GB1599160A - In situ cast beams - Google Patents

Description

(54) IMPROVEMENTS RELATING TO IN SITU CAST BEAMS (71) We, PYNFORD LIMITED, a British company, of 74 Lancaster Road, Stroud Green, London, N.4, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The invention is concerned with the construction of in situ cast beams in the walls of buildings, and stools for use in the construction of the beams.

Such beams are used in the underpinning and repair of buildings, for example when underpinning a cracked wall, the fundations 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. The 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.

A conventional beam is constructed by cutting away the wall and inserting props, which in this context are generally, and are hereinafter referred to as stools, at horizontally spaced positions. The stools are built in to support the wall above. With the intervening wall between the stools cut away, reinforcing rods are inserted, formwork is erected, and an in situ beam is cast incorporating the reinforcement. Mortar is then packed into the space between the top of the cast beam and the raw wall above betwen the stools to pin up the beam along its full length.

Conventional stools are complicated metal fabrications or complex multi-piece concrete castings. Since a comparatively large number of stools have to be handled and sacrificed in the construction of a beam, it is desirable that they should be of the cheapest and simplest possible construction and as small and as light in weight as possible although adequately sturdy.

The pinning up of stools is a laborious business and time has to be allowed for the mortar, which is used for the pinning up, to set before the wall between the stools can be cut away and the beam cast. It is known to use, in association with the stools, a screw jack in order to tighten and pin up the stools quickly. For example the stools disclosed in our specification No. 827,838 incorporate jacking screws between upper and lower plates of the stool and there is described in our specification No. 1,497,412 a thin plate screw jack for insertion between the top of the stool and the wall above.However, these earlier proposed screw jacks involve the use of screws which are short by comparison with the height of the stool and, although they are sufficient to enable the stool to be pinned up, the stroke is sufficient to lift the wall above, if cracked, sufficiently to close the cracks to any significant extent.

The stitching up and filling of the cracks is a further laborious operation. Furthermore, the earlier integral or plate screw jacks are expensively constructed items and add to the cost of the operation, either in the time required for their recovery during the construction of the beam or in their cost if they are sacrificed by being left within the beam.

In accordance with the present invention a stool for use in the construction of an in situ cast beam comprises two bodies, one of which is provided with a screw threaded socket and the other of which is provided with an abutment; a screw threaded spindle which engages in the socket and extends towards the other body where an end of the spindle engages the abutment; and means enabling rotation of the spindle relatively to the screw threaded socket for extending the spindle relatively to the one body for forcing the two bodies apart; wherein at least one of the two bodies is formed by a substantially circularly cylindrical shell filled with a load bearing grout into which a member incorporating the respective one of the screw threaded socket or abutment is cast.

The outer shell may be made of steel, such as mild steel, but could alternatively be made of other materials such as metals or plastics material such as are used for drainpipe sections.

The load bearing grout with which the shell is filled is preferably cement or concrete.

The stool bodies of the stool in accordance with the invention are effectively combined with a screw jack and provide a simple and cheap extensible stool with an appreciable working stroke.

Preferably, both of the stool bodies are formed in a similar manner, the one body having a cast in member incorporating the screw threaded socket and the other body having a cast in socket in which the adjacent end of the spindle is freely rotatable and the bottom of which forms the abutment. The bodies will be used spaced apart in axial alignment with the screw threaded spindle extending between them.

The means for rotating the spindle preferably comprises a nut fixed on the spindle closely adjacent to the other one of the bodies. This stool will be used with the other one of the bodies lowermost thereby facilitating the manipulation of a spanner applied to the nut since the spanner head can rest on the lower stool body when engaged with the nut without the operator having to take the weight of the large heavy spanner. Furthermore, the stool bodies provide significantly large bearing surfaces both at the top and bottom of the stool thereby distributing the reaction across the width of the wall.

This is particularly important when the wall is a cavity wall and a local reaction in align- ment with the cavity might break a plate inserted between the stool body and wall.

The stool may also comprise upper and lower rigid load bearing plates between which the stool bodies and spindle are arranged to be mounted so that extension of the spindle forces the two plates apart.

When the plates are made of precast concrete, they may be provided on their upper and lower surfaces respectively with a steel plate, which may be cast in, to provide a bearing for the interposed jacking assembly.

Each stool could be provided with two of the spindles, which are alternately extended and pinned up by jacking, to provide an increased effective lift of the upper plate relative to the lower plate and tighten up the wall above bv a corresponding amount.

