ABAQUS : Effect of Pre-load on Random Response Analysis

[thomascae]

I am running a random response analysis on a structure which has a static load applied prior to *Frequency and *Random response analysis.

What affect, if any does the preload have on the streses obtained in the Random Response analysis step?
As preload stresses are measured in MPa but the "Maximum stress" output (S) of the Random Response analysis step is in MPa^2/Hz.

Any ideas?

 

[GregLocock]

In a linear passive structure the stresses at a particular frequency can ONLY be affected by loads at that frequency. Therefore the preload will not affect stresses at a higher frequency.

Note that the total stress will be affected, obviously. Cheers

Greg Locock

 

[llianhui]

hi,

In a linear random analysis, you can add the static load stress to the mean value stress calculated by random analysis. To a nonlinear random analysis, the frequency response approach is unusable.

 

[brad]

The effect of prestresses will of course change the stiffness matrix of the structure. For the random response analysis in ABAQUS, the stiffness state (due to the preloads) at the end of the previous general step (presuming nonlinear geometric effects were included) will be operated upon for the actual random response analysis.

Reported stresses are perturbation stresses about the base state (hence do not include the actual stresses which are in the base state).

As ilianhui implies, adding these (inherently linear) random stresses to the (potentially nonlinear) general stresses may result in errant answers.

I hope this makes sense.
Brad

 

[thomascae]

Thanks guys!