Steel 02, clarification regarding $sigInit option.(

[sriram]

Hi silvia, Frank and others:

I am trying to model initial stress in rebar using the steel02 with $sigInit option. To test the material model, I used a truss element. The option seem to be working to give the correct stain, however, the stress in the truss element is wrong at that strain level ( see the output file I posted at the end) . I am attaching the TCL script i used. please let me know if you think I am doin gsomething wrong? I really appriciate all the help I can get. I need to figure this out for finishing my thesis.
here is the Tcl file for material testing. I am also posting first few lines of the output file.

TCL file:
( I am using opensees 2.0.0)
____________
###--------------------- Material Modelling for the NEESR_WALL Project------------------####
####----------------- Written By Sriram Aaleti, Iowa State University ------------------####
##-- Comparison of the experimental and OpenSEES Material Properties for RC Wall Mterials--##
##-----------------------------------------------------------------------------------------##

### the stress-srtain behavior of the materials is obtained by using a truss element
### with unit area and unit length.
####--------------- Simulation Parameters---------------------
set specimen RWN;
#-----------------------------------------------------------------------------
set lelement 1.0; #lenght of the element
set Aelement 1.0; # area of the element.
set ndm 2;
set ndf 3; #no.o fdegrees of freedom.
set node1 1;
set node2 2;
#----------------------------------------------------------------------------
model basic -ndm $ndm -ndf $ndf

#defining the nodes for the model.
node $node1 0 0;
node $node2 $lelement 0;


#apply the boundary conditions
fix $node1 1 1 1; # the y displacement and rotaion is fixed.
fix $node2 0 1 1;
#-------------------------------------------------------------------------------
#defining the material behavior
set mattag 500;
uniaxialMaterial Steel02 $mattag 60. 29000. 0.1 15 0.925 0.15 0.0 1.0 0.0 1.0 -25.;
set outputfile ptbar; #output file name for the stress-strain behavior.



#-------------------------------------------------------------------------------
#defining the elements connecting the nodes
element truss 1 1 2 $Aelement $mattag
#Define the loads
# Define reference load in X direction
pattern Plain 1 "Linear" {
# Fx Fy Mz
load $node2 1 0 0
}
pattern Plain 2 "Constant" {
load $node2 -0.1 0 0
}
#------------------------------------------------------------------------------

recorder Node -file $specimen$outputfile.out -time -node $node2 -dof 1 disp;
#------------------------------------------------------------------------------
set tolerence 1.0e-5
set nItr 100
set maxstrain 0.01;
set ndata 500;
set du [expr $maxstrain/$ndata];

#system SparseSPD
system SparseGeneral -piv
numberer Plain
constraints Plain
integrator LoadControl $node2 1 1 0 0
test NormDispIncr $tolerence $nItr 1
#test NormUnbalance $tolerence $nItr 1
algorithm KrylovNewton
analysis Static
analyze 2

integrator DisplacementControl $node2 1 $du
analyze $ndata


OUTPUT file:
____________
0 0.000858621
1 0.000893103
1.58 0.000913103
2.16 0.000933103
2.74 0.000953103
3.32 0.000973103
3.9 0.000993103
4.48 0.0010131
5.06 0.0010331
5.64 0.0010531
6.22 0.0010731
6.8 0.0010931
7.38 0.0011131
7.96 0.0011331
8.54 0.0011531
9.12 0.0011731
9.7 0.0011931
10.28 0.0012131
10.86 0.0012331
11.44 0.0012531
12.02 0.0012731
12.6 0.0012931
13.18 0.0013131
13.76 0.0013331
14.34 0.0013531
14.92 0.0013731
15.5 0.0013931
16.08 0.0014131
16.66 0.0014331