چكيده فارسي :
An existing platform should undergo the assessment process if one or more of
the following conditions exist: 1) Addition of personnel 2) Increased loading on Structure 3)
Damage found during inspection and etc.
A structure should be evaluated based on its current status, accounting for any damage,
repair, or other factors affecting its performance. Analyses consist of both design level
analysis and ultimate strength analysis. The latter is more desired and common in offshore
work. Push-over and nonlinear time-domain analysis methods are acceptable in ultimate
strength analysis. The main result of such analysis is Reserve Strength Ratio (RSR).
Acceptance or rejection of structure fitness is dependant on this ratio. In conventional pushover
analysis, wave dynamic loading is simulated by equivalent quasi static load and dynamic
affects such as added mass, damping and inertial force are neglected. However, in timedomain
analysis, dynamic effects are considered and subsequently ultimate strength can be
estimated better with more precision.
In this current study, two platforms were selected for case study analysis. Push-over
analyses and nonlinear dynamic analyses were applied to both platforms and the relevant
results were compared to each other. "ABAQUS" software was used for modeling and
analysis. Pile-soil interaction is modeled by nonlinear springs and in the meantime analyses
took into account the effect of large displacement, plasticity and strain hardening, as well.
In the course of limited investigation, it was concluded that in nonlinear dynamic analysis,
reserve strength of jacket structures was estimated to be higher than that of static push-over
and that structures can bear more partial failure before global failure.
