Offshore Structure Loads and Strength - Offshore Structures: Design, Construction and Maintenance - page 44

Average degree of salt

●

Mud temperature at seabed at 0 m, 1.0 m, 1.5 m and 2.0 m ●

Snow maximum thickness and average thickness ●

For all directions and wind angles of approach to the structure, wind actions on
vertical cylindrical objects may be assumed to act in the direction of the wind.
Actions on cylindrical objects that are not in a vertical attitude should be calculated
using appropriate formulae that take into account the direction of the wind in rela-
tion to the altitude of the object. Actions on walls and other flat surfaces that are not
perpendicular to the direction of the wind should also be calculated using appro-
priate formulae that account for the skewness between the direction of the wind
and the plane of the surface. Where appropriate, loads caused by wind should
be calculated with due account for increased exposure area and surface roughness
due to ice. Local wind effects, such as pressure concentrations and internal pres-
sures, should be considered by the designer where applicable.
In accordance with the above observations, attention should be given to
which velocity (in magnitude and direction) and which area are to be used.
Similarly, the direction of the resulting action vector should be carefully consid-
ered. The basic relationship between the wind velocity and the wind load on an
object is presented by the following equation:

F = 1/2 ρ a V w C s A (2.7)

where F is the wind action on the object, ρ a is the mass density of air (at standard

temperature and pressure), V w is the wind speed, C s is the shape coefficient and
A is the area of the object.
In the absence of data indicating otherwise, the shape coefficients in
Table 2.14 are recommended for perpendicular wind approach angles with
respect to each projected area.

TABLE 2.14 Shape Coefficients, C s , for Perpendicular Wind Approach

Angles

Component Shape Coefficients, C s

Flat walls of buildings 1.5

Overall projected area of structure 1.0

Beams 1.5

Cylinder 0.5

10 5

Smooth R e > 5 × 0.65

10 5

Smooth R e ≤ 5 × 1.2

Rough all R e 1.05

Covered with ice, all R e 1.2