Developing a SIM strategy for offshore jacket platforms based on the FE model updating and a novel simplified method

Abstract Lack of data of the jacket structures may result in a high uncertainty about the structures ability to endure harsh marine environmental conditions. An experimental measurement from structural behavior under harsh marine environmental conditions is necessary to reduce this uncertainty in practical structural monitoring process of jacket structures. As an alternative, a novel and robust simplified methodology based on the empirical investigation could be a practical approach of better understanding the structures integrity. Hence, these methodologies are often termed as model reduction schemes. In this article, model reduction schemes include simplified platform model and static reduction. This work introduces a structural integrity assessment strategy for jacket structures based on the finite element (FE) model updating and a novel simplified method. Hereof, model reducing and model updating procedure is established based on a novel optimization technique. Since the number of measured degrees of freedom is most of the time restricted in practice, this paper represents a methodology using the cross model cross mode (CMCM) method in combination with an iterative procedure which uses limited, spatially incomplete modal information. One of the important advantages associated with the proposed method is that measuring the rotational degrees of freedoms, which is most of the time very expensive and inaccurate, is not needed. This research is an empirical study on a laboratory model of a jacket structure with the aim of establishing Refined Simplified FE Model (i.e. RSM) to conduct damage detection. The studied jacket structure is a reduced scale 2D frame fabricated and tested at the Laboratory of Modal Analysis of the Tabriz University, Iran. Hereof, experimental vibration tests are accomplished on a physical 2D platform model to record dynamic responses and acquire dynamic features of damaged structure. In addition to eliminate the uncertainty effects in the damage detection results, RSM technique is employed because of practical considerations and also this technique provides a fast damage zone diagnosis procedure. Also, improved reduction scheme is utilized based on static reduction scheme to carry out damage detection in jacket structure. Improved reduction technique eliminates the bad influence of model reduction procedure on the proposed new methodology. The results demonstrate that the presented new technique is completely successful in conducing damage identification in jacket structures.