When putting a shelf on a wall, are the “L” brackets providing more strength when placed above (or below) the shelf?
It seems to me that you should position the brackets below the shelf-as then, the screws attaching the shelf to the brackets will not be under tensile stress…and the screws attaching them to the wall will be under less outward force.
Which is right?
I can’t say I’ve ever seen the brackets above the shelves. First off, placing the brackets below the shelf (the proper way), the screws the attach the shelf to the bracket bear no weight at all. They’re really only there to keep the shelf from sliding off the bracket. With the bracket above, all the weight is on the screws, and more importantly, the area the the screw head and washer spreads it out over.
As for the force on the screws attached to the wall, I’d guess it would be about the same either way.
On top of that, the brackets, depending on the style that you get, are typically designed not to bend more then 90 degrees. However, I don’t think they’re engineered to specifically resist unbending, at least not the once piece stamped/pressed ones.
ETA, putting the brackets above the shelf also uses up valuable shelf real estate.
The brackets are attached to the walls as an inverted L. Then the shelf is placed on top of the horizontal part that sticks out. That way, the brackets support the shelf, rather than the shelf “hanging” from them. And the brackets won’t be interfering with whatever’s on the shelf.
Yes, but I think the OP is asking if it would be better to install them as an upright L, but still screw the horizontal part under the shelf.
For most shelf brackets this is a moot point, since the brackets have a crease at the bend for extra strength, meaning that the shelves would have to sit pretty far away from the wall, if the brackets were mounted above the shelf.
This is not true. A free-body diagram on the shelf bracket will show that whether it’s anchored to the wall above or below the shelf, the forces on the wall attachment screws will be a function of:
-the weight on the shelf
-the distance of the weight from the wall
-the vertical height of the bracket’s footprint (distance between screws) on the wall
I recently installed some shelves/brackets in my garage, with the brackets under the shelves. I used stamped sheet metal brackets, and these each had one wall screw at the bottom, and two wall screws at the top (immediately below the shelf). In this configuration the two top screws (immediately below the shelf) are under tension, while the bottom screw (10" below the shelf) isn’t really bearing a tensile load; the bracket is pushing against the wall at that point.
Suppose instead that I had installed the brackets above the shelf. Now the two screws immediately above the shelf aren’t bearing any tensile load (the bracket is pushing against the wall here), while the single top screw (10" above the shelf) is under tension. Since there’s only one screw in each bracket that’s bearing all the tensile load in this configuration, the load capacity is reduced (assuming the screw pulls out of the wall before the bracket itself fails).
If the brackets you’re using don’t have a three-screw configuration (two screws proximal to bend, one screw distal), then it doesn’t matter whether you put the brackets on top or bottom - except that, as has been noted, the screws holding the shelf to the brackets will be bearing the weight of the shelf, which is probably not a good idea.
Agree 100% with Machine Elf. But …
Regardless of whether the vertical = wall side of the bracket is above or below the shelf, you can place the shelf on top of the horizontal arm of the bracket. You don’t have to hang the shelf under the horzontal arms.
Yes, some variants of these brackets have a small gusset at the inside angle and therefore a shlef placed atop the horizontal arms will be not be quite flush with the wall when the vertical arm is nstalled above the shelf. But that’s a minor point. Dependng on what items you load on the shelf & how they’re arranged, there may be no difference in the effective lever arm of the load.