why is the eigen value of two models so different?

[jyokou]

Hello~~
I have made two models with different section command. One is a 3story 3bar steel frame in which the cross-section is defined by "aggregate" command. The other one is defined by fiber section. Even though I have used the same cross-section, the two models' eigen values were extremely different.
Here are the scripts.
I highly appreciate your kind reply.
############################# T1=0.9984254920072939s, T2=0.3439299621661737s
model BasicBuilder -ndm 2 -ndf 3;
set Data Nofiber
file mkdir $Data
cd $Data

set Data1 nodedisp
file mkdir $Data1
set Data3 Column
file mkdir $Data3
set Data4 Beam
file mkdir $Data4
set Data5 damper
file mkdir $Data5
set Data6 rotation
file mkdir $Data6
cd ../
#
#
#
set x1 0
set x2 3500
set x3 7000
set x4 10500
set x5 14000
set x6 17500
set x7 21000

set y1 0
set y2 1750
set y3 3500
set y4 5250
set y5 7000
set y6 8750
set y7 10500

node 11 $x1 $y1
node 12 $x1 $y2
node 13 $x1 $y3
node 14 $x1 $y4
node 15 $x1 $y5
node 16 $x1 $y6
node 17 $x1 $y7

node 23 $x2 $y3
node 25 $x2 $y5
node 27 $x2 $y7

node 31 $x3 $y1
node 32 $x3 $y2
node 33 $x3 $y3
node 34 $x3 $y4
node 35 $x3 $y5
node 36 $x3 $y6
node 37 $x3 $y7

node 43 $x4 $y3
node 45 $x4 $y5
node 47 $x4 $y7

node 51 $x5 $y1
node 52 $x5 $y2
node 53 $x5 $y3
node 54 $x5 $y4
node 55 $x5 $y5
node 56 $x5 $y6
node 57 $x5 $y7

node 63 $x6 $y3
node 65 $x6 $y5
node 67 $x6 $y7

node 71 $x7 $y1
node 72 $x7 $y2
node 73 $x7 $y3
node 74 $x7 $y4
node 75 $x7 $y5
node 76 $x7 $y6
node 77 $x7 $y7


fix 11 1 1 1
fix 31 1 1 1
fix 51 1 1 1
fix 71 1 1 1

mass 13 20 1.00E-08 1.00E-08
mass 33 20 1.00E-08 1.00E-08
mass 53 20 1.00E-08 1.00E-08
mass 73 20 1.00E-08 1.00E-08

mass 15 20 1.00E-08 1.00E-08
mass 35 20 1.00E-08 1.00E-08
mass 55 20 1.00E-08 1.00E-08
mass 75 20 1.00E-08 1.00E-08

mass 17 20 1.00E-08 1.00E-08
mass 37 20 1.00E-08 1.00E-08
mass 57 20 1.00E-08 1.00E-08
mass 77 20 1.00E-08 1.00E-08

set E 205000
set Fy 235
set b 0.002

#Material
#column
set AB1 110.5e+2
set IB1 10300e+4
set ZpB1 975e+3
set EIB1 [expr $E*$IB1]
set EAB1 [expr $E*$AB1]
set MyB1 [expr $ZpB1*$Fy]
uniaxialMaterial Steel01 2 $MyB1 $EIB1 $b
uniaxialMaterial Elastic 3 $EAB1
section Aggregator 1003 3 P 2 Mz

set AB2 166.3e+2
set IB2 14400e+4
set ZpB2 1410e+3
set EIB2 [expr $E*$IB2]
set EAB2 [expr $E*$AB2]
set MyB2 [expr $ZpB2*$Fy]
uniaxialMaterial Steel01 4 $MyB2 $EIB2 $b
uniaxialMaterial Elastic 5 $EAB2
section Aggregator 1002 5 P 4 Mz

set AB3 204.3e+2
set IB3 26200e+4
set ZpB3 2120e+3
set EIB3 [expr $E*$IB3]
set EAB3 [expr $E*$AB3]
set MyB3 [expr $ZpB3*$Fy]
uniaxialMaterial Steel01 6 $MyB3 $EIB3 $b
uniaxialMaterial Elastic 7 $EAB3
section Aggregator 1001 7 P 6 Mz

