A flexible diaphragm can be modeled by considering independently acting frames in the diaphragm in such a way that each frame is expected to resist a fraction of story\diaphragm forces. Thus, the implemented approach allows the user to explicitly define what percentage of the story\diaphragm force is resisted by each frame at the story\diaphragm.

To this end, you are expected to enter effective participation values for each frame in this dialog, and then the program uses the participation values to distribute calculated story\diaphragm shears and masses accordingly. Once the story\diaphragm shears are resolved for each frame, they are further distributed among members and finally applied as a nodal load on members' joints.

Thus, for each load case type, different effective percentages for the frames can be entered. Also, the effective percentage values defined for one load case type can be copied over other load case types by invoking Apply These Percentages to Other Load Types. It should be also noted that the section Dynamic is used only for distributing calculated story masses among the frames.

The dialog also indicates the total sum of effective percentages for each diaphragm. It is usually assumed that the sum should be equal to 100 per cent, but having less or more than 100 per cent is also allowed in the dialog.

Once story or diaphragm shears are resolved for each frame, they are further distributed over frame members, and finally applied as nodal loads at frame members' joints. Two alternative methods are provided for distribution of the loads over frame members. Either they are equally distributed among the members, or they are distributed based on relative rigidities of the frame members (i.e., stiffer members take more of the loads). This choice can be carried out by choosing either Frame Members Equally or Frame Members Based on Their Relative Stiffness.