GB2627779A

GB2627779A - A truss structure, assembly and method of manufacture

Info

Publication number: GB2627779A
Application number: GB2303006.7A
Authority: GB
Inventors: Robert Coward Andrew
Original assignee: Net Zero Projects Ltd
Current assignee: Net Zero Projects Ltd
Priority date: 2023-03-01
Filing date: 2023-03-01
Publication date: 2024-09-04
Anticipated expiration: 2043-03-01
Also published as: WO2024180335A1; GB202303006D0; GB2627779B

Abstract

A truss structure which has a main part comprising a compression chord 1 and webs 2 connecting between the compression chord and a tension chord 3, the compression chord having a non-linear centreline and being separated from the tension chord by the webs, and the tension chord crossing the centreline of the compression chord at at least one point, wherein, in use, the compression chord is in compression. Preferably the compression chord and webs are 3-D printed using an additive material, preferably concrete, and the tension chord is a steel cable or bundle of cables. The tension chord may pass through the compression chord and undulate.

Description

A truss structure, assembly and method of manufacture FIELD OF THE INVENTION This invention relates to structural trusses, assemblies and methods of manufacture.

BACKGROUND

Concrete is a common construction material that is generally low in cost. It is strong in compression and weak in tension. When combined with steel reinforcing bars to make reinforced concrete (RC), the composite material can be strong in both tension (for flexural resistance) and compression.

Concrete is rarely used in trusses but is very commonly used in beams. It is rarely used in trusses because trusses typically require tensile strength as well as compressive strength. When a reinforced concrete member is put into pure tension, the concrete must crack to engage the tensile strength of the steel, so there can often be problems with corrosion protection and maintenance. Also, the formwork and placement of reinforcement in concrete trusses is costly and labour intensive.

Trusses can span from columns or walls and support slabs. In countries where the material costs are lower than the labour costs, e.g. Great Britain, the design of RC beams is focused on minimizing labour costs. This typically results in uniform rectangular beam cross-sections which are simple to build but do not necessarily minimize the quantity of material used. An exemplary structure of this nature is shown in Figure 1, which comprises a plurality of beams 100, each of which spans and is supported by an adjacent pair of columns 10.

Steel reinforced concrete trusses are possible and there are examples in bridge construction from the 20'h century. The tension capacity is provided by the steel reinforcement within the concrete. However, they are relatively unusual due to their high cost of manufacture. They are also only applicable to large bridge spans (20m to 50m, say) because of the fact that forming reinforced concrete elements is not practical below a certain size or thickness. In one example, the smallest thickness incorporating two layers of reinforcement is 150mm. Therefore, the web members would be limited to minimum 150mm x 150mm, far in excess of what might be required in a beam for a typical span in a building. These concrete trusses would follow the principles of steel trusses and require the web members to resist tension or compression.

The field of 3D printed concrete can reduce manual labour input and costs by forming the RC beams by using robotics. In principle, any geometry can be created at no additional cost, which means that the cost of a 3D printed beam is directly related to the efficiency of the geometry and therefore the quantity of material. However, for a beam to resist bending, it must still have some tension capacity regardless of the method of manufacture. It is not currently possible to 3D print reinforced concrete because there is no way to print the steel reinforcing bars inside the concrete or during the concrete printing. There are examples of printing layers of concrete and having a person (or a second robot) lay a piece of reinforcing steel in between the layers before the printer head returns to the original location but this is slow, imprecise and interrupts the printing process which can bring its own disadvantages. Therefore, 3D printed concrete remains a technique that is useful for compression-only structures, such as walls, arches and, in some cases, columns.

3D printing with concrete: printing concrete without aggregates is easier because the fluid is easier to control and print and a smaller printer nozzle size can be used (no large particles), yielding a higher print resolution. Concrete without aggregates should be described as mortar. If aggregates are included in the mix, the material is a true concrete but this does place limitations on the size of the printer nozzle and the resolution of the printed element.

It was previously not possible to benefit from a 3D concrete printing process to print a truss structure because the resultant structures were unable to provide a bending structure due to their inability to incorporate the steel reinforcing bars in the concrete structure without interrupting the printing process: the reinforcing bars being necessary to resist the tension loads present in some of the structural elements.

