This invention relates to engineering members or structures. In some aspects it relates to civil engineering structures such as bridges or buildings, and in particular to structures which are economical in the use of materials.

In its civil engineering aspect the invention is particularly applicable to bridge construction although many other civil engineering structures such as towers or buildings may also embody the invention.

In other aspects the invention relates to engineering members such as beams which offer improved performance and better use of modern materials.

The presently preferred type of bridge for spanning large distances is the .suspension bridge in which a deck, which may comprise a plurality of linked deck elements, is suspended from longitudinally extending cables suspended from towers. Bridges have also been built for many years using arches which can use materials which are strong in compression and do not require materials which are strong in tension, and a more recent develoment has been the building of beam type bridges which rely on the strength of pre-stressed reinforced concrete.

The conventional bridge and other civil engineering structures do not take full advantage, however, of the materials available, and may well be, for instance, over-engineered, that is to say more massive than need be and less efficient in material use than is now necessary.

So far as present-day engineering members are concerned, the world has for many years been dominated by the use of metals. These have been highly successful, of course. They are relatively cheap, easy to form and so tough that they are strong in tension in all shapes.

Recent developments in materials science, however, have provided both materials which are particularly strong in tension and materials which are strong in compression and which are also lightweight and the present invention provides structures and members which can take full advantage of these qualities.

The present invention aims to improve on conventional structures and members in the above respects, and provides engineering structures and members formed by a number of components urged together so as to form a continuous stable structure. In general, the adjacent components are not actually connected to one another, but are restrained from, or as to, relative movement by reason of being urged together. Usually they are pre-stressed.

Accordingly, the present invention provides an engineering structure or member including a plurality of first components abutting one another and second components for urging the first components towards each other so that the structure is adequately stable.

A structure or member according to the invention will generally consist of a combination of first components forced into compression by second components which are in tension. Thus the structure or member is pre-stressed.

It is the intention that the first components should be selected by material and/or shape to be adapted to withstand compression, and that the second components be selected by material and/or shape to be adapted to withstand tension.

This enables the invention to use the benefits of modern high strength materials more effectively.

The selection of component shape is preferably governed by considerations such as the following. In tension, failure is initiated by a crack or defect which propagates across the material at high speed to break it. Thus a multiplicity of ligaments is likely to be beneficial, so that failure of one is not catastrophic. In compression, failure usually occurs by buckling. There is a lower energy state if the material folds. Slender components such as ligaments, which are best in tension, are worst in compression because they fold easily. Thus, bulky or stocky components are needed to withstand compression. Incidence of cracking does not matter in compression because the cracks close up.

Thus shape or form is as important as choice of material. Glass, for instance, is useful as a tensile material when in fibrous form, or a compressive material when in block form. Other materials such as ceramics are usually of bulky form, and are much better than metals in compression being stronger, often lighter and sometimes cheaper. Other materials are most efficient in fibrous form and again offer advantages over metals when in such

forπt.

The present invention therefore results in part from a realisation of the importance of form in obtaining advantageous engineering structures and members. Combinations of materials and forms of materials, i.e. materials used together to take the better qualities of each, or of their shapes, allow structures and members which are stiffer and stronger than those of metal.

The next aspect of the present invention is the preference for pre-stressed composites. Note that conventional fibre/resin composites are not pre-stressed; the fibres are not stressed and may even be compressed due to contraction on curing of the matrix. Also, resins are weak in compression relative to the best strong materials. Thus, conventional composites are relatively poor in compressive performance, while the tensile performance is not what it might be due to waviness of the fibres. Further, the bonds between resin and fibres in composites are a problem area.

Pre-stressed composites avoid these problems. An advantage of this invention is that there is no need for the first components to be bonded or attached to each other, or for the second components to be bonded or attached to each other, or for any first component to be bonded to any second component. The interaction between first and second components is preferably only by contact pressure.

When the composite is in compression the fibres

can be in tension, and the compressive strength can be that of the compressively strong bulky matrix component. In tension, the tensile component, i.e. the fibres, provides the tensile strength and blocks of compressively strong material can still remain in contact. Also, initial pre-stress leads to good fibre alignment.

