GB2048334A - Stool for in situ cast beam - Google Patents

Abstract

A prop for temporary support of a wall (20) during the construction of an in situ cast reinforced concrete beam (23) has a body (4, 6, 7) and a top plate (13) which can be forced upwards relative to the body by screwing a spindle (9) upwards out of the body. After the wall (20) has been supported above the beam (23) by means of mortar (25), the spindle (9) can be retracted whereupon inclined side faces (14) on the top plate (13) allow it to be separated from the mortar (25) and withdrawn for reuse. <IMAGE>

Description

SPECIFICATION Stool for in situ cast beam The invention is concerned with stools for use in the construction of in situ cast beams in the walls of buildings. Such beams are used in the underpinning and repair of buildings, for example when underpinning a cracked wall, the foundations of which have been subject to subsidence. The beam is inserted in the wall of the building parallel to the plane of the wall and the load will then be redistributed by the beam onto the foundations, which may be renewed at the same time. Such beams are also used as lintel beams which are inserted into the wall prior to cutting away the wall beneath the central portion of the beam.

Such a beam is conventionally constructed by cutting away the wall and inserting stools at horizontally spaced position. The stools are built in and pinned up to support the wall above and we have recently proposed the use of stools incorporating a screw jack to facilitate the pinning up. With the intervening wall between the stools cut away, reinforcing rods are inserted, formwork is erected, and an in situ concrete beam is cast incorporating the reinforcement and the stools.

The cast beam does not extend up as high as do the stools and the wall above the beam is pinned up from the top of the beam, between adjacent stools, usually by packing earth dry mortar into the gap between the top of the beam and wall above.

A beam constructed in this way is hereinafter referred to as of the kind described.

A comparatively large number of stools have to be used in the construction of a beam of the kind described and there would be a cost saving if part of each stool could be recovered, rather than sacrificed with the rest of stool.

In accordance with the present invention, a stool for use in constructing a beam of the kind described comprises a body portion which is arranged to be supported on the wall below and which includes a screw threaded socket having a vertical axis, a screw threaded spindle which screws through the socket and includes means for rotating the spindle relatively to the socket, and a separate top plate which is arranged to be supported on top of the spindle and to be force upwards into load bearing engagement with the wall above upon screwing of the spindle upwards out of the socket, the side faces of the top plate which, in use, extend transversely of the wall, being so inclined relatively to one another that, in use, after construction of a beam of the kind described incorporating the stool, and the packing of mortar into the gap between the cast beam and wall above and between and closely adjacent to the adjacent side faces of the top plates of adjacent stools, upon screwing the spindle a little way downwards into the socket to release the load bearing engagement between the spindle and the top plate, the top plate may be readily released from the mortar which is packed adjacent to its side faces and recovered by being withdrawn through a face of the wall.

The recovery of the top plate for reuse represents a significant cost saving.

The top plate might be a reinforced concrete casting but the overall height of the stool will be less if the top plate is, as is preferred, a steel plate of perhaps 3/8 inch thickness.

The inclination of the side faces of the top platemay result from a convergence of the side faces of the top plate towards one another so that, as seen in plan, the top plate is frusto-wedge shaped.

Alternatively, and preferably additionalJy, the side faces are splayed downwards and outwards relatively to one another. These forms of shaping will enable the top plate to be released readily from the adjacent packed mortar by, for example, striking the top plate with a hammer or other tool to break any bond with the mortar. If the top plate is wedge shaped, it can then be immediately withdrawn with the wider side of the plate leading and if the side faces are splayed, a slight lowering of the top plate relatively to the adjacent packed mortar will similarly enable ready withdrawal of the top plate.

In use the beam will be cast up to a level below the lower edges of the side faces of the top plate, so that the cast beam does not impede the withdrawal of the top plate. It may then be necessary to provide some means to mask the gap between the lower edges of the side faces of the top plate and the top of the cast beam to prevent the ingress of the mortar during pinning up of the wall above from the beam. Such masking may be effected by laying strips of material, such as wood or metal, on the cast beam leaning against the side faces of the top plate.

