I'm installing a corner shower in an apartment with concrete floors. I can not break up the floor to install a conventional drain trap. Is there a trap for low clearances? If so how high do I have to raise the shower base to clear the trap. I plan to run the drain to where the vanity drain meet the floor and tie it in there.

6-8 inches for standard P trap. I have seen people make a running trap out of 45 degree ells but I would worry about trap siphoning and not sure if they are legal. If you Google "low clearance traps", you can find some examples too.

Running trap is absolutely illegal and will eventually cause a siphoning of the trap as "stuff" accumulates... ;)