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?