GB2492176A

GB2492176A - Beam with web having apertures with straight and curved edges

Info

Publication number: GB2492176A
Application number: GB201112512A
Authority: GB
Inventors: Konstantinos Daniel Tsavdaridis; Cedric D Mello
Original assignee: City University of London
Current assignee: City St Georges University of London
Priority date: 2011-06-24
Filing date: 2011-07-21
Publication date: 2012-12-26
Also published as: GB201112512D0; GB201110761D0

Abstract

A structural beam 34 has a web. The web may be a two part web comprising a first web part 36 and a second web 38. In one aspect each web part has a curved concave edge 44 and two straight edges 46, 48 that define a recess 42. The web parts 36, 38 are coupled together such that the recess 42 defined by one web part cooperates with the recess 42 defined by the other web part to define an opening 40. The concave portions may be opposed along an axis perpendicular to the length of the beam or they may be offset. In an alternative embodiment the recesses may be defined by a concave edge and two convex edges.

Description

I

STRUCTURAL BEAM

Field

The present invention relates to structural beams, particularly but not exclusively to so-called "perforated structural beams".

Background

One type of structural beam commonly used in the construction industry is illustrated in Fig. 1. Such a beam 10 is typically made of steel and comprises a substantially rectangular member 12 (often known in the art as a "web"), and one or more flanges 14 that protrude laterally from the web. Structural beams 10 have many different forms, for example structural beams with I, H or T shaped cross sectional profiles are known in the art and generally referred to as I, H or T beams respectively.

During construction of a typical building, services (such as gas or water pipes and electrical cables) cannot be installed through a traditional structural beam 10, and as a consequence architects usually need to provide extra space between floors (for example, in the form of raised floors or dropped ceilings) through which services may be routed. In larger buildings, one consequence of this is that the number of floors that can be provided in the space (building volume) available is reduced.

Efforts have been made in the past to alleviate such problems. For example, EP0324206 discloses a structural beam 16 that is provided with a series of openings 18 along the length of its web (see Fig. 2), and hence is known as a "perforated beam".

Persons skilled in the art will appreciate that the openings 18 shown in Fig. 2 may be referred to as cellular openings. However the term "perforated beam" is intended to encompass beams with one or more openings of any shape extending through its web.

One advantage of using beams of the kind shown in Fig. 2, as compared with structural beams of the type shown in Fig. 1, is that services (e.g. gas or water pipes and electrical cabling) can be routed through the openings 18 in the perforated beam 16, thereby reducing the need for false floors or ceilings and hence the space required between floors in a building. In tall buildings, the reduction of space required for services can often mean that additional floors can be installed.

A perforated structural beam 16 of the type shown in Fig. 2 is typically produced, as shown in Fig. 3, by cutting first and second profiles 20, 22 along the length of the web of an otherwise uncut structural beam (i.e. a beam of the type depicted in Fig. 1). The material between the first and second cuts 20, 22 is then removed and the two halves of the cut beam are separated. The profiles cut along the lengths of structural beams in EP0324206 comprise, in one embodiment, a series of parabolic curved portions 24 and rectilinear portions, each such rectilinear portion defining a flat edge 26. After separation corresponding fiat edges 26 of the two beam halves are aligned and coupled together, for example by welding, to provide a perforated structural beam where the parabolic curved portions 24 cooperate to define openings 18 in the web of the beam.

One disadvantage with this method of making perforated structural beams is the level of waste material produced during the cutting process. Fig. 4 schematically represents, by way of cross hatchings, the amount of material that is typically wasted during the introduction of perforations into a structural beam using the foregoing method.

Although the amount of waste material may not at first sight appear to be significant, it will be appreciated that when perforated beams 16 are mass produced the amount of waste material may become substantial.

ArcelorMittal provide perforated structural beams by means of a method that produces less waste than the method previously described. As shown in Fig. 5 the process employed by ArcelorMittal involves cutting a single profile 28 into an otherwise uncut structural beam. The two halves of the cut beam are then separated and corresponding maxima 30 and minima 32 of the beam half profiles are aligned. Once aligned the corresponding maxima 30 are coupled together so that the aligned minima 32 cooperate to define openings. A perforated structural beam formed by means of this process is known as an AngelinaTM beam.

Looking now at Fig. 6, it is apparent that the maxima 30 and minima 32 comprising the AngelinaTM profile are substantially fiat and that the shape of the AngelinaTM profile between these extremities is curved. As a consequence of this geometry, when a load is applied across an AngelinaTM beam no high stress concentrations are typically produced in the vicinity of the web openings because the web openings are not defined by any sharp edges (in contrast to a castellated structural beam which has hexagonal openings along its web or a perforated beam with square or rectangular openings).

As the fiat minima 32 are located close to the edge of an Angelina TM beam (such that there is only a relatively small amount of material between each of the minima 32 and the respective beam edges adjacent the flanges) the concentration of stress in the vicinity of the minima 32 upon application of a load is generally increased. It is also the case that the joints between the maxima 30 of an Angelina TM beam can form structural pinch points where the concentration of stress in the vicinity of the maxima 30 upon application of a load is increased.

