One of the major concerns regarding large offshore structures is the heavy deck loads resulting in large reaction forces on the foundations. If these reaction forces can be reduced by some methods such as using buoyancy-type large members as structural components, then large scale offshore platforms may be successfully employed for the development of ocean spaces. When a large offshore platform has to be constructed in the area of seismic activity, it is important to evaluate the effects of the seismic loads in addition to those of wave loads. The seismic responses are determined with typical power spectra of seismic motions. The reliable evaluation of the dynamic response can be carried out using the random vibration method and the second moment approach. It is suggested that the reliability index, which is computed by the second moment approach, provides a good evaluation to these environmental loads with different characteristics.
One of the possibilities for developing the ocean space effectively may be the construction of large-scale offshore structures. These structures with wide deck areas may be used as residential or commercial areas, airports, waste disposal sites and so on. Since large offshore structures have heavy dead loads, reaction forces on the foundation become severe and require very firm foundations. In this study, the dynamic response of offshore platform with buoyancy-type large members subjected to wave loads, current loads and earthquake loads are examined. The governing equation of the total system is obtained using the substructure method and the response analysis is carried out using the frequency-domain random-vibration approach.
The wave force is one of the most important loads among the dynamic loads. Since sea surface motion has stochastic properties, it is generally represented with a power spectrum.
