EP2604768A1

EP2604768A1 - Lattice girder

Info

Publication number: EP2604768A1
Application number: EP12196631.1A
Authority: EP
Inventors: Hugo Van den Broecke
Original assignee: Intersig NV
Current assignee: Intersig NV
Priority date: 2011-12-13
Filing date: 2012-12-12
Publication date: 2013-06-19

Abstract

The present invention relates to lattice girders, methods for the production thereof and the use thereof. The lattice girder according to the present invention comprises two base joists and a top joist, said joists forming edges of a triangular prism, wherein each of said base joists is joined to said top joist via two or more truss members comprised of a wire which is connected to said base joist in N locations and to said top joist in N-1 or N+1 locations, wherein N is an integer greater than 1.

Description

FIELD OF THE INVENTION

The present invention relates to lattice girders comprising longitudinal wires connected by truss members and methods for the production thereof. The lattice girders can be used as a construction material, for example in concrete structures.

BACKGROUND OF THE INVENTION

Lattice girders are girders where the flanges are connected by a lattice web. The lattice web provides resistance to bending of the girder with a minimal amount of material. Because of this combination of strength and economy, lattice girders are a popular construction material, which is for example used for the manufacture of reinforced concrete.
Various types of lattice girders are known in the art. In many types of lattice girders, the lattice web consists of a single longitudinal bar with a more or less sinusoidal shape, which extends over the total length of the lattice girder. An example thereof is the lattice girder described in patent EP0079892 . However, the use of such longitudinal bars can be impractical during the manufacture of lattice girders. Indeed, the bars are inconvenient to handle due to their length and shape. Furthermore, the design of these girders provides few adjustable parameters, thus limiting the possibilities to produce custom girders which are adapted to the needs of the user.
A further limitation in the production of custom girders lies in the process for manufacturing the girders. Typically, a change in the lattice girder design such as a different wire thickness takes a long changeover time of the production units, in which time the production stops. Therefore, the number of changeovers is typically reduced to a minimum by producing a large stock of lattice girders between each changeover. However, this is not feasible for the production of custom girders as this would require an almost unlimited stock.
Accordingly, there is a need for improved lattice girders and methods for the production thereof.

SUMMARY OF THE INVENTION

The present invention relates in general to lattice girders and methods for the production thereof.
In a first aspect the present invention provides a lattice girder comprising two base joists and a top joist, said joists forming edges of a triangular prism, wherein each of said base joists is joined to said top joist via two or more truss members comprised of a wire which is connected to said base joist in N locations and to said top joist in N-1 or N+1 locations, wherein N is an integer greater than 1. In particular embodiments, N is an integer between 2 and 8.
More particularly, the present invention relates to a lattice girder comprising two base joists and a top joist, said joists forming edges of a triangular prism, wherein each of said base joists is joined to said top joist via two or more truss members comprised of a wire which is connected to said base joist in Nb locations and to said top joist in Nt locations, wherein the sum of Nb and Nt is an integer equal to 5 or more, and wherein Nt is equal to Nb-1 or Nb+1.
In particular embodiments, the truss members form alternatively inverted triangular or trapezoidal spaces along the length of the lattice girder.
In certain embodiments, the neighboring truss members connecting the top joist and one of the base joists are interconnected via a weld on the top joist or base joist.
In particular embodiments, the lattice girder according to the present invention comprises two or more truss members having a different diameter. In certain embodiments, at least one of said joists has a diameter which is different from the diameter of the other joists.
In particular embodiments, the truss members comprise angled portions, forming alternatively inverted equilateral triangle-shaped spaces along its length. In certain embodiments, the truss members comprise alternatively straight and angled portions, wherein said angled portions slope up towards one point along the length of said lattice girder. In certain embodiments, the truss members comprise alternatively straight and angled portions, wherein said angled portions slope down towards one point along the length of said lattice girder.
In a further aspect, the present invention provides a method for manufacturing a (custom) lattice girder as described herein, comprising the steps of:

a) selecting metal wires for manufacturing said joists based on the required characteristics of said lattice girder;
b) selecting or manufacturing four or more truss members based on the required characteristics of said lattice girder;
c) unwinding said metal wires selected in step a) from a role;
d) straightening and cutting said metal wires for manufacturing said joists; and
e) joining said joists with said truss members, thereby obtaining said lattice girder.