The increase in stress concentration towards the edge and around the joints, of an AngelinaTM beam, means that such beams are typically not well suited for use in structures that will be subjected to intermittent applications of stress (e.g. a bridge), as repeated applications of stress to an Angelina TM beam could cause the beam to fatigue (where high stress concentrations are located) and to fail (i.e. crack) more quickly than an otherwise solid beam or a perforated beam 16 of the kind shown in Fig. 2.

Further disadvantages of the aforementioned perforation processes arise from the difficulty of cutting a curved profile into a structural beam (as opposed to cutting a straighter profile). Due to the increased difficulty of cutting a curved profile as opposed to a straighter profile, structural beams embodying a greater extent of curved profile edges are more likely to be incorrectly cut than beams with a greater extent of straighter profile edges. This tends to increase the amount of waste produced when such beams are manufactured. One way of addressing this problem would be to cut curved beam profiles more slowly and carefully than straight beam profiles, however this would reduce the number of perforated beams that can be manufactured in any given time.

The present invention has been devised with the foregoing problems in mind.

S ummarv According to an aspect of the present invention there is provided a structural beam comprising a web having two opposing concave internal edges between which straight internal edges extend, wherein said concave edges and said straight edges cooperate to define an opening.

The concave edges may each define a semi-circle.

The concave edges may each define less than half a circle.

The web may comprise first and second web parts located on first and second sides respectively of an axis substantially extending along the length of the web.

The first and second web parts may be joined together to form said web.

The first and second web parts may be different portions of said web, said web being formed as a single body.

The first and second web parts may be are integrally joined.

Each web part may have a concave edge that co-operates with two straight edges to define a recess.

The recess defined by one web part may cooperate with the recess defined by the other web part to define said opening.

Each web part may have two straight edges that are not parallel with one another.

Each web part may have one straight edge that is at a non-zero angle to an axis extending along the length of the beam.

Each web part may have two straight edges that are both at a non-zero angle to an axis extending along the length of the beam.

Each web part may have two straight edges that diverge away from the concave edge of said web part.

One web part may have a first straight edge that is parallel with a first straight edge on the other web part.

One web part may have a second straight edge that is parallel with a second straight edge on the other web part.

A first straight edge on one web part, and a second straight edge on the other web part, may terminate adjacent one another.

A first straight edge on one web part, and a second straight edge on the other web part may, co-operate to define a V-shape.

The concave edges may be substantially in alignment and face one another.

The centre points of the circles which the concave edges partly define may be substantially located on an artificial line which extends transversely to an axis along the length of the beam.

The concave edges may be offset from one another and only partially face one another.

The centre points of the circles which the concave edges partly define may be substantially located on an artificial line which extends at a non-zero angle less than 90 degrees to an axis along the length of the beam.

The opening may not be wider than 75% of the height of the beam measured along a line extending transversely to an axis along the length of the beam.

The opening may not be wider than 80% of the height of the beam measured along a line extending transversely to an axis along the length of the beam.

The beam may have more than one said opening.

Adjacent openings may not be closer to one another than 10% of the width of an individual opening, measured along a line extending along the length of the beam.

Adjacent openings may not be closer to one another than 15% of the width of an individual opening, measured along a line extending along the length of the beam.

The beam may have differently shaped openings.

The beam may have alternating differently shaped openings along the length of the beam.

The sum of the lengths of said straight edges may be greater than the sum of the lengths of said concave edges.

According to a second aspect of the present invention there is provided a structural beam comprising a web wherein: a) the web comprises two recesses each of which is defined by a non-parabolic concave internal edge and two non-parallel internal straight edges; and b) the recesses co-operate to define an opening.

A structural beam according to the second aspect of the present invention, and any arrangement of the first aspect of the present invention may further comprise at least one flange extending therefrom and may have a substantially I, H or T shaped cross sectional shape.

According to a third aspect of the present invention there is provided a structural beam comprising a web wherein: a) said web comprises two recesses; b) each said recess is defined by: i) a concave internal edge that defines part of a circle of radius RI and ii) two convex internal edges that each define part of a circle of radius R2; and c) the recesses co-operate to define an opening.

Radius RI may be greater than radius R2.

The first web part may define one said recess and the second web part may define the other said recess.

The first and second web parts may have been joined together to form said web.

The first and second web parts may be integrally joined.

The concave edge of each web part may be located between the convex edges of said web part.

The concave edges may each define less than half a circle and said convex edges may each define less than quarter of a circle.

The convex edges on one web part may both terminate adjacent respective convex edges on the other web part.

The concave edges may be substantially in alignment and face one another.

The opening may not be wider than 80% of the hei9ht of the beam measured along a line extending transversely to an axis along the length of the beam.

The beam may have more than one said opening.

Adjacent openings may not be closer to one another than 10% of the width of an individual opening, measured along an axis extending along the length of the beam.

Adjacent openings may not be closer to one another than 15% of the width of an individual opening, measured along an axis extending along the length of the beam.

The beam may have differently shaped openings.

At least one opening may have a first set of RI and R2 values and at least one other opening has a second set of RI and R2 values.

