Hello,

When I try to breathe low my abdomen squeezes as my ribs start to expand. Is it normal ?

Hi Ray! It's normal at first, but we want to retrain the belly to relax and expand out when you inhale. Here's an article I wrote that may help: https://makingmusicmag.com/breathing-exercises-for-singing/. 

Thank you very much,

do ribs needs to stay expanded all the time, or they expand and contract with each breath cycle ?

There are a few different perspectives on that. For the "best" support, you do want to keep the ribs lifted as you sing. BUT I don't stress that too much (especially with beginning students) because that can introduce tension, if the singer is locking or squeezing their abdomen to keep the ribs lifted. So it's a good goal, but not worth pursuing to the detriment of your relaxation. It takes a while to feel that "outward" support without locking up.