EP0808401A2

EP0808401A2 - Pre-cast building methods and components

Info

Publication number: EP0808401A2
Application number: EP96900655A
Authority: EP
Inventors: Mohamed Omar Abdul Latif Bakoor Jazzar
Original assignee: Don Trust, University of, Trustees of
Current assignee: Don Trust, University of, Trustees of
Priority date: 1995-02-07
Filing date: 1996-01-24
Publication date: 1997-11-26
Also published as: WO1996024735A2; PL321703A1; JPH11501706A; BR9607100A; ZA96573B; WO1996024735A3; AU4455796A

Abstract

Methods of joining pre-cast buidling units (76A, 76B) of U-shaped cross section are disclosed, including earthquake-attenuating joints, and combinations of the units and support pillars for forming large open-plan areas. Methods of incorporating insulation or lightweight foamed material into the wall and horizontal panels of the units are also disclosed.

Description

PRE-CAST BUILDING METHODS AND COMPONENTS

BACKGROUND OF THE INVENTION

FIELD OF THE INVENTION

This invention relates to modular building components of pre-cast concrete construction such as are disclosed in my prior U.S. Patent 5,081,805, PRECAST CONCRETE BUILDING UNITS AND METHOD OF MANUFACTURE THEREOF, issued January 21, 1992. My prior patent discloses a free standing pre-cast concrete building unit of u-shaped cross-section with a generally plain top section or web from opposite edges of which extend a pair of spaced generally parallel flanges or leg sections. The bases of the legs are provided with complementary male and/or female members to provide interlocking shear keys when two identical units are assembled in leg to leg inverted relationship to complete top and bottom halves or sides of a room. The outside top edges of each unit are formed with complementary alternating tabs and voids of rectangular configurations to provide interlocking of the adjoining edges of identical units when placed in diagonally adjacent top to top inverted relationship.

SUMMARY OF THE INVENTION

I have now developed greatly improved methods of connection as well as the fabrication of the unit with greatly increased stability and strength. In particular, first aspects of the present invention provide a joint for installation between building components as defined in claims l or 3. Such joints present a unique way of joining the units in stacked form to provide a structural assembly of the units which can completely withstand minor earthquakes or hurricanes and minimize dislocation or damage to the structure in the case of serious earthquakes. This concept protects the fixtures and contents of the units as well as the occupants and the integrity of the units themselves.

The units are connected together in a manner that will provide attachment structures between the units that yield before the stresses on the unit reach a level that would destroy the integrity of the primary structural components. For example the units may be mounted on rectangular rubber pads which absorb the low dynamic motion caused by earthquakes, the units also being connected by high strength bolts that are designed to yield prior to the failure point of the concrete components.

In this way, there are three stages of protection; shearing of the bolts, relative shifting of the units on their pads and finally rupturing of the pads. After the earthquake, the component units may be realigned and the heavy duty rubber pads replaced as necessary. The bolts inhibiting the pad's motion would also have sheared and have to be replaced.

In a preferred embodiment, plates are bolted to individual components in recesses formed at their corners. The plates have apertures to receive shear bolts between the units and to sandwich a heavy rubber block or pad adhesively secured between the plates. Thus, it is designed so that in the case of lateral shifts of the units the bolts shear, absorbing energy, and then if there is more unexpended energy, the units may further shift laterally with respect to each other on the rubber pads, by deforming the pad. Each step absorbs quake energy and takes away from the stresses that otherwise would be directed to the monolithic walls themselves. This minimizes displacement and destruction of the units. In other words the connections will progressively fail before any failure of the units themselves. An alternative connection between units includes a first crank arrangement which in an earthquake is alignable with the direction of lateral ground movements, and optionally a second crank arrangement carried by the first which converts further lateral ground movements into vertical movement of the unit.

Such an earthquake attenuation system is automatically reloaded or primed for any following quakes. Unless the quake exceeds the limits of the attenuator device, the attenuator components bring the building components back to the original pre-quake positions without the necessity of a crane to restack the components together as in many prior cases. In addition, it is not necessary to repair or change parts each time the quake occurs.