The stool in accordance with the invention may be made in one or only a few standard sizes and when a stool of greater height is required the heiht of the stool may be extended by the use of an adaptor similar in construction to one of the stool bodies. The adaptor bodv will be used end to end with the stool bodv and may be located relatively to it by means for example of a rod extending with its ends received in axial passageways in each of the two bodies. If the slenderness ratio (width to length ratio) of the stool so dictates, the adaptor body may have a larger diameter than that of the adjacent stool body.

When the stool is provided with the upper and lower plates, these plates may be substantially rectangular and along those edges of the plates which, in use will extend along the rear of the beam, each of the plates may be provided with a lip projecting towards the other plate. These lips are useful to locate shuttering formwork, provided for example by a thin sheet of pressed board, at the far side of the wall from which the operator is working. (In this specification the front of the beam is to be considered as at that side of the wall from which the operator works, normally the outer surface of an exterior wall). It will be appreciated that this formwork sheet at the rear of the beam will then extend above the level to which the concrete is cast so that the stiff mortar which is packed into the gap above the top of the cast concrete may be packed against the formwork sheet.A formwork sheet at the front of the beam may be secured in position by for example nailing to wooden inserts in the adjacent edges of the upper and lower plates, or held in position by wire passing around the stools, drawn through holes in the sheet, and tightened up.

In the construction of a beam it is necessary to locate the reinforcement, usually consisting of longitudinal rods interconnected by transverse stirrups, relative to the stools. This may be achieved by passing the longitudinal rods through hollow portions of the stools, or by wiring the rods to the stools.

The grout-filled body of the stool according to the invention is substantially solid and this makes it difficult to locate the reinforcing rods relatively to the stool bodies.

We find that this problem can be overcome by providing the or at least one of the bodies formed by the shell and grout on at least one side with a notch which opens in a part circumferential slot in the shell and which is arranged to accommodate a horizontal reinforcing rod when the stool is used with the cylindrical axis of that body upright. The stool may have two such notches in diammetrically opposite positions.

The notches provide shoulders for at least partially supporting the reinforcing rods prior to casting of the concrete. The stool may be used with the notch or notches extending transverselv of the beam for supporting for example one or both arms of a transverse U-shaped stirrup the ends of which project transversely to the beam beyond the stool body to provide further supports for longitudinal reinforcing rods. Alternatively, if the stool is used with the notch or notches extending longitudinally of the beam, they may accommodate the longitudinal reinforcing rods directly.

A stool of this construction has the advantage, when used with the notch or notches extending longitudinally of the beam, of being substantially solid whilst being capable of accommodating the longitudinal reinforcing rods within its plan area, assuming that the notches have a depth of at least as great as the diameter of the reinforcing rods.

The rods will then be covered by as much concrete as are the stools when a beam is cast incorporating the stools and reinforcement.

The base of each notch is preferably straight and extends across a chord of the cylinder so that if a reinforcing rod having a diameter substantially equal to the maximum depth of the notch at the centre of the notch is used, the outer edge of the rod will be substantially tangential to the cylindrical shell.

If each notch has a width along the axis of the cylindrical shell substantially twice its maximum depth, it can accommodate two reinforcing rods, thereby allowing overlap of reinforcing rods at a stool.

In a typical application, in which the notches are used to support the longitudinal reinforcing rods, diametrically opposite notches will be provided adjacent to each end of the stool so that two layers of reinforcing rods can be supported. The rods may be located in the stool notches by conventional wiring. Alternatively, the pairs of rods located in the notches on the opposite side of the stools may be held in engagement with the notches by some form of restraining means between the pairs of rods at positions between the stools to prevent the rods from moving apart. Such restraining means may consist for example of rectangular U-shaped pieces of wire rod which are placed over the pairs of rods extending between the stools.

When there are upper and lower pairs of rods, a rectangular U-shaped piece of wire rod with short legs may be placed over the lower pair of rods and a piece with longer legs placed over the upper pair of rods so that the legs of the upper piece extend down and overlap the legs of the lower piece. Provided that the wire rod pieces then have sufficient substance, wiring of the legs of the two pieces of wire together then form in situ not only the restraining means for maintaining the longitudinal rods in engagement with the stool notches, but also a stirrup for contributing to the reinforcement within the beam to be cast.

