A Methodology to Nondestructively Evaluate the Safety of Offshore Platforms

摘要

The object of this paper is to describe a practical methodology to continuously monitor the safety of complex structures such as offshore platforms. A Level IV nondestructive damage evaluation methodology is one in which damage is not only detected and sized but the impact of the damage on the performance of the structure is also evaluated. The methodology of interest here is a Level IV nondestructive damage evaluation (NDE) method which can nondestructively assess the condition of the existing structure and simultaneously evaluate the safety of that same structure utilizing structural reliability concepts. The methodology proposed in this paper deals with two broad activities: (1) periodic nondestructive damage localization and severity estimation; and (2) the assessment of structural safety based on the results of the nondestructive damage detection. To meet this objective, an established methodology which yields information on the changes in sectional stiffness properties (e.g., axial, bending, and torsion) from changes in dynamic properties (i.e., mode shapes and frequencies) of the pre-damaged and post-damaged structures is reviewed. Next, an efficient technique to directly assess the reliability of a complex structural system (such as an offshore platform) from the reliabilities of the components of the structure is developed. This technique is then numerically validated via an example using established approaches in structural systems reliability theory. The efficacy of the combination of these two activities (i.e., the nondestructive damage detection and the structural reliability evaluation) is demonstrated using pre-damage and post-damage modal data obtained from numerical simulations of the dynamic responses of a frame.