Thanks for the reply, I set damping through the eta and delta coefficients.

I'm running into some issues with linear dynamic analyses. In the attached model (a simple frame made with beam in XZ plane) I get very different results with OOFEM and other solvers with the same model. Please see below the difference in displacement for node 7 (relative disp=disp of node 7 - ground displacement).

I checked all the stiffnesses involved, and I get exactly the same results with a static analysis. After SAP2000, I tried also with Abaqus, and I get more or less the same results as SAP, so I believe there's something wrong in OOFEM, which differs of over 100 times!

Can you help on that? I tried all I was able to do.

EDIT 05 17: I changed the integration method among the ones available:
    TD_ThreePointBackward  =  0,     ///< Three-point Backward Euler method
    TD_TwoPointBackward    =  1,     ///< Two-point Backward Euler method
    TD_Newmark             =  2,     ///< Newmark-beta method
    TD_Wilson              =  3,     ///< Wilson-theta method

The best results (and very similar to SAP2000 with Newmark) is obtained with 0, while 2 and 3 seems to be broken (they give results too far to be acceptable).
Please tell which is the difference between 0 and 1, I know the general Euler method but I cannot figure out the difference between 0 and 1.

Hi, thanks for the reply.
I'm using the version from my copy here. I cannot figure out why, I used your Git repo too under windows and it gives the same results in any case.

Can you suggest which files to check?

It seems that my copy of diidynamic.c is completely identical to yours, except that I added this to print reactions:

void
DIIDynamic::terminate(TimeStep *tStep)
{
    StructuralEngngModel::terminate(tStep);
    this->printReactionForces(tStep, 1);
    fflush(this->giveOutputStream());
}

EDIT: even if I revert such mod and I delete the added function ("terminate"), results are different.

EDIT2: I tried also with a version compiled from the official repo updated to the last commit of 6 days ago. Same problem as before (sorry, I said the opposite some lines above, but I noticed that I used an old .exe compiled BEFORE your fix for lumped masses in DIIDynamic). Can the compilation in visual studio in windows be the problem? Cannot figure out how do you get the same values for all the analyses.

ok, got some insight now. I can obtain almost the same results (for different integration schemes) for displacements, for acceleration, there is some difference and more differences in accelerations. See attached figure showing the history of displacement, velocity and acceleration for node 7. Based on that I would say, that the agreement is good. The integration scheme 2 shows more differences, but I would expect that with reduced time step they should be reduced.
I compiled windows version using VisualStudio, ver 14 and got the same results.