Further aspects of the invention defined in claims 7 and 9 provide lightweight and/or insulated floor and wall panels. The floor slabs and walls are fabricated to include a sandwiched layer of low density (e.g. foamed polystyrene) or insulation material usually from two to six inches (50-100 mm) thick. For a given weight, the units may be fabricated thicker, achieving greater rigidity and strength. Lighter units also reduce the building inertia, in turn reducing earthquake imposed forces.

In one embodiment, the slabs of polystyrene foam have spaced openings of about five inches (13 mm) diameter generally on two foot (0.6 m) centres which are subsequently filled with concrete to form keys tying the two reinforced layers of concrete together.

Appropriate concrete reinforcing bars pass through these openings and are tied into reinforcing grids in each of the lateral concrete slabs.

The openings in the polystyrene are provided with smooth rounded edges to facilitate the flow of concrete through the polystyrene foam and thereby connecting the outer layers of the slab to each other.

The resultant product is a unitary unit with integral insulation with the opposed spaced concrete slabs keyed together with reinforcing pins that are surrounded with up to 3 inches (100 mm) of concrete to form a wall structure.

In another embodiment, insulated, lighter, and more rigid floor and ceiling slabs are obtained by incorporation of spaced, parallel polystyrene cylinders. These may be supported during moulding on cut and bent ends of wire mesh reinforcing material incorporated into the slab above and below the cylinders. In between the cylinders, the solid concrete is in the form of I-beam cross sections. Typically, the polystyrene provides sound deadening to the floor and ceiling portions of the resulting half unit and additionally makes the resulting unit much lighter without any loss of strength. The polystyrene cylinders are suspended in the concrete generally about two inches (50 mm) from the top and bottom surfaces of the slab.

The resultant slab is lighter than prior slabs, the I beam cross sectional configuration strengthens the capability to withstand stress and lessens the size of cranes needed for the erection job. Also, because of both the lightness and stiffness of the slabs one can span longer distances beyond the usual limits.

An additional aspecr of the system provided according to the present invention is the joining of multiple units together or connecting them to other building components by means of extended steel reinforcement in the form of loops facilitating the addition/connection of other concrete elements, advantageously without the appearance of any construction joints, simulating poured in place concrete. This minimizes a major deficiency in pre-cast concrete construction, that of visible connections of units. This aspect of the invention is defined in claim 11.

Still further aspects of the invention are set out in claims 16 and 20. Various preferred features of the invention are set out in the dependent claims, or will be apparent from the following description, in which illustrative embodiments of the various aspects of the invention are described by way of example and with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:-

Fig. 1 is a perspective expanded view showing the components of a wall slab having a polystyrene foam layer sandwiched in between concrete panels;

Fig. 2 is a perspective view of the components showing the concrete being poured;

Fig. 3 is a sectional view along lines 3-3 of Fig. 2;

Fig. 4 is a sectional view along lines 4-4 of Fig. 3;

Fig. 5 is an enlarged sectional view of a portion of the completed unit shown in Figs. 1-4;

Fig. 6 is an expanded sectional view of the components of a floor slab unit incorporating polystyrene cylinders;

Fig. 7 is an assembly of the unit shown in Fig. 6 ready for pouring;

Fig. 8 is an end view of the assembly of Fig. 7; Fig. 9 is a sectional view along lines 9-9 of Fig. 8 and

Fig. 10 is an end view of the completed poured slab;

Fig. 11 shows a view of the U-shaped half room reinforcing bars according to an alternate embodiment;

Fig. 12 shows the half room unit after completion of the pour using the reinforcing rods of Fig. 11;

Fig. 13 shows matched units according to this embodiment;

Fig. 14 shows the top and bottom units in place prior to being joined together;

Fig. 15 is a sectional view along lines 15-15 of Fig. 14 of a form in place for joining the units together;

Fig. 16 is a perspective view, partially in phantom, showing the form used for joining the two units together;

Fig. 17 is a top view of an example showing how units may be joined to form different assemblies;

Fig. 18 is a perspective view of an alternate embodiment of the invention showing a mechanism for joining the corners of the individual units together in stacked form, for absorbing the energy of earthquakes;

Fig. 19 is a different perspective of the units joined together utilizing this embodiment, shown after relative lateral shifting of the units during an earthquake;

Fig. 20 is an enlarged sectional view showing the structure of the components of the connecting unit of Figs. 18 and 19 ;