The notches may each be formed by forming a pair of slits in the cylindrical shell, extending partly around the circumference of the shell, and then pressing the strip of material between the slits radially inwardly prior to casting of the concrete filling of the shell. However, this pressing in of the strip of material between the slits tends to distort the shell at the ends of the strip and is somewhat unsatisfactory. Preferably, therefore, the cylindrical shell is formed from a substantially rectangular flat sheet of steel and elongate slots are stamped or otherwise cut in the sheet at positions corresponding to the intended notches, The sheet is then rolled into a cylinder and the edges welded up to form the shell.Pieces of formwork, such as elongate wooden pieces, corresponding in section to the notch to be formed, are then inserted in the slot or slots in the wall of the shell during casting of the filling. A single formwork piece can extend through the notches on one side of the empty shells during casting. This leads to the possibility of filling a number of rows of shells by means of a casting board having at one end one or more horizontal elongate formwork pieces positioned respectively at the heights of the notches in the shells. A row of shells are first brought into engagement with these pieces. One or more separate elongate pieces are then inserted along the notches on the other side of the first row of shells and a second row of shells are brought into engagement with those pieces.This is repeated until a number of rows of shells have been assembled with elongate formwork pieces between them, and finally one or more elongate formwork pieces are inserted into the notches on the exposed side of the last end row of shells. A pressure between the formwork pieces engaging the outer faces of the first and last row of shells maintains the whole array in position with the formwork pieces in all the notches whereupon the cement or other grout can be cast in the shells and left to set prior to dismantling the array.

The ends of the cylindrical shells may introduce a potential weakness, particularly if the notches are formed by stamping out strips of steel. It may therefore be desirable to reinofrce the shell at its ends, for example by one or more metal bars extending between and welded at their ends to end portions of the shell with one or both ends in alignment parallel to the axis of the shell with the notch or opposed notches, respectively. Preferably two of these reinforcing bars are used and their extent axially of the shell may be substantially the full extent between the adjacent notch or notches and the adjacent end of the shell.

A further disadvantage of the existing technique in forming a beam is that during the final packing operation, an irregular gap between the top of the cast beam and the raw cut undersurface of the wall above between the stools has to be filled, and this is a laborious process involving the use of earth dry mortar. However well this mortar is packed, it will not be under the same pressure as the stools so that the wall above is not completely evenly supported along the beam.

In the construction of an in situ cast beam in the wall of a building utilising stools each of the kind previously referred to with an upper and a lower plate, the arrangement is preferably such that at least the upper plates being rectangular and substantially as wide as the beam and the adjacent upper plates of adjacent stools substantially abutting one another, a concrete beam is cast encapsulating at least sufficient of the jacks to support temporarily the load above and up to a height short of the upper plates, and after the concrete is set, the upper plates are pinned up from the concrete beam.

4n important feature of this method is that the upper plates of the stools substantially abut one another along the beam so that the whole of the wall above is evenly supported along the length of the beam and only a small gap of even width between the top of the cast concrete and the under surface of the upper plates has to be packed as a final operation and stiff mortar can be used.

Whereas with the conventional beam inserted in a typical nine inch wall, the stools are usually inserted at about three feet centres, the upper plates of the stool used in the new method would need to be thicker than desirable if there were to be some three feet long, so as to abut one another if inserted at three feet centres. If the upper plates are precast concrete plates some 13 inches thick, they may be used in lengths of about 18 inches. This implies that the stools must be inserted at 18 inch centres if the upper plates are to abut one another.However, by making the adjacent edges of the upper plates of adjacent stools alternately chamferred on their upper and lower surfaces so that they overlap one another, and providing chamfers at both edges of the lower surfaces of the plates of alternate stools, it may be possible to remove the jacks of the alternate stools, leaving their upper plates supported in a manner of a Welsh arch, prior to casting the concrete.

In this way jacks will be used at about 18 inch centres for tightening up the wall but jacks at 3 feet centres will be sufficient to support the wall temporarily while the beam is cast and only half the total number of jacks will need to be sacrificed.

The construction of a beam in accordance with the invention by utilizing jacking stools in accordance with the invention is illustrated in the accompanying drawings, in which: Figure 1 is an axial section through part of one stool; Figure 2 is a section taken on the line 11-11 in Figure 1; Figure 3 is an elevation showing an initial stage in the construction of the beam; Figure 4 is a section taken on the line IV-iV in Figure 3 during a later stage in the construction of the beam; Figure 5 is a diagrammatic elevation showing the completed beam; and Figure 6 is a diagrammatic plan showing an alternative method of supporting reinforcing rods.

The beam is produced by first cutting the horizontal slot 6 in a wall 7, which as shown in Figure 4, may be a cavity wall having inner and outer leaves 7A and 7B, and inserting and tightening up a series of jacking stools 8. A portion of the slot is cut, a stool 8 is inserted and tightene up, and the cycle repeated working successively along the wall.