#beam
set A1 46.78e+2
set I1 7210e+4
set Zp1 542e+3
set EI1 [expr $E*$I1]
set EA1 [expr $E*$A1]
set My1 [expr $Zp1*$Fy]
uniaxialMaterial Steel01 8 $My1 $EI1 $b
uniaxialMaterial Elastic 9 $EA1
section Aggregator 1006 9 P 8 Mz

set A2 83.29e+2
set I2 22600e+4
set Zp2 1280e+3
set EI2 [expr $E*$I2]
set EA2 [expr $E*$A2]
set My2 [expr $Zp2*$Fy]
uniaxialMaterial Steel01 10 $My2 $EI2 $b
uniaxialMaterial Elastic 11 $EA2
section Aggregator 1005 11 P 10 Mz

set A3 118.5e+2
set I3 20200e+4
set Zp3 1480e+3
set EI3 [expr $E*$I3]
set EA3 [expr $E*$A3]
set My3 [expr $Zp3*$Fy]
uniaxialMaterial Steel01 12 $My3 $EI3 $b
uniaxialMaterial Elastic 13 $EA3
section Aggregator 1004 13 P 12 Mz


#Transf
geomTransf Linear 1
geomTransf PDelta 2

#column
element dispBeamColumn 1 11 12 5 1001 2
element dispBeamColumn 2 12 13 5 1001 2
element dispBeamColumn 3 31 32 5 1001 2
element dispBeamColumn 4 32 33 5 1001 2
element dispBeamColumn 5 51 52 5 1001 2
element dispBeamColumn 6 52 53 5 1001 2
element dispBeamColumn 7 71 72 5 1001 2
element dispBeamColumn 8 72 73 5 1001 2

element dispBeamColumn 9 13 14 5 1002 2
element dispBeamColumn 10 14 15 5 1002 2
element dispBeamColumn 11 33 34 5 1002 2
element dispBeamColumn 12 34 35 5 1002 2
element dispBeamColumn 13 53 54 5 1002 2
element dispBeamColumn 14 54 55 5 1002 2
element dispBeamColumn 15 73 74 5 1002 2
element dispBeamColumn 16 74 75 5 1002 2

element dispBeamColumn 17 15 16 5 1003 2
element dispBeamColumn 18 16 17 5 1003 2
element dispBeamColumn 19 35 36 5 1003 2
element dispBeamColumn 20 36 37 5 1003 2
element dispBeamColumn 21 55 56 5 1003 2
element dispBeamColumn 22 56 57 5 1003 2
element dispBeamColumn 23 75 76 5 1003 2
element dispBeamColumn 24 76 77 5 1003 2

#beam
element dispBeamColumn 25 13 23 5 1004 1
element dispBeamColumn 26 23 33 5 1004 1
element dispBeamColumn 27 33 43 5 1004 1
element dispBeamColumn 28 43 53 5 1004 1
element dispBeamColumn 29 53 63 5 1004 1
element dispBeamColumn 30 63 73 5 1004 1

element dispBeamColumn 31 15 25 5 1005 1
element dispBeamColumn 32 25 35 5 1005 1
element dispBeamColumn 33 35 45 5 1005 1
element dispBeamColumn 34 45 55 5 1005 1
element dispBeamColumn 35 55 65 5 1005 1
element dispBeamColumn 36 65 75 5 1005 1

element dispBeamColumn 37 17 27 5 1006 1
element dispBeamColumn 38 27 37 5 1006 1
element dispBeamColumn 39 37 47 5 1006 1
element dispBeamColumn 40 47 57 5 1006 1
element dispBeamColumn 41 57 67 5 1006 1
element dispBeamColumn 42 67 77 5 1006 1

set nEigenI 1;
set nEigenJ 2;
set pi [expr 2.0*asin(1.0)];
set list [eigen [expr $nEigenJ]];
set w1s [lindex $list [expr $nEigenI-1]];
set w2s [lindex $list [expr $nEigenJ-1]];
set w1 [expr pow($w1s,0.5)];
set w2 [expr pow($w2s,0.5)];
set T1 [expr 2.0*$pi/$w1];
set T2 [expr 2.0*$pi/$w2];
puts "T1 = $T1 s"
puts "T2 = $T2 s"