The present invention provides a truss, assembly and method of manufacture according to the accompanying claims.

BRIEF DESCRIPTION OF THE DRAWINGS

In order that the present invention can be more readily understood, embodiments thereof will now be described, by way of example, with reference to and as shown in the accompanying drawings, in which: Figure 1 shows a prior art assembly comprising conventional concrete beams; Figure 2 shows an exemplary assembly comprising a truss arrangement according to the present invention supported by a plurality of columns; Figure 3 shows a truss arrangement according to the present invention; Figure 4A shows a sectional view through A as indicated in Figure 3, Figure 4B shows a sectional view through B as indicated in Figure 3, and Figure 4C shows a sectional view of an alternative arrangement as it would appear through B as indicated in Figure 3; Figure 5 shows a truss arrangement according to the present invention; Figure 6A shows a sectional view through A as indicated in Figure 5, Figure 6B shows a sectional view through B as indicated in Figure 5, and Figure 6C shows a sectional view of an alternative arrangement as it would appear through B as indicated in Figure 5; Figure 7 shows a truss arrangement according to the present invention; Figure 8A shows a sectional view through A as indicated in Figure 7, and Figure 8B shows a sectional view through B as indicated in Figure 7; Figure 9 shows a truss arrangement according to the present invention; Figure 10A shows a sectional view through A as indicated in Figure 9, and Figure 10B shows a sectional view through B as indicated in Figure 9; Figure 11 shows a truss arrangement according to the present invention; Figure 12A shows a sectional view through A as indicated in Figure 11, and Figures 12B and 12C show sectional views through B as indicated in Figure 11 according to two exemplary arrangements; Figure 13 shows a partial view of an exemplary assembly comprising a pair of compression chords supported by a column; Figure 14 shows a partial view of an exemplary assembly comprising a pair of compression members supported by a column; Figure 15 shows a partial view of an assembly an exemplary assembly comprising a truss arrangement supported by a column; Figure 16 shows a partially constructed test piece for explaining a possible method of manufacture.

DESCRIPTION OF EXAMPLES OF THE INVENTION

The present invention relates to truss structures or beams, assemblies incorporating the same, and methods of manufacture.

In broadest terms, there is provided a truss structure, which has a main part comprising a compression chord 1 and webs 2 connecting between the compression chord 1 and a tension chord 3, the compression chord 1 having a non-linear centreline 4 and being separated from the tension chord 3 by the webs 2, and the tension chord 3 crossing the centreline 4 of the compression chord 1 at at least one point, wherein, in use, the compression chord 1 is in compression and the tension chord 3 comprises a tension member. The centreline 4 of the compression chord is preferably curved or faceted.

As mentioned below, where any element/profile of the present disclosure is described as being curved, it may be that it comprises a smooth curve or that it comprises a faceted arrangement.

Figure 2 shows an exemplary assembly that comprises a truss arrangement according to the invention supported by a plurality of columns 10. In the arrangement of Figure 2 there are five columns 10 shown. Each adjacent pair of columns 10 is spanned by a compression chord 1. A tension chord 3, which is common to all five of the compression chords 1, is provided. The tension chord 3 extends for substantially the entire length of the truss structure, as shown. It should be appreciated that the tension chord may comprise a single length or may comprise one or more lengths that are spliced or otherwise joined end to end, such as when there is a particularly long arrangement of spans. The tension chord 3 is fixed at its first end to the compression chord provided in a first end region of the truss structure and at its second end to the compression chord provided at a second end region of the truss structure. The tension chord 3 crosses the centreline of each of the compression chords 1 at least once, as shown.

The arrangement of Figure 2 is not to be taken as limiting in any way. Numerous alternative arrangements will be readily conceived. For example, the number or spacing of the columns may be altered in different arrangements. Moreover, as will be appreciated, the truss structure may be used in different scenarios. For example, it may be used other than to span columns. It could be used to form cantilevered arrangements or otherwise.

