1. Calculate the center of mass for each rigid diaphragm (where control joint is to be located) considering the mass model of the structure. The mass must be modeled using mass reference load. See TR.31.6 Defining Reference Load Types
2. Create, internally, an analytical node at the center of mass location to be included during analysis (unless a control node is specified) if an existing analytical node exists at this point, then the existing joint is used in lieu of creating a new joint.
   Tip: The center of mass of each diaphragm is included in the preprocessing output. To include the center of rigidity in the post-processing output, you must include the PRINT DIAPHRAGM CR command. See TR.42 Print Specifications
3. Search all nodes available within a diaphragm and add them as dependent nodes; with the control node located at the center of mass for the diaphragm (or at the specified control node)

Soft Story and Irregularities Checks

Notes

1. One full diaphragm definition should be provided per line. However, if there is joint-list, the list can extend to the second line with a continuation sign ("-").

   DIA f1 TYP RIG YR f2 f3 JOI XR f4 f5 ZR f6 f7
   DIA f11 TYP RIG YR f21 f31 JOI XR f41 f51 ZR f61 f71
   DIA f12 TYP RIG JOI 35 45 51 TO 57 59 TO 83 -
   90 TO 110

   where f1, f11, and f12 are three rigid diaphragms located at floor height ranging between f2 and f3, f21 and f31, and the joints lying in the plane as indicated by their global Y coordinates respectively.

2. Diaphragms should be specified in ascending order (i.e., diaphragms at first floor level should be specified first before specifying that on 2nd floor level and so on).
3. If a user-defined control joint is specified in one diaphragm, then user-defined control joints should be specified for all diaphragms. Combination of user-defined control joint for one diaphragm and program calculated control joint for another diaphragm is not supported.
4. The mass model (in terms of reference load; see TR.31.8.3 Mass Model Using Reference Load for details) must be specified before specifying floor diaphragm. The following reference load cases will be used as the mass model (in the given order of precedence):
   1. all reference load cases defined as LOADTYPE MASS, otherwise
   2. if there are no MASS load cases, the all load cases defined as LOADTYPE GRAVITY, otherwise
   3. if there are no MASS or GRAVITY load cases, then load cases defined as LOADTYPE DEAD and LIVE. At least one load case must be defined as DEAD
   Note: If no load cases have been defined as either MASS, GRAVITY, or DEAD, then an error will be given in the output.

   Refer to G.17.3.2 Mass Modeling for additional details.

5. Floor diaphragms can be specified only once in an input file.
6. Floor diaphragm cannot be specified along with the FLOOR HEIGHT command (refer to TR.31.2.9.1 Identification of Floor Level).
7. Floor diaphragm cannot be specified along with the CONTROL-DEPENDENT command (refer to TR.28.1 Control/Dependent Specification).
8. Floor diaphragm cannot be specified with the SET Z UP command.
9. Sloped diaphragms are not supported.
10. Base level (or ground floor level or support level) is taken as the minimum of Y coordinates defined. Different base level can be specified using the BASE b1 option in the command. If used, this option must be the last line of the floor diaphragm system.
11. The maximum number of diaphragms allowed by the program (default value) is 150. If more than 150 diaphragms need to be specified, then SET RIGID DIAPHRAGM n must be specified before specifying joint incidence, where n = total number of diaphragms in the structure.