According to a fourth aspect of the present invention there is provided a structural beam comprising a web wherein: a) the web comprises two recesses; b) each said recess is defined by a concave internal edge, that defines part of a circle of radius RI, and two convex internal edges, that each define part of a circle of radius R2 which is less than RI; c) the concave internal edge of each said recess is located between the two convex internal edges defining that said recess; and d) the recesses co-operate to define an opening.

The concave edges may each define less than half a circle and said convex edges each define less than quarter of a circle.

A structural beam according to any arrangement of the fourth aspect of the present invention, and any arrangement of the third aspect of the present invention, may comprise a flange extending therefrom and may have a substantially I, H or T shaped cross sectional shape.

Brief Description of the Drawings

Various aspects of the teachings of the present invention, and arrangements embodying those teachings, will hereafter be described by way of illustrative example with reference to the accompanying drawings, in which: Fig. I is a schematic perspective view of a prior art structural beam; Fig. 2 is a schematic side view of part of a prior art perforated structural beam; Figs. 3 and 4 are schematic side views of the beam in Fig. 2 at a stage during the manufacturing thereof; Figs. 5a to Sc are schematic side views of part of a third prior art structural beam at different stages during the manufacturing thereof; Fig. 6 is a schematic magnified view of part of the perforated beam in Fig. Sc; Fig. 7 a schematic side view of a perforated structural beam that embodies the teachings of the present invention; Fig. 8 is a schematic side view of part (i.e. the top tee-section) of the beam shown in Fig. 7; Fig. 9 a schematic side view of part of another perforated structural beam the embodies the teachings of the present invention; Fig. 10 is a schematic side view of a perforated structural beam comprising two of the components shown in Fig. 9 (i.e. top and bottom tee-sections); Fig. 11 is a schematic side view of a perforated structural beam having openings of the kind shown in Figs. 7 and 10; Figs. 12 to 14 are schematic side views of the perforated structural beam in Fig. 7 at different stages during the formation thereof; Fig. 15 a schematic side view of part of yet another perforated structural beam that embodies the teachings of the present invention; Fig. 16 is a schematic side view of part of the perforated structural beam shown in Fig. 15; and Figs. 17 to 19 are schematic side views of the perforated beam in Fig. 15 at different stages during the formation thereof.

Detailed Description of Preferred Embodiments

Illustrative implementations of the teachings of the present invention will now be described with particular reference to an I beam. However, this particular application is merely illustrative and the teachings of the present invention may equally be applied to structural beams of any cross sectional shape (such as H beams or T beams). As a consequence, the following detailed description should not be construed as limiting the scope of the present invention to I beams, but should instead be construed to include beams of any cross-section shape.

With the above proviso in mind reference will now be made to Fig. 7 of the accompanying drawings in which there is depicted a schematic side view of an I beam 34 that embodies the teachings of the present invention.

The I beam 34 has a two-part web comprising first and second web parts 36, 38 (i.e. first and second tee-sections 36, 38). Such web parts 36, 38 are coupled together (for example by welding) so that their cross sectional profiles cooperate to define at least one opening 40 along the length of the I beam 34. Axis 35 shown in the drawings substantially extends along the length of the web parts 36, 38 and therefore the length of the I beam 34.

Now referring to Fig. 8, the cross sectional profile of the web parts 36, 38 will now be discussed in more detail. Each web part 36, 38 defines at least one recess 42. The innermost part of the or each recess 42 is defined by a non-parabolic concave edge 44.

In one arrangement the concave edge 44 defines a semi circle (preferably less than half a circle). One side of the concave edge 44 meets (i.e. joins with) and extends into a first substantially straight edge 46 whereas the other side of the concave edge 44 meets (i.e. joins with) and extends into a second substantially straight edge 48. The concave edge 44 and the first and second straight edges 46, 48 cooperate to define the recess 42.

In one arrangement the first and second straight edges 46, 48 of each recess 42 diverge away from one another in a direction away from concave edge 44. Specifically, the first and second straight edges 46, 48 extend at a non-zero angle relative to an artificial line 50 (see Fig. 8) that extends between such edges transversely to axis 35 (which, as aforementioned, extends along the length of the web part). The angle between the first or second straight edge 46, 48 and the aforementioned artificial line 50 may be any angle from 10 to 40 degrees although any non-zero angle less than 90 degrees is envisaged.

With further reference to Fig. 8 the first and second straight edges 46, 48 of each recess 42 terminate (and are joined at a non-zero angle) with third and fourth substantially straight edges 52, 54 respectively. Such third and fourth straight edges 52, 54 are substantially parallel with one another and with axis 35 (which, as aforementioned, extends along the length of the web part). In one particular arrangement the maximum width of the concave edges 44 (i.e. the distance along axis between the respective interfaces of the concave edge 44 with the first and second straight edges 46, 48) is substantially equal to the length of each of the third and fourth straight edges 52, 54.

With the foregoing in mind, a perforated I beam 34 of the kind illustrated in Fig. 7 may be formed by: a) obtaining two web parts 36, 38 of the kind illustrated in Fig. 8; b) inverting one of the web parts relative to the other; c) substantially aligning and bringing the third and fourth edges 52, 54 of one web part into contact with corresponding third and fourth edges of the other web part respectively; and d) coupling the substantially aligned contacting third edges and the substantially aligned and contacting fourth edges of the respective web parts together (for example by welding). The step of coupling the third and fourth 52, 54 edges of respective web parts together in the foregoing manner provides that the recesses 42 of the two web parts cooperate to define one or more openings 40 along the length of the resulting I beam 34.