Figure 1 shows an equivalent assembly to Figure 2 but is constructed using conventional concrete beams 10 in place of the truss structure of the present invention. A conventional beam design can be modelled for use in determining a suitable form for the truss structure. Factoring in the beam span, and anticipated loads, a bending moment diagram can be produced for the arrangement of Figure 1 (or any other conventional design that it is desired to replace with an arrangement according to the present invention). The bending moment diagram can then be used for designing the truss structure, including the profiles of the compression chords and the tension chord. The truss structure is configured so that the axial force in the tension chord, which preferably comprises a cable (as discussed below), is substantially constant along its length.

The arrangement of Figure 2 effectively defines a continuous beam formed by the plurality of compression chords (arranged end to end) and the continuous tension chord which extends for substantially the entire length of the truss structure.

The centreline 4 of each compression chord 1 is shaped according to the bending moment diagram. The centreline 4 of each compression chord 1 is the effective "line of action" of the compression force.

With further reference to Figure 2, aspects of possible truss structure arrangements will be considered further.

Each compression chord 1 is preferably arranged to curve concavely down in use, as shown. The tension chord 3 preferably curves concavely up in each portion where it extends below the centreline 4 of one of the compression chords 1, and concavely down in each portion where it extends above the centreline 4 of any of the compression chords (having crossed the centreline 4), as clearly seen. By such an arrangement, the tension chord undulates. Notably, the compression chord 1 and/or the tension chord 3 may be faceted, wherein the term curved as used herein is aimed at covering truly curved profiles and profiles that are formed by facets. The geometry of the tension chord is determined to avoid rapid direction changes or kinks. It follows a substantially smooth path. It should be appreciated that if a cable is used for the tension chord 3, then it will become straight between nodes (at the points where the tension chord 3 intersects with the webs 2) when the truss is loaded, i.e. the chords end up being faceted, and the location of the nodes follows a curve.

The tension chord 3 extends beyond at least one end of each of the compression chords 1. As noted, it is fixed to the end (or outer) compression chords 1, this may be such that it does not extend beyond the outer ends of these compression chords 1. For each of the intervening compression chords 1, the tension chord 3 extends beyond both ends of the compression chord 1.

The tension chord 3 crosses the centreline of each of the compression chords at at least one point. The fixing of the tension chord 3 to the end (or outer) compression chords 1 may be such that it does not cross the centreline 4 of these compression chords 1 at its ends. In this case it will cross the centreline 4 of these compression chords 1 only once. For each of the intervening compression chords 1, the tension chord 3 crosses the centreline of the compression chord 1 twice.

The webs 2 are not particularly limited in form. They preferably take the form of posts, as shown, which may be provided at appropriate angles based on loading.

They may alternatively be triangular in form, or otherwise shaped.

The material of the compression chords 1 and/or the webs 2 is preferably an additive material. It is most preferably a 3-D printed additive material. The additive material may comprise a mortar or a concrete (including aggregates). As described with reference to the manufacturing method detailed below, it may be that a profile of the compression chords and/or webs is formed by 3-D printing the additive material and the bulk is pumped/poured instead of being printed (using the same or a different material to the additive and the same equipment i.e. the printer head can be used to pump the concrete into the cavity, or different equipment).

The tension chord 3 may comprise a steel cable or a bundle of steel cables, or otherwise.

As will be exemplarily discussed in greater detail below, with particular reference to Figures 3 to 12C, the tension chord 3 may pass through the compression chord 1 or may pass outside the compression chord 1, in particular in regions where the tension chord 3 crosses the centreline 4 of the compression chords 1. However, the invention is not particularly restricted in this regard.

As will also be exemplarily discussed in greater detail below, with particular reference to Figures 3 to 12C, in order to provide a substantially flat upper support surface, for supporting a floor, roof or otherwise, one or more support elements 5 may be provided above the centrelines 4 of the compression chords 1. Such support elements 5 are also not particularly limited in form and numerous suitable arrangements will be readily appreciated. The invention is not to be restricted in this regard. The support elements may be unitarily formed with the compression chords 1 or may be formed separately.

Consideration will now be given to the arrangements shown in Figures 3 to 15. It must be noted that the features of the different arrangements may be mixed with one another, as will be readily appreciated by those skilled in the art. The arrangements discussed differ from one another primarily in respect of the following aspects: i) The form/path of the tension chord 3.

ii) The form of the support elements 5.

iii) The means of support by and/or attachment to the columns 10.

