EP1961887B1

EP1961887B1 - Method of manufacturing a structural beam with openings

Info

Publication number: EP1961887B1
Application number: EP07102970A
Authority: EP
Inventors: Claude Vasconi; Louis-Guy Cajot; Olivier Vassart; Alain Wallerich; Bruno Theret
Original assignee: ArcelorMittal Commercial Sections SA
Current assignee: ArcelorMittal Commercial Sections SA
Priority date: 2007-02-23
Filing date: 2007-02-23
Publication date: 2011-08-10
Anticipated expiration: 2027-02-23
Also published as: PL1961887T3; ATE519901T1; ES2370267T3; EP1961887A1

Abstract

A method for manufacturing a beam (10) with openings comprising the steps of: providing two T-beams (20 1 , 20 2 ), the web (12a) of each of said T-beams having a respective free edge (22) describing an undulated line with peaks (24) and bases (26), the peaks being further essentially flat and parallel to a common axis; positioning the two T-beams (20 1 , 20 2 ) in face-to-face relationship so that the peaks (24) of their web edges come into contact and substantially coincide; welding the two T-beams together along their coinciding peaks (26) to form a beam with openings (18) located in its web. The undulated web edge lines (22) of the T-beams (20 1 , 20 2 ) are designed in such a way as to comprise a curvilinear line portion each side of each flat peak (26), such curvilinear line portion having a slope progressively approaching the slope of the flat peak (26).

Description

TECHNICAL FIELD

The present invention generally relates to structural beams of the type having a web between two flanges, in which the web is not continuous but has apertures therein, and to a method of manufacturing such beam.

BACKGROUND ART

Structural beams with openings located in their web, hereinafter also referred to as castellated beams, are commonly used in construction works (buildings, multi-level car parks, etc.).
As it is well known, castellated beams are typically made from universal beams, e.g. hot rolled I- or H-sections that are cut along their web according to a specific pattern. The resulting two T-beams are then re-assembled by welding. This technique is conventionally used to produce beams with circular, hexagonal or octagonal opening as well as cambered beams with such openings.
A well-known method for the manufacturing of a castellated beam is for example disclosed in GB 882 175 . An H-section beam is separated into two T-beams by cutting into its web along a predetermined cutting line, e.g. by means of a cutting torch. The cutting line describes a substantially periodical undulation with peaks and bases, these peaks and bases being flat and parallel to one another and to the flanges. One T-beam is then longitudinally displaced so that the peaks of the upper and lower T-beams coincide and the abutting peaks are finally welded together.
A method for manufacturing castellated beam with circular openings is described in EP 0 324 206 . In this method, a first continuous cut is made along the web of a universal beam and a second continuous cut is made along the web on a path different from that of the first cut. The cuts are such as to define rectilinear sections lying on alternate sides of the centreline of the web and at least partly curvilinear sections joining the closest ends of the rectilinear sections. The cut halves (two T-beams) of the beam are separated and are then welded together in regions formed by juxtaposition of rectilinear sections of the two halves.
Other methods of manufacturing castellated beams are disclosed in FR 835808 , US 3 066 394 and CA 2 404 320 .
FR 835808-A discloses a beam according to the preamble of claim 1.
A recurrent problem in the above-described methods is the difficulty of properly aligning the opposite flat peaks (rectilinear segments) of the web edges in order to proceed with the welding operation. Indeed, any shift or misalignment between two flat peaks is easily perceptible to the eye in the case of circular or hexagonal openings due to the regularity of the shapes. This problem of alignment of coinciding flat peaks is even more important in the case of pre-cambered beams.
Hence there is a need for an alternative method of manufacturing such beams, wherein alignment problems of coinciding summits are alleviated.
Accordingly, there is provided a method according to claim 1.

GENERAL DESCRIPTION OF THE INVENTION

According to the present invention, a method for manufacturing a beam with openings comprising the steps of:

a) providing two T-beams, each having a flange and a web, the web of each of said T-beams having a respective free edge describing an undulated line with peaks and bases, the peaks being remote from the respective flange and the bases being close to the respective flange, the peaks being further essentially flat and parallel to a common axis;
b) positioning the two T-beams in face-to-face relationship so that the peaks of their web edges come into contact and substantially coincide;
c) welding the two T-beams together along their coinciding peaks to form a beam with openings located in its web.