Looking again at Fig. 7 an opening 40 of the kind as heretofore described has two pairs of parallel straight edges. One pair of such parallel edges comprises the first straight edges 46 of the web parts 36, 38 that define the opening 40. The other pair of parallel straight edges comprises the second straight edges 48 of such web parts that define the opening 40. More specifically the first straight edge 46 on each web part terminates adjacent a second straight edge 48 on the other web part, thereby substantially defining a V-shape. Also, the area A of each one of the openings 40 in the I beam 34 illustrated in Fig. 7 is defined by equation I below.

72R+ (2R+2(#-R)tane)\ d0-2R A=ffR2+2 K 2 2) Equation 1 where: ii = a constant R = the radius of the circles which the concave edges 44 partly define d = the height (depth) of the web opening of the perforated I beam 34 (see Fig. 7) U = the angle between the artificial line 50 and the first or the second edge 46, 48 Fig. 9 schematically illustrates another web part 136, 138 that embodies the teachings of the present invention wherein all parts like with those illustrated in Figs. 7 and 8 are labelled with corresponding reference numerals increased by 100. In this arrangement the or each recess 142 has a first straight edge 146 (or alternatively a second straight edge 148) that is parallel with the artificial line 150 (which is perpendicular to an axis 135 extending along the length of the web part). The second straight edge 148 (or alternatively the first straight edge 146) of the or each recess 142 is at a non-zero angle relative to the artificial line 150, for example any angle between 10 to 40 degrees although any non-zero angle less that 90 degrees is envisaged.

To produce a perforated I beam 134 of the type illustrated in Fig. 10 corresponding third and fourth straight edges 152, 154 of two separate web parts 136, 138 (shown in Fig. 9) are aligned and coupled together in the manner already described in relation to foregoing web part arrangement shown in Figs. 7 and 8. Upon doing so, the recesses 142 of the two web parts 136, 138 will cooperate to define one or more openings 140 along the length of the resulting I beam 134 as shown in Fig. 10.

The or each opening 140 in the perforated I beam 134 has two pairs of parallel straight edges. Both of the edges in one parallel edge pair (i.e. straight edges 146 in Fig. 10) are substantially perpendicular to axis 135 along the length of the I beam 134.

Both of the edges in the other parallel edge pair (i.e. straight edges 148 in Fig. 10) extend at a non-zero angle relative to the aforementioned artificial line 150.

Furthermore, for each opening 140, the first straight edge 146 on each web part terminates adjacent the second straight edge 148 on the other web part. This provides that the concave edges 144 of each recess 142 defining an opening 140 are offset from one another along the length of the I beam 134. The area B of each one of the openings in the I beam 134 illustrated in Fig. 10 is defined by equation 2 below.

/2R+ (2R+(-R)tane)\ d0-2R B=ffR2+2 2 2) Equation 2 where: ii = a constant R = the radius of the circles which the concave edges 144 partly define d0 = the height (depth) of the web openings of the perforated I beam 134 (see Fig. 10) o = the angle between artificial line 150 and the edges inclined relative thereto (i.e. edges 148 in Fig. 10) It is also envisaged that a perforated I beam may comprise a plurality of openings with different shapes (i.e. openings of different cross sectional shapes and/or sizes) along its length. In one particular arrangement such openings may alternate in shape along the length of an I beam. Fig. 11 schematically illustrates a perforated I beam with openings 40 and 140 heretofore described along its length.

A perforated I beam may comprise openings 140 (see Fig. 10) with different amounts of shear (the shear of an opening being defined as the extent to which the concave edges 144 of the recesses 142 defining the opening 140 are off set along the length of an I beam). Also, in one particular arrangement some openings along the length of an I beam may be sheared in one direction (to the same or different extents) whereas one or more other openings may be sheared in the opposite direction (to the same or different extents).

It is also envisaged that at least one end of an I beam may define part of an opening (as in Figs. 7, 10 and 11 which show a recess at each end of the web, each such recess having a shape corresponding to that of part of the web openings).

However in other arrangements at least one end of an I beam may not define a part of an opening.

In one implementation of each of the aforementioned perforated I beam arrangements, the or each opening along the length of an I beam is not deeper than 80% (and in one particular arrangement 70%) of the height of the I beam (i.e. d0 «= 0.8 h wherein h is the height of the perforated beam).

Also, in one arrangement all of the openings along the length of a perforated I beam having more than one opening may or may not have the same width at their widest part (labelled W' in Figs. 7 and 10).

It is also envisaged that the distance between the centre points of adjacent openings (shown as S in Figs. 7 and 10) satisfies the relationship S »= R wherein R is the radius of the circles which the concave edges 44, 144 partly define.

