Question about the UniformExcitation and Multiplesupport

[weiguo]

Hello all,

I built a FEM of a cable-stayed bridge in OpenSees for seismic analysis. Model A is loaded by unform exciatiaion and Model B is loaded by multiplesupport exciation. The displacement time-history used in Model B was obtained by two times integration of an earthquake acceleration time-history used in Model A. The only difference is the different input methods of the earthquake loads. So why I got two different displacenment time-historys of the tower top? I think they should be same. The displacemt time-history of the fixed node at tower base was already substracted from the displacement time-history of the tower top in Model B.

Here is the code for unform exciatiaion :

timeSeries Path 2 -filePath input/EX.txt -dt $dtx -factor $Scale
pattern UniformExcitation 2 1 -accel 2

Here is the code for multiplesupport exciatiaion :

set iGMfile1 "input/E1.txt"; #E1,E2,E3,E4 are the same
set iGMfact "1";
set dispSeries1 "Series -dt $dtx -filePath $iGMfile1 -factor $iGMfact";

set iGMfile2 "input/E2.txt";
set iGMfact "1";
set dispSeries2 "Series -dt $dtx -filePath $iGMfile2 -factor $iGMfact";

set iGMfile3 "input/E3.txt";
set iGMfact "1";
set dispSeries3 "Series -dt $dtx -filePath $iGMfile3 -factor $iGMfact";

set iGMfile4 "input/E4.txt";
set iGMfact "1";
set dispSeries4 "Series -dt $dtx -filePath $iGMfile4 -factor $iGMfact";

#pier 1and2
pattern MultiSupport 101 {
groundMotion 1 Plain -disp $dispSeries1
imposedMotion 656 1 1
imposedMotion 655 1 1
imposedMotion 583 1 1
imposedMotion 582 1 1
}
#tower 1
pattern MultiSupport 102 {
groundMotion 2 Plain -disp $dispSeries2
imposedMotion 302 1 2
imposedMotion 301 1 2
}
#tower 2
pattern MultiSupport 103 {
groundMotion 3 Plain -disp $dispSeries3
imposedMotion 1033 1 3
imposedMotion 1032 1 3
}
#Pier 3and4
pattern MultiSupport 104 {
groundMotion 4 Plain -disp $dispSeries4
imposedMotion 758 1 4
imposedMotion 757 1 4
imposedMotion 674 1 4
imposedMotion 673 1 4
}

Thank you very much!

[selimgunay]

Can you try specifying the acceleration, velocity and displacement series as input in the multi-support excitation case?

[weiguo]

selimgunay wrote:
> Can you try specifying the acceleration, velocity and displacement series
> as input in the multi-support excitation case?

Thanks for replying this.
Only the displacement serie was input in the multi-support excitation case, and it was obtained by using the SeismoSignal with a acceleration time-history.

[selimgunay]

Okay, there is an option to input displacement, velocity and acceleration together