Thus, with this aspect of the invention, each component is chosen for its tensile or compressive qualities, as much on the basis of shape and form as on the basis of material. Preferably, the tensile components are internally stressed against the compressive components during manufacture. A typical example is a spine of ceramic blocks, e.g. of alumina, surrounded by an envelope of glass fibres, these components being respectively in compression and tension. No adhesive or binding material is necessary between compressive or tensile components.

Thus, preferably, the first components in structures and members of the invention are of low aspect ratio, being bulky, and the second components are a plurality of elongate ligaments.

In preferred forms there is a line of first components aligned in a row end to end, preferably of ceramic material and preferably, or possibly, hollow. A plurality of elongate second components extend along and/or through the first components to anchor points at ends of the row where they are wound or fixed. The second components are glass or other fibres and the member is

pre-stressed.

Such a construction offers advantages over a construction such as a single rod. It may well be easier to make, as smaller items are needed for the bulky first components. If of ceramic, for instance, such items are significantly easier to make. Also, in compression, in the event of overload and failure there may be only a relatively small local collapse of one component. Further, there is a possibility of slight relative motion between components, e.g. curved engagement surfaces, permitting perhaps some distortion without breakage. So far as tensile performance is concerned, there is an important benefit in that in the event of substantial loading the gap between adjacent first components may open up. With a single member, breakage would occur. This means, too, that the stress-strain response of the member is more predictable and reliable, because no tensile load is taken by the first components, the slope of the response changes when the gaps between first components open. With a continuous member, there would be a discontinuity in the response upon breakage.

Contemplated within the scope of the invention is the use of a tubular envelope which comprises the second components to surround compressively strong first components when these are aligned, and which can be open at each end and, perhaps, anchored to the ground. Alternatively an envelope which is incomplete in cross section might be employed. Also within the scope of .the

invention is the possibility of a taut cabling linking the end components of an aligned row of first components. Cabling in loop form is particularly advantageous as it avoids the need for secure anchoring, but end anchoring is also possible. Cabling can be within or outside the first components, e.g. in grooves on the surfaces of the first components.

Thus when the envelope is provided it can, so to speak squeeze the first components in at least one direction and, in most embodiments, in at least two and usually three dimensions. Desirably it creates an axial and a radial compressive field on the assembly of first components. It can form in effect a skin around an assembly of substantially rigid components, holding them together so that they do not move relative to one another.

The first components may all be in one line, usually a straight line though it might be somewhat curved, or may be in lines positioned side by side. Preferably, the envelope is in the form of a mesh or net, though it could alternatively have a continuous surface over part or all of its extent.

The first components may be all the same or different from one another, and may be, it is contemplated, quite massive. They may be hollow, and may be designed with projecting parts adapted to engage corresponding parts on adjacent such components, in other words they can be essentially frame-like in construction. In general, the only contact between the first components will be a

pressure contact. The invention allows structures to be made without any of the presently conventional connections, fastenings and adhesions between parts, though of course these could still be employed with the invention, for instance during construction or as weatherproofing.

There is no perceived limit to the range of structures in which the present invention could be employed. The invention can be employed in civil engineering structures, where one particular application is in the field of bridges. It can also be used in the construction of individual engineering members, e.g. beams or, for example, robot arms.

A bridge embodying the present invention preferably comprises a line of abutting elements (which in such embodiments are the first components of the preceding discussion) which are urged into abutment with each other by a surrounding mesh of ropes. Conveniently, the mesh consists of a number of parallel, spaced longitudinal cables suspended from towers or supports and a number of spaced hoops of cable suspended from the longitudinal cables. The mesh normally consists of a large number of separate longitudinal and hoop cables. The cables may be bound together at the intersections between longitudinal and hoop cables. Both these features mean that any damage resulting e.g. from breakage in one cable will be localized and accommodated. The longitudinal cables are either linked at their ends to the two end elements and tensioned to squeeze the elements together, or are run around the end

of the elements and joined underneath to provide continuous loops surrounding the elements, the loops being tensioned so as to squeeze the elements together to provide a substantially rigid and stable arrangement. Alternatively, they may possibly be attached to some other fixed point so long as they act to press the elements together. The elements are supported in the cradle formed by the bottoms of the hoop cables suspended from the longitudinal cables, and the compression holds them fixed relative to each other. The elements may themselves provide surfaces, e.g. internal or top surfaces, to act as the bridge deck. Alternatively, a bridge decking can be located on support points in all, or some elements.

