GB623729A - Method of constructing concrete surfaces adapted to accommodate heavy loads, and applicable more particularly to runways for heavy aircraft - Google Patents

Abstract

623,729. Reinforced concrete. FREYSSINET, E. Jan. 31, 1946, No. 3143. Convention date, Aug. 14, 1945. [Class 20(iv)] A reinforced concrete surface, e.g. an aircraft runway, is made from exceptionally large and thin elements, free to slide over their foundation, which are pre-stressed in two directions parallel to their faces and connected by expansion joints. The joints belong to one of two types, according to whether the concrete elements are prestressed and free to slide independently or not. In the first type (Fig. 3), the joint 6 is filled with soft wood or other deformable material, and shearing stresses are transmitted by pre-stressed local concrete foundations 16 covered by a frictionless layer 20 of kraft paper, tarred paper or bitumen. The elements are additionally strengthened at the joint either by increasing their thickness or by a local intensity in the pre-stressing. In the second type, one element is free to slide or roll relative to the other to a limited extent, longitudinally of the joint. For example, the joint may comprise two relatively slidable metal sheets or a rubber sheet between the elements, shearing stresses being transmitted by interengaging longitudinal flutings; or balls, or metal or reinforced concrete rollers 19 (Fig. 6) having surfaces 19a cooperating with the joint surfaces 21, 22, the intervening space being filled with deformable material 23. The joint may be made before casting the concrete elements, in which case steel rolling surfaces 24 may be provided; or the rollers may be cast at the same time as the elements and spaces left which are subsequently filled with the jointing material 23. Parallel steel or concrete links may be used 'instead of rollers, adapted to slide and pivot at each end on cylindrical surfaces. Pre-stressing. The pre-stressing of the concrete elements may be obtained by known methods such as tensioning steel wire reinforcements and then casting concrete on the wires. The reinforcements may be cables comprising a number of twisted wires which may be arranged in bitumen filled channels so that they can be tensioned after the concrete has set and may be opened out and distributed in the concrete at 48b (Fig. 10) adjacent a joint 6. As shown, the cables are arranged at 45 degrees to the axis of a concrete runway and their embedded ends are secured to anchoring devices 46 protected by concrete masses 47. This method can be applied to curved ways. In another form, the concrete surface bears at its ends on stationary abutments and energy is stored and transmitted by means of springs in the joints, the longitudinal pre-stressing being obtained by these springs or by means of jacks or wedges. The springs may comprise pneumatic rubber tubes 56 (Fig. 14) protected by a flexible casing 57 and connected to a compressed fluid reservoir, the concrete elements resting on a local foundation 55. In the form shown in Fig. 16, transverse steel cables 76a are stretched across joints 78 dividing the concrete into wedge-shaped elements, the joints being of sawtooth shape in plan and constituted in part by both the first and second type (previously referred to). In a modification, some of the concrete elements may form transversely opposed triangular wedges. The transverse pre-stressing is effected by tensioning the cables 76a which in the neighbourhood of the joints are embedded in sheaths 93 filled with deformable material, e.g. rubber or bitumen. Other modifications and different combinations of the above features are described. The Specification as open to inspection under Sect. 91 describes also further methods of pre-stressing and other features. As shown in Fig. 12 (Cancelled), the reinforcing cable 40 is isolated from the concrete element by a tube, sheath or plastic coating, passes underneath and through the thickened end portion of the element and is tensioned by jacks acting on a headpiece 41 subsequently held by wedges 43. The reinforcements may also comprise bars embedded in highly compressed concrete prisms or cylinders. Subsequent tensioning of the reinforcements may be effected at temporary joints made in the concrete. Vertical ground enclosing means may be used if desired. Instead of pneumatic tubes, the springs for transmitting energy across the joints may comprise long concrete elements embedded in the ground and connecting consecutive joints, or steel cables 62 (Fig. 22- Cancelled) stretched along zigzag joints 61. These cables contact projecting rollers 90 and are tensioned by means of head-pieces 87, 88 having stress-transmitting connecting rods 89 bearing on the concrete. This subject-matter does not appear in the Specification as accepted.