Problem

Missing or incorrect loads on perimeter beams, or excessive loads on the first interior beams.

Explanation

Since the advent of free form slab edges, there have been a few framing slab edge configurations that can lead to unexpected loading on the perimeter beams.

In the image below, the slab edge is slightly skewed to the perimeter beam, and crosses it at one point. Consequently beam 8 may be assumed outside of the slab edge and will not receive loads from the one-way deck.

Another situation that can cause problems is a perimeter where the beams perpendicular to the edge all cantilever out but there is no perimeter member between the cantilevers defined. In this case, the cantilevers won't be loaded by the deck as intended and the load will be applied to the supporting girder instead.

Avoidance

The best way to avoid the problem when using one way decks is to align the slab edge with the perimeter beams and use at least a 1" outboard overhang. Furthermore, make sure the perimeter framing creates a closed loop around the diaphragm. Small gaps in the perimeter framing can also cause problems.