Structural integrity assessment under uncertainty for three dimensional offshore structures

A novel structural integrity assessment technique using uncertain response information is under development by the research team at the University of Arizona. The team successfully verified the method for two dimensional truss and frame structures. The team is now in the process of extending the method for three dimensional (3D) truss type structures. The essential feature of the procedure is that it is a finite element based linear system identification technique which can accurately identify a structure without causing any disruption to the normal operating condition. Using only the noise contaminated response information, the procedure is capable of identifying defect at the element level of a structure by tracking changes in the stiffness parameters of the elements. The information on the dynamic excitation is not necessary. The procedure identifies the dynamic loading as a by-product. It is referred in this paper as the 3D Modified Iterative Least Squares with Unknown Input (3D-MILS-UI). The procedure and its verification are presented in this paper. The procedure is verified assessing structural integrity of a 3-D truss type offshore tower. The tower is subjected to one or multiple sinusoidal loadings and impact loadings; types of loadings expected during the operation of the tower. Three types of damage scenarios of the tower are considered - multiple broken members, multiple damaged elements in terms of the reduction in the cross sectional areas and a combination of broken members and damaged elements. Both noise-free and noise-contaminated responses are considered for the defect identification purpose. The results indicate that the 3D-MILS-UI procedure can accurately assess structural integrity by locating the defective elements and quantifying the severity of defects in them.