GB2594037A

GB2594037A - Helical structural framework with torsional integrity

Info

Publication number: GB2594037A
Application number: GB2002553.2A
Authority: GB
Inventors: Silver Peter
Original assignee: Individual
Current assignee: Individual
Priority date: 2020-02-13
Filing date: 2020-02-24
Publication date: 2021-10-20
Anticipated expiration: 2040-02-24
Also published as: GB2594037B; GB202001991D0; GB202002553D0

Abstract

A helical structural framework includes an assembly of at least one pair of linear members to which a torsional force has been applied such that each member has a helical form and is under elastic tension, the torsional force of a first member of the pair being equal to but in the opposite direction to the torsional force of the second member of the pair. The members are locked in position by spacers in at least two places along their length, so that the resultant three-dimensional diagrid has independent structural integrity. The helical members may be connected to at least one circular connection plate which may have recesses to receive the helical members. At least two connecting plates may have different diameters. The framework may form a vertical cylindrical structure or may form a conical structure. The framework may have a single helical pitch.

Description

HELICAL STRUCTURAL FRAMEWORK WITH TORSIONAL INTEGRITY

Field of the Invention

This invention relates to a helical structural framework with torsional integrity. The invention relates in particular to those structural frameworks with a high strength-to-weight ratio and that therefore rely significantly upon their tensile characteristics. More specifically, the invention relates to a structural framework consisting of an elastic, helical diagrid with torsional integrity.

Backqround to the invention There is a continuing need to develop lightweight but strong structures that are quick and easy to assemble. Diagrid structures may be used as frameworks for buildings and roofs, e.g. Lamella domes, because they use less structural material than conventional frames thereby minimising the use of natural resources in artificial constructs. Weight savings are also critical to structural efficiency.

Lightness in structures also arises through the strength-to-weight ratio of materials. There is therefore a significant reliance on the tensile characteristics of structural elements, including the application of elements that are in pure tension, such as with cable-stayed or suspension structures. The most efficient principle for these types of structures is known as "Tensegrity", an assembly of discrete structural elements where the compressive struts do not connect directly but rather are held in place spatially by tensile wire or rope (patented by R. Buckminster Fuller) The present invention seeks to provide a three-dimensional structure based primarily on the principle of stiffening linear elements with a low elastic modulus to form arcs. It has long been established that potential mechanical energy, or "elastic energy", stored in the member after it has been deformed, through for example flexing, bending or buckling causes that member to stiffen.

This principle is established for example through the use of traditional bow and arrows, splining rods (as used in naval architecture), poles used for the sport of pole vaulting, woven structures using for example bamboo, or elastic gridshells.

Following a similar principle, modern, lightweight tents and kites are formed using synthetic materials such as nylon-or carbon-fibre rods that are held in tension (buckling, to form arcs) by pattern-cut fabric to create the required shapes and volumes.

A number of helical structural frameworks are known from the prior art, however the applicant is not aware of any that provide helical elements under elastic tension.

JP2011196118A, for example, describes the act of pre-stressing concrete with steel reinforcing bars. Twisting opposing rebars into a helical cylinder and holding them in place under tension with discs (as shown in Figure 11 in the document) makes it similar geometrically to the invention proposed herein. This application is not however relevant to the fundamental structural principle of the invention, where the helical elements are under elastic tension in opposing directions within the assembly, the elastic energy of the opposing forces cancelling each other out to create a stable framework which has independent structural integrity.

0N202347728U describes a structural member for use in the aerospace industry, and is designed to mimic the material properties of bamboo in "an imitation bamboo truss structure".

Figure 5 in the document shows that the structure is similar geometrically to the invention proposed herein, except that it also incorporates a series of straight, linear elements around the perimeter of the cylinder. This application is not however relevant to the fundamental structural principle of the invention proposed herein where_the helical elements are under elastic tension in opposing directions within the assembly, the elastic energy of the opposing forces cancelling each other out to create a stable framework which has independent structural integrity.

US2157042A discloses a structure that shows two pairs of opposing helixes in a cylindrical formation, the key to the application being the detail of the connections at the point of intersection, allowing continuous lines of force through the helixes. Figure 1 shows that the structure is similar geometrically to the invention proposed herein, however it is not relevant to the fundamental structural principle of the invention proposed herein where_the helical elements are under elastic tension in opposing directions within the assembly, the elastic energy of the opposing forces cancelling each other out to create a stable framework which has independent structural integrity.

Statements of invention

According to a first aspect there is provided a structural framework including an assembly of at least one pair of linear members to which a torsional force has been applied such that each member has a helical form and is under elastic tension, the torsional force of a first member of the pair being equal to but in the opposite direction to the torsional force of the second member of the pair, the members being connected in at least two places along their length.

Preferably the framework has at least two pairs of opposing helical members. Preferably, the linear members take the form of rods.

Preferably the opposing linear members are at 1800 to each other perpendicular to the direction of the helix using spacers.

