Heavy duty floating shelves
Real strong steel brackets with solid wood materials are difficult to find in typical online stores. Most store bought units are made from cheap metal brackets for light weight hollow wood box shelves.
You can buy rolled steel brackets which are hand made in the USA on ETSY or EBAY. These are strong and are made from flat steel with round rods welded on. You will need wood thick enough to drill 3/8″ holes through most of the shelf material. You could also make or buy a boxed shelf to mount on this type of bracket.
How much weight can floating shelves hold
The key to being able to hold the weight of books or other heavy items is having the brackets securely screwed directly to the wall studs or anchored with proper fasteners on a brick wall. You will be able to hold up to 40 pounds per screw.
Using wing style drywall anchors reduces this rating down to 10 pounds or less per anchor. The typical shelf will have up to 4 anchors.
This gives you up to 160 pound capacity if you install them correctly with strong fasteners, brackets and shelf material such as thick solid wood. Make sure to account for the weight of the wood as well.