I am checking design of an S-shaped high pressure (150MPa) jacketed pipe dumping line. Jacket is 8” and tube ID70mm / OD152mm. The dynamic load due to the sudden pressure surge during dumping is 800kN (before DLF).
The line is already installed with one holdown, 3 guides and one “flexible” anchor. According to design document these supports (holddown - vertical and 3 guides - horizontal) are specified with preloads of +/-50kN. These preloads come from pre-tightening of bolts against stacked “spring discs” (compression washers), that are supposed to act as shock absorbers.
In Caesar's static analysis I specify these preloads as F1s and add them to all cases (WNC, OPE and SUS)
In dynamic analysis (Time History) F1s are ignored.
I would appreciate if someone would explain why.
Do I need to specify these preloads as lumped masses?
What about when we have springs? Is H ignored in the dynamic model?

Calculated dynamic response is based on mass and stiffness (and damping), not static load. These applied loads would play a role only if they pushed the system into yield (which affects stiffness and damping).