object movement

Does anyone have any ideas how I can make a little bridge rotate up 45 degrees randomly about every 10 to 20 seconds? also when it rotates up I want it to stop my player. I have the art for the bridge down and raised. I know it can't be that hard I just can't figure it out.

http://mfa.aquadasoft.com/upload/1398632330-Bridge.mfa

Here is a quick example. The bridge rotates 90 degrees, but maybe it will give you an idea.

Thanks! That's exactly what I was looking for