Inconsistency between elements and nodes

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MichaelTar
Posts: 3
Joined: Wed Jul 20, 2011 11:12 am

Inconsistency between elements and nodes

Post by MichaelTar » Mon Jul 25, 2011 8:03 am

Hi everyone,

I am trying to model a CBFrame with pinned connections. The problem that I have is that the base shear is almost 50% higher than the combined force of the braces at each time (dof 1 of course). The relationship between shear force and the combined forces of the braces is linear. I checked all elements and there is no moment anywhere. What could be wrong.
Thanks alot


wipe;
model basic -ndm 2 -ndf 3;

file mkdir data;

set slend 0.600

set Ab 0.03
set Ib 0.0000000000001
set Ac 0.0132
set Ic 0.0000000000001

set D 0.354
set tw 0.012
set B $D
set tf $tw

# define GEOMETRY
# nodal coordinates:
node 1 0 0
node 2 5 0
node 3 10 0
node 4 0 4
node 5 5 4
node 6 10 4
node 7 2.51 1.98
node 8 7.49 1.98
node 44 0 4
node 66 10 4
node 51 5 4
node 52 5 4
node 53 5 4
node 54 5 4


equalDOF 5 51 1 2
equalDOF 5 52 1 2
equalDOF 5 53 1 2
equalDOF 4 44 1 2
equalDOF 6 66 1 2
equalDOF 5 54 1 2


fix 1 1 1 0
fix 2 1 1 0
fix 3 1 1 0


geomTransf Corotational 1


#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 355e6] [expr 210e9] 0.05 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 dispBeamColumn $eleTag $iNode $jNode $numIntgrPts $secTag $transfTag #
#element nonlinearBeamColumn eletag i j numofintpoints section transf
element dispBeamColumn 1 1 7 $noip 1 1
element dispBeamColumn 2 7 51 $noip 1 1
element dispBeamColumn 3 53 8 $noip 1 1
element dispBeamColumn 4 8 3 $noip 1 1

#Beams and Columns

#element elasticBeamColumn eletag i j $A $E $Iz transf
element elasticBeamColumn 5 1 44 $Ac [expr 210e9] $Ic 1
element elasticBeamColumn 9 2 52 $Ac [expr 210e9] $Ic 1
element elasticBeamColumn 8 3 66 $Ac [expr 210e9] $Ic 1
element elasticBeamColumn 6 4 5 $Ab [expr 210e9] $Ib 1
element elasticBeamColumn 7 54 6 $Ab [expr 210e9] $Ib 1

#Recorders

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

pattern Plain 1 Linear {
load 5 1000.0 0.0 0.0
load 4 1000.0 0.0 0.0
load 3 1000.0 0.0 0.0
}
test EnergyIncr 1.0e-5 30 0
algorithm Newton
system UmfPack
numberer RCM
constraints Plain
analysis Static

source DispHistory,0.600.tcl

set LoopLength [array size disp]

set h 1
set controlNode 5
set currentDisp [nodeDisp $controlNode 1 ]

## Run the static cyclic analysis
while {$h < $LoopLength} {
set controlNodeDisp [nodeDisp $controlNode 1 ]
set dU [expr 0.01*$disp($h)]
integrator DisplacementControl $controlNode 1 $dU 1 $dU $dU
set ok [ analyze 100]
set h [expr $h + 1 ]
}

fmk
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Posts: 5866
Joined: Fri Jun 11, 2004 2:33 pm
Location: UC Berkeley
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Re: Inconsistency between elements and nodes

Post by fmk » Thu Aug 04, 2011 9:52 am

tighten up your convergence tolerance A LOT .. your model has achieved convergence based on your rather loose criteria.

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