It is possible for the hoop cables to be suspended at an angle to the vertical so that they may also exert a longitudinal compressive force on the elements in compression. Adjacent hoop cables may be inclined in opposite directions so that the compressive forces are transmitted evenly to the elements in compression.

Preferably, the towers or supports for the structure are in the form of relatively large diameter curved hoop-like structures with the longitudinal cables of the mesh spaced around and supported by the upper half thereof. The deck of the bridge preferably runs through a gap provided in the lower part of the structure which is supported either directly on a foundation pontoon or on legs extending from the foundation pontoon.

Alternatively the supports could be in the form

of inverted U-shapes, with the deck of the bridge passing between the limbs of the U.

It will be appreciated that the support itself will be in compression, in a plane transverse to the length of the bridge. The support could be a structure of the invention in itself. It could also be under compression in the longitudinal direction of the bridge from the elements which provide the bridge surface.

A typical bridge will consist of several spans, the ends of each span being defined by a support with a separate structure according to the invention for each span, or one extending throughout the bridge length.

With a bridge constructed as just discussed, gravity also plays a part in ensuring the strength and security of the construction. The cables need not act on the upper sides of the elements (i.e. the first components which are normally under compression), because gravity does that. Accordingly, space is available within the structure above such elements, and the structure is opened out to provide such space by the supports. The cabling (i.e. second components) runs along and transversely of the first components, and is arranged so that the tension within it urges the elements together. Direct support for the elements may actually come from the hoop cables only. Longitudinal cables can be provided on all sides of the cross section, including top and bottom, or perhaps only at the top.

In all types of embodiments the cables in the

esh can be made from a material which is strong in tension, e.g. steel, carbon fibre, KEVLAR (Registered Trade mark), polymer or natural fibres or glass fibres and the supports and deck elements are made from a material which is strong in compression, e.g. concrete, glass, ceramics, high strength steel or cast iron.

In bridges, the cross-sectional shape of the mesh will be decided to some extent by the shape of the support and to some extent by the tenεioning and arrangement of cables in the mesh, the mesh may have an approximately circular or other curvilinear shape tubular cross-section. The cross-section will, in fact, vary along the span of the bridge depending on the distance from the support, becoming smaller furt __h___er from the supports so that the net adopts an approximate hour-glass shape.

It is also preferable for the elements of the bridge structure to be arched upwardly so that the arching allows gravity to add to the compressive force in the structure. However, the deck may be flat or concave so that it is lower in the middle.

Each of the elements of bridges of the invention may be solid, for instance for a sub-structure, but more usually each has one or more hollow spaces within them so that the structure is lightweight. Each element may have one concave end and one convex end so that when the deck elements abut each other, relative vertical displacement of the deck elements is limited but the structure may, nevertheless, flex. Preferably, the

curvature of the convex ends is greater than the curvature of the concave ends so that a greater degree of flexing is permitted without the elements disengaging. Alternatively the elements may have both ends slightly convex so that the deck may flex, relative vertical displacement of the elements being hindered by friction between them. The concavity and convexity may be cylindrical, so that there is line contact, or perhaps three dimensional so that there is point contact. These possibilities also apply to other structures and members of the invention.

Conveniently one or more of the compressive elements in the structure is adjustable, e.g. may be lengthened or shortened, or their position relative to each other may be adjusted, e.g. by means of hydraulic or screw jacks between the elements, so that the compressive forces in the rigid part of the structure can be adjusted. This allows the structure to be tightened-up after construction and even to be adapted to changes in its conditions, surroundings, or load during construction.

It will be apparent that any of the rigid components in structures of the invention e.g. the deck elements may embody the invention in their own right by being constructed from a number of stiff components urged into compression with each other to form a member of the invention.

It is also possible for some of the cables in the mesh to be adjustable so that the tension forces in the net may be adjusted.

The invention is also applicaable to other types of structure, e.g. dome or other shaped buildings which consist of a frame of rigid elements forced into abutment with each other by tensioned skin.