In accordance with an aspect of the present invention a first manner in which I beams are perforated will now be described. Firstly, with reference to Fig. 12, a profile is cut along the length of an otherwise uncut I beam (for example by oxy-cutting or plasma cutting). The profile cut should effectively split the web of the I beam being cut into two web parts wherein each web part should define at least two peaks (also referred to as web posts) and one or more troughs along its length. Each trough should have a shape corresponding to the shape of any one of the aforementioned recesses 42, 142 (in the case of Fig. 12 the troughs each have a shape corresponding to that of the recesses 42 in Fig. 8).

Secondly, now referring to Fig. 13, an end section is cut off each web post in a direction substantially along the length of the respective web parts, thereby forming the aforementioned third and fourth flat edges 52, 54, 152, 154 (the web posts thereby taking on a substantially rectilinear shape). The material between the third and fourth fIat edges and the base of the troughs (shaded out in Fig. 13) is then removed and the web parts are separated. Corresponding third and fourth edges of the two separated web parts are then substantially aligned and coupled together (for example by welding) in the before described manner such that the troughs of the web parts cooperate to form one or more openings along the length of the resulting I beam.

The web height htinaj of an I beam perforated with either non-sheared openings or sheared openings 140 in accordance with this perforation process is determined by equation 3 below.

= --tAb -2R Equation 3 where: hrinai = the web height of a perforated I beam (equivalent to h in Figs. 7 & 10) hinitiai = the web height of an I beam before it has been perforated d = the distance between the edge of the web of the first web part 36, 136 and the or each recess 42, 142 defined by that web part (see Fig. 7) db = the distance between the edge of the web of the second web part 38, 138 and the or each recess 42, 142 defined by that web part (see Fig. 7) R = the radius of the circles which the concave edges 44, 144 partly define hfinal will be equal to hinitiai if a structural beam is perforated using the cut out technique.

The presence of concave edges 44, 144 (as opposed to flat edges as in the case of the Angelina TM beam) adjacent the edges of the web of a beam having at least one opening 40 or 140 provides that when a load is applied to such a structural beam, lower stress concentrations are produced/developed in the vicinity of the web part edges (particularly at the concave edge of each of the top and bottom tee-sections). In other words lower stress concentrations are produced/developed towards the edges of the web than would be produced in the vicinity of the web part edges of an Angelina TM beam if the same load were to be applied thereto. Also, the stress concentration points are formed close to each other, thereby forming a narrow critical "opening length" (see Fig. 14) which is more stocky in comparison to the slender wide critical "opening length" obtained when the Angelina TM beam is used.

It will be appreciated that in each of the above envisaged web part arrangements the sum of the lengths of straight edges (i.e. first, second, third and fourth edges 46, 48, 52, 54) is greater than the sum of the lengths of curved edges (i.e. concave edges 44).

This increases the ease and speed with which web parts of the kind envisaged herein can be cut, thereby increasing the speed at which perforated structural beams can be mass produced and reducing the number of beams discarded as waste due to being cut incorrectly.

It will also be appreciated that locations at which the web parts of the envisaged beams engage one another are easier to be located than in the case of the prior art. In particular, looking at Figs. 8 & 9, the first straight edge 46, 146 and the third straight edge 52, 152 meet at a corner. Similarly the second straight edge 48, 148 and the fourth straight edge 54, 154 meet at a corner. When the web parts of the envisaged beams are in contact with one another as shown in Figs. 7 & 10, the first and second straight edges of the two web parts substantially define a pair of V shapes. The apex of the Vs (and therefore the points at which the web parts contact each other) is easier to be located than where the curved internal edges of the web parts shown in Fig. 2 terminate. This increases the ease and speed at which the web parts 36, 38 & 136, 138 are able to be coupled together (for example by welding).

Other reasons why the perforated beams shown in Figs. 7, 10 and 11 are better than the acknowledged prior art include: 1) when the web openings 40, 140 are closely spaced any stress concentrations produced in the beam are located at specific areas; 2) more openings 40, 140 can fit along the length of the beams, thereby resulting in lighter (i.e. less heavy) beams which deflect less (i.e. are more resistant to bending); and 3) when a beam has web openings 40, 140 cut into it in the manner heretofore described, the web of the resulting beam 34, 134 is deeper than if the same beam had been perforated with circular openings. The deeper that a beam 34, 134 is then the greater is its second moment of area and therefore load carrying capacity.

Reference will now be made to Fig. 15 in which there is depicted a schematic side view of another perforated I beam that embodies the teachings of the present invention (wherein all parts like with those illustrated in Figs. 7 and 8 are labelled with corresponding reference numerals increased by 200). The I beam 234 has a two part web comprising first and second web parts 236, 238 (first and second tee-sections 236, 238) which are coupled together (for example by welding) so that their cross sectional profiles cooperate to define at least one opening 240 along the length of the I beam 234.

Axis 235 shown in the drawings substantially extends along the length of the web parts 236, 238 and therefore the length of the I beam 234.

