EP2599929A1

EP2599929A1 - Asymmetrical lattice girder

Info

Publication number: EP2599929A1
Application number: EP11191712.6A
Authority: EP
Inventors: Hugo Van den Broecke
Original assignee: Intersig NV
Current assignee: Intersig NV
Priority date: 2011-12-02
Filing date: 2011-12-02
Publication date: 2013-06-05

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 arranged in parallel relative to each other, each of said joists forming an edge of a triangular prism. The lattice girder further comprises truss members spatially connecting each of said base joists with said top joist. The cross-section of said lattice girder, perpendicular to said 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.

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 .
The size and shape variation of the typical lattice girders used in construction is small. While the size and shape of the wires may vary, the width and height variation is limited, typically providing lattice girders with heights between 100 and 160 mm and widths between 70 and 95 mm. These constraints are required in order to maintain the structural force that the lattice girders provide. Lattice girders are often used in construction as reinforcement material for concrete floors. In order to improve the structural strength the size of the wires is often increased, especially when a high structural strength in the longitudinal direction is required. However, once the concrete floors are completely finished, and the lattice girders are entirely embedded in the concrete floor, the improved the structural strength by the larger wires of the lattice girders no longer perform their function as the concrete now has enough structural strength of its own. Therefore the larger wire size constitutes in a waste of material and only performs its function during the drying of the concrete.
Also, in the cases where an increase in wire diameter does not provide enough structural strength to the concrete, the concrete slabs reinforced with lattice girders are typically used on the first or higher floors of a building where the floors can be supported from underneath.
Accordingly, there is a need for improved lattice girders which are able to provide an improved structural support to concrete floors 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 an asymmetrical lattice girder supporting frame comprising:

two base joists and a top joist arranged in parallel relative to each other, each of said joists forming an edge of a triangular prism, and
truss members spatially connecting each of said base joists with said top joist, wherein the cross-section of said lattice girder, perpendicular to said 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.

More particularly, the present invention relates to a lattice girder wherein the size difference between the edges joining the top joist corner with each of the base joist corners is at least 1.5%, more preferably at least 2.5% and most preferably at least 10%, for example 10%, 15% or 20%. In particularly, the present invention relates to a lattice girder wherein the cross-section of said lattice girder, perpendicular to said joists, provides an acute triangular geometry. More particularly, the present invention relates to a lattice girder wherein the height of the lattice girder ranges between 60 and 200 mm, and the width of the lattice girder ranges between 50 and 120 mm. More particularly, the present invention provides a lattice girder wherein as least one of said joists has a diameter which is different from the diameter of the other joists. More particularly, the present invention relates to a lattice girder wherein said lattice girder further comprises at least one guiding feature for guiding support columns through said lattice girder. More preferably, said guiding feature is a pipe, preferably of a cylindrical shape, attached to said lattice girder passing between said top joist and one of said base joists. More preferably, the central axis of said pipe is perpendicular to the direction of said joists. Typically, the diameter of said guiding feature ranges between 15 and 60 mm, and more preferably between 20 and 30 mm, for example 20, 22, 24, 26, 28 or 30 mm.
In a further embodiment, the present invention relates to a method for manufacturing an asymmetric lattice girder according to the present invention, comprising the steps of:

a) selecting metal wires for manufacturing a top joist and two base joists based on the required characteristics of said lattice girder;
b) optionally unwinding said metal wires selected in step a) from a role;
c) optionally straightening and cutting said metal wires for manufacturing said joists;
d) selecting or manufacturing one or more truss members of a first size and one or more truss members of a second size; and;
e) spatially connecting said first base joist with said top joist through said truss members of a first size and spatially connecting said second base joist with said top joist through said truss members of a second size, thereby obtaining an asymmetrical lattice girder.

More particularly, the present invention relates to a method wherein step e) includes welding the ends and apexes of said truss members to said joists.
In another embodiment, the present invention relates to a lattice girder floor comprising a precast concrete slab with one or more cast in lattice girders according to the present invention.
In another embodiment, the present invention relates to the use of a lattice girder or a lattice girder floor according to the present invention as a construction material. More particularly, to the use of a lattice girder or a lattice girder floor according to the present invention for guiding support columns, and more particularly to the use of a lattice girder or a lattice girder floor according to the present invention for supporting floors.

