This paper presents a methodology to detect and locate damage in a jacket platform structure. The methodology utilizes damage indices on the changes in the distribution of the modal compliance of structure due to damage. The changes in the modal compliance distribution are obtained using the mode shapes of the pre-damaged and post-damaged states of the structure. In the method, each member of the jacket platform is treated as a truss element and damage indices are formulated using modal strain energy of truss structure. Several damage cases are simulated numerically. The cases range from the structure being damaged in one location to the structure being damaged in three locations. The damage detection results using three mode shapes of pre- and post-damaged jacket platforms are provided and the performance of the method is discussed.
The jacket platform structure was a one of the representative type of off-shore plant. Many jacket platform structures have been constructed in the world to exploit natural resources since 1960s. The development of oil-fields in the Gulf of Mexico had brought about the full-scale constructions of jacket platform structures. The jacket platform was mainly used for offshore, in the depth of 100–150 m sea water. The majority of jacket platforms are now becoming obsolete because of the exhaustion of the resources and the shift of oil-production business to the deep sea. Some efforts are found in re-use of the existing jacket platform such as the wind power plant or the lighthouse. To date, numerous nondestructive damage detection (NDD) methods have been proposed and developed using various experimental and theoretical techniques. Some of the well-known experimental techniques include ultrasonic, radiography, magnetic particle, dye penetrant, and eddy current (Asklend, 1994). These techniques have been applied to small scale systems and a specific portion of large scale structures.