Now referring to Fig. 16, the cross sectional profile of the web parts 236, 238 will now be discussed in more detail. Each web part 236, 238 defines at least one recess 242. The or each recess 242 is defined by a non-parabolic concave edge 244. In one arrangement the concave edge 244 defines part of a circle (preferably less than half a circle) having a radius RI. Each side of the concave edge 244 meets (i.e. joins with) and extends into a convex edge 245. Each of the two convex edges 245 define an non-parabolic shape. In one arrangement each convex edge 245 defines part of a circle (preferably less than half a circle and in one arrangement less than quarter of a circle) having a radius R2. In one envisaged arrangement R2 is less than RI. One side of each convex edge 245 meets (i.e. joins with) and extends into the concave edge 244. ln the arrangement shown in Fig. 16 the other side of each convex edge 245 terminates with a substantially flat edge portion 247 which extends substantially parallel with an axis 235 extending along the length of the web part 236, 238. The concave edge 244 and the two convex edges 245 cooperate to define the recess 242.

With the foregoing in mind, a perforated I beam 234 of the kind illustrated in Fig. is formed by: a) obtaining two web parts 236, 238 of the kind illustrated in Fig. 16; b) inverting one web part relative to the other; c) substantially aligning the flat edge portions 247 on one web part with those on the other web part and bringing such corresponding aligned flat edges 247 into contact with one another; and d) coupling the contacting flat edge portions 247 together (for example by welding). The step of coupling the flat edge portions 247 of the respective web parts 236, 238 together in the foregoing manner provides that the recesses 242 of the web parts cooperate to define one or more openings 240 along the length of the resulting I beam 234.

Looking again at Fig. 15 in one arrangement the openings 240 heretofore described each substantially comprise the shape of a circle with two opposing recess portions 249 (which may be referred to as fillets) extending outwards therefrom, the recess portions 249 (i.e. fillets) being aligned on an axis 235 extending along the length of the I beam 234. The area C of each one of the openings 240 in such an arrangement (see Fig. 15) is defined by equation 4 below.

C = rr-2. + (4r2 -Equation 4.

where: ii = a constant d0 = the depth of the web openings 240 of the perforated I beam 234 (see Fig. 15) r = the radius of the circles which the convex edges 245 partly define Various other arrangements are envisaged in which RI and R2 have different relative sizes.

In one web part arrangement adjacent convex edges 245 of neighbouring recesses 242 may actually meet and extend into one another such that there is no substantially straight edge portion 247 between the two convex edges 245 (such convex edges instead defining a continuous curve). In an I beam having two such web parts it is the corresponding continuous curves defined by adjacent convex edges 245 that are joined together to form a perforated I beam rather than corresponding flat edge portions 247.

In one implementation, the or each opening 240 along the length of a perforated I beam 234 (or any envisaged variation thereof) is not deeper than 80% (and in one particular arrangement 70%) of the height of the I beam (i.e. d0 «= 0.8 h wherein h is the height of the perforated beam).

It is also envisaged that the distance between the centre points of adjacent openings (shown as S in Fig. 15) satisfies the relationship S > d0. In an arrangement in which r = 25mm then S »= 1.2 d0. In an arrangement in which r = 45mm then S »= 1.3 d0.

It is envisaged that in some arrangements of a perforated I beam 234 having more than one opening along its length, all of the openings may or may not have the same width at their widest part (shown as W' in Fig. 15).

It is also envisaged that a perforated I beam 234 may comprise a plurality of openings with different shapes (i.e. openings of different cross sectional shapes and/or sizes) along its length. In one particular arrangement different openings 240 along the length of an I beam 234 may have different sets of RI and R2 values. It is also envisaged that the openings 240 may alternate in shape along the length of an I beam 234.

In accordance with an aspect of the present invention a second manner in which I beams may be perforated will now be described. Firstly, with reference to Fig. 17, a profile is cut along the length of an I beam (for example using a technique known as oxy-cutting or a technique known as plasma cutting). The profile cut (which in Fig. 17 is shown to correspond with the shape of the cross sectional profile of the web part in Fig. 16) should effectively split the web of the I beam being cut into two web parts. Each of the two web parts should have at least two peaks (also referred to as web posts) and one or more troughs along their respective lengths. In particular each trough should have a shape corresponding to that of a recess 242 (or any envisaged variation thereof).

Secondly, now referring to Fig. 18, a similar profile cut is made along the length of same I beam such that the web posts of the first profile cut extend into the troughs of the second profile cut and the web posts of the second profile cut extend into the troughs of the first profile cut. The material between the recesses 242 defined by the first and second profile cuts (shaded out in Fig. 18) is then removed and the web parts are pulled apart. If the web posts (labelled P in Fig. 18) of the web parts have straight profile edges 247, the material between the straight edges and the base of the recesses 242 is also removed.

Corresponding web posts of each web part are then aligned (as in Fig. 19) and coupled together in the before described manner (using welding for example) such that the troughs of the web parts cooperate to form one or more openings along the length of the resulting I beam.

The presence of concave edges 244 (as opposed to flat edges as in the case of the Angelina TM beam) adjacent the edges of the web of a structural beam having at least one opening 240 provides that when a load is applied to such a structural beam, lower stress concentrations are produced/developed in the vicinity of the web part edges (particularly towards the edges of the first and second tee-sections). In other words lower stress concentrations are produced/developed towards the edges of the web than would be produced in the vicinity of the web part edges of an Angelina TM beam if the same load was applied thereto. The envisaged perforated beam 234 therefore has a higher load carrying capacity than an Angelina TM beam.

