GB661307A - Method of constructing a truss bridge of reinforced concrete - Google Patents

Abstract

661,307. Reinforced concrete bridges; supports for beams. FINSTERWALDER, W. and JECHT, R. April 21, 1949 [April 22, 1948]], No. 10589/49. Classes 20(i) and 20(ii) In a multi-span reinforced concrete bridge, Fig. 1 the spans are supported by cantilever trusses 4, 5, 6, 7, constructed as networks of compression and tension members, which extend symmetrically from foundation pillars 2, 3 in both directions; the opposed ends of adjacent cantilevers being separated by a gap 1 and vertically interconnected by a known linkage, Fig. 3 (not shown), while the ends of the bridge are vertically supported on foundations 8, 9 by conventional means (e.g. roller bearings). In construction, Fig. 8, the reinforcement of the first two bays of each cantilever above each of the pillars is erected according to conventional structural steel practice and the compression members (the lower chord 21 and the vertical posts 22) are embedded in concrete, while the tension members (the upper chord 24 and the diagonals 23) are left uncoated. An auxiliary movable scaffold comprising a plurality of parallel beams 17 distributed over the width of the bridge and resting on the last two completed junctions 18 is erected to project beyond the end bay by a distance corresponding to one additional bay, and supports scaffolding and shuttering 19 whereby the reinforcement of the following bay is erected and sleeve jointed to the completed construction. The compression members are embedded in concrete and the scaffolding shifted for the construction of the following bay. When a cantilever is completed, the tension members are prestressed by the vertical load and are then embedded in concrete. In a modification, Fig. 6, the vertical posts 33 on the upper chord 31 are tension members while the diagonals 30 and the lower chord are compression members. The short reinforcing bars of the vertical posts and the upper chord are anchored at each junction, while the upper chord also contains other long bars 35 which run the whole length of the bridge, to which their ends are anchored. The tension members are prevented from bonding with the concrete by, e.g. a coating of plastic material and after each bay has been constructed and the concrete in which the reinforcement is embedded has set, a predetermined tension is applied to the short bars. and when the cantilever is complete the long bars are prestressed to prevent any tension being exerted on the upper chord concrete by the maximum load on the completed bridge. The reinforcement of the tension members may run in bores in the concrete, which are later filled with cement.