The invention will be further described by way of non-limitative example, with reference to the accompanying drawings, in which:-

Figure 1 is a schematic perspective view of a bridge according to the present invention;

Figure 2 is a schematic side view of the bridge of Figure 1;

Figure 3 is a cross-sectional view on the line III-III of Figure 2;

Figure 4 is a cross-sectional view on the line IV-IV of Figure 2;

Figure 5 is a cross-sectional view on the line V-V of Figure 2;

Figure 6 is a schematic view of an alternative part of the structure according to the invention;

Figure 7 is an enlarged cross-sectional view of part of the structure of Figure 1;

Figure 8 is a schematic fragmentary view of the structure of Figure 1;

Figure 9 is a schematic fragmentary view of part of the structure of Figure 1;

Figure 10 shows a further structure according to the present invention;

Figures 11 to 14 show an engineering member of

the invention and the steps in its assembly;

Figure 15 shows two views of the end cap arrangement in such member; and

Figure 16 is a perspective view of an end of the bridge of Figure 1 showing the arrangement of longitudinal cables there.

Figure 1 shows a bridge constructed according to the principles of the present invention and which embodies the present invention. The bridge consists of a taut mesh of ropes or cables 1 which is suspended between supports 3 and supports a deck 5 made from an assembly of individual deck elements 7. The mesh 1 consists of longitudinally extending ropes or cables 11 and other ropes or cables in the form of hoops 13 inclined to the vertical and which are connected to the longitudinal cables at the intersections so that the mesh is rather similar to a large open weave stocking or taut skin. Normally the hoop cables 13 are outside the longitudinal cables 11, so as to hang from them. There is a large number of cables so that the event of breakage in a few cables is not catastrophic to the structure. The ropes or cables in the mesh can be connected at their intersections so that any breakage will be localized. The ropes or cables 11 and 13 are made from a material which is tough and strong in tension such as steel, carbon fibre, KEVLAR or other polymer or natural fibres or glass fibre. At each end of the bridge longitudinal cables may be secured to the end deck elements, under tension and so as to compress such

elementε. Alternatively, the longitudinal cables may be looped around the end deck elements and continue underneath the deck so that the net comsists of longitudinal loops and transverse hoops. Again, the longitudinal cables may be hoops which pass beneath the end deck elements, being connected thereto to compress the elements. The mesh may, alternatively, be attached to a fixed point provided it acts to compress the elements together. The deck elements are thus supported in a cradle formed by the bottoms of the hoop cables 13 and are squeezed together in a longitudinal direction so as to adopt a solid configuration by tension in the longitudinal cables 11.

Figure 16 shows an end of the bridge of Figure 1. Longitudinal cables 11 here converge on approaching a small end support 4. Some hoop cables 13 suspend the elements 7 from the cables 11. Between the end support 4 and the fixed abutment 9 the longitudinal cables extend down to the elements 7 and pass beneath them. The cables 11 therefore may be as loops, being hooked onto the undersides of selected elements 7 in that region. The cables 11 could alternatively be attached to the elements 7 in those regions.

The net 1 does not have a uniform mesh. As can be seen from Figure 9, which is a schematic view (in reality, there are many more cables and the cables are not as thick as those shown) longitudinally extending cables are concentrated over the upper part of the net. The longitudinally extending cables may be formed into loops

with the return part of the loop positioned beneath the deck. Alternatively, as described above, the longitudinally extending cables may be linked to the end deck elements.

By way of example only, the longest diameter of the net at a rib section may be about 200 m and the minimum diameter of the net in the middle of the span may be about 50 m. It is expected that the mesh supporting the bridge may have about 10 hoop cables for each longitudinal cable and the diameter of the hoop cables may be about one fifth that of the longitudinal cables. For example it is contemplated that for a bridge with spans of about 2 Km the net might have several hundred hoop cables about 100 mm in diameter set at a pitch of about 2 m suspended from, say, 80 longitudinal cables about 500 mm diameter.

During construction of the bridge, the net is tensioned so that it exerts a longitudinal compressive force on the deck elements 7; this forces the deck elements together and maintains the structure in a generally stable configuration. As can be seen from Figure 1, the deck passes through a gap in the lower part of the support 3 and it should be understood that the deck is not rigidly coupled to the support 3 since this would interrupt the compressive force exerted in the deck by the net.

Figure 2 shows a bridge which consists of a number of identical spans each of 2 Km. The deck elements typically have a width of 30 to allow them to carry two carriageways of road or a combination of road and railway

and will be about 50 m long.

