Floating shelves for cats - advice wanted!

Hi! I want to put up a bunch of floating shelves for my cats to have more high spaces. Floating shelves I've bought in the past are hollow and not great. I want to build them myself so they are solid, don't sag, and can take the load of cats jumping on them (a lot more than their weight).

SHELVES A - MY PLAN: 18mm thick plywood, 250x400mm. I watched a video recommending these brackets: https://www.amazon.co.uk/dp/B07FYNDJWL?ref=ppx_yo2ov_dt_b_fed_asin_title for floating shelves, but I'm not sure if they will work for me project. My concerns - is 18mm plywood thick enough for a 10mm dowel bracket, and is 120mm embedded dowel length enough for a 250mm depth shelf? Is there a way to calculate the load bearing of this set up? I am intending to use two brackets per shelf and will make sure at least one for each shelf is attached to a stud.

SHELVES B - MY PLAN: In addition, I want to create "steps" off and existing set of shelves that are build into the alcove. The current shelves are 18mm thick. I have a load of squares of plywood that are 12mm thick, and 230mm along each length. Two ideas - one is to attach the squares edge to edge with the existing shelf using a large/heavy duty flat metal plate to attach the two parts. The other idea is to place the squares partway under the shelves and simply screw in from below (probably using quite a few screws). Pics of me holding the squares in the two poss positions attached in case this is not clear from the description. Any thoughts welcome on which may be most secure / if either version will be strong enough!

Thanks!!

Any shelf will hold a cat the problem is friction, they need to be covered with carpet .

foxhole said:

Any shelf will hold a cat the problem is friction, they need to be covered with carpet .

Click to expand...

True re grip, but in terms of load the force can be 4x their weight if they jump on the shelf, so for my big cat that could be 30kg