The formwork at the exposed surface of the beam, through which the top plate is withdrawn, will not generally be supported at its upper edge against the top plate of the new stool, as has been usual with conventional stools. The upper edge of the formwork shuttering may be supported by means of a bifurcated clip having a pair of legs which are arranged to straddle the sides of the upper edge of the shuttering and a head which is arranged to extend upwards from the upper edge of the shuttering and to bear against the face of the wall above.

The top of the spindle may present a spigot or socket for cooperation with a complementary socket or spigot in the underside of the top plate for purposes of location as the stool is pinned up by extension of the spindle. The means for rotating the spindle is preferably a non-circular section adjacent to its upper end, for example a nut welded on to the spindle adjacent to its upper end, and providing a bearing surface on which the top plate can be balanced during pinning up.

The body portion may take a variety of forms but particularly may consist of a base plate and a cross head supported above the base plate by legs and incorporating the screw threaded socket. The spindle with screw through the cross head and its lower retracted portion is preferably accommodated in a sleeve which may be loosely located between the cross head and base plate surrounding the spindle and possibly filled with grease. The sleever will protect the spindle from the surrounding concrete when the beam is cast, and enable the screwing down of the spindle a little way through the socket to release the top plate prior to its recovery.

The lower end of the spindle may be unthreaded so that it is unable to pass through the socket, thereby limiting upward screwing of the spindle while there is still secure engagement between the spindle and socket.

One example of a stool constructed in accordance with the invention and its use in the construction of a beam of the kind described are illustrated in the accompanying drawings in which: Figure 1 is a side elevation of a wall incorporating the beam and showing one stool and adjacent parts of the beam in central vertical section; Figure 2 is a side elevation of the stool; and, Figure 3 is a plan of the stool.

The iliustrated stool comprises a steel base plate 4 resting on a reinforced concrete plate 5.

Welded to and extending upwards from the base plate 4 are two steel angle sectioned legs 6 to the upper ends of which is welded a steel plate forming a cross head 7. The cross head 7 has a central tapped hole 8 forming a screw threaded socket through which there screws a screw threaded spindle 9. A nut 10, by means of which the spindle 9 can be rotated, is welded onto the spindle 9.

A projecting portion 11 of the spindle 9 above the nut 10 forms a spigot which fits into an unthreaded socket 12 formed by a central hole in a steel top plate 13. The edge of the top plate 13 around the hole 12 rests on top of the nut 10. As seen in Figures 1 and 3, one opposite pair of side edge faces 14 of the top plate 1 3 diverge outwardly and downwardly. The depth of the side faces may optionally be increased by welded on flanges 1 5 at the same inclination as the rest of the side faces. As shown in Figure 3, the side faces 14 also converge in the plane of the top plate so that the plate is frusto wedge shaped in plan.

A lower end 1 6 of the spindle 9 is unthreaded to limit the extent to which the spindle 9 can be screwed up through the socket 8. The part of the spindle 9 below the cross head 7 is accommodated within a sleeve 1 7. The sleeve may be a section of steel tube welded to the base plate 4 and cross head 7. However it is generally sufficient if it is loosely, but fairly closely, fitted between these two parts and in that case it may be a section of plastics tubing. The tube 1 7 is preferably filled with grease but if it is not, and if the unthreaded portion 16 of the spindle 9 is for some reason omitted, the sleeve may be made of a transparent or translucent material so that the length of spindle 9 below the cross head 7 is observable through the tube 1 7.

In the construction of a beam, the wall is cut away and stools are inserted at horizontally spaced intervals. Thus as shown in Figure 1 the stool is inserted so that the reinforced concrete plate 5 rests on the raw cut masonry of the wall 1 8 below, with an interposed fibrous sheet 19. In the case of a cavity wall the plate 5 will extend across the cavity and rest on both leaves of the wall. The spindle 9 is extended upwards out of the socket 8 by turning the nut 10, thereby forcing the top plate 1 3 upwards to develop the necessary load bearing reaction with the wall 20 above, with another fibrous sheet 21 interposed between the top plate 13 and the wall above.

