about seismic response of free field

[zhangji]

hi, i built a simple free field PlaneStrain model , and adopted UniformExcitation pattern to input ground motion at the soil base, but i didnot obtain relative sesimic response on the soil surface(the response was always zero), could anyone help me? the problem troubled me a lot ...
here are the codes:
wipe
model basic -ndm 2 -ndf 2

# define soil nodes:
node 1 0.0000 0.0000
node 2 0.0000 2.0000
node 3 0.0000 4.0000
node 4 0.0000 6.0000
node 5 1.0000 0.0000
node 6 1.0000 2.0000
node 7 1.0000 4.0000
node 8 1.0000 6.0000

# define fixities for soil nodes:
fix 1 1 1
fix 5 1 1

#-----------------------------------------------------------------------------------------
# 2. CREATE SOIL MATERIALS
#-----------------------------------------------------------------------------------------

set Vs(3) 200.0
set Vs(2) 300.0
set Vs(1) 400.0

set dnsty(3) 1800.0
set dnsty(2) 1900.0
set dnsty(1) 2000.0

set miu(3) 0.25
set miu(2) 0.25
set miu(1) 0.25

set Emodulus3 [expr $dnsty(3)*$Vs(3)*$Vs(3)*2.0*(1.0+$miu(3))]
set Emodulus2 [expr $dnsty(2)*$Vs(2)*$Vs(2)*2.0*(1.0+$miu(2))]
set Emodulus1 [expr $dnsty(1)*$Vs(1)*$Vs(1)*2.0*(1.0+$miu(1))]
puts $Emodulus3
nDMaterial ElasticIsotropic 1 $Emodulus1 $miu(1)
nDMaterial ElasticIsotropic 2 $Emodulus2 $miu(2)
nDMaterial ElasticIsotropic 3 $Emodulus3 $miu(3)

#-----------------------------------------------------------------------------------------
# 4. CREATE SOIL ELEMENTS
#-----------------------------------------------------------------------------------------

element quad 1 1 5 6 2 0.1 "PlaneStrain" 1 0 $dnsty(1) 0 0
element quad 2 2 6 7 3 0.1 "PlaneStrain" 2 0 $dnsty(2) 0 0
element quad 3 3 7 8 4 0.1 "PlaneStrain" 3 0 $dnsty(3) 0 0
puts "Finished creating all soil elements..."

#-----------------------------------------------------------------------------------------
# 12. CREATE RECORDERS
#-----------------------------------------------------------------------------------------

# record nodal displacment, acceleration
recorder Node -file node4.out -time -node 4 -dof 1 2 disp
recorder Node -file node8.out -time -node 8 -dof 1 2 accel
recorder Element -ele 2 -file stress2.out -time material 2 stress
#-----------------------------------------------------------------------------------------
# 13. DYNAMIC ANALYSIS
#-----------------------------------------------------------------------------------------

constraints Transformation
#test NormDispIncr 1.E-6 25 2
algorithm Linear
numberer RCM
system BandGeneral
integrator Newmark 0.50 0.25
set mSeries "Series -factor 3 -filePath elcentro.txt -dt 0.01"
pattern UniformExcitation 1 1 -accel "Series -factor 3 -filePath elcentro.txt -dt 0.01"
analysis Transient
analyze 40 0.01

puts "Finished with dynamic analysis..."

wipe

here is the elcentro.txt
0
0
0
0
0
0
0
0
0
0.0309015
0.061803
0.0487557
0.0357084
0.02271015
0.0097119
0.02584935
0.0419868
0.0581733
0.0743598
0.0906444
0.106929
0.0869166
0.0669042
0.04703895
0.0271737
0.00730845
-0.0125568
0.011772
0.0361008
0.0604296
0.0847584
0.1090872
0.133416
0.10236735
0.0713187
0.04027005
0.0092214
0.0252117
0.041202
0.03144105
0.0216801
0.0118701
0.0020601
0.02280825
0.0435564
0.06430455
0.0850527
0.10580085
0.126549
0.14715
0.167751
0.06705135
-0.0336483
-0.13454415
-0.23544
-0.1663776
-0.0973152
-0.0282528
0.0408096
0.0463032
0.0517968
0.1068309
0.161865
0.2172915
0.272718
0.327654
0.38259
0.3114675
0.240345
0.16897725
0.0976095
0.0959418
0.0942741
0.09255735
0.0908406
0.0891729
0.0875052
0.0199143
-0.0476766
-0.1155618
-0.183447
-0.2506455
-0.317844
-0.32373
-0.329616
-0.445374
-0.561132
-0.503253
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-0.386514
-0.327654
-0.320787
-0.31392
-0.307053
-0.300186
-0.293319
-0.286452
-0.278604
-0.270756
-0.337464
-0.404172
-0.469899
-0.535626
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-0.669042
-0.7352595
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-0.417906
-0.4203585
-0.422811
-0.330597
-0.238383
-0.14592375
-0.0534645
0.03899475
0.131454
0.223668
0.315882
0.4085865
0.501291
0.5930145
0.684738
0.7774425
0.870147
0.65727
0.444393
0.23097645
0.0175599
-0.19575855
-0.409077
-0.621954
-0.834831
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-1.26549
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-1.26549
-1.0550655
-0.844641
-0.8588655
-0.87309
-0.8873145
-0.901539
-0.9157635
-0.929988
-0.9226305
-0.915273
-0.9069345
-0.898596
-0.914292
-0.929988
-0.9451935
-0.960399
-1.1129445
-1.26549
-1.008468
-0.751446
-0.4939335
-0.236421
0.0210915
0.278604
0.536607
0.79461
1.054575
1.31454
1.5696
1.82466
2.084625
2.34459
2.251395
2.1582
2.065005
1.97181
1.88352
1.79523
1.702035
1.60884
1.52055
1.43226
1.505835
1.57941
1.65789
1.73637
1.515645
1.29492
1.0746855
0.854451
0.6332355
0.41202
0.1906083
-0.0308034
-0.2518227
-0.472842
-0.694548
-0.916254
-1.135017
-1.35378
-1.57941
-1.80504
-2.025765
-2.24649
-2.467215
-2.68794
-2.908665
-3.12939
-2.790945
-2.4525
-2.11896
-1.78542
-1.446975
-1.10853
-0.7725375
-0.436545
-0.100062
0.236421
0.572904
0.909387
1.2443985
1.57941
1.917855
2.2563
2.58984
2.92338
2.59965
2.27592
1.95219
1.62846
1.3003155
0.972171
0.646479
0.320787
-0.004905
-0.330597
-0.6557985
-0.981
-1.309635
-1.63827
-1.962
-2.28573
-2.60946
-2.93319
-1.48724505
-0.0413001
1.40670495
2.85471
2.526075
2.19744
1.868805
1.54017
1.208592
0.877014
0.547398
0.217782
-0.111834
-0.44145
-0.1309635
0.179523
0.4905
0.801477
1.1119635
1.42245
1.731465
2.04048
1.95219
1.8639
1.770705
1.67751
1.515645
1.35378
1.18701
1.02024
0.854451
0.688662
0.523854
0.359046
0.19399275
0.0289395
-0.13611375
-0.301167