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 Illustration of a lattice girder
Figure 2 Cross-section illustration of lattice girder according to a specific embodiment of 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 asymmetrical in that the triangular geometry of the cross-section of said lattice girder us such that the size of the edges between the top corner and the side corners are unequal. By providing such an asymmetrical lattice girder the structural force of the lattice girder is reduced, as compared to normal lattice girders having a symmetrical form. While one would normally not consider reducing the structural strength of the lattice girder, the inventors have now found that an asymmetrical lattice girder according to the present invention provides the benefit of enabling the use of additional support structures supporting the lattice girder. When using lattice girders in a concrete floor, the structural strength of the lattice girder mainly plays a role during the initial phase where the concrete has to harden and dry in order to obtain its strength, once this is done the, lattice girder only provides a minor contribution to the strength of the floor structure. By using the asymmetrical lattice girders according to the present invention, additional removable support structures may be provided through the lattice girder, the support structures providing support to the lattice girder during the construction stages where the lattice girder need to offer structural support, but once the concrete is in place and provides structural support, the support structures can be removed. Normal symmetrical lattice girders do not offer enough room to position such support structures. The inventors have now found that an asymmetrical lattice girder, although providing less structural support, can offer enough room to position support structures through the lattice girder. 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 an asymmetrical lattice girder, herein also referred to as "girder". The asymmetrical girder according to the present invention comprises:

The base joists are herein also referred to as first base joist and second base joist. The three joists of the girder are positioned parallel to each other, and each of the joists forms an edge of a triangular prism. Each base joist is joined to the top joist via truss members.
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 and to the top joist. 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.
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 or 5 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 lattice girder according to the present invention is asymmetrical in that the cross-section of said lattice girder, perpendicular to said 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. More particularly, the size difference between the edges joining the top joist corner with each of the base joist corners is at least 1%, 1.5%, 2 %, 2.5%, 3 %, 3.5%, 4 %, 4.5%, 5 %, 7.5% or at least 10%, for example 12.5%, 15%, 17.5% or 20%. The percentage is based on size difference in respect to largest edge. Depending on the dimensions of the lattice girder according to the present invention the size difference percentage may vary. Typically, the size difference between the edges is 1 mm or more. By providing this size difference an asymmetrical lattice girder is obtained wherein one of the sides enables to insert support structures through the lattice girder thereby enabling the lattice girder to be supported when used.
According to a particular embodiment, the present invention relates to asymmetrical lattice girders wherein the cross-section of said lattice girder, perpendicular to said joists, provides an acute triangular geometry. With acute triangular geometry is meant a triangular geometry wherein all interior angles of the triangular geometry measure less than 90°. In particular embodiments the triangular geometry is scalene, meaning that all sides are unequal. More particularly, said geometrical triangle is scalene and acute.
According to a particular embodiment, the present invention relates to asymmetrical lattice girders wherein the height of the lattice girder ranges between 60 and 200 mm, for example 60, 80, 100, 120, 140, 160, 180 or 200 mm, and the width of the lattice girder ranges between 50 and 120 mm, for example 50, 70, 90, 110 or 120 mm. 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 10 m. The distance between the base joists is typically between 50 mm and 120 mm, more particularly between 70 and 95 mm, for example 70, 75, 80, 85, 90 or 95 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 200 mm, more particularly between 100 and 170 mm, for example 110, 120, 130, 140, 150, 160 or 170 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°, for example 85°, 80°, 75°, 70°, 65°, 60°, 55°, 50°, 45°, 40°, 35°, 30° or lower.
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 300 mm, for example 100, 125, 150, 175, 200, 225, 250, 275 or 300 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.
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 a 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 galvanization 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 4 mm and 45 mm (such as 5, 7, 9, 11, 13, 15, 17, 19, 21, 23, 27, 29, 31, 33, 35, 37, 39, 41 and 43 mm), preferably between 6 mm and 18 mm. The metal wires forming the truss members may be chosen within a diameter range ranging between 3 mm and 15 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.
According to a particular embodiment, the present invention relates to asymmetrical lattice girders wherein as least one of said joists has a diameter which is different from the diameter of the other joists. Preferably, the diameter of said top joist is different from the diameter of said base joists.
According to a particular embodiment, the present invention relates to asymmetrical lattice girders wherein said lattice girder further comprises at least one guiding feature for guiding support columns through said lattice girder. Whereas an asymmetrical lattice girder according to the present invention may be provided such that support structures such as support columns are provided through the lattice girder, in particular embodiments the lattice girder may be further provided with guiding features that allow passing through support structures such as support columns. Whereas traditional lattice girders could only be used for the construction of floors on the first floor or above, the latter allows the use of lattice girders for the construction of ground floors where the room underneath is not or difficult to access. As support structures such as support beams have to be removed when the floor is structurally stable, normal lattice girders could not be used when the area underneath the floor was not accessible. The lattice girders according to the present invention allow the introduction and removal of support structures for the lattice girders at all times during the construction process.
According to a particular embodiment, the present invention relates to asymmetrical lattice girders wherein said guiding feature is a pipe, preferably of a cylindrical shape, attached to said lattice girder passing between said top joist and one of said base joists. Other shapes of the guiding feature can also be envisaged, including square or rectangular shaped guiding features. The pipe as used herein can be any shape considered by a skilled person, including, but not limited to cylindrical, oval, square, rectangular, etc.
According to a particular embodiment, the present invention relates to asymmetrical lattice girders wherein the central axis of said pipe is perpendicular to the direction of said joists.
According to a particular embodiment, the present invention relates to asymmetrical lattice girders wherein the diameter of said guiding feature ranges between 15 and 60 mm (such as 15, 20, 25, 30, 35, 45, 50, 55 or 60 mm), and more preferably between 20 and 30 mm.
In a further aspect, the present invention provides a method for manufacturing an asymmetrical lattice girder as described herein. 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. 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 b) and c) may be repeated for each of the identical wires.
According to a particular embodiment, the present invention relates to a method wherein step e) includes welding the ends and apexes of said truss members to said joists.
In a further aspect, the present invention provides a lattice girder floor comprising a precast concrete slab with one or more cast in lattice girders according to the present invention. Lattice girder floors typically comprise a thin reinforced precast concrete slab and one or more lattice girders wherein the base joists are embedded into the concrete slab. These structures are most frequently used reinforced floor type is used for all applications in residential and commercial construction. The fundamental benefits are amongst other things a high-quality product at a reasonable price, extreme dimensioning versatility and rapid on site installation. In a particular embodiment said lattice girder floor is further provided with a guiding feature, such as for instance a hollow pipe, passing through the lattice girder and the concrete slab thereby forming a hole through the concrete slab and allowing support structures to be guided through the lattice girder floor structure.
In a further aspect, the present invention provides in the use of a lattice girder or a lattice girder floor according to the present invention as a construction material more particularly the use for guiding support columns and most particularly the use for supporting floors.
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.

