Partial Moment release

[Enhineyero]

Hi all, with all these Structural analysis program we use now a days, there is this option of Partial Moment release.

How does one determine the amount of Partial moment to be released? How does one detail a n% moment release connection? My guess is that you assume a partial moment release, then run the analysis after running the analysis you get the forces on that joint and detail it to the accommodate the corresponding forces.

Is my thinking correct? or is there some kind of literature to determine the amount of fixity on a connection?

 

[asixth]

For steelwork, if the connection is capable of transferring 50% of the moment capacity of the weakest member at the connection the I assume the connection rigid (this is my rule so use with caution). Otherwise I use a pin connection and any benefits of continuity are an added bonus.

Base connections I use 0.1*4*E*I/h for pinned and 0.9*4*E*I/h for fixed connections at service conditions.

 

[SteelPE]

asixth

I am interested in how you derived the .1*4*E*I/L equation. This is an equation I often used for pinned foundation/column connections. I know how it was derived on my end, just interested in your end.

 

[dhengr]

Google “Semi Rigid Connections.”

 

[faisal45]

what will be the partial moment release for the rcc structure??

Thank you.

 

[slickdeals]

Depends on the degree of cracking.

It’s no trick to get the answers when you have all the data. The trick is to get the answers when you only have half the data and half that is wrong and you don’t know which half - LORD KELVIN

 

[asixth]

I derived it from the regular conversations on this forum. I think someone posted sometime ago a technical note from the British steel institue.

How did you derived yours?

 

[SteelPE]

Mine came from a seminar given by the AISC a number of years ago. The conversation was in regards to the foundation/column interface and how you could provide some additional fixity at the base for pinned connections since a pin was never truly a pin. They said that in the "K charts" they allowed for G to be taken as 10 for practical purposes. They used this number and plugged it into the 4EI/L equation to get 0.4EI/L. I have used this number ever since when designing moment frames.

 

[patswfc]

Think i may have posted the base fixity equation a long time ago. It comes from the SCI guide on portal frame design P252. Its not meant to be used for strength calcs, unless the foundation is designed to cater for the base moment. Here is the relevant paragraph from the design guide:

For a nominally pinned base:
Where a column is nominally pin-connected to a foundation that is designed assuming that the base moment is zero, the base should be assumed to be pinned when using elastic global analysis to calculate the moments and forces in the frame under ULS loading.

The stiffness of the base may be assumed to be equal to the following proportion of the column stiffness:
• 10% when checking frame stability or determining in-plane effective lengths
• 20% when calculating deflections under serviceability loads

 

[Enhineyero]

@ Slickdeals: I think the degree of cracking depends on the magnitude of the moment, right? and if the amount of moment is dependent on the fixity, then we go the full circle of this question.

 

[DST148]

@Enhineyero: Try link

http://www.revistas.ibracon.org.br/index.php/riem/article/viewFile/54/80

- Partially Restained Beam-Column Connections in Reinforced Concrete by G.M.S. Alva et. el. See if this paper helps.
The paper also brings about clear distinction between moment redistribution coefficients and partial fixity / release......which I am posting here.......
"Within the designing practice there has been some misunderstanding between the moment redistribution coefficient and the partial restriction coefficient. The first is related to moment redistribution, which is caused by cracking in concrete and by yielding of longitudinal reinforcement in the support region, and possesses values limited by the Brazilian Code (ABNT NBR 6118) [2] for linear analyses with redistribution. The latter is not directly related to the type of structural analysis (linear, linear with redistribution, plastic, non-linear), but rather with the most realistic representation
of the conditions of connection between beam and column, in other words, the condition between the fixed and pinned condition. This misunderstanding has become evident from the utilization of commercialized computer systems that allow reductions in negative beam moments."