According to the present invention, the undulated web edge lines of said T-beams are designed in such a way as to comprise a curvilinear line portion each side of each flat peak, this curvilinear line portion having a slope progressively approaching the slope of the flat peak.
According to the present invention the curvilinear portions have the characteristics defined by the characterising portion of claim 1.
As expressed in a more mathematical way, the derivative of the curve described by the curvilinear line portion at a point is the slope of the line tangent to the curve at that point, expressing the rate of change of the curvilinear line portion. According to the invention, the slope of the tangent to the curve varies progressively, in direction of the peak, until the tangent is aligned with the direction of the flat peak.
In other words, in the vicinity of the peaks, the undulations of the web edge line is designed such that its curvature varies until it becomes tangent to the flat peak line. The practical consequence of this design is that there is no discontinuity of the free edge profile in the vicinity of the flat peaks that will be abutted against similar, coinciding peaks of the other T-beam, contrary to the well known beams with circular, hexagonal or octagonal openings. The tangency and varying curvature of the web edge about the peaks makes it difficult to notice the exact beginning and ending locations of the flat peaks, so that slight shifting and misalignments will be less perceptible to the eye and thus facilitates the alignment task during beam production. Further, the welding operator may also weld together opposite web edge lines in the region of the curvilinear lines portions to mask any misalignment and/or reinforce the welding at the peaks. It thus appears that the use of such undulated design greatly simplifies the assembly of the two T-beams and thus the manufacturing of the castellated beam.
In one embodiment, the two T-beams are cut out from a single beam having a web extending between two flanges, preferably a hot-rolled I- or H-section beam. The cutting may be done according to a continuous cutting line along the web of such beam. In this case, the cutting line will thus define the shape of the undulated line of the free web edges of the resulting two T-beams.
In one embodiment based on manufacturing from a single H-beam (or I), the continuous cutting line further defines flat end sections extending from each end of said undulated line to the respective beam extremity, one of the flat end sections being closer to one flange while the other is closer to the opposite flange. After cutting of the H-beam along such continuous cutting line extending between both beam extremities, one of the T-beams is turned over 180°, and the two T-beams are positioned according to step b). It will be understood that such construction mode-facilitated by symmetry of design-needs taking into account size and axial position of the peaks, as well as the height of the peaks with respect to the flanges in order to obtain coinciding peaks over the beam length upon rotation of one beam.
It may be appreciated that the presence of flat end sections at both ends of the undulated line, opposed with respect to the beam centre line, permits to automatically obtain a continuous web portion at one end of the beam. Indeed, when one of the beam is rotated over 180°, due to the cutting line design, the flat end sections come into abutment at one extremity of the beam whereas there is an opening at the other extremity. The abutting flat end sections may thus be welded together while at the opposite beam extremity the opening is preferably closed using welding and appropriate material, thereby forming a castellated beam with continuous web sections at both ends. In addition, undesired end beam portions may be cut off, in order to have end sections of similar length.
In an alternative manufacturing method, the two T-beams, upon cutting along a continuous cutting line, may simply be separated and shifted axially to bring the opposite peaks into abutment.
Although manufacturing from one single beam is very convenient when working with symmetric patterns, since it allows minimizing costs and scrap, the two T-beams to be assembled can be cut out from two different beams. As long as the undulating shape of their web edges is designed so that they may be joined by their peaks, a variety of designs/patterns is possible.
To improve the quality of welding at the peaks and thus strengthen the joining between the T-beams, one may advantageously weld together facing curvilinear line portions over a given length, on the lateral sides of the peaks.
In one embodiment, the T-beams are cambered before welding in step c). A difficulty in the manufacture of pre-cambered beams is that the length of coinciding peaks is modified due to bending. However, due to the particular design of the undulating lines at the peak sides providing tangency of the curvilinear line portions, there is no discontinuity between the flat peaks and the edge line about the peaks. The slight difference in peak length is thus visually imperceptible due to the design of the openings about the peaks; again thereby avoiding long adjustment before welding and need for additional matter to restore the shape of the edge lines. Further, tangency and varying curvature of the web edge about the peaks make it possible for the operator to easily extend the welding to the region of the curvilinear line portions in order to weld together the opposite, proximate web edges.
According to another aspect of the present invention, there is proposed a beam with openings having a web and two flanges and consisting of two assembled T-beams each having a flange and a web. The web of each of the T-beams has a respective edge line describing an undulated line with peaks and bases, the peaks being remote from the respective flange and the lows being close to the respective flange. The peaks are essentially flat and parallel to a common axis and the T-beams are joined by their peaks that are welded together.
It is to be appreciated that the undulated web edge lines of the T-beams are designed in such a way as to comprise a curvilinear line portion each side of each flat peak, this curvilinear line portion having a slope progressively approaching the slope of the flat peak.
The openings in the beam thus close longitudinally by regions where upper and lower web edges meet at the adjoined peaks (that form the uprights of the beam) in a tangential manner.
Such beam results from the construction of two T-beams having specific web edge design that permits an easier assembly. This design proves even more interesting in the case of pre-cambered beams, as already explained hereinabove.
In the vicinity of the peaks, the shape of the meeting web edge lines can be characterised by the axial extent (or approaching distance) of the curvilinear line portion, as measured by projection on a parallel to the beam axis. The approaching distance may range up to 200 mm, and is at least 150 mm as defined by claim 1.
Another distinctive parameter is the distance between opposite (upper and lower) web edge lines over the approaching distance. This distance does not exceed 20 mm over the approaching distance, more preferably not more than 15 mm.
In one embodiment, both T-beams are cut out from a single H or I section beam so that peaks and bases are flat, parallel and of same length. Alternatively, the two T-beams can be prepared from two different beams, which allows more flexibility in design and shapes, but is economically less interesting.
In one embodiment, the proportion of continuous web (i.e. extending continuously between lower and upper flange) in one unitary pattern element (measured e.g. between the middle of two consecutive peaks) is in the range of 5 to 20%, preferably 6 to 13%. These values are particularly suited for flooring applications, composite constructions and the like.
As is conventional in the art, studs may be provided on a flange.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be more apparent from the following description of several not limiting embodiments with reference to the attached drawings, wherein:

