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CHAPTER 4: THE CONSTRUCTION PROCESS OF SEGMENTAL BRIDGES - page 36 / 47

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Chapter 4: The Construction Process of Segmental Bridges

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alternatives of a steel plate girder and a precast segmental concrete bridge “to foster competition and thus reduce the project cost.”

Construction of the concrete structure began in 1981 after a longer bidding process. The dimensions of the two parallel box girder superstructures are 2.4 km in length with a 38-m high navigation clearance and a width of 22 m. Balanced cantilevering under a launching girder was chosen for erection of the 1,592 precast segments. A heavy-duty truck delivered segments weighing about 110 to 145 metric tons on the bridge. They were placed with the 287-m long, 1,540 metric tons heavy launching girder. “Thus, during construction, the new bridge is subjected every day to far heavier loads that it will ever experience after it is opened to traffic” (Anon. 1988, p70).

During construction all expansion joints were blocked against movements “by inserting temporary high-strength concrete blocks”, which are fixed with tie-downs (Anon. 1988, p71). In late 1982 an accident occurred when these blocks failed in one of the joints, which caused the respective superstructure to tilt and sag at one end, damaging bearings, joints, and a pier footing that was forced out of the vertical. The subsequent investigation concluded that the main cause for this incident “was construction loads at the particular location that were too heavy” (Anon. 1988, p71). Difficult repair works were undertaken to realign and reinforce the pier at its base. Adjacent soil was temporarily frozen for stabilization and a major concrete counterweight was placed. Afterwards, pile holes were drilled and filled with concrete, on which the reinforced pier base was erected. “A structural steel frame was fabricated and erected on top of the new footing, and fitted with 12 hydraulic jacks” (Anon. 1988, p72) that should help realigning the superstructure. After new bearings and connecting cables to the counterweight had been installed the superstructure was brought back into alignment and construction work commenced again until opening in 1988.

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