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For the generation of floor and ceiling masses, as well as for flat roofs, the program generates area elements representing rectangular portions of the floor, ceiling or roof with different depths in the direction of the seismic force. These areas of the floor, ceiling or flat roof do not currently include building material properties, and are not designed by Shearwalls.
Since the design codes and standards require analysis in both directions of force, separate sets of diaphragm building masses are required for analysis in the E-W direction and in the N-S direction.
Area Element Display
Generated area elements appear on the screen in Load Generate action only, with labels F1, F2, F3 etc. in the center of the element. A separate set of elements labeled in this fashion appears for each force orientation on each building level. For this reason, while in Load Generate action, the program will only let you view area elements, building masses, and seismic loads in one force orientation at a time. When returning to Load Input action, both load orientations are reactivated.
The program displays the area element partitioning regardless of whether you have chosen for building masses to be generated from the floor, flat roof, or ceiling areas on a level.
Floor Area Elements
The floor of the first storey is not considered to contribute to seismic force, as it is connected directly to the foundation, and is not used to generate total mass, area element masses, or seismic loads. Thus, a single-storey building does not have floor area elements. For a two-storey building the only floor area is the floor of the second level, which is the first level diaphragm. The area elements that appear in the second level are ceiling diaphragms; these appear on the top story of any structure if ceiling self-weights are entered.
Ceiling Elements
For gable and hip roofs, area elements are generated for the ceiling on the uppermost level, and these are the areas that appear in plan view when the uppermost level is selected. Building masses can be generated for these ceiling diaphragms even if the ceiling depth in the Structure input is zero, as both the ceiling and roof may be resting on the upper story walls. If no ceiling mass is desired, then the self-weight for ceilings is set to zero in Load Generation view.