For lateral members the assigned fixity of beam and columns are used in the analysis. If a structural instability occurs during the analysis, due to the fixity conditions of one or more lateral members, the user will need to modify the member's fixity in either RAM Modeler or in RAM Frame.

All non-concrete gravity beams by default are assumed to be pinned (released) for bending about both axes at each end, and fixed against torsional rotation to avoid instabilities in the finite element model. Gravity beams of material type ‘Other’ and type ‘Concrete’ can be assigned fixities in the RAM Modeler. Gravity Concrete beams can also be assigned fixity from the Assign-Beams-Fixity command in the Concrete Analysis Program.

For concrete gravity beams, fixity can be assigned along with the beam line number on the member (as in gravity concrete beams with an assigned beam line number can be made continuous (fixed at their ends)). Beam line numbers can be assigned and cleared from members as described in Section 2.6.3.

All non-concrete columns are assumed to be fixed at both ends, except for the column located directly above the story, whose lower end is pinned. While gravity columns may be thought of as being pinned, providing the fixity described should not affect the final results as gravity members framing into the columns will be pinned and not transfer any moments into the column (note however a beam pinned to a column is assumed to be supported at the face of a column and will produce a moment in the column equal to the beam reaction times distance from face of column to the column centroid. Providing the fixity also avoids instability issues, which currently cannot be corrected directly by the user.

The user can however explicitly designate the top of a concrete gravity column to be pinned for bending by selecting the ‘Pin top of gravity concrete column’ option from the Analysis Criteria dialog available from the Criteria-Analysis command. Similarly the bottom of a gravity concrete column can be pinned when supported by a transfer member by selecting the ‘Pin bottom of column on transfer member’ command in the same Analysis Criteria dialog box. The user also has the option of pinning concrete gravity columns for bending about both axes at the foundation. See Analysis Criteria in Section 2.5.2 for how to set these options.