EXAMPLE

Figures 1 and 2 illustrate lattice girders according to specific embodiments of the present invention. The lattice girders typically comprise two base joists (1,2) and a top joist (3) arranged in parallel relative to each other and truss members (4,5) spatially connecting each of said base joists (1,2) with said top joist (3). The cross-section view of the lattice girder is provided in figure 2, clearly illustrating the asymmetrical character of the lattice girder wherein the triangular geometry provides that the size of the edges between the top joist corner and each of the base joist corners are unequal. It can be seen that the distance between the top joist (3) and base joist (2), bridged by truss member (5), is larger compared to the distance between the top joist (3) and base joist (1), bridged by truss member (4), thereby proving the asymmetrical lattice girder according to the present invention.

Claims

An asymmetrical lattice girder supporting frame comprising:
- two base joists and a top joist arranged in parallel relative to each other, each of said joists forming an edge of a triangular prism, and

- truss members spatially connecting each of said base joists with said top joist, wherein the cross-section of said lattice girder, perpendicular to said 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.
The lattice girder according to claim 1, wherein the size difference between the edges joining the top joist corner with each of the base joist corners is at least 1.5%.
The lattice girder according to claim 1 or 2, wherein the cross-section of said lattice girder, perpendicular to said joists, provides an acute triangular geometry.
The lattice girder according to any one of claims 1 to 3, wherein the height of the lattice girder ranges between 60 and 200 mm, and the width of the lattice girder ranges between 50 and 120 mm.
The lattice girder according to any one of claims 1 to 4, 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 5, wherein said lattice girder further comprises at least one guiding feature for guiding support columns through said lattice girder.
The lattice girder according to any one of claims 1 to 6, wherein said guiding feature is a pipe attached to said lattice girder passing between said top joist and one of said base joists.
The lattice girder according to claim 7, wherein the central axis of said pipe is perpendicular to the direction of said joists.
The lattice girder according to any one of claims 6 to 8, wherein the diameter of said guiding feature ranges between 15 and 60 mm.
A method for manufacturing an asymmetric lattice girder according to any one of claims 1 to 9, comprising the steps of:
a) selecting metal wires for manufacturing a top joist and two base joists based on the required characteristics of said lattice girder;

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

c) optionally straightening and cutting said metal wires for manufacturing said joists;

d) selecting or manufacturing one or more truss members of a first size and one or more truss members of a second size; and;

e) spatially connecting said first base joist with said top joist through said truss members of a first size and spatially connecting said second base joist with said top joist through said truss members of a second size, thereby obtaining an asymmetrical lattice girder.
The method according to claim 10, wherein step e) includes welding the ends and apexes of said truss members to said joists.
Lattice girder floor comprising a precast concrete slab with one or more cast in lattice girders according to any of claims 1 to 9.
Use of a lattice girder according to any one of claims 1 to 9 or a lattice girder floor according to claim 12 as a construction material.
Use of a lattice girder or lattice girder floor according to claim 13 for guiding support columns.
Use of a lattice girder or lattice girder floor according to claim 13 or 14 for supporting floors.