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TR.22.1 Member Release Specification

This set of commands may be used to fully release specific degrees of freedom at the ends of frame members. They may also be used to describe a mode of attachment where the member end is connected to the joint for specific degrees of freedom through the means of springs.

General Format

member-list  {START | ENDBOTH } { *{ FXFY | FZ | MX | MY | MZ } | *{KFX f1 | KFY f2 | KFZ f3 | KMX f4 | KMY f5KMZ f6 } | {MP f7 | *{    MPX f8 | MPY f9MPZ f10 }} }


FX … MZ represent force-x through moment-z degrees of freedom in the member local axes
KFX f1 … KMZ f6 spring constants for these degrees of freedom, in current units
MP f7 partial moment release factor for all three moments
MPX f8, MPY f9, MPZ f10 partial moment release factors for each moment separately. The moment related stiffness coefficient will be multiplied by a factor of (1 - fn) at the specified end. Release factors must be in the range of 0.001 through 0.999.
Note: If FX through MZ is used, it signifies a full release for that degree of freedom and if KFX through KMZ is used, it signifies a spring attachment.


  1. Member releases are a means for describing a type of end condition for members when the default condition, namely, fully moment and force resistant, is not applicable. Examples are bolted or riveted connections. Partial moment releases are a way of specifying bending and torsional moment capacity of connections as being a fraction of the full bending and torsional strength.
  2. It is important to note that the factor f1 indicates a reduction in the stiffness corresponding to the rotational degrees of freedom MX, MY, and MZ. In other words, you should not expect the moment on the member to reduce by a factor of f1 . It may be necessary to perform a few trials in order to arrive at the right value of f1 that results in the desired reduction in moment.
  3. The START and END are based on the MEMBER INCIDENCE specification. The BOTH specification will apply the releases at both ends.
  4. At any end of the member—for any particular DOF—full, partial, and spring release cannot be applied simultaneously. Only one out of the three is permitted.
  5. If MY (or MZ) is fully released at both ends, then VZ (or VY) cannot be transmitted through the member. The final shears in the member will be entirely due to loads applied directly to the member. 


1 3 TO 9 11 12 START KFX 1000.0 MY MZ
1 10 11 13 TO 18 END MZ KMX 200.0

In this example, for members 1, 3 to 9, 11 and 12, the moments about the local Y and Z axes are released at their start joints (as specified in MEMBER INCIDENCES). Further, these members are attached to their START joint along their local x axis through a spring whose stiffness is 1000.0 units of force/length. For members 1, 10, 11 and 13 to 18, the moment about the local Z axis is released at their end joint. Also, the members are attached to their END joint about their local x axis through a moment-spring whose stiffness is 200.0 units of force-length/Degree. Members 1 and 11 are released at both start and end joints, though not necessarily in the same degrees of freedom.

Partial Moment Release

Moments at the end of a member may be released partially using the MP option (to provide the same partial release in all . This facility may be used to model partial fixity of connections. The following format may be used to provide a partial moment release. This facility is provided under the MEMBER RELEASE option and is in addition to the existing RELEASE capabilities.


15 TO 25 START MP 0.25

The above RELEASE command will apply a factor of 0.75 on the moment related stiffness coefficients at start node of members 15 to 25.