Page 327 - Marine Structural Design

Chapter I4 Offshore Structures Under Impact Loads 303

14.5 Conclusions

A consistent procedure has been presented for collision analysis. A nonlinear force-
displacement relationship has been derived for the determination of the local indentation of the
hit member and a three-dimensional beam-column element has been developed for the
modeling of the damaged structure. The elastic large displacement analysis theory and the
plastic node method have been combined in order to describe the effects of large deformation,
plasticity, and strain hardening of the beam-column members.
The accuracy and efficiency of the beam-column elements have been examined through
simple numerical examples by comparing the present results with those obtained by
experiments and finite element program analyses using the MARC and ABAQUS programs. It
is shown that the present beam-column elements enable accurate modeling of the dynamic
plastic behavior of frame structures by using the absolute minimum number of elements per
structural member.
In addition, examples, where the dynamic elastic-plastic behavior of offshore platforms and
bridges in typical collision situations is calculated, have been presented.
All examples show that strain-hardening plays an important role in the impact response of the
struck or affected structure. The strain-hardening results in smaller deformations and more
energy will be absorbed by the striking structure. Therefore, the impact force is bigger. Thus, a
rational collision analysis should take the strain hardening effect into account.

14.6 References
1. Bai, Y., (1991), “SANDY-A Structural Analysis Program for Static and Dynamic
Response of Nonlinear Systems”, User’s Manual, Version 2, Department of Ocean
Engineering, The Technical University of Denmark.
2. Bai, Y. and Pedersen, P. Temdrup, (1991), “Earthquake Response of Offshore
Structure”, Proc. 10th int. Conf. on Offshore Mechanics arctic Engineering, OMAEP1,
June.
3. Bai Y. and Pedersen, P. Temdrup, (1993), “Elastic-Plastic Behavior of Offshore Steel
Structures Under Impact Loads”, Intemat. J. Impact Engng, 13 (1) pp.99-117.
4. Ellinas, C.P. and Walker, A.C. (1983), “Damage of Offshore Tubular Bracing
Members”, Proc. IABSE Colloquium on Ship Collision with Bridges and Offshore
Structures, Copenhagen, pp. 253-261.
5. Fujikubo, M., Bai, Y., and Ueda, Y., (1991), “Dynamic Elastic-Plastic Analysis of
Offshore Framed Structures by Plastic Node Method Considering Strain-Hardening
Effects”, Int. J. Offshore Polar Engng Conf. 1 (3), 220-227.
6. Fujikubo, M., Bai, Y., and Ueda, Y., (1991), “Application of the Plastic Node Method
to Elastic-Plastic Analysis of Framed Structures Under Cyclic Loads”, Int. Conf. on
Computing in Engineering science, ICES’91, August.
7. Petersen, M.J., and Pedersen, P. Temdrup, (1981), “Collisions Between Ships and
Offshore Platforms”, Proc. 13th Annual offshore Technology Conference, OTC 41 34.
8. Pedersen P. Temdrup and Jensen, J. Juncher, (1991), “Ship Impact Analysis for
Bottom Supported Offshore Structures”, Second Int. Conf. on advances in Marine