use of rigid zone factor

[odco]

Hi all!

Well, I have a question:
In some computer programs (SAP, ETABS, RCBE...) the rigid zone factor is set ti 0 (zero) by default. But, when I use this factor as 1 (one) the drifts of the building goes up and the steel reinforcement also goes up a little. Can any one tell me whic factor should I use and in what cases?, I mean, 0 when there is a pinned member as steel structure and 1 when is concrete? OR 0 when the columns and beams are quite equal in sectios and 1 when the columns is more rigid than the beam?, please, help me!

Thanks,

odco

 

[MikeT14]

RAM has the same setup. I too was wondering what factor to use for what case.

Hope someone can help . . .

 

[whyun]

Per ETABS version 8 Manual:

Rigid-Zone Factor

The rigid-zone factor specifies the fraction of each end offset assumed to be rigid for bending and shear deformations. When a fraction of the end offset is specified as rigid, the outside portion of the end offset is assumed to be rigid; that is, the portion at the end of the frame member. By default, the program assumes the
rigid end factor to be zero; that is, the end offsets are fully flexible and they have the same frame section properties as those assigned to the rest of the member.

The rigid zones of the end offsets never affect axial and torsional deformations. The full element length is always assumed to be flexible for those deformations.

Output forces for the end of a frame member are provided at the inside face of the end offset along the length of the member. No output forces are produced within the end offset.


*** Therefore rigid-zone factor of 1 assumes that the entire member is infinitely rigid and does not allow any rotation at the nodes.

 

[WillisV]

Typically the Rigid End Zone (REZ)factor of 0 would assume a centerline based model which is typical of most basic analysis and should be accurate enough in general practice.

Using a REZ of 1.0 assumes there are zero deformations within the area at the intersection of the columns and beams known as the "Panel Zone" (it is infinitely rigid). The "true" case lies somewhere in between and could be modeled using a rotational spring layouts (e.g. a scissors or krawinkler model) that is beyond the scope of RAM.