Any of the different aspects (i), (ii) and (iii) shown in any of the depicted arrangements may be incorporated into any of the other arrangements, and, moreover, the different aspects of the different arrangements may be combined in a single arrangement.

With reference to Figures 3, 4A and 4B, there is shown an arrangement in which the support elements 5, for providing a flat upper surface, are integrally formed with the depicted compression chord 1. An arch-like construction is thereby provided. The support elements have a constant width equal to the width of the compression chord 1 with which they are integrally formed, as is clear from the sectional views through A and B in Figure 3, which are shown in Figures 4A and 4B, respectively.

The webs 2 in any of the arrangements may be provided with shoes, brackets or other convenient means for capturing the tension chord 3. Figure 4A shows the provision of shoes 6. In one possible arrangement, shoes 6 may be provided that have pin inserts which can be located before the concrete has fully hardened. Regardless, the shoes, when provided, sit at the ends of the webs 2 and restrain the tension chord 3 from lateral movement. The shoes 6 preferably have a rounded (half-moon horizontal profile) contact surface so that the cable(s) can pass over the shoes 6 with minimal friction -thus the cables can slide with respect to the shoes. The tension chord 3 is restrained from lateral movement at the ends of the webs 2 by the shoe structures and the chords can slide with respect to the shoes -there is no bending moment between the tension chord 3 and the webs 2.

In some arrangements, the shoes 6 at the connection points on the ends of the webs 2 may be channels or grooves formed as an integral part of the ends of the webs 2 so that the tension chord 3 sits within the ends of the webs 2 distal from the compression chord 1. The tension chord 3 may be encased in a plastic or steel duct which avoids the cable(s) rubbing directly on the webs 2. The cable duct with the tension chord 3 inside may sit in the web channel or groove so no discrete shoe or positive connection is required at the web connection points.

Standard (e.g. 12.5mm, 15.7mm) diameter steel cables can be used, the same as those used for post-tensioning concrete which would be familiar to precast concrete manufacturers. The cables can be coated to provide enhanced fire protection in most circumstances, unless the beams are used in external locations (in which case they would only need corrosion protection). This fire protection is to be determined but could be achieved using a post-applied intumescent paint, or other spray-on coating.

In the case of using a duct to contain the cables, the duct can also provide the necessary fire and corrosion protection. The cables can be individually coated in the factory prior to being bundled during the beam assembly.

The cables could be replaced with a chain (or other element possessing no bending stiffness), solid bars, or steel flats or other suitable high tension materials such as carbon fibre rods and other composite materials such as glass-fibre reinforced plastic, graphite-fibre reinforced polymer and fibre reinforced plastic. Whilst the strength of the material is significant, it is the stiffness (Young's modulus) which is potentially more important so no minimum yield strength is specified. In practice, with post-tension cables, the yield strength will be 1860 MPa, far higher than is actually required in this application.

In the arrangement of Figure 3, the tension cable 3 passes along the outside of the compression chord 1. It is split into two to travel either side of the compression chord 1 (and the column 10) and is received in shoes 6, as seen in Figure 4B, as it passes along the outside of the compression chord 1.

Figure 4C shows an alternative arrangement in which, rather than passing outside the compression chord 1, the tension chord 3 passes through the compression chord 1, which is provided with a suitable opening, as shown. The opening may be formed, for example, by suitable ducting.

With reference to Figures 5 and 6A to 6C, there is shown an alternative arrangement in which the support elements 5 are again integrally formed with the compression chord 1. However, in contrast to the arrangement of Figures 3 and 4A to 4C, the support elements have a reduced width as compared to the remainder of the compression chord 1. A stepped profile is provided, as shown in Figures 6B and 6C.

Note that Figure 6C, like Figure 4A above, provides for the modification of the arrangement of Figures 5 with the tension cable 3 passing through compression chord 1. The reduced width of the support elements 5 offers a material saving over the arrangement of Figure 5.

With reference to Figures 7 and 8A and 8B, there is shown a further alternative arrangement in which the support elements 5 are again integrally formed with the compression chord 1. As with the arrangement of Figure 5, the support elements 5 have a reduced width as compared to the remainder of the compression chord 1. However, there is an additional step introduced to the profile, as seen in Figure 8B.

