[Perceived] The bridge shudders under your next step, and the normally quiet creaking increases in volume and frequency. You catch a few bits of the construction shift and fall away out of the corners of your eyes. The entire structure feels ready to collapse at any moment.
[Triggered] A thunderous crack rings out, and the bridge spits at the midpoint. The structure seems to hold, but then the first chunks start to fall. As the integrity weakens, more and more pieces plummet downward in a storm of debris.