Also, the amount of waste material produced during the perforation process described with reference to Figs. 17 to 19 is less than that produced in the perforation

process described in prior art document EP0324206.

Other reasons why the perforated beam 234 shown in Fig. 15 is better than the acknowledged prior art include: 1) welding the web parts 236, 238 together becomes easier because the start notch point (i.e. the inner most part of each of the fillets 249) is easily identifiable; 2) the final depth of the resulting perforated I beam 234 is slightly increased (relative to the height of an otherwise uncut I beam) hence the second moment of area is increased and the beam 234 has a better response to bending (in other words the perforated beam 234 is less easily bent). When a beam has web openings 240 cut into it in the manner heretofore described, the web of the resulting beam 234 will have a height greater than if the same beam had been perforated with openings of the kind described in EP0324206.

It will be appreciated that whilst various aspects and embodiments of the present invention have heretofore been described, the scope of the present invention is not limited to the particular arrangements set out herein and instead extends to encompass all arrangements, and modifications and alterations thereto, which fall within the spirit and scope of the appended claims.

Also, any references to straight edges or flat edges herein are intended to be references to edges that are at least substantially straight or substantially flat respectively. Any of the perforated structural beams described herein may be formed of metal such as iron, steel and aluminium for example. Such beams may alternatively be made of composite materials such as fibre reinforced plastic or laminated materials for example. Furthermore, a structural beam can be perforated using the cut out technique (rather than any of the other cutting techniques described herein) to produce a perforated structural beam having one or more openings of any shape envisaged herein.

The cut out technique involves removing a plate-like portion of the web of a structural beam to define an opening. If the cut out technique is used to create a perforated beam 34 of the kind shown in Fig, 7 then an envisaged critical web post width i.e. the length of each straight edge 52, 54 (shown as P in Fig. 7) »= 30mm. If the cut out technique is used to create a perforated beam 234 of the kind shown in Fig, 15 then an envisaged critical web post width i.e. the length of the straight edge 247 (shown as P in Fig. 15) »= 20mm.

For purposes of completeness it shall hereby be stated that I beams (and I beam sections) in Figs. 7 to 19 have been schematically illustrated without flanges to enhance the clarity of the drawings.

Lastly, it should also be noted that whilst the accompanying claims set out particular combinations of features described herein, the scope of the present invention is not limited to the particular combinations hereafter claimed, but instead extends to encompass any combination of features herein disclosed.

