Offshore Structure Platform Design - Offshore Structures: Design, Construction and Maintenance - page 108

3.5.1 Global Structure Analysis
The steps of using software in design are:

1. The designer must define the structure in terms of physical dimensions,
member size and materials properties.
2. The designer must input the soil conditions (as interpreted by the soil
specialist); in some programs this requires a p-y curve.
3. All loads must be entered into the program.
4. The wave load is applied through the structure at several azimuth angles to
determine the direction that produces higher reactions, and the current load
is as presented in Figure 3.13 .
5. The computer advances the wave through the structure at specified incre-
ments, calculating total shear and overturning moment on the structure at
the mud line.
6. For each load condition, the computer analysis provides:
A. Total base shear and overturning moment
B. The member end forces and moments
C. Joint rotation and deflection
D. External support reaction
7. After calculating the stresses, the computer compares them with the allowable
stresses as defined by the American Institute of Steel Construction (AISC).
8. The pile is replaced by lateral springs in two directions, an axial spring and
a moment spring.

C D C M

Wave
kinematics
factor

Smooth
Rough

0.65 1.6

1.05 1.2

Conductor
shielding
factor

100-yr wave
height
associated
wave period
and storm
water depth

Morison
equation:
local
member +
current
forces

2D wave
theory with
Doppler effect

Wave +

current
kinematics

Wave
kinematics

Distributed
forces

Vector
sum

Riser and
appurtenances
hydrodynamic
models

Associated
current

Marine
growth

Global
forces

Current
blockage
factor
(0.7-1.0)

FIGURE 3.13 Applied environmental loads.