Each stool is tightened up not only to provide a reaction to support the share of the load above and to transmit this to the wall below, but in many cases also to tighten up looseness which has appeared in the masonry of the wall above as a result of subsidence of the original foundations. When the beam is completed, it will transmit the load of the wall above to new foundations which may be conventional concrete blocks, or piles.

As shown in Figure 3, each stool incorporates a rectangular precast concrete upper plate 9 which bears against the raw cut masonry above, and a rectangular precast concrete lower plate which rests on the masonry below. Dry mortar or a wet mortar impregnated board, or a sheet of polystyrene, may be inserted between the top of each plate 9 and the bottom of each plate 10 and the adjacent raw cut masonry, to provide a good load bearing contact. Each plate 9 and 10 is provided with a projecting lip 11 along its rear edge.

Sandwiched between the plates 9 and 10 is a separate assembly consisting of upper and lower stool bodies 12 and 13 and a screw threaded spindle 14. Each of the bodies 12 and 13 is formed of a circularly cylindrical steel shell 15 made of 18 gauge material filled with concrete grout 16. Dja- metrically opposed part circumferential notches 17 are cut in the steel shell and formed in the concrete filling to receive horizontal reinforcement rods 18 substantially within the plan area of the body. The ends of the shell 15 adjacent to the notches 17 are reinforced with a pair of metal bars 19.

The stool bodies 12 and 13 are each approximately 6 inches in diameter and approximately 5Q inches long.

Cast into the concrete filling 16 of the upper body 12 is a mild steel tube 20 to which is welded a nut 21 forming a screw threaded socket through which the spindle 14 screws. The spindle 14 has welded on a nut 22 forming an effective bolt head for the spindle 14, together with a non-screw threaded projecting end portion 23 which is freely rotatable within a mild steel socket 24 cast in the filling 16 of the lower body 13. The socket 24 is welded to a bottom plate 25 on which the bottom of the end portion 23 of the spindle rests. It will be appreciated that, by resting a spanner on top of the body 13 in engagement with the bolt head 22, and manipulating the spanner, the spindle can be extended out of the nut 21 thus forcing the bodies 12 and 13, and hence the plates 9 and 10, apart to tighten the stool.This arrangement prevents any wandering, when the bolt head is turned, of the kind which might occur if the bolt head directly engaged a stationary surface. A blob of grease is preferably inserted initially in the socket 24 for lubrication purposes.

As shown in Figures 3 and 5, the adjacent edges of adjacent top plates 9 have complementary overlapping chamfers 26.

The effect of this is that, after all the stools have been inserted, alternate ones 8A of the stools 8 can be removed, leaving their top plates 9A supported from the adjacent top plates in the manner of a welsh arch.

This reduces the number of stools which have to be sacrificed in the beam and is acceptable for the short period in which the beam is cast.

A rear shuttering sheet 27 is then inserted behind the remaining stools and retained by the lips 11. Longitudinal reinforcement rods 18 are then inserted in the stool body notches 17 and wired to conventional stirrups 28. A front shuttering is then erected and a mass of concrete 29 cast, encapsulating the remaining stools 8 and reinforcement. The top of the cast concrete is separated from the raw masonry of the wall above between the stools, by a small gap 30. When the concrete has set at least the front shuttering is removed and the gap 30 is packed with earth dry mortar, i.e. mortar containing just sufficient moisture for the mortar to remain compacted when compressed.

Figure 6 shows an alternative way of supporting the longitudinal reinforcing rods 18.

In this case a stool is used with a body 13 having a single notch 17 and the stool is oriented so that the notch extends transversely to the concrete beam 29. A rectanou- lar U-shaped piece of wire rod 31 is fitted with one leg in the notch 17 and the other leg abutting against the opposite side of the stool body 13. If the arms of the piece 31 are rigid, this will be sufficient to hold the piece 31 in a horizontal plane. Alternatively, the stool body 13 could be provided with two diametrically opposite notches 17, as in the previous example, and, provided that the legs of the piece 31 are slightly more closely spaced than are shown in Figure 6, both legs of the piece could then be accommodated in notches 17.The piece 31 projects laterally of the beam beyond the stool body 31 and the longitudinal rods 18 rest on the projecting portions of the piece and may be wired to them. In this case the diameter of the stool body will need to be slightly less than in the earlier example so that the longitudinal rods 18 can be accommodated outside the body 13 and yet still sufficiently within the lateral sides of the concrete beam 29 for the rods to be adequately covered by the concrete.

