Fixed But Support

Question

Hi, 
 I 
 I dont quite understand how to use KMX , KMY, KMZ to release some of the moments from a support. 
 What is meant by the unit kn.m/deg. ?? 
 How can I set a reasonable release for the attached STAAD Model , to activate the back fixed support . 4278.Cantilever 2019 - Copy.std

Sye · Answer

For releasing moments at supports, you do NOT need to define KMX, KMY or KMZ. To do that you simply need to check the appropriate boxes on the left under the Release. For example to define a pinned support but which is restrained from rotation about the global vertical axis (Y), you need check the boxes for MX and MZ. 
 You only need to specify KMX, KMY or KMZ when you want to define rotational springs. The unit is in kN-m/deg because the value you are expected to provide here is the value of moment ( in kN-m units ) that would cause a one degree rotation at the support.

Sye · Answer

If you have an idea of the rotational stiffness offered by the support you may use KMX. If you are using a trial value then you may as well consider using a PINNED support at these locations. Defining partial release is not a problem provided the connections at the end can take up any resulting moments that may be generated. I did not see any warnings without the releases when I run the file in the latest STAAD.Pro CE (22.01.00.39). 
 You may want to add the LOAD LIST 4 TO 11 command before the design to ensure that design is carried out for the load combinations only. A modified file is attached for your reference 5661.Cantilever 2019 - Copy_rev.std

Sye · Answer

You should not release FY as otherwise the shears even due to selfweight of the members cannot be transferred to the supporting members. 
 Use the following 
 MEMBER RELEASE 
 12 13 16 17 START MY MZ 
 12 13 16 17 END MY MZ

Sye · Answer

3 - 5 mm deflection does not seem high unless the structure is really sensitive to deflection. Anyway you may use KMX but ensure that what you are using is realistic.

Sye · Answer

This is an engineer's call. If you are unsure talk to other engineers involved in the project.