Wind story forces can be automatically calculated based on the building diaphragm heights and widths, including the effects of parapets. For models with slab edges modeled in the RAM Modeler the extents of the diaphragms are calculated by RAM Frame based on the over-all dimensions of the diaphragm layout, slab edge to slab edge. For levels with multiple diaphragms, the extents of each diaphragm are listed. For models without slab edges these values must be determined and input by the user using the Loads - Exposure command if the automatic wind force generators are to be used.

For the top level and for any level where the building steps, the parapet height must be input in order for the area of the parapet to be considered in the story force calculation. Except at the uppermost level, parapets are only considered when the building steps, that is, the extent of the level above perpendicular to the direction of the applied wind force is less than the extent of a given level.

Occasionally there are small partial diaphragms that do not contribute significantly to the lateral force resisting system or to which it is not desirable to have a generated wind force assigned. In such a situation the "exposure" at that diaphragm can be set to None (rather than Full). The story forces of the two adjacent diaphragms will then be calculated ignoring the presence of the intermediate level.

Extents, parapet heights, and the exposure flags can be input and modified using the Loads - Exposure command. The information is only required when wind diaphragm forces are going to be automatically generated for a model with a diaphragm specified as rigid.

The Exposure Boundaries report (Reports – Exposure Boundaries) shows the boundaries determined and used by the program to calculate the wind story forces. If that report does not reflect the actual conditions of wind loading, the extents should be modified, or user-specified story forces should be used rather than the automatically generated story forces.

Refer to Story Forces: Wind for more information on the generated wind story forces.