The profile provides shoulders for supporting the tension chord 3, as shown. In this arrangement, the elevation of the shoulders will vary to support the tension chord 3 along its path as seen in Figure 7.

In the arrangements of each of Figures 3, 5 and 7, the support elements 5 comprise solid upstands/panels, which may have a constant or variable thickness, as discussed.

Figures 9, 10A and 10B show an arrangement in which the form of support elements is varied from the panels of the earlier described arrangements. The support elements 5 comprise a beam 7 that is supported by upper webs 8. The beam 7 and upper webs are preferably integrally formed with one another and with the compression chord 1, preferably by 3-D printing from any desired material as discussed herein. They may otherwise be formed separately. The beam 7 provides an upper flat support surface and is supported on the compression chord 1 by the upper webs 8, which may include reinforcement. Shoes 6 may be provided on the upper webs 8 as shown in Figure 10B.

Figures 11, 12A and 12B show a variation of the arrangement of Figure 9. The support elements 5 comprise a beam 9 that is supported by upper webs 8. However, the beam 9 is separate to the upper webs 8, and may be formed from different materials to the upper webs 8 and/or compression chord 1, such as steel, timber, or otherwise. The arrangement be such that the beam is readily demountable. The beam 9 may take any of a wide range of forms. Figure 12B, by way of example, shows the beam 9 as an inverted T-section, whilst Figure 12C, again by way of example, shows the beam 9 as an upturned U-section. Numerous alternative beam 9 profiled will be readily conceived.

In the arrangements of Figures 9 and 11, the upper webs 8 may vary in length and inclination to suit the geometry.

It should be appreciated that in any of the arrangements described herein including those of any of Figures 2, 3, 5, 7, 9 and 11, the compression chords 1 may be supported by the columns 10 (or alternative support structures), to form joints, in any conventional manner. Adjacent compression chords 1 may meet at a column 10 or compression chords 1 may span a column, or a combination of these arrangements may be included. Moreover, the tension chord 3 may pass around/outside the columns 10 or pass through the columns 10, in a duct or otherwise, or a combination of these arrangements may be included.

Figures 13 to 15 are provided to show some possible exemplary arrangements for supporting compression chords 1 with columns 10.

In Figure 13, the column 10 is effectively continuous through a joint. It should be noted, however, as with any of the other arrangements that the column may be made in multiple parts to be connected together so as to allow transport, for example.

Vertical shear transfer is provided in the arrangement of Figure 13 by shear studs or reinforcement within the connection, in a conventional fashion.

In Figure 14, the column is again effectively continuous through the joint. Vertical shear transfer is provided by a corbel at a base of the connection. Some reinforcement may be provided to ensure tension continuity at the base of the connection and allowing for some amount of load reversal.

In Figure 15, the truss structure is continuous through the joint, wherein the columns start and stop above and below the truss structure, as shown.

As discussed, in each of the exemplary arrangements of Figures 13 to 15, the truss structures may take any of the described forms discussed herein.

The preferred principle method of manufacture for the present invention is, as discussed, by printing with concrete, i.e. 3D printing.

It is noted that most of the tailoring of the structural characteristics of the truss structure are undertaken by manipulating the configuration of the compression chord 1 and webs 2. So, it is extremely convenient and very flexible to be able to print the compression chord 1/webs 2 in whatever configuration is called for. The printer can be programmed to deliver the desired configuration and the program can simply be changed for the next "print run" and a different web configuration delivered. Embodiments of the present invention facilitate an extremely adaptable mechanism for delivering customised or tailored structures. Controlling and delivering the critical configurations by 3D printing to order and providing a tension chord 3 in the form of an easily draped, attached and tensioned tension member provides a technically advantageous method of manufacture.

An exemplary manufacturing process will be discussed with reference to Figure 16.

The compression chord 1 and the webs 2 (and possibly also the support elements 5 of any desired form) may be formed together by printing in appropriately shaped layers a boundary. At the time of printing the boundary, pockets may be formed at the boundary for receiving anchors, ducts or otherwise for guiding or securing the tension chord 3.

The boundary, when complete, creates a formwork.