FIG. 1: is a schematic view of a preferred embodiment of a castellated beam in accordance with the present invention;
FIG. 2: is an enlarged view of the beam of Fig.1;
FIG. 3 a) to f): are schematic views illustrating steps of a preferred manufacturing method of the beam of FIG.1;
FIG. 4: is a schematic view comparing two opening designs;
FIG. 5: is a schematic view of another embodiment of a castellated beam;
FIG. 6: is an enlarged view of the beam of Fig.5; and
FIG.7: is a detail illustrating the closing region of an opening where the web edge lines of opposite T-beams meet tangentially at a peak;
FIG. 8 a) to e): are schematic views illustrating steps of a preferred manufacturing method of the present beam.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

FIG.1 illustrates a castellated beam 10 according to a preferred embodiment of the present invention, having a web 12 extending between two parallel flanges, the lower flange being indicated 14 and the upper 16. Located in the web 12 are a number of openings 18 (7 openings in this embodiment).
The beam 10 is formed from two T-beams, designated 20₁ and 20₂, that are joined by welding. As can be understood from Fig.1, the web of each T-beam 20₁, 20₂ has a respective free edge describing an undulated line 22 with peaks 24 and bases 26. The peaks 24 are remote from the respective flange and the bases 26 are close to the respective flange. In the present embodiment, peaks 24 and bases 26 are essentially flat and extend parallel to the central axis 25 of the beam 10. The welding of the two T-beams is carried out at their peaks 24. On each longitudinal side of the beam 10 is an end section with continuous web.
It shall be appreciated that the undulating line 22 of the web edges is designed in such a way as to comprise a curvilinear line portion each side of each flat peak 24, the curvilinear line portion having a varying slope progressively approaching the slope of the flat peak 24. In other words, the intermediate edge section connecting a base 26 to a peak 24 in each T-beam 20₁, resp. 20₂, has a shape such that in the vicinity of the peak 24, its slope progressively varies to become tangent to the flat peak 24. Since the web edge profile is similar on both T-beams 20₁ and 20₂, the openings 18 have a specific shape where the junction point between the upper and lower web edges at the peaks 24 is not readily distinguishable to the eye, thus allowing some flexibility during the joining/welding operation, namely by reducing the required efforts for alignment.
The shape of the openings 18 in the embodiment of Fig.1 can be more precisely seen in Fig.2, where the longitudinal extent of each portion or section of the undulating line 22 is indicated below the beam 10. Peaks 24 and bases 26, respectively indicated p and b, are flat sections of same length that are parallel to the beam centre line 25. Intermediate sections connecting between peaks and bases are indicated s. The end portion of an intermediate section s close to a peak that forms the curvilinear line portion becoming tangent to the flat peak 24 is indicated w. The curvilinear line portion w is thus a terminal part of the intermediate section s.
It may be noted that the intermediate section s could be given any shape, provided that in the vicinity of each peak 24 it describes a curvilinear line portion w that becomes tangent to the peak. If the two T-beams were not manufactured from a single beam according to the below method (which implies that the shape of one peak in one T-beam defines the shape of one base in the other T-beam), the bases would not need be flat and of same length as the peaks.
A preferred method for manufacturing the beam of Fig.1 will now be explained in detail with regard to Fig.3. A starting H-section beam 10a is illustrated in Fig.3 a). This starting beam 10a is cut along its web 12a following a continuous cutting line 22a by means of e.g. a laser or plasma cutting device, cutting torch or chip removing device, thus creating the two T-beams 20₁ and 20₂. The respective free web edge profile 22 of the two T-beams 20₁ and 20₂ thus results from the shape of the continuous cutting line 22a.
The two T-beams 20₁ and 20₂ are then separated (Fig.3 b) and the lower T-beam 20₁ is rotated over 180° (Fig.3 c). Next the two T-beams 20₁ and 20₂ are positioned so as to bring coinciding peaks 24 of their web edges into contact. It may be appreciated that in the present embodiment, the shape of the cutting line 22a, and thus of the edge lines 22 is such that upon rotation, the peaks 24 of the lower and upper T-beams coincide. It thus suffices so bring the T-beams 20₁ and 20₂ into abutment and weld them together at the coinciding, adjoining peaks 24.
It will be understood that to enable such beam construction mode, the web edge design, as defined by line 22 (and created by cutting line 22a) must meet several requirements. In that respect, some of the important design parameters of the undulated line are:

length of the peaks: coinciding peaks (i.e. peaks that will be adjoined upon rotation) must be of same length;
axial position of the peaks: the peak axial positions are designed so that peaks from upper and lower T-beams coincide upon rotation of one T-beam;
peak to flange distance: the sum of peak to flange distance of coinciding peaks must correspond to desired beam height (whether unique or varying), for all peaks.

