Pseudo-flexible diaphragms were added to simplify the process of modeling flexible diaphragms, which require manually calculating lateral loads and placing them as nodal loads in Elevation mode of RAM Modeler. They are referred to as “pseudo-flexible” since the behavior of the flexible diaphragm is not directly captured by considering the finite stiffness of the diaphragm, but rather by considering frame portioning of the diaphragm (i.e., by use of independently acting frames with distributed story shears).
In order for the pseudo-flexible diaphragm properties to recognize the frames within the diaphragm boundary, frame numbers must be assigned to a vertical frame member (wall, column, or brace). If all vertical frame members assigned to a given frame number are outside the diaphragm boundary, then that frame number will not appear in the dialog. If only beams are assigned to a given frame number, then that frame number will not appear in the dialog. If no frame numbers have been assigned, then only Frame 0 will appear in the dialog.
In many instances, a single column is part of two different frames. One example is a corner column that is part of a both a x-direction frame and a y-direction frame. RAM Frame permits only a single frame number assignment to each member. When a frame is part of two different frames, consider one of the following approaches:
Nodal loads that are generated for pseudo-flexible diaphragms are applied in the global x or global y direction only. If a frame is skewed in the XY plane, there will always be a force or mass component that acts in the out-of-plane direction. This out-of-plane component will result in large deflections or instability errors. The following are better options for skewed frames:
The important thing to remember about the pseudo flexible diaphragm in RAM Frame is that it is no diaphragm at all. The behavior is exactly the same as if you set the diaphragm to "Flexible/None." Unless the frames are interconnected with frame members or horizontal braces, they will displace independently.
The following are common issues that lead to errors that prevent the RAM Frame Analysis from running to completion:
RAM Frame - Criteria - Diaphragms
RAM Frame - Semirigid Diaphragms
RAMSS Eigenvalue Error