Method proposed for construction of multispan cable-stayed bridges

A new method of construction for multispan cable-stayed bridges is described. This method is one of several options developed for construction of the 13-km-long fixed link across the Northumberland Strait connecting Prince Edward Island with New Brunswick in eastern Canada. A 250-m-long cable-stayed span is constructed by launching a 525-m-long steel truss underneath the bridge deck. The special feature of the method is the casting of the concrete deck slab of the 250-m span in one operation in an elevated position (approximately 0.5 m above the final position). While the reinforcing and prestressing steel for the deck is placed, the stay cables are installed and temporarily anchored to the top chords of the steel truss. Because of the elevated deck position, the cables near the pylon are slack, and those further away are stressed much lower than the final level. By lowering the truss supporting the hardened deck by about 1 m, all the stay cables are stressed fully and the deck is suspended at the desired level. The truss is then launched to the next casting position. To support the truss during launching, flotation tanks are submerged from the ends of the truss into the water, exerting a constant uplift force of approximately 3 MN.