Page 30 - Marine Structural Design

Chapter I Introduction 7

Buckling Strength Fracture Strength
Loads Compressivehhear force Tensile loads
Geometrical and residual Defects due to fabrication I
I Imperfection stress due to welding etc. and fatigue loads
Linear Solution Elastic buckling Linear fracture mechanics
Design criteria Curve fitting of theoretical Curve fitting of theoretical
equations to test results equations to test results

In general, the strength criteria for code development may be derived using the following
approaches:
to derive analytical equations based on plasticity, elasticity and theory of elastic stability,
to conduct nonlinear finite element analysis of component strength,
to collect results of mechanical tests,
to compare the analytical equations with the results of finite element analysis and
mechanical testing,
to modify the analytical equations based on finite element results,
to finalize the upgraded formulations through comparisons with numerical and mechanical
tests,
to further calibrate the derived strength equations on design projects.
From the above discussions, it is clear the theoretical knowledge and practical design
experience are vital for the successfhl development of ultimate strength criteria.
As an alternative to criteria in rules and codes, mechanical testing and finite element analysis
may be applied to determine the ultimate strength of structural components. For simple
components, the prediction of finite element analysis and rule criteria is usually close to the
results of mechanical testing. Hence, mechanical testing is now mainly applied to subjects on
which less experience and knowledge have been accumulated.
Subjects that warrant future research on ultimate strength analysis include, e.g.
development of strength equations for combined loads
calibration of partial safety factors using risk assessmek and structural reliability analysis
standardization of the finite element models and benchmark of the models
development of procedures for the determination of partial safety factors for finite element
analysis and strength design based on testing

1.2.2 Design for Accidental Loads

The accidental loads that should be considered in the design of ship and offshore structures are
e.g.: