abutment modeling

[noha]

hello everyone,
I am trying to model a simple spring representing soil back-fill capacity to make sure it is well defined and yields the desired response before being incorporated into the bridge model. Zero length element is used with hyperbolic gap material.

However the opensees isn't able to run as seen below:

ProfileSPDLinDirectSolver::solve() - aii < 0 (i, aii): (0,0)
DisplacementControl::newStep(void) - failed in solver
StaticAnalysis::analyze() - the Integrator failed at iteration: 0 with domain at
load factor 0
OpenSees > analyze failed, returned: -2 error flag



here is the tcl code:
# SET UP ----------------------------------------------------------------------------
# all units in KN, m ,S
wipe; # clear memory of all past model definitions
model BasicBuilder -ndm 1 -ndf 1; # Define the model builder, ndm=#dimension, ndf=#dofs


node 1 0;
node 2 0;
fix 1 1;

#spring elements for abutment backfill
#define parameters
set matTagHypr 10;
set Kabutm 235983.24; #Abutment stiffness kn/m ,19665.27kn/m of abutm width =12m
set kurAbut $Kabutm; #unloading/reloading stiffness
set Rf 0.7; #failure ratio
set FultAbutm -4512; #ultimate passive resistance (376 x abut. width)
set gapAbutm -0.08; #abutment gap 8cm

#define backfill material
#uniaxialMaterial HyperbolicGapMaterial $matTag $Kmax $Kur $Rf $Fult $gap
uniaxialMaterial HyperbolicGapMaterial $matTagHypr $Kabutm $kurAbut $Rf $FultAbutm $gapAbutm;

#element zeroLength $eleTag $iNode $jNode -mat $matTag1 $matTag2 ... -dir $dir1 $dir2
element zeroLength 47 1 2 -mat $matTagHypr -dir 1 ;

# Define loads
# Create a Plain load pattern with a Linear TimeSeries
pattern Plain 1 "Linear" {

# Create nodal load at node2
# nd FX
load 2 -1000;
}
;

# define analysis control for static analysis



constraints Transformation; # how it handles boundary conditions
numberer RCM; # renumber dof's to minimize band-width (optimization), if you want to
system ProfileSPD; # how to store and solve the system of equations in the analysis
test NormDispIncr 1.0e-8 10 ; # determine if convergence has been achieved at the end of an iteration step
algorithm ModifiedNewton; # use Newton's solution algorithm: updates tangent stiffness at every iteration
integrator DisplacementControl 2 1 0.000001; # determine the next time step for an analysis,
analysis Static; # define type of analysis static or transient
analyze 200000; # push to a displacement 20cm (0.000001x200000)
loadConst -time 0.0; # hold gravity constant and restart time


puts "Model Built"