############################# T1=1.9025818029388715s, T2=0.45993784581704605s

model BasicBuilder -ndm 2 -ndf 3;
set Data fiber-patch
file mkdir $Data
cd $Data

set Data1 nodedisp
file mkdir $Data1
set Data3 Column
file mkdir $Data3
set Data4 Beam
file mkdir $Data4
set Data5 damper
file mkdir $Data5
set Data6 rotation
file mkdir $Data6
cd ../

set x1 0
set x2 3500
set x3 7000
set x4 10500
set x5 14000
set x6 17500
set x7 21000

set y1 0
set y2 1750
set y3 3500
set y4 5250
set y5 7000
set y6 8750
set y7 10500

node 11 $x1 $y1
node 12 $x1 $y2
node 13 $x1 $y3
node 14 $x1 $y4
node 15 $x1 $y5
node 16 $x1 $y6
node 17 $x1 $y7

node 23 $x2 $y3
node 25 $x2 $y5
node 27 $x2 $y7

node 31 $x3 $y1
node 32 $x3 $y2
node 33 $x3 $y3
node 34 $x3 $y4
node 35 $x3 $y5
node 36 $x3 $y6
node 37 $x3 $y7

node 43 $x4 $y3
node 45 $x4 $y5
node 47 $x4 $y7

node 51 $x5 $y1
node 52 $x5 $y2
node 53 $x5 $y3
node 54 $x5 $y4
node 55 $x5 $y5
node 56 $x5 $y6
node 57 $x5 $y7

node 63 $x6 $y3
node 65 $x6 $y5
node 67 $x6 $y7

node 71 $x7 $y1
node 72 $x7 $y2
node 73 $x7 $y3
node 74 $x7 $y4
node 75 $x7 $y5
node 76 $x7 $y6
node 77 $x7 $y7

fix 11 1 1 1
fix 31 1 1 1
fix 51 1 1 1
fix 71 1 1 1

mass 13 20 1.00E-08 1.00E-08
mass 33 20 1.00E-08 1.00E-08
mass 53 20 1.00E-08 1.00E-08
mass 73 20 1.00E-08 1.00E-08

mass 15 20 1.00E-08 1.00E-08
mass 35 20 1.00E-08 1.00E-08
mass 55 20 1.00E-08 1.00E-08
mass 75 20 1.00E-08 1.00E-08

mass 17 20 1.00E-08 1.00E-08
mass 37 20 1.00E-08 1.00E-08
mass 57 20 1.00E-08 1.00E-08
mass 77 20 1.00E-08 1.00E-08

set E 205000
set Fy 235
set b 0.002

#Material
#column / beam
uniaxialMaterial Steel01 1 $Fy $E $b
uniaxialMaterial Elastic 2 $E

#Fiber

#column I J K L
section Fiber 1 {
patch quad 1 4 2 -150 -150 150 -150 150 -131 -150 -131
patch quad 1 4 2 -150 131 150 131 150 150 -150 150
patch quad 1 4 2 131 -131 150 -131 150 131 131 131
patch quad 1 4 2 -150 -131 -131 -131 -131 131 -150 131
}

section Fiber 2 {
patch quad 1 4 2 -125 -125 125 -125 125 -106 -125 -106
patch quad 1 4 2 -125 106 125 106 125 125 -125 125
patch quad 1 4 2 106 -106 125 -106 125 106 106 106
patch quad 1 4 2 -125 -106 -106 -106 -106 106 -125 106
}

section Fiber 3 {
patch quad 1 4 2 -125 -125 125 -125 125 -113 -125 -113
patch quad 1 4 2 -125 113 125 113 125 125 -125 125
patch quad 1 4 2 113 -113 125 -113 125 113 113 113
patch quad 1 4 2 -125 -113 -113 -113 -113 113 -125 113
}

