Offshore Structure Platform Design - Offshore Structures: Design, Construction and Maintenance - page 189

Critical zone with high
stress and strain

FIGURE 3.53 Critical zone for denting member.

For simplified calculation of the strain at the critical zone of the oval, we
need to find the geometry and the minimum radius of the oval. The main
assumption is “ the circumferences of the circle tubular and deformed elliptic

are similar. s minimum radius, the strain can be checked

against 15% strain to calculate the denting limit. A simplified method for dent-
ing limit calculation is presented in the following section.
This method is valid only for boat landing members with bending behavior. For
checking accidental impact on the jacket members (e.g., legs) with axial loads, the
simplified method is not valid and more detail analysis needs to be done.

” After finding the oval '

Simplified Method for Denting Limit Calculation
The denting calculation will be calculated based on converting the circle shape
of the member to an oval after impact load, as shown in Figure 3.54 .

The circle ' s perimeter is

P c = 2 π R (3.147)

s perimeter has a different equation and the following equation
has a higher accuracy.

The ellipse '

2/3

a 1 : 5 + b 1 : 5

2

P e 2 π (3.148)

Note that in the case of denting of the cylinder section, the perimeter of the
circle will be the same after denting and will be like the ellipse.

2/3

a 1 : 5 b 1 : 5

+

2 π R = 2 π

2

(3.149)

2/3

a = ð 2R 1 : 5 − b 1 : 5

Þ

where y is the dent distance

b = R − y/2 (3.150)

Knowing the dent distance y and the radius of the section R, we can obtain b
from Equations (3.149) and (3.150) .