The plans were very specific about how the bridge had to be installed, but even as a layman watching news footage from the installation, you can tell the plan wasn't followed. The movers had to use load speaders to avoid damaging the bridge, they didn't use any. The movers had to carry the bridge at specific points, but only 1 mover (out of 2 used), was in the correct position. The other one had been moved towards the middle. Naturally, the side that was unsupported was the side that gave way and caused the collapse later on.