#beam
section Fiber 4 {
patch quad 1 4 2 -150 -150 150 -150 150 -135 -150 -135
patch quad 1 4 2 -150 135 150 135 150 150 -150 150
patch quad 1 2 4 -5 -135 5 -135 5 135 -5 135
}

section Fiber 5 {
patch quad 1 4 2 -100 -200 100 -200 100 -188 -100 -188
patch quad 1 4 2 -100 188 100 188 100 200 -100 200
patch quad 1 2 4 -4.5 -188 4.5 -188 4.5 188 -4.5 188
}

section Fiber 6 {
patch quad 1 4 2 -75 -150 75 -150 75 -141 -75 -141
patch quad 1 4 2 -75 141 75 141 75 150 -75 150
patch quad 1 2 4 -3.25 -141 3.25 -141 3.25 141 -3.25 141
}

#Transf
geomTransf Linear 1
geomTransf PDelta 2


#column
element dispBeamColumn 1 11 12 5 1 2
element dispBeamColumn 2 12 13 5 1 2
element dispBeamColumn 3 31 32 5 1 2
element dispBeamColumn 4 32 33 5 1 2
element dispBeamColumn 5 51 52 5 1 2
element dispBeamColumn 6 52 53 5 1 2
element dispBeamColumn 7 71 72 5 1 2
element dispBeamColumn 8 72 73 5 1 2

element dispBeamColumn 9 13 14 5 2 2
element dispBeamColumn 10 14 15 5 2 2
element dispBeamColumn 11 33 34 5 2 2
element dispBeamColumn 12 34 35 5 2 2
element dispBeamColumn 13 53 54 5 2 2
element dispBeamColumn 14 54 55 5 2 2
element dispBeamColumn 15 73 74 5 2 2
element dispBeamColumn 16 74 75 5 2 2

element dispBeamColumn 17 15 16 5 3 2
element dispBeamColumn 18 16 17 5 3 2
element dispBeamColumn 19 35 36 5 3 2
element dispBeamColumn 20 36 37 5 3 2
element dispBeamColumn 21 55 56 5 3 2
element dispBeamColumn 22 56 57 5 3 2
element dispBeamColumn 23 75 76 5 3 2
element dispBeamColumn 24 76 77 5 3 2

#beam
element dispBeamColumn 25 13 23 5 4 1
element dispBeamColumn 26 23 33 5 4 1
element dispBeamColumn 27 33 43 5 4 1
element dispBeamColumn 28 43 53 5 4 1
element dispBeamColumn 29 53 63 5 4 1
element dispBeamColumn 30 63 73 5 4 1

element dispBeamColumn 31 15 25 5 5 1
element dispBeamColumn 32 25 35 5 5 1
element dispBeamColumn 33 35 45 5 5 1
element dispBeamColumn 34 45 55 5 5 1
element dispBeamColumn 35 55 65 5 5 1
element dispBeamColumn 36 65 75 5 5 1

element dispBeamColumn 37 17 27 5 6 1
element dispBeamColumn 38 27 37 5 6 1
element dispBeamColumn 39 37 47 5 6 1
element dispBeamColumn 40 47 57 5 6 1
element dispBeamColumn 41 57 67 5 6 1
element dispBeamColumn 42 67 77 5 6 1

set nEigenI 1;
set nEigenJ 2;
set pi [expr 2.0*asin(1.0)];
set list [eigen [expr $nEigenJ]];
set w1s [lindex $list [expr $nEigenI-1]];
set w2s [lindex $list [expr $nEigenJ-1]];
set w1 [expr pow($w1s,0.5)];
set w2 [expr pow($w2s,0.5)];
set T1 [expr 2.0*$pi/$w1];
set T2 [expr 2.0*$pi/$w2];
puts "T1 = $T1 s";
puts "T2 = $T2 s";

[fmk]

why don't you use an Elastic section to find how were you are messing up .. and instead of doing a model with multiple elements, just look at a cantilever.

[jyokou]

fmk wrote:
> why don't you use an Elastic section to find how were you are messing up ..
> and instead of doing a model with multiple elements, just look at a
> cantilever.

Thanks for your help. I have solved it.