equalDOF command: master and slave node problem

[chbus]

I have modeled a four story 2D frame with buckling restrained braces (BRB) and a leaning column in OpenSees Navigator. The beams are pinned and the columns are continuous over the building height. While verifying the period against a similar ETABS model, I realized that the periods were different. The drift for a given lateral load was the same (so the lateral stiffness is the same) and the mass were properly adjusted. I realized that changing the beam stiffness (EI) had an effect over the period in the OpenSees model witch is not correct (the beams are pinned so they don’t contribute to the lateral stiffness).

A diaphragm constraint was assigned to each floor using the EqualDOF command assigned to the same level nodes in the horizontal direction. The master nodes were the nodes of the leaning column. The pinned connexion of the beams was done by taking two superposed nodes with the EqualDOF command assigned to the vertical DOF only (horizontal DOF already assigned by the diaphragm constraint). To do so, the master node was the beam node and the node of the column was the slave node. After checking on multiple parameters, I realized that the period was correct only if the master node was the column node. I don’t understand the difference of assigning the master node to the beam or column node. Does anyone has encounter this problem before and could explain me?

Thank you!

[MohsenShani]

its simple

you must use element zerolenght to equal element.
and if you want model shear story (like rigidDiaphragm in 3D ) you must use rigidLink -beam.

######################################################################################

material for element zerolenght :
set Fy_S 1000000000000000000.
set Esc 2100000000000000000.
set v 0.02
set zerolenghtmaterial 1
uniaxialMaterial Steel02 $zerolenghtmaterial $Fy_S $Esc $v 5 0.925 0.15 0.0005 0.01 0.0005 0.01

element zeroLength $elementtag $masterNode $SloveNode -mat $zerolenghtmaterial $zerolenghtmaterial -dir 1 2

if 3D mode i can explain more for you
#########################################################################################

rigidLink beam $StartNodeFloor $EndNodeFloor


if you want model send me a email

civilshani@yahoo.com