Patent GB-740121-A (GB)
Title: Composite structures of concrete and steel, and, in particular, flexed structures
IPC: E04C3/293
Filed: 1954-04-13
Abstract: 740,121. Reinforced concrete. FREYSSINET, E. April 13, 1954 [April 22, 1953], No. 10862/54. Class 20(4). A ferro-concrete structure, e.g. a beam, comprises a flat reinforcement or rein. forcements, and a flat external steel member which bears against and encloses at least a part of the surface of the concrete, and means whereby the external member, the reinforcement or reinforcements, and the concrete are maintained in bond by applying a transverse compressive force to the whole structure. In Fig. 1, reinforcements 3 are spaced across the section of a beam the concrete 1 of which is partly enclosed by the side members 5. Bond between the steel and concrete is maintained by the compressive force exerted by tensioned cables 7. The reinforcements 3 are made by dividing a H-section member, Fig. 2, along the web. The line of division is preferably undulating as shown at 4, which further increases the bond with the concrete. The .concrete 1 is further compressed by con. ventional longitudinal pre-tensioned reinforcements 2, the compressive force being transmitted also to the steel members 3, 5. The reinforcements 3 are not necessarily of the same length as the beam, but may be present, or used in greater numbers, only in those parts of the beam which require the greater degree of reinforcement. Further reinforcing strips, e.g. of plain, U or T-section may be forced into the wet concrete between the flanges of the reinforcements 3. In Fig. 6 is shown a structure intended for large spans, e.g. for roadways, the beam portion comprising a deep web 17, top flanges 15 and a lower tension member. The flanges 15 consist of H-sections 14 bonded with the concrete by transverse tensioned cables 21. The lower tension member comprises concrete prestressed by cables 19 and held in transverse compression by cables 22 which bear against side H-members 20. The web is reinforced by members 18, and, in a modification the web is precast, is prestressed at the lower parts, and has concrete applied between its sides and the members 20, the said concrete being applied around tensioned longitudinal cables so that, when set, the concrete receives a compressive force. The unstressed members 20 are then forced against, and thus bonded to, the concrete by the transverse cables 22. The invention may be applied to a lattice structure consisting of an upper part comprising transversely spaced steel-concrete beams which are integral with steel-concrete flooring which closes the spaces and is, like the beams, provided with longitudinal H-section reinforcements, the whole being bonded together by transverse tensioned cables ; lower tension members parallel with the upper beams and constructed of steel-concrete in transverse and longitudinal compression as described above ; and vertical and diagonal ties and struts joining the upper and lower members. The struts and ties are of transversely compressed steel-concrete, the outer steel members being of U-section to enclose the concrete, are welded to gusset plates which project into the concrete of the upper and lower members and are bonded thereto by the transverse compression which is applied. Where gussets welded to two oppositely inclined ties meet, a plate transverse to the gussets may be welded thereto, so that the bond with the concrete is enhanced by the longitudinal compression in the concrete acting upon the transverse plate. Figs. 11, 12 show the invention applied to the securing together of two aligned girders, or sets of girders, 61a, 61b, of H-section. Plates 62a, 62b are welded at right angles to the flanges of the H-sections and become interleaved when the guides 61a, 61b are positioned for joining. The interleaved plates are surrounded by a mass of concrete in which flat jacks 68, parallel to the plates 62a, 62b are embedded, and the whole is encircled by a helical reinforcement 67. Transverse compression is applied to the steel-concrete assembly by inflating the jacks 68, either by a hardening liquid e.g. cement or synthetic resin, or by an ordinary liquid, e.g. water, in which case the pressure may be vented to release the steel and concrete from bond. This permits an adjustment to be made in the length of the assembly after which the bond is restored by reinflating the jacks. Rubber strips 69 are provided between the butt ends of the plates 62a, 62b and the flange of the opposite girder section to accommodate the adjustments. Fig. 15 shows a connection between a steel-concrete floor, transversely compressed by cables 21, and a strut or the member 45. As shown the member 45 is arranged diagonally, but it may be vertical. The concrete adjacent to the main H-members 43 is formed at 46a into an abutment for a plate 47 between it and the end of the member 45. The member 45 is strained against the abutment 46a by looped reinforcements 46 which are tensioned to an extent depending on the working stress in the member, i.e. if it is a tensile stress, the tension in the reinforcements 46 exceeds this, but if it is a compressive stress, the tension in the reinforcement is much less. The flanges of the girders incorporated in the member 45 are cut at 45a and bent inwardly at 50 to form girders for the reinforcement. An arc-shaped channel 51 is formed in the concrete for the passage of the reinforcement. In all the constructions, the surfaces of the steel parts may be roughened, e.g., by sand-blasting, or projections may be welded on to the surfaces, or hollows formed therein, to increase the bond with the concrete. Instead of the concrete being poured in situ as described above, the concrete posts may be precast and may be subdivided transversely and longitudinally in any manner conducive to easy manufacture.