Long-Term Structural Monitoring of a Steel Jacket Offshore Platform. Validation of Meteo-Marine Data and Implications for Maintenance

Since 1988 onwards the VEGA-A platform, a steel jacket offshore structure operating in the Mediterranean sea near Siracusa in Sicily, is equipped by a monitoring system collecting environmental data (intensity and direction of wind, sea wave and sea direction) and structural response data (main frequencies and mode shapes). For these structures, in which the major part of the components is in the deep-water, analysis of the collected structural data and their cross-validation with the meteo-marine ones plays an important role in the maintenance schedules. In fact, a modification of the main frequencies and corresponding mode shapes over time may be related to a structural damage so, the capability to correlate structural and meteo-marine data allows a correct planning of the yearly maintenance operations. After a description of the monitoring system installed on the VEGA-A platform, this paper reports a statistical interpretation of the structural response over about 30 years of activity. The dynamic response of the platform under different sea conditions over these years is analyzed, focusing on the correlation between the dynamic parameters and the corresponding atmospheric and sea conditions.