I would think that 3/16" diameter cable would be adequate for this application. The chart below will help to explain why I recommended 3/16" (assuming you use the 1x19 type of "stainless steel aircraft cable").
Related Topic
- How to mount a shelf above a closet door
- Use these brackets to make wall mounted bookshelves
- Wood – Is “unstructural plywood” suitable for shelving carrying a microwave oven
- Drywall – How to anchor to a 1″ thick hollow wall with a very shallow cavity
- Best/strongest material to build a weatherproof shelf
- Walls – AAC (aka Aircrete, Thermalite) wall + IKEA ALGOT shelf weight load capacity
Best Answer
There is a cool site for this: The "sagulator" for computing this. It's intended more for freespan shelves (like a book case), but you might be able to use it to answer your question. Hope it meets your needs. Ed makes a good point about support as well. With that weight it will need to be fastened to studs with multiple brackets.
Edit: Forgot the link, here it is: https://www.woodbin.com/calcs/sagulator/