Fig. 21 is a side view, partially in phantom, showing the connection completed between two joined units;

Fig. 22 shows an elevational view of the units of Fig. 21;

Fig. 23 is a cross-section in elevation of the joined units laterally displaced by an earthquake force;

Fig. 24 is an enlarged perspective view, partially in phantom, showing an alternate embodiment of earthquake energy absorbing components for joining units together;

Fig. 25 is a perspective view, partially in phantom, of details of the device shown in Fig. 24;

Fig. 26 is side view of the device of Fig. 24;

Fig. 27 is a view similar to Fig. 26 with the device aligned by a quake force;

Fig. 28 shows the position of the device with one unit raised up from the lower unit during an earthquake;

Fig. 29 shows it returning to a normal position.

Fig. 30 shows an improved joint for abutting corners of the U-shaped building units;

Fig. 31 is a section taken on line 31-31 of Fig. 30;

Fig. 32 is a section taken on line 32-32 of Fig. 30;

Fig. 33 is a sectional view corresponding to Fig. 31 showing abutted corners of two units; Fig. 34 is a sectional view corresponding to Fig. 32 showing abutted corners of two units;

Fig. 35 shows a unit mounted on a handling sling;

Fig. 36 shows a building unit modified for use with column supports;

Fig. 37 shows such a column support;

fig. 38 is a detail showing a corner of the unit of Fig. 36 assembled with the column support of Fig. 37;

Fig. 39 shows column supports connected by a crossbeam;

Fig. 40 is a perspective view from below of a unit for use with the columns of Fig. 39; and

Fig. 41 is a perspective view from below of two units as in Fig. 36 secured together side-by-side.

ILLUSTRATIVE SPECIFIC EMBODIMENTS

In the accompanying drawing Fig. 1 shows reinforcing rods and a polystyrene insert prior to forming a wall slab. The unit is generally referred to as 2. The outside wall forms at 4 and 6 are spaced, depending upon the thickness of the final wall desired, usually two to three inches (50- 75 mm) from the respective reinforcing bar grids 8 and 10. A four inch (100 mm) slab of polystyrene foam 12 has openings 14 formed therein with the edges 16 thereof rounded off as shown in Figs. 4 and 5 in order to facilitate the flow of liquid concrete as the unit is formed. Reinforcing bars 18 pass through each of the openings 14 and are appropriately tied into the respective reinforcing grids 8 and 10 of the lateral panels as shown at 20 in Figs. 2, 3, and 4. The openings are generally located on two foot (0.6m) centres and are generally about five inches to seven inches (130-180 mm) in diameter.

Fig. 4 shows the cross section of the wall with the forms 4 and 6 in place as the concrete 24 is poured and showing the vertical reinforcing bars 22 crossing the horizontal bars 26 with the bars 18 connecting the grids 8 and 10 through the openings 14 in the polystyrene slab 12 which are now filled with concrete, connecting two sections of concrete together forming the unified wall.

Liquified concrete 24 is poured in as shown in Fig. 3. Fig. 5 shows a cross section of the completed wall with the forms 4 and 6 removed and the two layers 28 and 29 of the concrete connected with concrete fingers 30 extending through the openings 14.

The resulting wall is very strong, rigid and lighter to move because of the foamed polystyrene which also serves as heat and sound insulation for the walls between the units.

Referring to Fig. 6, forms 31 and 32 for a ceiling or floor panel 54 are shown with upper and lower reinforcing bar grids 33 and 35 cut and the resulting bar ends turned inwardly and outwardly as indicated at 40, 42, 44 and 46. The inwardly turned ends such as 40, 46 penetrate into the sections of polystyrene 48, 50 and 52 respectively so as to hold them in place during the concrete pour. Outwardly turned ends such as 42, 44 may optionally be used to position the grids 33, 35 relative to the forms 31, 32. The assembled foam unit is shown ready for pouring in Figs. 7 - 9. Fig. 8 shows an end view of the polystyrene units 48, 50, and 52 in place connected to the reinforcing bar grids 34 and 36 in Fig. 7.

