Pinned connection in CBF

[MichaelTar]

Hi everyone,
I am trying to model a pinned connection in a 1-story concentrically braced frame. The thing is that when I am checking the moment reaction at the slave node at the end of the brace I find there is a moment there. Removing the equalDOF command from the model (all connections are now moment connections) I find a difference both in the natural period and the max displacement. Is it normal to have this moment at the end of the braces? I am posting my script here. Help will be very appreciated.
Thanks
Michael

wipe;
model basic -ndm 2 -ndf 3;

file mkdir data;

set numoftimesteps 5000
set timestep 0.01
set groundmotion 1
set slend 1.69
set Ac 0.03
set Ic 0.00098777
set Ab 0.03
set Ib 0.00044078
set m 145000
set D 0.2
set tw 0.02
set B 0.2
set tf 0.02

# define GEOMETRY
# nodal coordinates:
node 1 0 0
node 2 6 0
node 3 12 0
node 4 0 4
node 5 6 4
node 6 12 4
node 7 3.03 1.985
node 8 8.97 1.985
node 9 0 0
node 10 6 4
node 11 6 4
node 12 12 0
node 13 0 4
node 14 12 4
node 15 6 4
equalDOF 1 9 1 2
equalDOF 5 10 1 2
equalDOF 5 11 1 2
equalDOF 3 12 1 2
equalDOF 4 13 1 2
equalDOF 6 14 1 2
equalDOF 5 15 1 2
fix 1 1 1 0
fix 2 1 1 0
fix 3 1 1 0

#Assign masses
mass 4 $m 0 0
mass 5 [expr 2*$m] 0 0
mass 6 $m 0 0
geomTransf Corotational 1
geomTransf PDelta 2

#Material Properties
set shr 0.02
set R0 16
set cR1 0.925
set cR2 0.15
#uniaxialMaterial Steel02 $matTag $Fy $E $b $R0 $cR1 $cR2 $a1 $a2 $a3 $a4
uniaxialMaterial Steel02 1 [expr 275e6] [expr 210e9] 0.002 15 0.925 0.15

#Section Properties
#Structural steel SHS-section properties
#Basic dimensions

#Depth of the web
set dw [expr $D-2*$tf]
set df [expr $B-2*$tw]
set A [expr $D*$B-$dw*$df]

#Section Coordinates
set y1 [expr -$D/2]
set y2 [expr -$dw/2]
set y3 [expr $dw/2]
set y4 [expr $D/2]

set z1 [expr -$B/2]
set z2 [expr -$df/2]
set z3 [expr $df/2]
set z4 [expr $B/2]

# Number of fibers
set nfdw 10; # number of fibers along web depth
set nftw 1; # number of fibers along web thickness
set nfbf 10; # number of fibers along flange width (you want this many in a bi-directional loading)
set nftf 3; # number of fibers along flange thickness

#Create Section
#section Fiber $SecTag {nfIJ nfJK yI zI yJ zJ yK zK yL zL}
section Fiber 1 {
patch quad 1 $nfbf $nftf $y1 $z4 $y1 $z1 $y2 $z1 $y2 $z4
patch quad 1 $nftw $nfdw $y2 $z4 $y2 $z3 $y3 $z3 $y3 $z4
patch quad 1 $nfbf $nftf $y3 $z4 $y3 $z1 $y4 $z1 $y4 $z4
patch quad 1 $nfbf $nftf $y2 $z2 $y2 $z1 $y3 $z1 $y3 $z2
}

#Element Properties

#Braces
set noip 5
#element nonlinearBeamColumn eletag i j numofintpoints section transf
element nonlinearBeamColumn 1 9 7 $noip 1 1
element nonlinearBeamColumn 2 7 10 $noip 1 1
element nonlinearBeamColumn 3 11 8 $noip 1 1
element nonlinearBeamColumn 4 8 12 $noip 1 1

#Beams and Columns

#element elasticBeamColumn eletag i j $A $E $Iz transf
element elasticBeamColumn 5 1 4 $Ac [expr 210e9] $Ic 2
element elasticBeamColumn 9 2 15 $Ac [expr 210e9] $Ic 2
element elasticBeamColumn 8 3 6 $Ac [expr 210e9] $Ic 2
element elasticBeamColumn 6 13 5 $Ab [expr 210e9] $Ib 1
element elasticBeamColumn 7 5 14 $Ab [expr 210e9] $Ib 1

#Recorders


recorder EnvelopeNode -file Data/$slend,[expr int(10000*$A)],$groundmotion.out -node 5 -dof 1 disp

#Define Gravity Load
pattern Plain 1 Linear {
load 4 0 [expr -$m*9.81] 0
load 5 0 [expr -2*$m*9.81] 0
load 6 0 [expr -$m*9.81] 0
}
numberer Plain
system BandGeneral
test NormDispIncr 1.0e-8 6
algorithm Newton
integrator LoadControl 0.1
analysis Static
analyze 10
loadConst -time 0.0

#Define time history analysis
timeSeries Path 2 -dt 0.01 -filePath $groundmotion.tcl -factor 9.81
pattern UniformExcitation 2 1 -accel 2
set freq [expr [eigen 1]**0.5]
set T [expr 6.2831853/$freq]
set zeta 0.02
rayleigh 0. 0. 0. [expr 2*$zeta/$freq]
wipeAnalysis
constraints Plain
numberer Plain
system BandGeneral
algorithm Linear
integrator Newmark 0.5 0.25
analysis Transient
analyze $numoftimesteps $timestep

[vesna]

You should remove equalDOF command from all the nodes whose master node has constraints assign to it (e.g., nodes 1, 2 and 3 can not be master nodes). Since nodes 1, 2, and 3 are already pinned I can not see why do you have nodes 9 and 12.

On what end and of what brace did you see the moment?

[MichaelTar]

Yes, of course. However I had some error warnings when I removed them so I kept them on. I used the node recorder command for the moment reaction at node 11 (top of the brace).

[vesna]

What did you exactly change and what was the error message?