ABSTRACT
Steel offshore structures are most usually fabricated in the form of jacket (or template) structures, as discussed in Chapter 2. Typical jacket offshore structures, with the associated structural components, are shown in Figure 8.1, viz., steel framed offshore structures with (a) an integrated deck [1] and (b) a modular deck assembly [2]. Hence, the structural analyst and designer must take into consideration the various conditions that need to be considered in the analyses and designs of the platform components. The jacket is normally fabricated using hollow cylindrical steel members both for main legs and the cross/horizontal bracings. The interior jacket legs are usually vertical, whereas the exterior legs and the supporting piles are often inclined so as to provide a broader and more efficient base for resisting horizontal loadings; as given earlier in Chapter 7.4, the maximum inclination of these legs is limited to 1:7 (in each direction, leading to a batter of 1:5 for the corner legs) because of on-site installation difficulties; it is much smaller for deepwater steel structures. The vertical and inclined support piles provide vertical support for the deck loading and minimize the pullout forces generated by the horizontal and vertical wind and wave loads. The penetration depth of these piles, into the ocean floor, is generally more than 200 ft. to provide the required horizontal and vertical resistance against the applied wind/wave loads. The analysis and design of a modular structure should also reckon with the presence of a deck support frame, as well as the launch girders for the modular deck.
