I've built a work bench by modifying some plans I found, and one part of the modification involved installing a shelf. The bench is 8' long, stable and solid, and I used 4x4x6 uprights in the back corners to mount the shelf onto.
To keep the shelf from flexing I used 2 2"x6"x8' as stringers between the 4x4s and attached the shelf ( 12"w 1/2" maple) to the bottom of one of the stringers with countersunk 2" #8 Robertson screws spaced every 12".
My question is: should I further brace this shelf considering the maximum load on it will likely be less than 100#? My suspicion is that I should install 3 triangular braces, one at each end and one in the center to prevent any sagging.
Edit: Here's the updated picture with both upper and lower. The curve in the small shelf is illusory, just need to touch it up with the router when I bullnose the front of the bench.