Everyone has seen book shelves that seem to defy physics and bow until they almost touch the books on the shelf below. This is a simple fix to extend the life of your bookshelf and help keep your OCD for straight lines in check.
I performed this fix on our bookshelf which also has a TV in it. The fix is less ideal for shelves above eye level because the reinforcement will be more obvious unless you paint it.
Step 1: Intro and Materials
For this fix you'll only need a couple things.
Aluminum C or U channel or similar
Hacksaw for cutting metal, or similar
Step 2: Clear Shelf
Remove all books and objects from the shelf.
Measure the width of your shelf.
Step 3: Remove Shelf
Remove the shelf
Cut Aluminum C channel the same length as your shelf (or a hair under, but not longer)
Step 4: Add Reinforcement
Place the C channel on the pins that hold up your shelf. I only put it on the back where most of the weight is, but if you have deep shelves or many heavy books then you may need to reinforce across both sets of pins.
If your C channel is too long, try to cut off a little or use a file.
Step 5: Replace Shelf
Put the shelf back UPSIDE DOWN if you can. This will allow the sagging and bowing to flatten back out from the weight of the books on top.
I added a red line so you can see the bow.
Step 6: Replace Books and Bask in Glory
Replace your books! Take the chance to organize them by series or theme or what not.