To illustrate how these preferred constructional parameters apply to the present embodiment, let us attribute an order number to the peaks of each T-beam. In respect of the upper T-beam 20₂ the peaks are numbered from right to left and for the lower T-beam 20₁ from left to right (see Fig.3 b).
As already stated, due to the particular design of the web edge line 22, upon rotation of the lower T-beam 20₁ all peaks coincide, whereby peaks of order number i are automatically facing each-other. It can be observed. Applying the above recommendation, that the length of peak i in the upper beam section 20₂ is equal to the length of peak i in the lower beam 20₂, and in fact all peaks are of same length.
It can also be observed that the distance from the right-hand extremity of upper beam 20₂ to peak i is the same as the distance from the left-hand extremity of lower beam to peak i. The peak to flange distance is the same for each peak nr. i.
It may be further noted that the cutting line 22a ends at both extremities with a flat end section. On the right-hand extremity, the flat end section 30 is closer to the lower flange 14 while on the opposite beam extremity the flat end section 30a is closer to the upper flange 16. Further, the flat end sections 30 and 30a are advantageously of same length. The reason for this design is that a continuous web is automatically obtained at one beam 10 extremity upon rotation of the lower T-beam 20₁, as can be seen in Fig.3 d).
In the configuration of Fig.3 e), all adjoining peaks 24 have been welded together and the abutting flat end sections on the right-hand extremity of the beam have been welded together, forming a continuous web end portion. Welded portions are materialised in Fig.3 e) by dashes.
It is clear that due to the design of the edge line 22, at the extreme openings 18, upper and lower web edge lines 22 meet towards the end sections e in the same way as at the peaks 24, forming these portions with tangential lines.
To improve the quality of welding at the peaks 24 and thus strengthen the joining between the T-beams, facing curvilinear line portions on the sides of the peaks are advantageously welded together over a given length (not shown in the drawings).
In Fig.3 e) the web is open at the left beam extremity. This opening in the web 12 is preferably closed using welding and appropriate materials (as illustrated by the grey area in Fig.3 f) so as to form a continuous web end portion. Undesired beam portions on the left hand-side are cut out, so that the final beam 10 has two end portions with a continuous web and of same length (indicated e in Fig.3 f).
Referring now to Fig.4, the opening defined by the continuous line is the same as in Fig.2 whereas the opening defined by the dashed line is an alternative opening shape even more adapted for pre-cambering and having an opening width closer to that of rectangular cable guides to be passed through the opening. This second opening design of course comprises curvilinear line portions indicated wb that become tangent to the peak 24. As can be seen, the extent of the curvilinear line portion wb is greater than for undulated line 22, whereby the beginning and ending of the abutting flat segments of the peaks are even more difficult to perceive. The greater length of curvilinear portion wb also allows for welding in this region for reinforcement.