WHAT WE CLAIM IS:- 1. A stool for use in the construction of an in situ cast beam, the steel comprising two bodies, one of which is provided with a screw threaded socket and the other of which is provided with an abutment; a screw threaded spindle which engages in the socket and extends towards the other body where an end of the spindle engages the abutment; and means enabling rotation of the spindle relatively to the screw threaded socket for extending the spindle relatively to the one body for forcing the two bodies apart; wherein at least one of the two bodies is formed by a substantially circularly cylindrical shell filled with a load bearing grout into which a member incorporating the respective one of the screw threaded socket or abutment is cast.

2. A stool according to claim 1, in which the load bearing grout is concrete.

3. A stool according to claim 1 or claim 2, in which both of the bodies are formed in a similar manner, the one body having a cast in member incorporating the screw threaded socket and the other body having a cast in socket in which the adjacent end of the spindle is freely rotatable and the bottom of which forms the abutment.

4. A stool according to any one of the preceding claims, in which the means enambling rotation of the spindle comprises a nut fixed on the spindle closely adjacent to the other one of the bodies.

5. A stool according to any one of the preceding claims, which also comprises upper and lower rigid load bearing plates between which the stool bodies and spindle are arranged to be mounted so that extension of the spindle forces the two plates apart.

6. A stool according to claim 5, wherein the upper and lower plates are substantially rectangular and along those edges of the plates which, in use, will extend along the rear of the beam, each plate is provided with a lip projecting towards the other plate.

7. A stool according to any one of the preceding claims, in which the or at least one of the bodies formed by the shell and grout is provided on at least one side with a notch which opens in a part circumferential slot in

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (19)

**WARNING** start of CLMS field may overlap end of DESC **. nut 22 forming an effective bolt head for the spindle 14, together with a non-screw threaded projecting end portion 23 which is freely rotatable within a mild steel socket 24 cast in the filling 16 of the lower body 13. The socket 24 is welded to a bottom plate 25 on which the bottom of the end portion 23 of the spindle rests. It will be appreciated that, by resting a spanner on top of the body 13 in engagement with the bolt head 22, and manipulating the spanner, the spindle can be extended out of the nut 21 thus forcing the bodies 12 and 13, and hence the plates 9 and 10, apart to tighten the stool. This arrangement prevents any wandering, when the bolt head is turned, of the kind which might occur if the bolt head directly engaged a stationary surface.A blob of grease is preferably inserted initially in the socket 24 for lubrication purposes. As shown in Figures 3 and 5, the adjacent edges of adjacent top plates 9 have complementary overlapping chamfers 26. The effect of this is that, after all the stools have been inserted, alternate ones 8A of the stools 8 can be removed, leaving their top plates 9A supported from the adjacent top plates in the manner of a welsh arch. This reduces the number of stools which have to be sacrificed in the beam and is acceptable for the short period in which the beam is cast. A rear shuttering sheet 27 is then inserted behind the remaining stools and retained by the lips 11. Longitudinal reinforcement rods 18 are then inserted in the stool body notches 17 and wired to conventional stirrups 28. A front shuttering is then erected and a mass of concrete 29 cast, encapsulating the remaining stools 8 and reinforcement. The top of the cast concrete is separated from the raw masonry of the wall above between the stools, by a small gap 30. When the concrete has set at least the front shuttering is removed and the gap 30 is packed with earth dry mortar, i.e. mortar containing just sufficient moisture for the mortar to remain compacted when compressed. Figure 6 shows an alternative way of supporting the longitudinal reinforcing rods 18. In this case a stool is used with a body 13 having a single notch 17 and the stool is oriented so that the notch extends transversely to the concrete beam 29. A rectanou- lar U-shaped piece of wire rod 31 is fitted with one leg in the notch 17 and the other leg abutting against the opposite side of the stool body 13. If the arms of the piece 31 are rigid, this will be sufficient to hold the piece 31 in a horizontal plane. Alternatively, the stool body 13 could be provided with two diametrically opposite notches 17, as in the previous example, and, provided that the legs of the piece 31 are slightly more closely spaced than are shown in Figure 6, both legs of the piece could then be accommodated in notches 17.The piece 31 projects laterally of the beam beyond the stool body 31 and the longitudinal rods 18 rest on the projecting portions of the piece and may be wired to them. In this case the diameter of the stool body will need to be slightly less than in the earlier example so that the longitudinal rods 18 can be accommodated outside the body 13 and yet still sufficiently within the lateral sides of the concrete beam 29 for the rods to be adequately covered by the concrete. WHAT WE CLAIM IS:-

