sistering joists?

My Garage was built over a hundred years ago and was built sturdily but loosely. I mainly use the second floor of it for storing wood that was there ever since it was built. The only problem is that the wood is not organized. the current floor is not strong enough to hold the wood in one place. the floor is just wood from old sides of box cars. it's about 1x4. and siting on 3 very old 4x12 . It has 3 bays and there s cars parking in all of them so all i can do is rip up the floor sister the joists and put a new stronger floor on right?