Have you tried both 225 and 450 in CAESAR II?
Verifying an analysis to your own satisfaction is healthier than accepting the advice found on a public forum.
If 450 is your peak-to-peak range of load, then enter 225 in CAESAR II. Amplitude (zero-to-peak) is the program input.
Are you applying this load on every straight run throughout the system with the appropriate phase angle? If so, please let us know how things work out. I usually use harmonics to evaluate response to a single load or displacement.