Large and Small Incrementally Launched Structures

The technology for incrementally launched structures has been known for several decades. It had not been utilized in South Australia until a recent flurry of activity revealed that this method could be economically utilized for both small and large structures. Within 3 years, four structures of various sizes were constructed using the technique. A double-T prestressed concrete recreational jetty was incrementally launched at one of Adelaide’s suburban beaches (Brighton Jetty). Twin single-cell prestressed concrete (PSC) box girders were incrementally launched over eight lanes of traffic at a busy signalized suburban road intersection without disruption to traffic (bridge over Port Wakefield Road). Two incrementally launched major bridges were constructed over the River Murray, Australia’s longest river. The first structure consisted of steel girders composite with a reinforced concrete deck (Berri Bridge, 330 m long), and the other structure was a single PSC box girder (Blanchetown Bridge, 410 m long). All these structures are mentioned, but the focus is on the PSC box girder structures. Construction problems associated with the use of permanent bearings as launch bearings and the sensitivity of box girders to construction tolerances are discussed, and the lessons to be learned are presented. Finally, an unsuccessful attempt to monitor the long-term prestress of the Blanchetown Bridge using state-of-the-art optical fiber technology is discussed, including the reasons for its failure and possible improved future methodology.