Moment Release

[Mexes4453]

can someone explain to me the practical meaning of moment release during a structural study. i see that often while working with FEA softwares (Abaqus).
why do we release moments at joints, fixities and boundary conditions?

Thanks as i anticipate your response.

 

[Bagman2524]

Most methods of truss analysis assume pinned connections at the joints

“Faith is taking the first step even when you don’t see the whole staircase.” MLK

 

[Archie264]

The goal is to have the model mimic reality. Fixed connections usually take additional deliberate effort and are more expensive to construct. Therefore, generally speaking, most connections behave more like they are pinned than fixed. A couple of exceptions are reinforced concrete frames and posts embedded deeply in the ground. I'm sure there are others. But, for a steel frame, for example, unless you intentionally make it a moment connection it's more likely to behave like a fixed connection.

 

[JoshPlumSE]

What Archie said.

But, I'll add an example of a Clip Angle or shear tab beam to column connection. Since the beam flanges are not welded to the column these connections are not capable of developing much in the way of moment transfer between beam and column. Therefore, we typically model them with Moment Releases.

 

[TehMightyEngineer]

It all has to do with the stiffness of the connection vs the stiffness of the member. Rotations and all that.

Maine EIT, Civil/Structural.

 

[rowingengineer]

I hope this "But, for a steel frame, for example, unless you intentionally make it a moment connection it's more likely to behave like a fixed connection.". meant to say "But, for a steel frame, for example, unless you intentionally make it a moment connection it's more likely to behave like a pinned connection."

http://www.nceng.com.au/

"Programming today is a race between software engineers striving to build bigger and better idiot-proof programs, and the Universe trying to produce bigger and better idiots. So far, the Universe is winning."

 

[Archie264]

Rowing, yes indeed, thank you for catching that!

 

[rb1957]

by default FE "welds" two beams together. But in your structure you know that beam1 cannot transfer Mx to beam2 (where it might be My) ... because there are no gussets; so you have to release these freedoms (so the model understands your structure).

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