Claims

CLAIMS1. A structural beam comprising a web having two opposing concave internal edges between which straight internal edges extend, wherein said concave edges and said straight edges cooperate to define an opening.
2. The beam of Claim 1, wherein the concave edges each define a semi-circle.
3. The beam of Claim 2, wherein the concave edges each define less than half a circle.
4. The beam of any preceding claim, wherein said web comprises first and second web parts located on first and second sides respectively of an axis substantially extending along the length of the web.
5. The beam of Claim 4, wherein said first and second web parts have been joined together to form said web.
6. The beam of Claim 4, wherein said first and second web parts are different portions of said web, said web being formed as a single body.
7. The beam of Claim 6, wherein said first and second web parts are integrally joined.
8. The beam of any of Claims 4 to 7, wherein each web part has a concave edge that co-operates with two straight edges to define a recess.
9. The beam of Claim 8, wherein the recess defined by one web part cooperates with the recess defined by the other web part to define said opening.
10. The beam of Claim 8 or 9, wherein each web part has two straight edges that are not parallel with one another.
11. The beam of Claim 10, wherein each web part has one straight edge that is at a non-zero angle to an axis extending along the length of the beam.
12. The beam of Claim 11, wherein each web part has two straight edges that are both at a non-zero angle to an axis extending along the length of the beam.
13. The beam of Claim 11 or 12, wherein each web part has two straight edges that diverge away from the concave edge of said web part.
14. The beam of any of Claims 4 to 13, wherein one web part has a first straight edge that is parallel with a first straight edge on the other web part.
15. The beam of Claim 14, wherein one web part has a second straight edge that is parallel with a second straight edge on the other web part.
16. The beam of Claim 15, wherein a first straight edge on one web part, and a second straight edge on the other web part, terminate adjacent one another.
17. The beam of Claim 16, wherein a first straight edge on one web part, and a second straight edge on the other web part, co-operate to define a V-shape.
18. The beam of any preceding claim, wherein the concave edges are substantially in alignment and face one another.
19. The beam of any of Claims 2 to 18, wherein the centre points of the circles which the concave edges partly define are substantially located on an artificial line which extends transversely to an axis along the length of the beam.
20. The beam of any of Claims I to 17, wherein the concave edges are offset from one another and only partially face one another.
21. The beam of any of Claims 2 to 18 and 20, wherein the centre points of the circles which the concave edges partly define are substantially located on an artificial line which extends at a non-zero angle less than 90 degrees to an axis along the length of the beam.
22. The beam of any preceding claim, wherein said opening is not wider than 75% of the height of the beam measured along a line extending transversely to an axis along the length of the beam.
23. The beam of any of Claims I to 21, wherein said opening is not wider than 80% of the height of the beam measured along a line extending transversely to an axis along the length of the beam.
24. The beam of any preceding claim, wherein the beam has more than one said opening.
25. The beam of Claim 24, wherein adjacent openings are not closer to one another than 10% of the width of an individual opening, measured along a line extending along the length of the beam.
26. The beam of Claim 24, wherein adjacent openings are not closer to one another than 15% of the width of an individual opening, measured along a line extending along the length of the beam.
27. The beam of any of Claims 24 to 26, wherein the beam has differently shaped openings.
28. The beam of claim 27, wherein the beam has alternating differently shaped openings along the length of the beam.
29. The beam of any preceding claim, wherein the sum of the lengths of said straight edges is greater than the sum of the lengths of said concave edges.
30. A structural beam comprising a web wherein: a) the web comprises two recesses each of which is defined by a non-parabolic concave internal edge and two non-parallel internal straight edges; and b) the recesses co-operate to define an opening.
31. A structural beam according to any preceding claim, further comprising at least one flange extending therefrom.
32. A structural beam according to Claim 31, wherein the beam has a substantially I, H or T shaped cross sectional shape.
33. A structural beam substantially as hereinbefore described and/or as shown in the drawings in Figs. 7, 10 or 11.
34. A structural beam comprising a web wherein: a) said web comprises two recesses; b) each said recess is defined by: i) a concave internal edge that defines part of a circle of radius RI and ii) two convex internal edges that each define part of a circle of radius R2; and c) the recesses co-operate to define an opening.
35. The beam of Claim 34, wherein radius RI is greater than radius R2.
36. The beam of Claim 34 or 35, wherein said web comprises first and second web parts located on first and second sides respectively of an axis substantially extending along the length of the web.
37. The beam of Claim 36, wherein the first web part defines one said recess and the second web part defines the other said recess.
38. The beam of Claim 36 or 37, wherein said first and second web parts have been joined together to form said web.
39. The beam of Claim 36 or 37, wherein said first and second web parts are different portions of said web, said web being formed as a single body.
40. The beam of Claim 39, wherein said first and second web parts are integrally joined.
41. The beam of any of Claims 37 to 40, wherein the concave edge of each web part is located between the convex edges of said web part.
42. The beam of any of Claims 34 to 41, wherein said concave edges each define less than half a circle and said convex edges each define less than quarter of a circle.
43. The beam of any of Claims 37 to 42, wherein the convex edges on one web part both terminate adjacent respective convex edges on the other web part.
44. The beam of any of Claims 34 to 43, wherein the concave edges are substantially in alignment and face one another.
45. The beam of any of Claims 34 to 44, wherein the centre points of the circles which the concave edges partly define are substantially located on an artificial line which extends transversely to an axis along the length of the beam.
46. The beam of any of Claims 34 to 45, wherein said opening is not wider than 75% of the height of the beam measured along a line extending transversely to an axis along the length of the beam.
47. The beam of any of Claims 34 to 45, wherein said opening is not wider than 80% of the height of the beam measured along a line extending transversely to an axis along the length of the beam.
48. The beam of any of Claims 34 to 47, wherein the beam has more than one said opening.
49. The beam of Claim 48, wherein adjacent openings are not closer to one another than 10% of the width of an individual opening, measured along an axis extending along the length of the beam.
50. The beam of Claim 48, wherein adjacent openings are not closer to one another than 15% of the width of an individual opening, measured along an axis extending along the length of the beam.
51. The beam of any of Claims 48 to 50, wherein the beam has differently shaped openings.
52. The beam of Claim 51, wherein the beam has alternating differently shaped openings along the length of the beam.
53. The beam of Claim 51 or 52, wherein at least one opening has a first set of RI and R2 values and at least one other opening has a second set of RI and R2 values.
54. A structural beam comprising a web wherein: a) the web comprises two recesses; b) each said recess is defined by a concave internal edge, that defines part of a circle of radius RI, and two convex internal edges, that each define part of a circle of radius R2 which is less than RI; c) the concave internal edge of each said recess is located between the two convex internal edges defining that said recess; and d) the recesses co-operate to define an opening.
55. The beam of Claim 54, wherein said concave edges each define less than half a circle and said convex edges each define less than quarter of a circle.
56. A structural beam according to any of Claims 34 to 55, further comprising a flange extending therefrom.
57. A structural beam according to Claim 56, wherein the beam has a substantially I, H or T shaped cross sectional shape.
58. A structural beam substantially as hereinbefore described and/or as shown in the accompanying drawing in Fig. 15.
59. A kit of parts comprising respective parts of a structural beam according to Claims 1, 4 and 5, wherein each said part has a web comprising a recess, said recess being defined by: i) a non-parabolic concave edge and ii) two straight edge portions, wherein the concave edge joins with and extends into each of the straight edge portions.
60. A kit of parts comprising respective parts of a structural beam according to Claims 34, 36 and 38, wherein each said part has a web which comprises a recess, the recess being defined by: i) a concave edge that defines part of a circle of radius RI and ii) two convex edges that each define part of a circle of radius R2 which is less than RI, wherein said concave edge is located between the convex edges and joins with and extends into the convex edges.