3D dam model diverges

[ja_abell]

Dear OpenSEES community,

I am performing a linear transient analysis on a big 3D earth-dam model.
This is a 3D model composed only of bbarBrick elements with ElasticIsotropic3D materials (different material for each brick).
I am using an acceleration record of 'El Centro' by assigning a pattern UniformExcitation load in the transverse direction.

I am assigning damping with the rayleigh command. The alpha and beta parameters are obtained by:

alpha = xi*w1
beta = xi/w1

Where xi is the percent critical damping at mode 1, and w1 is the angular frequency of mode 1. (I've also tried setElementRayleighDampingFactors, which is what I want to use in the first place to model strain dependent damping in the future).

My analysis options are:

system SparseSPD
constraints Transformation
test NormDispIncr 1.0e-3 40 1
algorithm Linear
numberer RCM
analysis Transient

I've tried many different combinations, but my analysis always diverges after a few seconds of analysis.

The analysis is performed inside an external for loop as in

for {set step 0} {$step < $NSteps} {incr step} {

...code

#Perform one analysis step
analyze 1 $DtAnalysis

....more code
}

This is so I can retrieve the element strains at each time step (i dont want big output files, I just need the element maximum strains), and perform some checking and estimate analysis time (usually about ~20hrs on my PC for a full analysis).

[fmk]

what integration scheme?

[zhuo1005]

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