Page 153 - Marine Structural Design

Chapter 7 Limit State Design of Offshore Structures 129

7.2.2 Plated Structures

The failure modes to be considered for plate structures are:
Yielding of the plates
Buckling of slender plates due to in-plane compressive stresses and lateral pressure
Buckling of plates due to concentrated patch loads
The plate panel may be part of a box girder, a pontoon, a hull, an integrated plated deck, or
merely a web or flange on a simple beam member. An example of a stiffened plate panel is
shown in Figure 7.1

STIFFENER

Figure 7.1 Stiffened Panel (NTS, 1998)

Ultimate strength capacity checks shall be performed for all structural components directly to
the longitudinal and transverse strength of the structure. The structural components to be
checked are all plates and continuous stiffeners including the following structures:
Main deck, bottom and inner bottom
Ship side, inner ship side, and longitudinal bulkheads
Stringers and longitudinal girders
Foundations of turret and topside structure
Transverse bulkheads
Transverse web frames
In finite element analyses, the plated area will generally be formed as one, of simple panel
elements. If the panel is stiffened, this strengthening may be ignored in an initial assessment
to avoid the need for the inclusion of all structural components, with some or all of the
stiffening included in subsequent analyses. While this is a valid approach, the effect of the