Prestressed Bridge over the River Main

Abstract

This project, which was adjudicated to the firm Polensky & Zöllner, consists of a prestressed concrete bridge of three spans, 85, 140 and 85 m in length. Their shape and slenderness is well adapted to the natural beauty of the surrounding scenery. The axes of the bridge and of the river make an angle of 72° with respect to each other. Also, the bridge, in planform, is a circular arc of 1400 m radius. In the vertical plane, the outline of the bridge is also a circular arc, but of 14000 m radius. Its concavity faces upwards, and the lowest point is near the crown. The concreting of the two box girders, which support the pavement and sidewalks, has been carried out by a combined method of cantilevering and moveable formwork. The formwork was supported by a sliding framework, which could be shifted from place to place, as the overhanging section of the girders increased. This framework enabled a section 7 by 3.5 m in area to be constructed. Work started at a pillar, and developed simultaneously on both sides of it. The prestressing has been the main aspect of the mixed type of construction adopted. The construction by sections, and the large number of longitudinal and transversal cables has required special care in anchoring and aligning the cables. To avoid cracking, a number of helix shaped tubes were placed in the fresh concrete to absorb the hydration heat of the setting concrete. During the process of construction the girders were rigidly joined to the piles, so that the whole bridge structure became a single monolithic unit.