It looked to me like the end of the beam fractured but it could also be that the end of the beam was cut with a torch and that it was held in place with a bracket welded across the middle. That would be a very, very crude way to build a building but I suppose it is possible. Hard to say without being there and looking at stuff. We only one one picture and it isn't that clear so I'm not jumping to a conclusion. Just saying that if a person wanted to know why it failed they should start by looking at the I beam.