Page 336 - Marine Structural Design

312 Part II UIiimate Strength

- 1200 1

Figure 15.6 Effects of Earthquake Acceleration Scale Factors

'2001 - Including drag forcer
---- Not including drag forces
- - ""t

E
E

-1200 t

-800

Figure 15.7 Hydrodynamic Damping Effect Associated With Drag Forces
(Earthquake Acceleration Scale Factor 3.0)

Figure 15.7 shows time histories of the lateral displacements at the deck of the platform in X-
direction for a scale factor 3.0. It is observed that in this example the hydrodynamic damping
effect associated with drag forces can be ignored.
Figure15.8. Presents foundation stifiess effects on the time histories of the lateral
displacements. The vibration period and maximum displacement increase greatly as the soil
stiffness decrease. No plastic node has been observed when soil stiffness has been scaled by a
factor 0.1. This figure also shows the importance of modelling soil-structure interaction
reasonably accurate. The maximum value of the lateral displacement will be very large and it
will cause problems for the piping system and equipment on the deck.