In particular embodiments, step e) includes welding the ends and apexes of said truss members to said joists.
In certain embodiments, step b) comprises the steps of:

b') selecting metal wires for manufacturing said truss members
b") unwinding said metal wires selected in step a') from a role; and
b"') cutting and bending said metal wires for manufacturing said truss members.

In a further aspect, the present invention provides the use of a lattice girder as described herein as a construction material.
The lattice girders according to the present invention comprise more than one truss member between the top joist and each base joist. The use of two or more truss members increases the number of adjustable parameters of the girders, which provides the possibility of manufacturing custom girders which are tailored to specific needs of the user. The method of manufacturing according to the present invention allows for a more flexible manufacturing process, which requires less changeover time of the production unit. This eliminates the need of producing a large stock between every changeover, and is therefore ideal for the production of custom girders.

BRIEF DESCRIPTION OF THE DRAWINGS

The following description of the figures of specific embodiments of the invention is merely exemplary in nature and is not intended to limit the present teachings, their application or uses. Throughout the drawings, corresponding reference numerals indicate like or corresponding parts and features.

Figure 1: Side view of lattice girders according to the present invention

DETAILED DESCRIPTION OF THE INVENTION

The present invention will be described with respect to particular embodiments but the invention is not limited thereto but only by the claims. Any reference signs in the claims shall not be construed as limiting the scope thereof.
As used herein, the singular forms "a", "an", and "the" include both singular and plural referents unless the context clearly dictates otherwise.
The terms "comprising", "comprises" and "comprised of" as used herein are synonymous with "including", "includes" or "containing", "contains", and are inclusive or open-ended and do not exclude additional, non-recited members, elements or method steps. The terms "comprising", "comprises" and "comprised of" when referring to recited members, elements or method steps also include embodiments which "consist of" said recited members, elements or method steps.
Furthermore, the terms first, second, third and the like in the description and in the claims, are used for distinguishing between similar elements and not necessarily for describing a sequential or chronological order, unless specified. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that the embodiments of the invention described herein are capable of operation in other sequences than described or illustrated herein.
The term "about" as used herein when referring to a measurable value such as a parameter, an amount, a temporal duration, and the like, is meant to encompass variations of +/-10% or less, preferably +/-5% or less, more preferably +/-1% or less, and still more preferably +/-0.1 % or less of and from the specified value, insofar such variations are appropriate to perform in the disclosed invention. It is to be understood that the value to which the modifier "about" refers is itself also specifically, and preferably, disclosed.
The recitation of numerical ranges by endpoints includes all numbers and fractions subsumed within the respective ranges, as well as the recited endpoints.
All documents cited in the present specification are hereby incorporated by reference in their entirety.
Unless otherwise defined, all terms used in disclosing the invention, including technical and scientific terms, have the meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. By means of further guidance, definitions for the terms used in the description are included to better appreciate the teaching of the present invention. The terms or definitions used herein are provided solely to aid in the understanding of the invention.
Reference throughout this specification to "one embodiment" or "an embodiment" means that a particular feature, structure or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrases "in one embodiment" or "in an embodiment" in various places throughout this specification are not necessarily all referring to the same embodiment, but may. Furthermore, the particular features, structures or characteristics may be combined in any suitable manner, as would be apparent to a person skilled in the art from this disclosure, in one or more embodiments. Furthermore, while some embodiments described herein include some but not other features included in other embodiments, combinations of features of different embodiments are meant to be within the scope of the invention, and form different embodiments, as would be understood by those in the art. For example, in the following claims, any of the claimed embodiments can be used in any combination.
The present invention generally relates to lattice girders that are highly customizable and provide a high degree of flexibility. This is achieved by providing lattice girders wherein the lattice web connecting the base joists of the lattice girder with the top joist no longer consists of a single longitudinal bar which extends over the total length of the lattice girder. The inventors have found that a greater flexibility can be achieved by no longer proving a single lattice web, but a multitude of smaller lattice webs. This allows the lattice girder to be provided with different types of lattice webs on different locations of the lattice girder, thereby providing a great degree of flexibility and also allowing the lattice girder to be optimized for its function. The latter allows the manufacturer to provide a high degree of support in the regions of the girder that are more susceptible for mechanical stresses while other parts of the lattice girder that are less susceptible for mechanical stresses can be provided with a smaller support. This allows a more economical manufacturing of the lattice girder.
