Long-Term Structural Health Monitoring of a Steel Offshore Platform. Optimal Sensors Position and Implications for Maintenance

Since 1988 the VEGA-A platform, a steel jacket offshore structure operating in Sicily (Italy), is equipped with a monitoring system that collects environmental and structural parameters. For these structures, where most of the components are in the deep-water, the long-term analysis of the structural data plays an important role both for safety issues and maintenance schedules. Over the past 30 years, the VEGA-A monitoring system has proven to be an effective component of the inspection plan, useful for optimizing the type and the number of underwater inspections. However, after 35 years of activities, it is now time to consider an efficient upgrading of the monitoring system. Today, technological development makes it possible to consider additional underwater accelerometer measurements. This would make it possible to identify not only the structural frequencies but also the main mode shapes, so as to improve ability of the monitoring system to control for damage in the largest numbers of main underwater elements. This paper reports on a possible improvement of the current monitoring system by investigating on an optimal position for new underwater accelerometer sensors. The final optimal sensor grid has to maximize the information content for the identification of the main mode shapes.