Fig. 9 shows a cross section through lines 9-9 of Fig. 8. After the pour, the same view in Fig. 8 will appear as in Fig. 10 with the completed slab 54. It is noted that polystyrene will serve to both deaden noise, lighten the resulting unit 54, and also that much of the concrete is in the form of parallel I beam units resulting in greater strength for unit weight. Instead of the polystyrene cylinders running transversely as shown in Fig. 8, they could run normal to the plane of the page as shown. In a further alternative, one of the cut reinforcing bar grids could be turned 90° in its own plane, from the position illustrated in Figs. 6 and 7. The cuts in adjacent bars can be staggered. Further uncut bars can be provided in the grid, parallel to and between the polystyrene cylinders.

A reinforcing bar grid 60 for a semi-room unit is shown in Fig. 11, the bars being crisscrossed for wall grids 68 and 70 and base grid 66 and looped at their ends 72 and 74 respectively. After a concrete pour, the loops 72 and 74 all extend from the edges of the base 82 and walls 78 and 80 of the poured unit 76 as shown in Fig. 12 to facilitate joining the units together as indicated in Fig. 13 where two units 76A and 76B are being joined together. Fig. 14 shows a form surrounding abutted wall edges at one side of the units, the loops 72 overlapping within the form as shown for the exposed wall edges. Fig. 15 is a cross-section of the form taken along lines 15-15 of Fig. 14.

Multiple units 76A and 76B can be joined utilizing apertures 86 made by placing PVC cylinders in the form when units 76 are poured. These are utilized for tying the joining forms together as described below.

The two units 76A and 76B are joined by overlapping their looped edges 72 and 74 as shown in Figs. 14 and 15 with the form 90 comprising sides 96 and 98 used to connect the two looped edges together. Bolts are passed through respective holes 97 and 99 in the form walls 96 and 98 and through PVC tubes 86 in the respective sections 76A and 76B for holding the form 90 in place. The ends 100 and 102 of the form 90 are tilted so as to slope downwardly and inwardly as shown in Figs. 13, 15 and 16. The form 90 has movable plates 106 and 107 at the ends to facilitate pouring the concrete. Within the section joined electrical outlets 84 and conduits 85 may be placed (Fig. 13).

The units may be joined in various formats such as shown in Fig. 17 where units 76A and 76B are joined at the section 94 as shown. Various other configurations may readily be accomplished.

Figures 18 through 23 illustrate a mechanism for securing completed units together in structures to minimize or prevent harm to the structural units, their contents, and occupants in earthquakes and hurricanes.

In the example shown an upper unit 120 is joined to a lower unit 124.

The top unit 120 has at its lower corner a recess 122 as shown with a corresponding recess 126 in an upper corner of the lower unit 124. The unit 124 has reinforcing mesh 128 with additional rods 130, 132, and 133. The reinforcing rods 130, 132, and 133 are welded to a plate 162 in wall 124 and corresponding reinforcing bars 130', 132', and 133' in the top unit 120 are welded to a plate 160.

Metallic U shaped members 140 and 142 respectively are bolted to plates 136 and 138 by bolts 134 or the bolts 134 may be sunk directly into the concrete of units 120 and 124. Normally the plates 136 and 138 respectively are welded to plates 160 and 162 respectively. The base 150 of the part 140 has arms 152 and 154 which correspond to parts 152' and 154' in the member 142. The parts 150 and 150' are bolted together by high tension bolts 144 which pass through apertures in the flanges 156, 156' and 158, 158' and nuts 145 as best shown in Figs. 20 and 21.

In between the members 150 and 151' is a heavy duty Neoprene rubber block 146 which is compressed slightly as the bolts 144 are tightened, drawing flanges 156, 156' and 158, 158' towards each other. Fig. 20 is an enlarged perspective view of the unit. Fig. 23 is a view showing it together with the extra reinforcing rods 130, 132, 133, 130', 132,' 133' welded to the base plates 160, 162. In Fig. 23, following a quake which reaches a magnitude severe enough to shear the bolts 144, the units 120 and 124 have shifted laterally with respect to each other. The movement is resisted by deformation of the heavy duty Neoprene rubber pad 146. Quake energy is absorbed in shearing the bolts 144 and deforming the block 146, as well as in sliding friction between the units 120, 124. The integrity of the units 120 and 124 is preserved as the connections are designed to deform and absorb energy at forces below those which would destroy the units 120, 124. To restore the units 120 and 124 after the quake they can be realigned, the bolts 144 replaced and, if necessary, new Neoprene blocks inserted and glued between the respective plates 150 and 151'.