In a first aspect, the present invention provides a lattice girder, herein also referred to as "girder". The girder according to the present invention comprises three joists, more particularly two base joists and a top joist. The base joists are herein also referred to as first base joist and second base joist. The three joists of the girder each form a (longitudinal) edge of a triangular prism. The term "triangular prism" as used herein refers to a longitudinal polyhedron, wherein the cross section of said polyhedron, perpendicular to the longitudinal axis of said polyhedron, provides a triangular geometry. In particular embodiments, the longitudinal edges of said polyhedron are parallel. The term "longitudinal polyhedron" typically refers to a polyhedron with an aspect ratio (i.e. the length divided by the height) of at least 2 (two).
Each base joist is joined to the top joist via two or more truss members. The use of two or more truss members instead of a single truss member ensures that the lattice girders are highly customizable and can be made according to specific requirements of the customer.
The truss members ensure that the relative position of the joists is fixed, and that the lattice girder can resist bending. In the lattice girder according to the present invention, each truss member is comprised of a wire which is connected to the base joist in N locations and to the top joist in N-1 or N+1 locations, wherein N is an integer greater than 1. More particularly, N is equal to 2, 3, 4, 5, 6, 7, 8 or more. Consequently, each truss member is comprised of a curved or bent wire. Thus, the truss members typically comprise one or more curved portions. In particular embodiments, the truss members have a zig-zag shape, e.g. a sinusoidal shape or sawtooth pattern.
In particular embodiments the truss members according to the present invention comprise of a wire which is connected to said base joist in Nb locations and to said top joist in Nt locations, wherein the sum of Nb and Nt is an integer equal to 5 or more, and wherein Nt is equal to Nb-1 or Nb+1. More particularly the sum of Nb and Nt is an integer equal to 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16 or 17.
The curved portions of the truss members may form sharp or rounded corners. This may depend on the wire type of which the truss members are comprised. In particular embodiments, the radius of curvature of the curved portions ranges between 0.01 cm and 10 cm, more particularly between 0.2 cm and 5 cm, for example 0.5 cm, 1 cm, 2 cm, 3 cm, 4 cm, 5 cm, 6 cm, 7 cm, 8 cm or 9 cm.
In particular embodiments, the connection between the truss members and the joists are made via the ends and apexes of the truss members. The apexes of the truss members are typically curved. Accordingly, in particular embodiments, the connection between the truss members and the joists are made via the ends and curved portions of the truss members.
The number of truss members connecting the base joists to the top joist may depend on a number parameters such as the length of the lattice girder and the value of N. In particular embodiments, each base joist is joined to the top joist via three, four, five, six, seven, eight, nine, ten or more truss members.
The dimensions of the lattice girder according to the present invention typically depend on the intended use of the girder. The length of the girders depends on the requirements of the customer and typically ranges between 1 and 15 m, such as 1, 3, 5, 7, 9, 11, 13 or 15 m. The distance between the base joists is typically between 50 mm and 120 mm (such as 60, 80, 90, 100 and 110 mm), more particularly between 70 and 95 mm (such as 75 and 85 mm). The height of the girder (i.e. the distance between the top joist and the plane defined by the base joists) is typically between 60 and 400 mm (such as 60, 80, 100, 140, 160, 200, 240, 280, 320, 360 and 400 mm), more particularly between 100 and 200 mm. The angle between the plane defined by the top joist and the first base joist and the plane defined by the top joist and the second base joist is typically below 90°. In particular embodiments, said angle is below 85°, 80°, 75°, 70°, 65° or 60°.
In certain embodiments, each truss member is comprised of a wire which is connected to the base joist in N locations and to the top joist in N+1 locations. In particular embodiments, N is an integer between 2 and 8 (i.e. 2, 3, 4, 5, 7 or 8), more particularly between 2 and 5, most particularly N is 3 or 4. The use of truss members where N is between 2 and 8 ensures that multiple truss members can be used for manufacturing the girder, which increases the number of adjustable parameters and therefore the customizability of the girder to the requirements of the customer. Moreover, truss members where N is 8 or lower are easier to handle during the manufacturing process than truss members where N is higher. In certain embodiments, each truss member is comprised of a wire which is connected to the base joist in 3 locations and to the top joist in 2 locations. An example of such a truss member is a truss member in the shape of the letter "M". In certain embodiments, each truss member is comprised of a wire which is connected to the base joist in 2 locations and to the top joist in 3 locations. An example of such a truss member is a truss member in the shape of the letter "W".
In certain embodiments, each truss member is comprised of a wire which is connected to the base joist in Nb locations and to the top joist in Nt locations, Nt being equal to Nb+1 locations. In particular embodiments, Nb is an integer between 2 and 8 (i.e. 2, 3, 4, 5, 7 or 8), more particularly between 2 and 5, most particularly Nb is 3 or 4. The use of truss members where Nb is between 2 and 8 ensures that multiple truss members can be used for manufacturing the girder, which increases the number of adjustable parameters and therefore the customizability of the girder to the requirements of the customer.