Once the boundary is printed, the desired structure may be formed by printing or by pouring concrete in a traditional manner. Any reinforcement may be placed prior to pouring, as shown in Figure 16. Any desired detailing may be introduced prior to pouring. Also, any reinforcement for the anchors to be received by the pockets may also be introduced prior to pouring.

The pouring will preferably occur prior to the boundary fully curing so that a unified structure is obtained.

The claimed invention is applicable to materials other than concrete which share similar characteristics in that the material is suitable for additive manufacturing (3D printing) and is useful for compression-only structures but is not suitable to make a bending structure as the material does not perform well in tension without incorporating some form of reinforcement. The bottom chord can be any material, like steel, which is suitable for use in tension. The claimed invention is applicable to concretes with and without the presence of aggregates.

When used in this specification and claims, the terms "comprises" and "comprising" and variations thereof mean that the specified features, steps or integers are included. The terms are not to be interpreted to exclude the presence of other features, steps or components.

The features disclosed in the foregoing description, or the following claims, or the accompanying drawings, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method or process for attaining the disclosed result, as appropriate, may, separately, or in any combination of such features, be utilised for realising the invention in diverse forms thereof. Further, features disclosed in the text and/or drawings of the specification can stand alone or may be combined, in any combination, with one or more other features disclosed in the text and/or drawings of the specification where there is no conflict between those features.

Protection may be sought for any features disclosed in any one or more published documents referenced herein in combination with the present disclosure. Although certain example embodiments of the invention have been described, the scope of the appended claims is not intended to be limited solely to these embodiments. The claims are to be construed literally, purposively, and/or to encompass equivalents.

Claims

CLAIMS: 1. A truss structure, which has a main part comprising a compression chord and webs connecting between the compression chord and a tension chord, the compression chord having a non-linear centreline and being separated from the tension chord by the webs, and the tension chord crossing the centreline of the compression chord at at least one point, wherein, in use, the compression chord is in compression and the tension chord comprises a tension member.
2. A truss structure as claimed in Claim 1, wherein the axial force in the tension chord is substantially constant along its length.
3. The truss structure of Claim 1 or 2, wherein, in use, the centreline of the compression chord is curved or faceted concavely down.
4. The truss structure of any preceding claim, wherein, in use, the tension chord is curved or faceted concavely up in a region below the compression chord.
5. The truss structure of any preceding claim, wherein, in use, the tension chord is curved or faceted concavely down in a region above the compression chord.
6. The truss structure of any preceding claim, wherein the tension chord undulates.
7. The truss structure of any preceding claim, wherein the tension chord extends beyond at least one end of the compression chord.
8. The truss structure of any preceding claim, wherein the tension chord extends beyond both ends of the compression chord.
9. The truss structure of Claim 8, wherein the tension chord crosses the centreline of the compression chord at two points.
10. The truss structure of any preceding claim, wherein the material of the compression chord and/or the webs is an additive material.
11. The truss structure of any preceding claim, wherein the material of the compression chord and/or the webs is a 3-D printed additive material.
12. The truss structure of any preceding claim, wherein the tension chord passes through the compression chord.
13. The truss structure of any of Claims 1 to 9, wherein the tension chord passes outside the compression chord.
14. The truss structure as claimed in any preceding claim, which comprises a beam.
15. The truss structure of Claim 14, which further comprises one or more support elements provided above the centreline of the compression chord, in use, for defining a substantially flat upper support surface of the beam.
16. The truss structure of Claim 15, wherein the support structure is unitarily formed with the compression chord or is formed separately.
17. The truss structure of any preceding claim, which comprises at least two of the compression chords, which are arranged end to end, and the tension chord is shared by the compression chords.
18. The truss structure of Claim 17, wherein one of the compression chords is provided in a first end region of the truss structure and another of the compression chords is provided in a second end region of the truss structure, and a first end of the tension chord is fixed to the compression chord provided in the first end region of the truss structure and a second end of the tension chord is fixed to the other compression chord provided in the second end region of the truss structure.
19. An assembly comprising a truss structure as claimed in any preceding claim and one or more columns for supporting the truss structure.
20. An assembly as claimed in Claim 19, when dependent on Claim 17 or 18, wherein each of the compression chords spans an adjacent pair of the columns.