Preferably the framework has at least two spacers.

Brief Description of the Drawinqs

The invention will now be described by way of example only with reference to the accompanying drawings in which: Figure 1 illustrates the principle of twisting a spline to form a helix configuration for use in a framework constructed in accordance with the invention; Figure 2 illustrates a framework element having two helical splines with opposing twists -clockwise and counter-clockwise Figure 3 illustrates an assembly of helical splines using a circular plate as a spacer; Figure 4 illustrates an assembly of helical splines using rotating joints as a spacer; Figure 5 illustrates a cylindrical structure formed from four helical splines; Figure 6 is a three dimensional schematic of the structure of figure 5; Figure 7 illustrates a cylindrical structure formed from six helical splines; Figure 8 is a three dimensional schematic of the structure of figure 7; Figure 9 illustrates a cylindrical structure formed from eight helical splines; Figure 10 is a three dimensional schematics of the structure of figure 9; Figure 11 illustrates a conical structure formed from helical splines; Figure 12 is a three dimensional schematic of the structure of figure 11; Figure 13 illustrates a randomly shaped structure formed from helical splines; Figure 14 is a three dimensional schematic of the structure of figure 13; Figure 15 illustrates the influence of Young's Modulus on the angle of the helixes in a cylindrical structure; Figure 16 illustrates the influence of Young's Modulus on the angle of the helixes in a 15 conical structure; Figure 17 is an example of the ratio between the diameter and the pitch of the helixes in a cylindrical structure; Figure 18 is an illustration of a structure in the form of a bridge, which is achievable using the present invention; and Figure 19 is an illustration of a further structure in the form of an open-web truss, which is achievable by the present invention.

Detailed description of preferred embodiments

The present invention relates to a three-dimensional structural framework including an assembly of elastically deformed anisotropic (linear) elements.

To this end, a linear element having a low elastic modulus (also known as "Young's Modulus") is placed under a torsional force to twist the element to form a helix. A material that has a low elastic modulus is one which has a low resistance to being deformed elastically.

The structural framework includes an assembly of at least one pair of linear helixes, the torsional force of the first member of the pair being equal to but in the opposite direction to the torsional force of the second member of the pair, the members being connected in at least two places along their length.

As the helical elements are under elastic tension in opposing directions within the assembly, the elastic energy of the opposing forces cancel each other out to create a stable framework in the form of a diagonal grid (a diagrid) which has independent structural integrity.

A variety of structural diagrid frameworks with a very high strength-to-weight ratio can be achieved. These structures may be applied as components such as, without limitation, struts, limbs, legs, columns, beams, trusses, masts, spas, or entire structures such as bridges, towers or domes.

For the purpose of this description the helical structural element under tension is referred to as a "spline".

Figure 1 shows the principle behind applying torsional force to a linear spline 2, for assembly within a structural diagrid framework.

Each spline 2 has an elongate construction and is made from 6mm nylon-fibre rod which will provide a pitch of 1600mm with a helix diameter of 200mm.

Other suitable materials with different dimensions and cross-sectional profiles may be employed providing they are able to undergo elastic deformation in the same way as described. Examples are natural materials such as bamboo, reeds, or young timber saplings (such as hazel or willow, green shoots), and synthetic materials such as carbon-and aramid-fibre or composites (such as those used for windsurf masts or vaulting poles).

Rods (splines), are desirable due to having a circular cross-section allowing omni-directional deformation. The rods may be constructed from bundles or weaves of rods of smaller diameter, similar to the structure of rope.

As can be seen in figure 1, as the spline 2 is placed under torsional force i.e. twisted, the spline 2 naturally buckles to become helical and form a helix configuration 4 A spline 2 that has been subject to elastic deformation through twisting is hereinafter referred to as a "helical spline".

Figure 2 shows a framework having two helical splines 4A, 43. The second additional spline 4B is twisted in the same plane but in the opposite direction to the first helical spline 4A. The helical splines 4 are then secured together at more than one location 6 along their length.

As the helical splines 4 are under elastic tension in opposing directions within the assembly, the elastic energy of the opposing forces cancel each other out to create a stable framework in the form of a diagonal grid (a diagrid) which has structural integrity.

The connections between opposing, left-twisted and right-twisted splines 4 secure the splines 4 in the horizontal plane i.e. perpendicular to the helixes. The connection is through a spacer that is connected to the splines 4 with an open (loose) joint. The spacers resist the compressive forces applied perpendicular to the helixes by torsioning of the splines 4.

One example of a connector is shown in figure 3. The connector takes the form of a circular plate 6. The periphery of the plate 6 is perforated in that the edge of the plate 6 has a plurality of accurate recesses 8 within which each spline 4 is received. In figure 3 there are two pairs of opposing recesses 8 spaced equally around the periphery of the plate 6, as the assembly has four helical splines 4. Clearly, the number of recesses 8 will equal the number of helical splines 4 within the assembly.

