Several times,
My own house, built when I was in my 20's, has no ties in the 2 story 14' wide section, and no ridgebeam. It has a 4/12 pitch, so for every pound of vertical load it produces 3 pounds of horizontal thrust... the flatter the pitch on a simple gable roof the higher the thrust. In its' 36' length it is divided by a stacked crosswall at 14' and then there is a wall about 1' off the peak that runs for about 12', unstacked, that is a non load bearing wall over the kitchen below. The center ~10' is open. We have had a slightly above design load snow load on it ~30psf. The roof held but did sag a bit and the wall bowed out a bit. I learned something in all that as well. The ridgeboard is a 2x12 and by chance it is spliced over bearings. The building wasn't fooled in the least, my non load bearing wall is indeed a load bearing wall and the floor sagged a bit. There is a designed load path and then there is the real load path. Many, many buildings have this scenario. While you are driving around, look at houses with swayback ridges, then sight down the eave walls, bet you'll start noticing it. They might not be collapsing but they also aren't relying on any designed load path.
A couple of weeks ago while we were talking about rafter thrust in another thread I was talking with a gentleman on another forum who put up pictures of his framing and I saw he had a problem. I brought it to his attention, the roof was not yet sheathed and the weight of the 12/12 rafters alone, with collar ties tight up under the ridge, had pushed the walls out of plumb by over an inch in several days. With a jack and ratchet straps they got it back and installed ties. The weight of sheathing it may well have collapsed it, but who's to say, he would also have been building a flexible diaphragm. The prescriptive code doesn't give much credit for that, but it is also an unblocked diaphragm. The top plates act somewhat as a beam between crosswalls, but it is undesigned, same for the soffits. I'm not opposed to beams at the top plates rather than at the ridge to resist that thrust... if you can take care of the reactions. Relying on these elements without consideration and saying "it doesn't happen" is also riding very deep into your safety belt and not knowing where you are.
I'm presently working on an old log barn that was built by someone who knew what they were doing. At some later point someone who didn't understand came in and removed the tie logs in the center to make one large mow that is easy to work in. It is now 4" wider in the middle up top and shoving out hard. We need to remove and replace the side sheds but, the shed diaphragms are restraining it although they are failing. We have some cable and ratchets and formulated a plan to pull the main structure back together and hold it temporarily this afternoon. I've seen several cases of the plate log rolling or sliding out under that thrust.
