GB747966A - Improvements in or relating to reinforced concrete constructions - Google Patents

Abstract

747,966. Roofs; bridges. WILLIAMS, Sir E. 0., and WILLIAMS, 0. T. Dec. 23, 1953 [Jan. 8, 1953], No. 642/53. Classes 20(1) and 20(4). In the construction of roofs, bridges or other spanning structures, the structure is built out from a pier or column, without support from below, progressively in sections which are tied to the pier by tensioned members which are subsequently encased in concrete. Fig. 1 shows one half of a bridge construction which includes two concrete piers 20 each having an anchor span 21, a central span being suspended between the piers. Pairs of strut towers 25 are erected on each pier 20 ; there may be one pair only, or one pair for the " up " road and one pair for the " down " road may be provided. The towers are spaced by bracing 19. The road deck of the anchor span 21 is first moulded in sections, e.g., each about 15 feet of road length, each section being connected by tension members 28-33 to the towers 25. A temporary staging 22 facilitates the construction of the anchor span. The suspended span is now cast in sections, beginning from the towers, each section being cast in a mould 40 which is supported on bogies 42 and is cantilevered out from a previously moulded section 38. It is anchored at 43 to another section 36. During the casting, each section is attached by its ties 45-49 to the tops of the towers 25, the tensioning of the respective ties being effected when the mould 40 is in use for the next section. The degree of tension may be determined to accord with maximum working load by adjustment of the positions of the anchor points 43. Whilst the ties are thus tensioned, they are concreted. The shore end of the anchor span is connected, in normal manner, to a counterweight 18 to prevent compressive stresses in the back stay 33. The ties 29-33 are finally con;, creted. Stiffening or distributing girders 50 and a rail 44, extending along each side of the carriage way, are constructed after the moulding of the deck sections, the girders 50 enclosing the anchorage points of the ties. Vertical bracing members 39 are provided at intervals. In a modification, Fig. 8, a bridge is built by casting sections, step-by-step symmetrically out from each pier 70, the sections, as before, being provided with ties connecting them to the tops of the towers. The spans are made alternately continuous, as at 71, and non-continuous with short links 72.