Relative or absolute displacements

[mlw]

Hi all,

I am recording displacements in X, Y, and Z directions using the following commands:
eval "recorder Node -file soilDispX.out -time -node $nodeList -dof 1 disp"
eval "recorder Node -file soilDispY.out -time -node $nodeList -dof 2 disp"
eval "recorder Node -file soilDispZ.out -time -node $nodeList -dof 3 disp"
The model consists of brickUP elements with a uniformExcitation acceleration pattern applied

My models are consistently underpredicting displacements, and I saw on the web page (http://opensees.berkeley.edu/wiki/index ... e_Recorder) that these recorders measure relative displacements.
What are they measuring relative to/how can I calculate absolute displacements?

Thank you for your time,

mlw

[vesna]

Check the example 2:
http://opensees.berkeley.edu/wiki/index ... e_Recorder

[mlw]

Thanks vesna, I will include the time series tag to get absolute displacements.
But the problem is stil not solved. I now have tried to simulate 3 case histories of shaking tables/centrifuges and the results from all three are the same. Displacement is half of the experimental value, and because displacement is half soil shear strain and bending moment of my pile are also half. Yet acceleration and excess pore water pressure are correct. Have you come across this before? Are there any other examples of where the opensees code (particularly displacements) has been verified against case histories for a pile in soil with dynamic loading?

Thanks

mlw

[vesna]

I do not have any experience with modeling pile in soil with dynamic loading. Try posting your question on the Soil Modeling board.