The Wandoo A (WNA) fixed platform was installed in 1993 with an intended service life of 15 years. It has subsequently undergone two 5-year life extension (recertification) studies – one in 2008 and another in 2013. The original design and both recertification studies followed API RP 2A WSD guidance (American Petroleum Institute, 2002).
The platform (see Fig. 1) is a braced caisson structure in 52m water depth. The structure supports five conductors: 1 through the main column, 2 external that penetrate through the skirt piles, 1 supported by an external riser caisson and 1 external. The foundation consists of five piles: 1 through the main column, 2 skirt piles, and 2 outrigger piles.
The system also features a tuned liquid damper (TLD) incorporated into the main column near El. (+)17m. This damper is intended to increase the structural damping and reduce system accelerations in response to environmental loading. The TLD is a set of three tanks filled to specific levels with water. The motion of the entrapped fluid provides the damping which has been tuned to the primary structural period.