1. A stool for use in the construction of an in situ cast beam, the steel comprising two bodies, one of which is provided with a screw threaded socket and the other of which is provided with an abutment; a screw threaded spindle which engages in the socket and extends towards the other body where an end of the spindle engages the abutment; and means enabling rotation of the spindle relatively to the screw threaded socket for extending the spindle relatively to the one body for forcing the two bodies apart; wherein at least one of the two bodies is formed by a substantially circularly cylindrical shell filled with a load bearing grout into which a member incorporating the respective one of the screw threaded socket or abutment is cast.

2. A stool according to claim 1, in which the load bearing grout is concrete.

3. A stool according to claim 1 or claim 2, in which both of the bodies are formed in a similar manner, the one body having a cast in member incorporating the screw threaded socket and the other body having a cast in socket in which the adjacent end of the spindle is freely rotatable and the bottom of which forms the abutment.

4. A stool according to any one of the preceding claims, in which the means enambling rotation of the spindle comprises a nut fixed on the spindle closely adjacent to the other one of the bodies.

5. A stool according to any one of the preceding claims, which also comprises upper and lower rigid load bearing plates between which the stool bodies and spindle are arranged to be mounted so that extension of the spindle forces the two plates apart.

6. A stool according to claim 5, wherein the upper and lower plates are substantially rectangular and along those edges of the plates which, in use, will extend along the rear of the beam, each plate is provided with a lip projecting towards the other plate.

7. A stool according to any one of the preceding claims, in which the or at least one of the bodies formed by the shell and grout is provided on at least one side with a notch which opens in a part circumferential slot in

the shell and which is arranged to accommodate a horizontal reinforcing rod when the stool is used with the cylindrical axis of that body upright.

8. A stool according to claim 7, in which the base of the notch is straight and extends across a chord in the cylinder.

9. A stool according to claim 7 or claim 8, in which the notch has a width along the axis of the cylindrical shell substantially twice its maximum depth.

10. A stool according to any one of claims 7 to 10, in which the stool body is provided on each of two diametrically opposite sides with one of the notches.

11. A stool according to claim 1, substantially as described with reference to Figures 1 and 2 of the accompanying drawings.

12. A method of making a stool according to any one of claims 7 to 11, when dependent on any of claims 1 to 4, wherein one or each of the bodies is produced by cutting one or more slots in a rectangular steel sheet at positions corresponding to the intended notch or notches, rolling the sheet into a cylinder and welding up the adjacent edges, inserting form-work in the or each slot to fill the intended notch, and casting grout within the shell to fill the shell and cast in the respective screw threaded socket or abutment, and the or each body being assembled with the other body of the stool and with the spindle and means for rotating the spindle.

13, A method of constructing a beam in a wall of a building, wherein the wall is cut away and there are inserted at the same level in the wall stools according to any one of claims 1 to 11, the spindles of the slots are rotated to tighten the stools in the wall and, with the intervening wall cut away, reinforcing rods are inserted, formwork is erected, and an in situ concrete beam is cast incorporating the reinforcement and the stools.

14. A method according to claim 13, when dependent at least on claim 5, wherein at least the upper plates being rectangular and substantially as wide as the beam and the adjacent upper plates of adjacent stools substantially abutting one another, the concrete beam is cast encapsulating at least suf- ficient of the stools to support temporarily the load above and up to a height short of the upper plates, and after the concrete is set the upper plates are pinned up from the concrete bearm.

15. A method according to claim 14, wherein the adjacent edges of the upper plates of adjacent stools are alternately chamfered on their upper and lower surfaces so that they overlap one another with chamfers on both edges of the lower surfaces of the plates of alternate stools, and the screw jacks of the alternate stools are removed, leaving their upper plates supported in the manner of a Welsh arch, prior to casting the concrete.

16. A method according to claim 14 or claim 15, when dependent at least on claim 6, wherein, prior to casting the concrete beam, a framework sheet is fitted at the rear of the beam resting on the lower plates and against the plate lips.

17. A method according to any one of claims 13 to 16 when dependent on any of claims 7 to 11, in which, prior to casting the concrete beam, reinforcing rods are provided resting in the notch or notches.

18. A method according to claim 13, substantially as described with reference to the accompanying drawings.

19. A beam which has been produced by a method according to any one of claims 13 to 18.