The tensioning of the mesh and the weight of the deck elements means that the mesh tapers towards the centre of each span. This is also apparent from Figures 3, 4 and 5 in which Figure 3 shows the cross-section along line III-III of Figure 2 near the centre of a span, Figure 4 shows a cross-sectional view along line IV-IV of Figure 2 which is near to a support or rib 3 and Figure 5 is a cross-sectional view along line V-V of Figure 2 through a rib or support. The elements 7, forming the deck, rest in the bottom of the mesh and may not be coupled to the net. This can give the structure a degree of flexibility, thus giving it an inherently good resistance to damage caused by ground movement, wind or impact.

The fact that the entire structure is made from a number of separate elements i.e. a number of longitudinal cables and hoop cables means that any damage caused, for instance by impact, will not run through the whole structure and indeed will not, normally, jeopardise the safety and the security of the structure.

The structure of one of the supports or ribs 3 can be seen clearly in Figure 5. It consists of an upper hoop-like part 15 on which the upper part of the mesh 1 is rested and it has a gap 17 in the lower part through which the deck 5 runs. The hoop part of the support is supported on two legs 19 extending from a foundation pontoon 21. The supports are made for instance of concrete or alternatively some other material which is strong in compression.

The hoop-like part 15 may, alternatively, be made of separate sections forming a ring, the sections being squeezed together by an external tensile mesh, loop or envelope.

It is also contemplated that the supports 15 can be attached directly to the pontoons if it is not necessary to have the bridge high above the surface it is spanning.

Figure 6 shows schematically an alternative form of support in which there are two hoop-like parts 23 (each similar to the part 15 of Figure 5) supporting the net and this double-hoop may be supported by two or more legs extending from the foundation pontoons.

The overall width of the hoop like parts of the supports 3 are wider in upper than lower parts. A

_____ le niscate shape is particularly desirable.

Figure 7 shows a cross-section of one of the deck elements 7. The deck element has an upper horizontal deck part 25 for carrying a road or railway and a lower frame part 27 whose outer surface is configured in a smooth curve on which the mesh 1 bears. For lightness, the deck element is not solid but contains hollow spaces 29. A typical deck element is about 15 m deep and has a cross-sectional area of about 130 m ² and is constructed from a material which is strong in compression, e.g. concrete, glass, ceramics, high strength steel or cast iron or a combination of such materials.

As mentioned above, the deck elements are forced against one another by the tension in the mesh, and perhaps

partly by gravity, because the elements form in effect a spine which is heavy and the abutting ends of the deck elements are configured so that this compression results in a relatively stable structure which, nevertheless, can flex to some extent. As can be seen from Figure 8, this can be achieved by giving the ends of the deck elements a substantially flat central portion 71 and bevelled edges 73. Relative vertical displacements of the deck elements is hindered by friction between the elements.

Alternatively, each element may be provided with one convex and one concave end so that the convex end of one deck element fits into the concave end of the adjacent deck element, thus providing a joint which resists relative vertical displacements of the elements but allows the deck to flex. Preferably, the curvature of the convex end of a deck element is greater than the curvature of the concave element since this will allow a greater relative rotation before the elements disengage. As described above, line contact, or point contact over a reasonable area, could be employed.

It will be appreciated from the drawings that the deck is not flat but is arched over the length of each span. This arching tends to increase the compressive force in the deck which adds to the structural stability.

It will be appreciated that there is a balance of forces in the bridge structure between the compression in the spine and the tension in the net. This results in a structure which is stiff .enough not to vibrate unduly yet

can accommodate, if necessary, substantial displacements without damage. This is important during construction when the structure will tend to be excessively distorted and also means that the structure can respond to wave motion or wind or ship impact without damage.

It is also envisaged that the compression forces in the deck should be adjustable. This can ^" be achieved either by incorporating hydraulic or screw jacks or shims between the elements, or by having special elements whose length may be adjusted. This. llows the bridge to be constructed "loose" and then tightened-up after construction by increasing the distance between the elements of lengthening the special elements. This adjustability will also facilitate replacement of parts of the structure and allows the structure to be adapted to some extent to changes in the surroundings or loads on the structure.

Further, the structure is relatively easy and economical to maintain since parts can be replaced relatively easily.

