Gravity analysis calculates the internal forces of structural elements by finding the load flow paths. This is done for vertical loads only. Other load types are ignored.
Loads are transmitted only from top to bottom, not vice versa.
The model is understood as a set of floors (levels). Each floor is analyzed independently. Only multi-span beams are solved as hyperstatic systems. All other elements are understood as isostatic. Frame behavior is not considered.
Each of the non-horizontal model elements must be supported by being placed on another element, or by being connected to a support. Hanging elements are not allowed. They are reported as model errors.
Trusses, bracings, diagonals, sloped columns, and complex structural elements are not allowed. If they are not reported as errors, they will be approximated, not calculated precisely.
Foundation slabs are considered only as elements supporting other elements. Slab behavior is not considered.
Walls are treated as separated elements, working on compression only. No shear or cantilever effects are considered.
The relationships between horizontally placed elements (load paths) are assumed based on the following rules:
Beams support slabs (slabs are placed on beams), and not vice versa.
When two beams intersect, the beam already supported is treated as the supporting element.
The stronger element is treated as a supporting element. The stronger element is the element whose section has a larger moment of inertia, or larger area (first the section's moment of inertia is considered, then section's area).
Beam ends may be released or fixed. A beam with fixed supports on ends is not treated as a continuous beam. Each member is solved separately. Middle supports in multi-span beams are treated as simple supports.
According to the IBC and ASCE/SEI 7 codes, the influence area is calculated as a multiplication of live load element factors by tributary areas. However, this application calculates the influence area as a total area supported by the element. This may cause some differences in results.
To ensure the live load reduction is accurate, for different types of occupancy with different load intensities define separate load cases and combine them afterwards. If you include uniform loads of different intensities in one load case, it is not clear from the analysis viewpoint, and may cause inaccurate results.
A one-way slab should be supported along the whole width. Otherwise, a warning displays and a load from the slab is transferred only to supports not parallel to the main reinforcement direction, and is distributed as for a two-way slab.
The model self-weight can be included automatically in the analysis; to do it, select the Add self-weight to option in the Analyze in Cloud dialog (see Performing the Analysis).
Note: Only the self-weight of the analytical model uploaded to the cloud is included in the analysis. However, it may differ from the self-weight of the physical model in the Revit project (see Structural Analytical Model Overview).