To prevent gross relative movement between adjacent units which is possible if the blocks 146 are ruptured, the units can be interconnected by rigid links or stops providing a suitable degree of lost motion: if a very severe earthquake occurs, the links or stops will prevent vertically stacked units from toppling, perhaps at the expense of some structural damage to the units themselves.

Another earthquake energy absorbing device is shown in Figs. 24 through 29. An upper unit 170 is joined to a lower unit 174 the upper unit 170 corner having a recess 172 and the lower unit 174 corner having a recess 176 to accommodate the device. Reinforcing bars 178, 180 and 182 shown in phantom in the wall section 170 are welded to plate 216 to which the device is mounted. A similar plate 217 is shown on bottom section 174. Depending from the plate 216 is a shaft 218 having a bumper stop 220 mounted thereon and a coil spring 222 secured between bumper 220 and a plate 190 pivotally mounted thereon. The plate 190 has an aperture 192 therein in which a shaft 194 is rigidly secured. At its lower end the shaft 194 is attached to a fixture 196 through which a cross bar 198 is rotatably received.

At either end, the bar 198 is secured in recesses 204 and 206 in vertically oriented wheels 200 and 202 respectively which in turn are rotably mounted on the horizontal ends 212 and 214 respectively of upright pins 208 and 210 which are secured to a plate 211 which is pivotally mounted on a shaft 215 and secured by a nut 213. At its base shaft 215 is welded to the mounting plate 217.

The device serves to initially orient the crank or eccentric formed by plate 190 and shaft 194 in the direction of lateral movement of the quake thereby absorbing energy as it turns, and simultaneously orienting the crossbar 198 transversely of the direction of quake movement. Such initial orientation can be seen by comparing Figs. 26 and 27, wherein the direction of quake movement is normal to the page. When plate 190 and shaft 194 are fully aligned but all the energy is not expended, it results in rotation of the wheels 200 and 202 and up and down movement of the eccentric cross bar 198, in effect, raising the unit 170 repeatedly up and down with respect to unit 174, and absorbing the force of the quake through these motions and the weight of the units rather than through a fracturing of the units themselves. Wheels 200, 202 and cross bar 198 form a second crank.

Building construction units joined by these energy absorbing devices will withstand the shocks of almost any earthquake expected to be encountered. The spring 222 in Fig. 28 is compressed as the shaft 218 is driven downwardly. Quake energy is absorbed by such compression and also by contact of the spring 222 and plate 190 with the bumper stop 220. Frictional or other damping may be provided against movement of plate 190 along shaft 218 and against rotation of plates 190, 211 about shafts 218, 211 respectively. The eccentric cross bar 198 has been rotated to a higher position in Fig. 28 and then downwardly in Fig. 29.

Figs. 30-34 show an improved, high strength joint configuration for use in uniting abutted corners of my U- shaped building units. As shown best in Fig. 30, the floor slab 302 of a unit 304 is connected to a wall slab 306 of the unit 304 by a series of lands 308 extending half way across the thickness of wall slab 306. Between the lands 308 are a series of indentations 310 which extend across the whole thickness of the wall slab 306 to leave small through gaps 312 between the wall and floor slabs. The lands and indentations are produced by incorporating suitable inserts and packing pieces into the moulding form. Reinforcing bars 314 are arranged to run from the floor slab through the lands 308 and into the wall slab 306 as indicated by dotted lines 314' in Fig. 30. Further reinforcing bars 316 are arranged to run from the floor slab 302 out into the indentations, forming exposed loops 318, and back into the wall slab 306. The encased portions of the bars 316 are indicated by dotted lines 316' in Fig. 1.

As shown in Figs. 33 and 34, pairs of units are assembled corner-to-corner, a given unit being inverted with respect to its neighbour, the vertical faces of the lands 318 of neighbouring units being abutted. The indentations 310 of the assembled units thereby co-operate to define void spaces 320, within which the reinforcement loops 318 of the respective units overlap. A locking bar 322 is then threaded through the overlapping loops 318 to form an interlocking reinforcement network. Wet concrete can then be poured and compacted through the uppermost gaps 312 to fill the void spaces 320. The lower gaps 312 can be used to check that the void spaces are being properly filled, after which they are plugged, for example by lengths of timber secured in the angle between the wall and ceiling slabs. When the concrete in the void spaces has set, a very strong unitary structure is obtained, having an effectively continuous tensile reinforcement network formed by the crossed and interlinked bars 316.

