Design and Fabrication of Prestressed Concrete Box Girder Bridge with U-Shaped Segments

Abstract

The bridge in this project is a two-span continuous prestressed concrete box girder bridge with U-shaped precast segments (PC composite U girder bridge) under construction across a valley in Tokushima, Japan. This bridge type was selected from among others for simplified on-site construction and optimum cost reduction. The bridge has a continuous structure prestressed with internal and external tendons. Large capacity tendons (19S15.2) were used to apply prestressing force externally at the support cross beams in two different stages: when the cross section was in a U shape and then in a composite shape. As compared to that in the composite section stage, the prestressing process in the U-shaped section stage could cause excessive tensile stress in the cross beams. The other concern was cracking risk associated with tensile stress occurring on the inside of the sloped webs of the U-shaped cross section of the main girder during the temporary storage of the precast segments. In order to investigate reinforcing methods, the authors carried out three-dimensional finite element analysis for the two cases: at prestressing of the tendons and at temporary storage of the segments. Measures were also taken to improve quality of the precast segments and construction efficiency during the fabrication process. This paper reports planning, design and construction of the PC composite U girder bridge.