When all the stools have been inserted and built in in this manner, and with all the intervening brick work cut away, reinforcement represented by longitudinal rods 22 are attached to the stools, formwork is erected, and a concrete beam 23 is cast on the wall 18, up to a height 24, encapsulating the stool bodies and reinforcement.

When the cast beam 23 has set, earth dry mortar 25 is packed into the gap between the top of the beam 23 and the wall 20 above to pin the wall up from the beam. This mortar may bear directly against the side faces 14 of the top plate 1 3, as shown on the right hand side in Figure 1, or the gap below the top plate 13 may be securely protected by wood or other strips 26 resting against the side faces 14 and on the beam 23.

When the mortar 25 has set, the spindle 9 is retracted slightly so that the top of the spigot 11 is slightly below the undersurface of the top plate 13. The spindle 9 is free to retract because it is protected from the cast concrete of the beam 23 by the surrounding sleeve 1 7. The top plate 13 can then be slightly displaced downwards out of firm engagement with the mortar 25, as a result of the downward and outward divergence of its side faces 14. It may be necessagy to tap the top plate 13 to loosen it from the mortar 25. Once the top plate 13 has been displaced downwards, it may be drawn upwards through a face of the wall. This withdrawal will be facilited if the top plate is frusto wedge shaped as seen in plan. The top plate 13 is thus recovered for reuse and if desired further pinning up of the wall 20 from the cross head 7, by packing further earth dry mortar into the gaps which are left may be carried out.

Claims (10)

1. A stool for use in constructing a beam of the kind described, the stool comprising a body portion which is arranged to be supported on the wall below and which includes a screw threaded socket having a vertical axis, a screw threaded spindle which screws through the socket and includes means for rotating the spindle relatively to the socket, and a separate top plate which is arranged to be supported on top of the spindle and to be forced upwards into load bearing engagement with the wall above upon screwing of the spindle upwards out of the socket, the side faces of the top plate which, in use, extend transversely of the wall, being so inclined relatively to one another that, in use, after construction of a beam of the kind described incorporating the stool, and the packing of mortar into the gap between the cast beam and the wall above and between and closely adjacent to the adjacent side faces of the top plates of adjacent stools, upon screwing the spindle a little way downwards into the socket to release the load bearing engagement between the spindle and the top plate, the top plate may be readily released from the mortar which is packed adjacent to its side faces and recovered by being withdrawn through a face of the wall.

2. A stool according to claim 1, in which the side faces of the top plate converge towards one another so that, as seen in plan, the top plate is frusto-wedge shaped.

3. A stool according to claim 1 or claim 2, in which the side faces of the top plate are splayed downwards and outwards relatively to one another.

4. A stool according to any one of the preceding claims, in which the means for rotating the spindle is provided by a nut welded onto the spindle adjacent to its upper end and providing a bearing surface on which the top plate can be balanced during pinning up of the stool.

5. A stool according to any one of the preceding claims, in which the body portion consists of a base plate and a cross head supported above the base plate by legs and incorporating the screw threaded socket.

6. A stool according to any one of the preceding claims, in which, below the socket, the lower end of the spindle is accommodated within a sleeve which is arranged to protect the spindle from the concrete during casting of the beam.

7. A stool according to claim 1, substantially as described with reference to the accompanying drawings.

8. A method of constructing a beam of the kind described, wherein the stools are constructed according to any one of the preceding claims, and after the wall above the beam has been pinned up from the top of the beam, the stool spindles are screwed a little way downwards into their sockets and the top plates of the spindles are recovered.

9. A method according to claim 8, wherein, prior to pinning the wall above the beam up from the top of the beam by packing earth dry mortar into the gap between the top of the beam and the wall above, the gap between the side faces ot tne stool top plates and the top of the cast beam are masked by laying strips of material on the cast beam leaning against the side faces of the top plates.

10. A method according to claim 8, substantially as described with reference to the accompanying drawings.