Rayleigh damping implementation

[mlw]

Hi all,

Can anyone please tell me if the Rayleigh damping parameters are updated during an OpenSees analysis.

The Rayleigh damping mass and stiffness matrices are calculated based on the mass and stiffness of a model at the start of an analysis. But if large strains occur (such as during the loading of a beam or during liquefaction analyses) then the stiffness of the can significantly system decrease. I read in Charney (2006) that both the Rayleigh stiffness matix and the stiffness proportional constant should be updated during the analysis to avoid overdamping in these cases.

So does OpenSees update both the Rayleigh stiffness matrix and the stiffness proportional constant during an analysis? Or just the stiffness proportional constant?

Thanks

mlw

[vesna]

In OpenSees you have an option of creating damping matrix from tangent stiffness matrix which is called committed. You can also do analysis in a loop and after each step of analysis you can calculate stiffness proportional coefficients. This way you will do both, updated stiffness matrix and updated stiffness proportional coefficients for each step of analysis.