Convergence Problem with Concrete02

[parsaparvanehro]

Dear OpenSees users
I modeled a simply supported RC beam in opensees. The beam (rec section) consists of fiber section with Concrete02 material model to consider tensile strength for concrete. I successfully performed the gravity analysis in first step and then I applied a two-pointed concentrated load on beam in the gravity direction. I push the beam with 100 steps to reach the target force (12 ton.f). The problem is that the analysis failed at step 97 with "Large trial compressive strain" error.
If I use concrete01 the analysis will end without any error. I checked the fiber stress-strain results and find that, even concrete or rebars do not undergo large stress or strain (remain almost in elastic range). in addition, in case of concrete01, the corresponding stress or strain values go beyond those of concrete02. Thus, in my opinion, the model is correct, and the errors raised from concrete02 material model. I also used Concret04 and got similar results.
Any help or suggestion are highly appreciated.
Regards
Parsa




wipe()
import PreTensioning

Nsteps=100
print("PreTensioning is applied to the beam")

# Set the gravity and pretensioning loads to be constant & reset the time in the domain
loadConst('-time', 0.0)

# create TimeSeries
timeSeries("Linear", 2)

# create a plain load pattern
pattern("Plain", 2, 1)

# Create the nodal load
PY = 10.5e4
load(3, 0, -PY, 0)
load(5, 0, -PY, 0)


recorder('Element', '-file', 'Top Concrete', '-time', '-ele', 3, 'section', 10, 'fiber', 200.0, 0.0, 1, 'stressStrain')
recorder('Element', '-file', 'Bot Concrete', '-time', '-ele', 3, 'section', 10, 'fiber', -200.0, 0.0, 1, 'stressStrain')
recorder('Element', '-file', 'Bot Strand', '-time', '-ele', 3, 'section', 10, 'fiber', -125,-105, 3, 'stressStrain')
recorder('Element', '-file', 'Bot Rebar', '-time', '-ele', 3, 'section', 10, 'fiber', -155,-105, 2, 'stressStrain')
recorder('Element', '-file', 'Top Rebar', '-time', '-ele', 3, 'section', 10, 'fiber', 160,-105, 2, 'stressStrain')

# ------------------------------
# Start of analysis generation
# ------------------------------

# create SOE
#system('BandGen')

# create DOF number
#numberer("RCM")

# create constraint handler
#constraints('Transformation')

# create integrator
#dU=-2.0 # Displacement increment

#integrator('DisplacementControl', 4, 2,dU,10,dU,dU)
integrator('LoadControl', 1/Nsteps)
#integrator('MinUnbalDispNorm', 1e2, 1,10,1e3)


# 1e-12 and a max number of iterations of 1000
test('NormDispIncr', 1e-8, 1000)
#test('EnergyIncr', 1e-8, 1000)
#test('NormUnbalance', 1e-1, 1000)

# create algorithm
#algorithm('ModifiedNewton', '-initial')
algorithm('Newton')
#algorithm('NewtonLineSearch',20)
#algorithm('Broyden',10)
analysis('Static')

analyze(Nsteps)