Problem about my program of SDOF

[hansxiaowisc]

Recently, I am trying to build a model of SDOF with EPP material. However, after testing , I found the results are wrong. How could I fix it?
Here follows the program.

# To get the number of T(Period) #
source LibUnits.tcl
set fileID_T [open Period.txt r]
gets $fileID_T C
set lengthT [llength $C]

set NumGM 269

for {set GMi 269} {$GMi<=$NumGM} {incr GMi 1} {

#
set fileDeltaT [open GM_record/GM_DeltaT.txt r]
set A [gets $fileDeltaT]
close $fileDeltaT
set DtAnalysis [lindex $A [expr $GMi-1]]

#
set fileSteps [open GM_record/GM_NumSteps.txt r]
set B [gets $fileSteps]
set Nsteps [lindex $B [expr $GMi-1]]
close $fileSteps

#
set GMfile GM_record/GM$GMi.txt

for {set Ti 1} {$Ti<=$lengthT} {incr Ti 1} {
set T [lindex $C [expr $Ti-1]]
set omega [expr 2*$PI/$T]
set M 1; # Mass is 1#
set K [expr $M*pow($omega,2)];

# set rayleigh damping #

set damp 0.05;
rayleigh [expr 2*$damp*$omega] 0. 0. 0.

set Ri 2

# build the SDOF model#
wipe
model basic -ndm 1 -ndf 1
node 1 0.0
node 2 0.0
fix 1 1
mass 2 $M

#取得epsyP #
set epsyE [open Maxdisp_Elastic/GM$GMi/maxdisp$Ti.txt r]
set D [gets $epsyE]
set epsyP [expr $D/$Ri]

# define the material#
uniaxialMaterial ElasticPP 1 $K $epsyP
element zeroLength 1 1 2 -mat 1 -dir 1

# record #
set filename SDOF_EPP_Analysis/GM$GMi/R$Ri
file mkdir $filename

recorder Node -file $filename/Displacement$Ti.out -time -node 2 -dof 1 disp; # 位移时程 #


# put in the earthquake data#
set accelSeries "Series -filePath $GMfile -dt $DtAnalysis -factor $g"
pattern UniformExcitation 2 1 -accel $accelSeries

# Analysis#
constraints Transformation
algorithm Linear
system ProfileSPD
numberer Plain
set gamma 0.5; # gamma value for newmark integration
set beta 0.25; # beta value for newmark integration
integrator Newmark $gamma $beta
analysis Transient
analyze $Nsteps $DtAnalysis
wipeAnalysis
}
}
}

Thank u!!!!!!!!!!!!!!!!!

[fmk]

the model looks o.k. .. i cannot see the numbers you are using .. i suggest you use a puts to make sure the numbers that you think you are reading from the file are the actual numbers you are using in the script .. if that fails, check the period using the eigen command after you create the Transint analyzis and before any analysis to make sure it is what you think it is.

[fylseu]

When Elastic-Perfectly Plastic Material is used in SDOF, the structure has no second stiffness. When structure yield, your computation will not converge?