GB853418A - Improvements in and relating to prestressed concrete slab structures such as airfield runways and the like - Google Patents

Abstract

853,418. Prestressed concrete structures; runways &c. LEE, D. H. March 24, 1959 [March 24, 1958], No. 9302/58. Class 20(4) In the prestressing of concrete slab structures such as airfield runways, roads or the like, the or each slab is lifted, as by jacking means, so that it is supported clear of the ground and a prestress is applied to the slab after or during lifting of the slab. The jacking means may be applied to lift and support each slab by forming a plurality of holes in spaced positions in each slab through which jacking thrust bars can project down to the surface of the ground beneath the slab or preferably on to a bearing plate on the ground. The jacking means may comprise a block 25, Fig. 3 secured on the underside of the slab 2 when cast, and having a threaded bore 26 adapted to receive a screw threaded lower end 29 of a rotatable thrust bar 28. The block 25 is located at the lower end of a steel lining tube 27. Alternatively hydraulic or pneumatic jacking means 16 may be applied between the upper end of the thrust bar 9, Fig. 1 and a stirrup 10 which is wedged into a steel tube 3 lining the hole 1 in the slab 2. After the jacking operation is completed the stirrup 10 and the bar 9 may be locked together by means of a clamp 17 and opposed serrated surfaces 18, so as to enable the jacking means 16 to be removed whilst maintaining the support of the slab at this point. In an alternative embodiment, each slab is lifted by water injected under pressure underneath the slab through non-return valves 36, Fig. 4 and tubes 35a lining holes 35 in the slab. In order to prevent escape of water from beneath the slab a thin waterproof membrane 38, e.g. of polyethylene sheet is provided. A layer of coarse sand 39 is laid over the membrane 38 and is covered by a layer of building paper 40. The membrane 38 is turned back inwardly at its margins 41 to overlie the margins of the building paper 40. A number of drainpipes 42 are provided for draining water from below the slab after the lifting operation.