The present invention is not only applicable to bridge building but is also applicable to other types of civil engineering structure, for instance a dome shaped building could be easily constructed from frame elements forced into abutment with each other by a tensioned skin and such a structure is shown in Figure 10. Other shapes of building could also be constructed in a similar way.

A bridge is an example where, due to the

inter ittent supports, the enveloping means may not contact the abutting components of the structure throughout. In other structures, the envelope may closely engage all round the abutting components.

An engineering member according to the invention and its assembly will now be described with reference to Figures 11 to 15. This is exemplary of members which can be small or alternatively very large or between these extremes.

As shown in Figure 11, a composite beam comprises a straight spine formed by a number of hollow cylindrical ceramic elements 30.

Capping each end of the spine is a steel disc, 31, which houses a screw adjuster, 32. The whole assembly is temporarily tied together by a steel bar, 33, secured by nuts, 34, as shown in Figure 11.

Heads, 35, shown separately in Figure 15 are then screwed right down onto the screw adjusters, 32, with two lugs of each head opposite each other. 2400 tex glass roving, 36, is then secured by an epoxy adhesive in a hole in one of the heads, and wound up and down the outside of the spine, turning 180° around a lug at each end. The glass is wound helically, turning just 1/4 revolution in each transverse of the spine, so that when tensioned it will exert a slight radial pressure on the spine. It is wound by hand and is hand tight at this stage. After the requisite number of passes, the roving is anchored in another hole in the same head. The beam is now at the

εtage shown in Figure 12.

The nuts, 34, and the steel bar, 33, are then removed. Studs, 37, are screwed into the heads which are urged apart for instance using a jack thus tensioning the glass fibres in the roving. Gaps open up between each of the segments 30, which is evidence that the tensile force is wholly in the fibres and not in the spine. See Figure 13.

When an average strain in the glass of approximately 1% is attained jacking is stopped, and maintaining the heads this maximum distance apart the screw adjusters 32 are screwed out of the heads 35 towards each other and the spine until all gaps are closed. Each screw adjuster has a ring of blind radial holes around its perimeter which can be reached by a tommy bar through gaps in the glass winding. The load across the two studs 37 is then removed, and the heads move slightly together, stressing the spine in compression with a force which is a little less than the maximum jacking force. The fibres lose a little of their initial stress due to the contraction of the spine under load.

The result is a stressed composite beam, shown in Figure 14, which is unloaded but which is stressed, the ceramic core compressed by the tensile fibre envelope.

Figure 15 shows the screw adjuster 32, which is in contact with the end one of the ceramic elements, and is screwed into a thread bore in the head 35. It can be seen that the head 35 has two circular profiled lugs one on each

side of a central section having the threaded bore. As shown, the studs 37 used in applying tension to the fibrous members e.g. via a jack are screwed into the other ends of the threaded bores. These may be removed when the member is complete.

Such a member is very strong. Its bending strength is high. Even if the gaps open on bending, this is not catastrophic. Tension and compression, i.e. pre-stressing, could be maintained by wedges or shims, for example, instead of by the screw threaded head arrangement above described. Insertion of such shims or ^' wedges needs to be carefully thought out as they may have to pass through windings of tensile material.

Of course, such a member can take a variety of shapes and be in a variety of sizes. Other arrangements of fibres can be used, e.g. if the compression elements are hollow the fibres could be inside, and out of sight. The fibres might also be in surface grooves. The point is that, in some way, pre-stressing occurs, with components which due to shape and/or material are strong in compression urged together by components strong in tension. The axial forces, then, are equal and opposite.

Finally, although the illustrated embodiments show compression members aligned, they could, alternatively be in other arrangements, e.g. all extending outwards from a centre with the tensile elements surrounding them or in a ring or other formation having a circumference around which the tensile elements can be located.

-24- While structures of the invention have been exemplified by a bridge, they are not restricted thereto. Any building could be made according to the principles of the invention. Thus, in a structure of the invention, some of the first components may be support components adapted to support the structure when built. They could support the structure from below. In an alternative form, the support components could be used to suspend a mesh of cables or ropes which hold abutting first components together. There may be a space within such mesh, usually above the first components as in the case of a bridge. In any member or structure of the invention, some first components can be enlarged relative to others to provide, possibly, some internal space in the region between them. In other forms, the first components can be hollow.