A connector that is specific to a cylindrical diagrid is shown in figure 4. Here, the connector takes the form of a rotating joint 10. The joint has four arms 12 extending perpendicularly from a central joint 14 to form a cross shape. The distal end of each arm has a tubular connector 16 through which to receive one of the helical splines 4. The tubular connectors 16 are rotatable about their respective arm 12 to accommodate the desired orientation of individual splines 4 within the assembly.

The number of helixes (helical splines 4) must always be even to allow directionally opposing elastic forces of pairs of splines 4 to cancel themselves out. The number of splines 4 used in the helical diagrid determines that diagrid's overall stiffness and stability. The greater the number of helical splines 4, the greater is the stiffness of the diagrid structure.

Figures 5 to 10 illustrate examples of cylindrical structures that can be achieved through connecting helical splines 4.

The cylindrical structure of figure 5 is formed from four helical splines 4 connected by a number cylindrical plates 6 as previously described. The plates 6 are spaced apart at equal lengths along the length of the structure to provide a cylindrical structure with a single helical pitch.

The cylindrical structure of figure 7 is formed from six helical splines 4, again connected by a (larger) number of spaced apart cylindrical plates 6 to provide a cylindrical structure with a single helical pitch.

Finally, the cylindrical structure of figure 9 is formed from eight helical splines 4, again connected by a (yet larger) number of spaced apart cylindrical plates 6 to provide a cylindrical structure with a single helical pitch.

The plates 6 are located at vertical intervals that are equivalent to a rotation of 360° divided by the number of splines 4. For example, for four splines the plates 6 are located at vertical intervals to a 90° rotation, for six splines the plates 6 are located at vertical intervals equivalent to a 600 rotation and for eight splines the plates 6 are located at vertical intervals equivalent to a 45° rotation.

The circular cross-section of the helical diagrids can vary from a constant extrusion, i.e. a cylinder, to a cone or dome, and include variations in-between such as a hyperboloid.

Figures 11 and 12 show a conical structure that can be achieved, in this case using sixteen helical splines 4. The helical splines 4 are connected at one end (near or at the top of the structure) using a cylindrical plate 6A of a first diameter, and at their other end (near or at the bottom of the structure) using a cylindrical plate 6B of a second, larger diameter.

As can be seen in figures 10 and 11, the assembly and orientations of the individual splines 4 within the structure is carefully selected to ensure that pairs of splines 4 having directionally opposing elastic forces that cancel each other out to provide stability to the overall structure.

The arrows shown in the figures indicate a right or left handed helix.

Figures 13 and 14 show eight helical splines 4 employed in a random structure with a single helical pitch. The splines 4 are connected through equi-spaced cylindrical plates along the length of the structure. The plates 6 have varying diameters. The crosshairs indicate the axis of rotation of individual splines 4.

Figures 15 and 16 show examples of the influence of Young's Modulus on the angle of the helixes in a cylindrical and conical structure respectively.

The ability of the material from which the splines 4 are constructed to resist elastic deformation determines the angle of the helix in relation to any given diameter. The lower the Young's Modulus, the lower is the angle. This in turn determines the ratio of the diameter of the helix to its pitch -the length (or height) of one complete turn measured parallel to the axis.

For the present invention, it is assumed that the degree of applied torque is maximised in relation to the ability of the spline to resist elastic deformation.

Figure 17 illustrates an example of the ratio between the diameter and the pitch of the helixes.

Circular cross-sections permit splines 4 to buckle in any direction (and thus satisfy the helical geometry. The diameter of the spline 4 will determine the overall size of the framework. The greater the diameter of the spline 4, the greater the size potential of the structure.

It may be possible to achieve structures with only one pair of helical splines 4, however structural integrity is unlikely without the addition of a rigid central spar.

A balance of elastic forces can be achieved at a 900 rotation with a full stable helix being achieved at a 3600 rotation.

Claims

CLAIMS1. A helical structural framework including an assembly of at least one pair of linear members to which a torsional force has been applied such that each member has a helical form and is under elastic tension, the torsional force of a the first member of the pair being equal to but in the opposite direction to the torsional force of the second member of the pair, the members being locked in position by spacers in at least two places along their length, so that the framework has independent structural integrity.
2. A framework according to claim 1, comprising at least two or more pairs of linear members.
3. A framework according to claim 2, the linear members take the form of rods.
4. A framework according to any one of claims 1 to 3, wherein each helical member is connected to at least one circular connecting plate.
5. A framework according to any claim 4, wherein the peripheral edge of each circular plate has recesses in which to receive a respective helical member.
6. A framework according to claim 5, having at least two connecting plates and wherein the at least two of the connecting plates have different diameters.
7. A framework according to any preceding claim forming a cylindrical structure in the vertical plane with a single helical pitch.
8. A framework according to any one of claims 1 to 6 forming a conical structure with a single helical pitch.