Extracting models from a simulation

I wanted to make a bunch of falling bricks and then when the pile formed was interesting extract it into a separate model but I’m having problems: I let the animation run, then stop it and try to duplicate the bricks in the desired shape and move them aside to leave the simulation, however this messes up the simulation. What would be to correct way to unlink the extracted objects from the animation/simulation/physics? This way weird things happen, the bricks disappear from their initial position (though duplicated) and the simulation turns unpredictable.
Thank you in advance!