I've used the symmetric restraint in past static studies very successfully. I know that depending on the symmetry condition applied (1/2 vs. 1/4) you need to adjust the load accordingly.

My question is how this pertains to a uniform base excitation load in a linear dynamic study -- specifically for random vibration & modal time history. Do I simply adjust the max. amplitude of either my PSD input (for vibration) or acceleration input (for modal time history) by half (for a 1/2 symmetry setup)?