Member Specification (KMX, KMZ)

Question

Hi, 
 I wish to know how and when to assign values for KMX and KMZ (unit: kN-m/deg.). 
 I've seen members with either KMX =0.001 or KMZ=1 or KMY=1 but I need to fully understand how did they get these values and why. 
 There are members with "checked" END MY (not free to rotate at Y) understanding its member-end and connection must be designed free to rotate only at X and Z but I have no confident understanding on values to use for KMX, KMY and KMZ. 
 Looking forward for someone who could help me. 
 Thank you very much in advance. 
 
 Regards, 
 Chelle

Modestas · Accepted Answer

In most of the cases it is enough to use either totally pinned or totally rigid connections in the analysis. However, if a user requires a more accurate analysis, one can calculate connection stiffness manually and then enter this stiffness value into STAAD.Pro as a KMX, KMY or KMZ value. 
 The calculation of the stiffness of the connection usually is described in the design code, i.e. in Eurocode 3 (EN1993-1-8). An engineer should decide if they need to use a more exact approach and use these stiffnesses in the model or use more simple approach and use rigid or pinned connections during the analysis.

Modestas · Answer

KMX, KMY and KMZ are rotational spring constants of beam. If you know the specific rotational stiffness of the connection, you can use KMX, KMZ or KMY spring release for that beam end connection. 
 If MY option is checked in the member release, then it means that this is a pinned connection about the local Y axis and a MY moment is not transferred. 
 As noted in the Technical Reference manual chapter 5.22.1 Member Release Specification: 
 "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."

Member Specification (KMX, KMZ)

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