2000 Pontiac Grand Am bent trailing arm?

I am wondering if you could help me. I jacked my car up on what I thought was a cross member and it bent. I was told it might be a trailing arm. It is in the rear of the car. On the drivers side. There are two . What look like flat plate steel but they are curved, they go all the way from one side of the car to the othere alond the axle. I jack the car up on one to fix a brake line and it bent. Can you tell me what it is and should the whole thing be replaced?