I have seen nothing in the reports of the damage which mentioned the alcove and transfer beam above it. While Partin makes much of the fact that some of the failed columns along the front of the building are further away than some undamaged ones in the interior, this is in fact easily explained by the existence of the alcove around or beside the failed columns.
The alcove is an essential part of the reason for the Murrah building's collapse. Not only because of the structural weaknesses it imposed, but also because of how it concentrated the blast forces. Had the wall been entirely flat, the air moving out from the blast could have been diverted upward and away from the building. The air would have out considerable pressure on the building, of course, since it has inertia and momentum. On the other hand, the initial wave front would have represented the peak pressure the structure would have to face. The length of the pressure wave would have affected the duration of the pressure, but not its peak value.
The alcove, however, created an entirely different situation. When the pressure wave hit the inside wall of the alcove, it could not just be reflected skyward because the third floor was in the way. Nor could it go left or right because there were walls there. Nor could it simply reflect out, since there was more high-pressure air behind it.
In short, something had to give.