In Iron Man 2 when Tony is working on trying to create a new element for his arc reactor, Coulson finds a familiar looking shield which Tony uses to prop a coil
Agent Coulson: [Pulls a familiar looking object out of a box] What’s this doing here?
Tony: That’s it. Bring that to me.
Agent Coulson: You know what this is?
Tony: [As Agent Coulson hands it to him] It’s exactly what I need to make this work. Lift the coil. Go, go. Put your knees into it. There you go. And… Drop it. Drop it. [The shield is now in position and the coil straight.] Perfectly level. I’m busy. What do you want?
Source: Transcripts Wikia
It seems to be implied that it's Steve's Shield that Howard Stark must have kept or something. But the thing is that it looks as if the Shield was in the middle of being rebuilt but Steve's shield wasn't damaged like during his battle with Red Skull on the Valkyrie.
So what happened to Steve's shield for it to get like this?