For maximum finished joint strength, the indentations 310 should be made to occupy as large a proportion as possible of the total depth d (Fig. 30) of the unit. The total depth of the lands 318 should therefore be minimised, providing just sufficient strength to hold the wall and floor slabs of the unit together during moulding, transportation and final placement. To reinforce the unit during handling, it can be braced by an internal framework 324, Fig. 35 of, for example, steel tubing or timber. A strap 326 may be secured around the unit, between the free ends of the wall slabs 306.

For ease of handling, plastics tubes 328 may be moulded into the unit 304 to form through holes in the wall slabs aligned along an axis which passes approximately through the centre of gravity of the unit. A support bar 330 can be inserted through the tubes 328 with its ends projecting outwardly of the wall slabs 306, to which ends a sling 332 and spacer beam 334 can be attached, for suspending the entire assembly from a crane hook 336. Using this arrangement a typical unit weighing several tonnes can be oriented and guided into place by a single workman, the unit 304 being rotated as necessary about the axis of the crane wire 338 and the axis of the support bar 330.

Figs. 36-41 show a modified form of my building unit for use in structures having vertical support columns 340, for example high-rise buildings or multi-storey car parks. Unit 342 shown in Fig. 36, like the building unitε disclosed in my US Patent No. 5081805, is of generally U-shaped cross-section but has wall slabs 344 of comparatively reduced height, for example about 0.6 m. These act as stiffening flanges for a floor slab 346. At its corners the unit 342 has cut-outs 348 made by appropriate inserts in the forming mould. These cut-outs co-operate with ledges 350 provided on the support columns to support the unit at a desired height. Tongues 352 between the cut-outs at opposite ends of the units project between pairs of the support columns 340, the tongues of adjacent units abutting to form a continuous floor surface. Corners 354 of the unit 346 rest on the ledges 350 to which they are secured, for example by studs 356 and nuts 358.

Fig. 40 shows a unit 360 modified for use with columns interconnected by crossbeams 362, Fig. 39. One end of the projecting tongue 364 is continued to lie flush with the outer edge of wall slab 366. Pairs of such units 360 are arranged side-by-side in mirror image fashion with their walls 366 abutted and their projecting tongues 364 resting on the cross beams 362, once again forming a continuous floor surface.

Fig. 41 shows a pair of units 342 like those of Fig. 36, interconnected for support by only four columns 340 instead of six. Steel trusses 368 are bolted in place between the wall slabs 344 at the ends of each unit. The abutting wall slabs 344 and adjacent ends of the trusses 368 are also bolted together. The cut-outs 370 at the outer corners of the interconnected units accommodate the support columns 340, whereas the central cut-outs 372 are plugged by suitable infill. If desired, three or more units 342 may be interconnected side-by-side in like manner.

In all cases the ledges 350 or other support formations are provided at suitable spacings on the columns 340 (typically 2.5-3.5 m) to give the required floor separations. The space between the depending wall slabs 344 can be used to accommodate building services such as electric cables, pipework and ducting. This space can if necessary be screened off from the room space below by a suspended ceiling. The system of units and columns shown in Figs. 36- 41 can thus be used to create large open-plan areas.

The foregoing developments to my on site prefabricated concrete building units can provide stronger, lighter reinforced, and insulated units that may be readily joined to each other and/or mounted one on top of the other in improved ways, optionally with energy absorbing means to prevent the destruction of the individual units and contents as well as harm to the occupants, thereby absorbing earthquake energy by allowing small amounts of relative motion between the units through means of their joining mechanism.

While the invention has been described by reference to illustrative embodiments, it is not intended that the novel building components and techniques be limited thereby, but that modifications thereof falling within the scope of the following claims are intended to be included.

Claims

AI-t-1^-

1. A joint for installation between building components for attenuation of forces transmitted therebetween, comprising a pair of fixtures each securable to respective adjacent building components, the fixtures being interconnected by a block of resilient material deformable to allow limited relative movement between the fixtures, the fixtures being rigidly secured together by a breakable connection whose breaking strength is less than that of the units.

