Well you'd have to have them tied to a func_door, then when you want it to break- have a render make the func_door dissapear and a func_breakable appear, and then break it-- this is how it was done in the original half-life game---(I got a decompiler[for that reason only]I use it when I need help on stuff that they did in the game)
It can get frustrating, It took me for ever-- first I had to have the normal door, I walked in and out of when I walked into this room I had aliens appear making them strike the door with there electricity the door broke and flew open and closed.So I had to make two doors one the normal door- and two, the broken door, and then the func_breakable, same as the first door,(only tied to a func_breakable instead of a func_door)... anyways Im going to stop blabbering on... lol