The lattice girders known in the art often comprise one or more triangular units constructed with straight members whose ends are connected at joints referred to as nodes. Such structures are also known as truss structures. External forces and reactions to those forces are considered to act only at the nodes and result in forces in the members which are either tensile or compressive forces. Torques are excluded because the nodes in a truss are treated as revolutes. Truss structures are typically comprised of triangles because of the simplicity and structural stability of such design. Accordingly, in particular embodiments, the truss members form triangular spaces along the length of the lattice girder, more particularly alternatively inverted triangular spaces. However, a similar structural stability can also be obtained using other shapes or combinations of shapes. In particular embodiments, the truss members form shapes along the length of the lattice girder selected from sinusoidal shapes, triangular spaces, trapezoidal spaces, parallelogram-shaped spaces, rectangular spaces and square spaces. The base of the triangular, trapezoidal, parallelogram-shaped, rectangular and/or square spaces typically ranges between 100 and 400 mm (such as 100, 120, 140, 160, 180, 200, 220, 240, 260, 280, 300, 320, 340, 360, 380, and 400 mm), preferably between 150 and 250 mm, for example 200 mm. In particular embodiments, the truss members form trapezoidal spaces along the length of the lattice girder, more particularly alternatively inverted trapezoidal spaces. In certain embodiments, the truss members joining two joists may form sinusoidal, triangular and/or trapezoidal spaces. Truss members forming triangular, trapezoidal and/or sinusoidal spaces provide the most effective support and are easy to handle in the manufacturing process.
Typically, the truss members comprise angled portions. Angled portions are portions of the truss members which are positioned in a direction which is not perpendicular to the joists to which the truss member is connected. Optionally, the truss members may further comprise straight portions. Straight portions are portions of the truss members which are positioned in a direction perpendicular to the joists to which the truss member is connected.
In particular embodiments, the angle between the angled portions and the joists to which the truss member is connected is between 55° and 65°, more particularly about 60°. In further embodiments, the truss members comprise angled portions, forming alternatively inverted equilateral triangle-shaped spaces along its length. The inventors found this to be the most effective and economical structure in most cases. In certain embodiments, the truss members comprise alternatively straight and angled portions, wherein the angled portions slope up towards one point along the length of the lattice girder. In further embodiments, this point is the center of the girder. Such a configuration of straight and angled portions between two joists is known in the art as a Howe truss. In certain situations, this configuration provides an optimized strength of the girder.
In certain embodiments, the truss members comprise alternatively straight and angled portions, wherein the angled portions slope down towards one point along the length of the lattice girder. In further embodiments, this point is the center of the girder. Such a configuration of straight and angled portions between two joists is known in the art as a Pratt truss. In certain cases, this configuration provides an optimized strength of the girder.
As described hereabove, each truss member is comprised of a wire which is connected to a base joist in N locations and to the top joist in N-1 or N+1 locations. In particular embodiments said truss members comprise a wire which is connected to said base joist in Nb locations and to said top joist in Nt locations, wherein the sum of Nb and Nt is an integer equal to 5 or more, and wherein Nt is equal to Nb-1 or Nb+l. In particular embodiments, these connections are obtained via welding. In particular embodiments, the neighbouring truss members connected to the same joists (i.e. the top joist and one of the base joists) may be interconnected, more particularly via a weld. In certain embodiments, the neighbouring truss members are interconnected via a weld on one of the joists. The interconnected truss members may then form a lattice web according to the girders known in the art, with the added advantage that the wire forming the lattice web may have varying and customizable parameters, such as the wire thickness, the shape of the spaces formed by the truss members and the base of said shapes, while maintaining the structural stability of the lattice girder.
Typically, the three joists have a straight shape. However, in particular embodiments, the top joist has a curved shape. More particularly, in certain embodiments, the girder comprises two straight and preferably parallel base joists, and a curved top joist. This results in a lattice girder with a variable height. For example, a girder can be made which is lower at the ends of the girder than in the center. This allows a reduction in the material costs. The design of the girders according to the present invention is particularly useful for the manufacture of such girders, as it allows the use of customized truss members.
In particular embodiments, the truss members between the top joist and the first base joist and the truss members between the top joist and the second base joist are symmetrical. More particularly, the truss members are symmetrical to the bisecting plane of the angle between plane defined by the top joist and the first base joist and the plane defined by the top joist and the second base joist.
In certain embodiments, the truss members between the top joist and the first base joist and the truss members between the top joist and the second base joist are not symmetrical. For example, the truss members may have different shapes, sizes and/or diameters. In particular embodiments, the truss members between the top joist and the first base joist have a different size than the truss members between the top joist and the second base joist, such that the cross-section of the girder, perpendicular to the joists, provides a triangular geometry wherein at least the size of the edges between the top joist corner and each of the base joist corners is unequal. Such an asymmetrical lattice girder enables the use of additional support structures supporting the lattice girder.