2. A joint as claimed in claim 1 wherein the fixtures are further interconnected by a substantially inextensible link or co-operating stops, said link or stops allowing limited relative motion between the fixtures.

3. A joint for installation between building components for attenuation of forces transmitted therebetween, comprising a first crank mechanism arranged in use with its axes of rotation substantially vertical, and a pair of fixtures for attachment to respective adjacent building components, whereby relative movement between the building components arising from an applied force results in alignment of the axes of rotation of the first crank mechanism towards a direction substantially parallel to the direction of the applied force.

4. A joint as claimed in claim 3 comprising a second crank mechanism mounted to the first with its axes of rotation substantially horizontal in use and substantially normal to the plane passing through the axes of rotation of the first crank mechanism, whereby further relative movement between the building components is by way of their relative up-and- down movement about the second crank mechanism.

5. A joint as claimed in claim 3 or 4, wherein at least one of the fixtures is resiliently mounted to a respective said crank mechanism.

6. A joint as claimed in any of claims 3-5 wherein damping is provided to resist movement of the crank mechanism(s) .

7. A building wall component comprising two layers of reinforced concrete spaced from each other by a slab of lightweight or insulating material, spaced openings in said lightweight/insulating material with reinforcing tie rods running through said openings and secured to the reinforcement in the respective concrete layers, said tie rods embedded in concrete keys passing through the openings.

8. A building wall component as claimed in Claim 7 wherein edges of the openings in said slab are curved to facilitate the flow of liquid concrete through said openings during the formation of the spaced layers of concrete from a liquid concrete mix.

9. A prefabricated floor or ceiling panel comprising upper and lower layers of concrete, said layers being spaced apart by elongate components of lightweight or insulating material; reinforcement in said upper and lower layers having spaced components with ends thereof turned inwardly of the panel so that during the formation of the panel said ends are embedded in the elongate components to keep them in a predetermined pattern during the pouring of concrete.

10. A floor or ceiling panel as claimed in claim 9 wherein the shape and disposition of the elongate elements results in the formation of I beam concrete cross sections in the panel.

11. A pre-cast building component of substantially U-shaped cross-section, having reinforcing members embedded therein and extending in loops from an edge thereof to facilitate the joining of the component to a like component with a reinforced joint.

12. A method of joining building components as defined in Claim 11 comprising putting edges having said extending loops in a juxtaposed relationship with said looped reinforcing rods in close relationship, placing forms around said juxtaposed edges, pouring concrete over the butting reinforcing rods, and curing the concrete.

13. A component as claimed in claim 11 wherein the loops extend from edges formed by recessed surfaces formed on an external corner of the component.

14. A component as claimed in claim 13 with which a like component can be abutted external corner to external corner, with the loops overlapping, whereby a further reinforcing member can be threaded through the loops to form an interlinked reinforcement network.

15. A component as claimed in claim 11, 13 or 14 comprising a through-slot through which liquid concrete can be poured to surround the loops.

16. A prefabricated building component comprising a floor member and a pair of substantially parallel wall members upstanding from opposite sides of the floor member, the wall members having sling attachment points aligned along an axis passing substantially through the centre of gravity of the unit.

17. A component as claimed in claim 16 wherein the sling attachment points comprise through holes in the wall members.

18. A method of lifting and handling a building component as claimed in claim 16 or 17, comprising the steps of installing a bracing framework between the wall members and attaching a lifting sling to the sling attachment points.

19. A method as claimed in claim 18 wherein the attachment points are through holes in the wall members, comprising the steps of passing a bar through the through holes so that its ends project outwardly of the wall members, and attaching the sling to the projecting bar ends.

20. A pre-cast building component comprising a floor panel having a pair of substantially parallel stiffening flanges depending from opposite edges thereof, corners of the component being adapted to be secured to a vertical support column.

21. A component as claimed in claim 20 comprising a projecting tongue for co-operation with an adjacent such component to form a continuous floor surface extending between a plurality of the support columns.

22. A component as claimed in claim 21 wherein the tongue is adapted to rest upon a beam spanning a pair of the support columns in use.

23. A component as claimed in any of claims 20 to 22 comprising trusses secured between the depending flanges.