The laws of physics are always obeyed. As soon as these structures are built the gravity is always pulling them downward. Add human activity such as stomping and rhythmic dancing and there is an additional destabilizing force. Its a wonder there are not more horrendous collapses. A few years back the Golden Gate Bridge featured a celebration where close to two hundred thousand people were all walking on it. Later engineers stated the bridge was not designed for that type of stress and fortunately it did not fall.
I think there's a kind of normalcy bias that compels people to think that all buildings have been built for the activities that happen in them. That's definitely NOT always true. Watching a group of people who had been drinking alcohol for hours jumping up and down on a structure that didn't seem engineered with sufficient strength to support their combined weight and synchronous impact on the floor was more than I could ignore. Fortunately, nothing horrible ever happened there, but it has since been demolished.
I forgot about that GG Bridge event. The photos showed the bridge deck being compressed to a straight horizontal line instead of a big unloaded hump in the mid span.