The truss members may be located partially or completely on the inside or outside of the triangular prism which is defined by the three joists of the girder. The location of the truss members relative to the prism, and therefore the joists, influences the ratio of compressive and tensile forces applied on the connections between the truss members and the joists. In particular embodiments, some or all connections between the truss members and the top joist are located on the inside of the prism. In certain embodiments, some or all connections between the truss members and the base joists are located on the outside of the prism.
The joists and truss members of the girder are typically made of metal wires. The term "metal wire" as used herein refers to a single, usually cylindrical, string of metal which is used to bear mechanical loads. The metal wire refers to a single, string of metal which may be used for a large number of applications. In fact the metal wire is an important raw material in industry and construction.
The material of the metal wires may be any type of metal or metallic alloy such as, platinum, silver, iron, copper, aluminium, gold, steel, brass or bronze. Optionally, the metal wires may be provided with a coating. Preferably the material of the metal core is steel or iron. When a steel metal core is used, the steel may provided with either low or high carbon content.
The metal wires may be provided with a coating, such as but not limited to metal wires provided with a galvanisation layer, a polymer coating or a metal oxide coating. The metal wires may have any cross-section such as round, square, rectangular, oval or half oval cross-sections. The metal wires forming the joists may be chosen within a diameter range ranging between 3 mm and 45 mm (such as 3, 5, 7, 9, 11, 13, 15, 17, 19, 21, 23, 27, 29, 31, 33, 35, 37, 39, 41 and 43 mm), preferably between 6 and 25 mm, more preferably between 6 mm and 18 mm. The metal wires forming the truss members may be chosen within a diameter range ranging between 2.5 mm and 15 mm (such as 3, 5, 6, 8, 9, 11, 12, 13, and 14 mm), preferably between 3 mm and 10 mm more preferably between 4 and 7 mm. Typically, the diameter of the joists is larger than the diameter of the truss members. In particular embodiments, the diameter of the joists is 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 or 11 mm larger than the diameter of the truss members.
In particular embodiments, the lattice girder comprises two or more truss members having a different diameter. This offers the ability to compensate for differences in expected load in various locations of the girder. This may result in a significant reduction of the amount of material needed for the production of the lattice girder, which is more economical and environmental friendly. Indeed, the use of truss members of different diameters offers the ability to use thick wires only where needed and thinner wires everywhere else. For example, the truss members located near the centre of the girder may have a different diameter than the truss members located near the edges of the girder.
In certain embodiments, the lattice girder comprises two or more joists having a different diameter. This may be done when there are differences in the expected loads of the three joists. For example, the top joist may have a larger diameter than the base joists. Again, this may result in a significant reduction of the amount of material needed for the production of the lattice girder.
As described hereabove, the girder may be designed and manufactured according to the expected loads. Accordingly, in particular embodiments, the lattice girder according to the present invention is a custom girder. In such a custom girders, one or more parameters may be selected such that the girder is optimized for its intended use. These parameters may for example be selected from the diameter of the truss members and/or joists, the number of truss members, the distance between the joists, the shape and length of the truss members, the number of contact points N and N+1 (or N-1), the length of the girder, the material of the metal wires of which the truss members and joists are comprised and the coating of the truss members and/or joists.
In certain embodiments, the base joists are separated and braced by cross bars. Typically, the cross bars are comprised of rods which are positioned and connected perpendicular to the base joists. In particular embodiments, the cross bars are welded to the base joists at the location of the connection between the base joists and the truss members.
In particular embodiments, the lattice girder is further comprises ancillary bars, which offer the ability to provide additional strength to certain regions of the girder. In certain embodiments, at least one joist of the girder is reinforced by one or more ancillary bars, which are positioned parallel with said joist and are joined to said joist. In certain embodiments, the base joists of the girder are provided with one or more of such ancillary bars. Typically, the ancillary bars are shorter than the joists, and are only used to reinforce certain regions of the girder. However, it is also envisaged that one or more ancillary bars have the same length as the joists. The diameter of the ancillary bars is typically smaller than the diameter of the joist to which it is joined. In particular embodiments, the ends of one or more of said ancillary bars are curved over an angle between 60° and 90°. This allows using shorter ancillary bars, which results in a reduced material use.
In a further aspect, the present invention provides a method for manufacturing a lattice girder as described herein. In particular embodiments, the lattice girder is a custom lattice girder. The method for manufacturing according to the present invention comprises the steps of:

In the methods for manufacturing lattice girders currently known in the art, typically five wires are selected: three wires for manufacturing the joists, and two for the truss members. As the individual joists and truss members are impractical to transport, the joists and truss members are typically manufactured in situ. Each of the five members is therefore unwinded from a different role, followed by manufacturing and joining of the joists and truss members, thereby obtaining the girder.
The metal wires selected in step a) may differ from each other. For example, the selected wires may have a different diameter. However, in many cases, at least two of the selected wires are identical. In this case, the identical wires may be unwinded from the same role, in contrast with the methods known in the art. Accordingly, in particular embodiments, the wires for manufacturing at least two joists of the girder are unwinded from the same role. In this case, steps c) and d) may be repeated for each of the identical wires.
This results in a significant reduction of the changeover time of the production unit between the production of different girders. Indeed, with the method according to the present invention, all roles of metal wire connected to the production unit can be different, whereas with the methods known in the art, this depends on the lattice girder's required properties. Moreover, in the methods known in the art, a selection of a different wire typically requires a replacement of a role, during which the production stops. In the method according to the present invention, the selection of a different wire only requires a replacement of a role when that wire is not comprised by the multitude of roles connected to the production unit.
The joists obtained in step d) may be completely straight or (partially) curved, depending on the required characteristics of the joists. Typically, the base joists are straight, whereas the top joist may be curved, as described hereabove.
In particular embodiments, the truss members may be prefabricated. Indeed, in contrast with a single truss member which extends over the entire length of the girder, the truss members used in the present method are typically small; therefore transportation of the truss members to the production unit is not a problem. In the case the truss members are prefabricated, step b) comprises selecting four or more truss members based on the required characteristics of said lattice girder. Additionally or alternatively, some or all truss members may be manufactured in situ. This eliminates the need of keeping a large stock of truss members, and further eliminates the need of transporting the truss members to the production unit. Therefore, the manufacture of the truss members in situ can result in a more efficient, faster, safer and cheaper process. Accordingly, in certain embodiments, step b) comprises the steps of:

