The Earthquake Engineering Online Archive

Model study of effects of damage on the vibration properties of steel offshore platforms

Shahrivar, Farid; Bouwkamp, Jack G.

UCB/EERC-82/05, Earthquake Engineering Research Center, University of California, Berkeley, 1982-06, 213 pages (545.1/S495/1982)

The selected vibration properties of an offshore platform model were studied, considering both damaged and undamaged conditions. The platform model was a 1/50th-scale, three-dimensional tower possessing the key features of a typical, eight-legged, k-braced steel offshore platform. Changes in the vibration frequencies and mode shapes of fixed offshore platforms can be used to detect damage. In this study, for the first time, quantitative information on mode shapes was utilized leading to improved damage detection capabilities. The scaling considerations, the model, and the experimental method are described. The experimental results are complemented with analytical results and show excellent correlation. In general, emphasis is placed on the vibration frequencies and deck modal displacements of the first two translational modes and the first torsional mode. The effects of a variation in deck mass are assessed both experimentally and analytically. Also, the effects of shifts in the position of the deck center of mass are assessed analytically. Both experimental and analytical results support the potential application of mode shape monitoring to detect structural damage. This study illustrates that when both frequencies and mode shapes are considered damage related changes differ in characteristics from variations not related to damage.

Available online: http://nisee.berkeley.edu/documents/EERC/EERC-82-05.pdf (16 MB)