The method of manufacturing according to the present invention is also useful for the manufacture of lattice girders comprising one or more ancillary bars, as described hereabove. Accordingly, in particular embodiments, step a) further comprises selecting one or more metal wires for manufacturing said ancillary bars, based on the required characteristics of said lattice girder. These wires are then also unwound from a role, according to step c). Then, step d) involves straightening and cutting said metal wires for manufacturing the joists and the ancillary bars. Finally, step e) involves joining the joists with the ancillary bars and the truss members, thereby obtaining the lattice girder.
In further embodiments, step d) further comprises bending the ends of one or more ancillary members over an angle between 60° and 90°.
In certain embodiments, step e) comprises welding the truss members to the joists. In further embodiments, step e) includes welding the ends and apexes of said truss members to said joists. In particular embodiments, step e) includes welding neighboring truss members between the same joists to each other, preferably via a weld on one of said joists.
In certain embodiments, the method for manufacturing according to the present invention further comprises the step of:

f) coating said lattice girder, for example with a galvanisation layer, a polymer coating or a metal oxide coating.

In a further aspect, the present invention provides the use of a lattice girder as described herein as a construction material. In particular embodiments, the present invention provides the use of a lattice girder as described herein as a rebar, for example in a reinforced concrete structure.
The present invention will be illustrated by the following non-limiting examples.

EXAMPLES

Example 1: Lattice girder with three truss members connecting each of the base joists with the top joist.

Figures 1 A to C illustrate lattice girders according to specific embodiments of the present invention. The lattice girders comprise a top joist (1) and two base joists (2) (only one visible). Each of said base joists (2) is joined to the top joist (1) via three separate truss members (3,4,5). These three truss members may be identical (figure 1A) or truss members (3) and (5) may be identical while truss member (4) may be of a bigger size (figure 1 B) or of a different form (figure 1 C).
According to specific embodiments (figure 1 D-E) the truss members (3) and (5) may comprise angled portions, forming alternatively inverted equilateral triangle-shaped spaces along its length.
The illustrations show that the lattice girders according to the present invention allow a high degree of customizing, providing lattice girders according to specific wishes of the customer.

Claims

A lattice girder comprising two base joists and a top joist, said joists forming edges of a triangular prism, wherein each of said base joists is joined to said top joist via two or more truss members comprised of a wire which is connected to said base joist in Nb locations and to said top joist in Nt locations, wherein the sum of Nb and Nt is an integer equal to 5 or more, and wherein Nt is equal to Nb-1 or Nb+1.
The lattice girder according to claim 1, wherein said truss members form alternatively inverted triangular or trapezoidal spaces along the length of said lattice girder.
The lattice girder according to claim 1 or 2, wherein Nb is an integer between 2 and 8.
The lattice girder according to any one of claims 1 to 3, wherein the neighboring truss members connecting said top joist and one of said base joists are interconnected via a weld on said top joist or base joist.
The lattice girder according to any one of claims 1 to 4, comprising two or more truss members having a different diameter.
The lattice girder according to any one of claims 1 to 5, wherein at least one of said joists has a diameter which is different from the diameter of the other joists.
The lattice girder according to any one of claims 1 to 6, wherein said truss members comprise angled portions, forming alternatively inverted equilateral triangle-shaped spaces along its length.
The lattice girder according to any one of claims 1 to 6, wherein said truss members comprise alternatively straight and angled portions, wherein said angled portions slope up towards one point along the length of said lattice girder.
The lattice girder according to any one of claims 1 to 6, wherein said truss members comprise alternatively straight and angled portions, wherein said angled portions slope down towards one point along the length of said lattice girder.
A method for manufacturing a lattice girder, comprising the steps of:
a) selecting metal wires for manufacturing said joists based on the required characteristics of said lattice girder;

b) selecting or manufacturing four or more truss members based on the required characteristics of said lattice girder;

c) unwinding said metal wires selected in step a) from a role;

d) straightening and cutting said metal wires for manufacturing said joists; and

e) joining said joists with said truss members, thereby obtaining said lattice girder;
wherein said lattice girder comprises two base joists and a top joist, said joists forming edges of a triangular prism, wherein each of said base joists is joined to said top joist via two or more truss members comprised of a wire which is connected to said base joist in Nb locations and to said top joist in Nt locations, wherein the sum of Nb and Nt is an integer equal to 5 or more, and wherein Nt is equal to Nb-1 or Nb+1.
The method according to claim 10, wherein step e) includes welding the ends and apexes of said truss members to said joists.
The method according to claim 10 or 11, wherein step b) comprises the steps of:
b') selecting metal wires for manufacturing said truss members;

b") unwinding said metal wires selected in step a') from a role; and

b"') cutting and bending said metal wires for manufacturing said truss members.
Use of a lattice girder according to any one of claims 1 to 9 as a construction material.