Fig.5 illustrates a further embodiment of a castellated beam 110 in accordance with the present invention, where the undulated line comprises, on the sides of each peak 124, a curvilinear line portion (indicated wc in Fig.6) the slope of which progressively approaches that of the peak 124. In Fig.5, like elements are indicated by same reference numbers as in Figs. 1-4, however preceded by 1. The welded flat segments of the peaks 124 are not represented and the reference numeral only indicates their position.
As can be understood from the above description, there can be various designs for the undulated lines 22 or 122, respectively cutting line 22a, provided that next to the flat peaks a curvilinear line portion w, wb or wc, is formed that tangentially meets with the flat peaks 24, 124. As has been understood, over the distance of the curvilinear line portion, the slope of the curvilinear line portion continuously decreases until it reaches that of the flat peak, in this case zero since the flat peak is horizontal.
It also clearly appears from Fig.4 that the shape of the curvilinear line portion w or wb may differ. In Fig.4, portion wb is considered to be of greater axial extent as portion w because its slope is closer to the tangent than for portion w over a longer distance from the peak 24. These shapes condition the visual appearance and for the design of the dashed line 22b, the meeting point of undulating lines at the peak 24 is even more difficult to distinguish, which further facilitates the assembly due to less stringent aligment requirements.
One may thus characterise the curvilinear line portions w, wb and wc by their axial extent (as projected along the axis), combined with the spacing between the upper and lower web edge lines meeting at a peak 24, 124. In Fig.7, letter wL illustrates the measurement of the axial extent of a curvilinear line portion tangentially meeting the peak 24; this corresponds to the measure of w, wb or wc. Letter DL indicates the measurement of the distance between the upper and lower web edge lines 22 at the beginning of the curvilinear line portion. Parameters wL and DL thus reflect the design of the curvilinear lines portions and the way the openings appear in the vicinity of the peaks 24, 124 that form the uprights in the final beam (continuous web portions between two peaks).

For the sake of exemplification only, table 1 below presents numerical values of several parameters of beams that are shown in the Figs.

Table 1

	Beam of Figs.1 &4; web edge design of line 22	Beam of Figs.1 &4; web edge design of line 22b	Beam of Figs.5 &6; web edge design of line 122
Starting beam type
Beam reference	HD400x187		IPE330
Height (h)	h = 368mm		h = 330mm
Flange width (fb)	fb = 391 mm		fb = 160mm
Web thickness (tw)	tw =15mm		tw =7,5mm
Flange thickness (tf)	tf =24mm		tf =11,5mm
Final beam
Length (L)	17 m		10m
Height (H)	618 mm		530 mm
Peak and base (p,b)	250 mm		150 mm
length	840 mm		1175 mm
Section (s) length	995 mm		1100 mm
End portion length (e)
Opening dimensions
Max. height (OH)	500 mm	500 mm¨	400 mm
Max width (OW)	1930 mm	1930 mm	2500 mm
Base-flange distance(BF)	35 mm	35 mm	54 mm
WL	100 mm	175 mm	150 mm
DL	17 mm	15 mm	15 mm

It is to be stressed that the beam of Figs. 1 & 4 with the web design of line 22 corresponding to the values of table 1 does not form part of the claimed invention.
It may be noted that although in the examples in Table 1 the peaks have a length of 250 or 150 mm, their length can be reduced to a very small value. The length of the peaks can indeed be varied depending on the application, and can be smaller where the application requires less resistance from the beam.
Alternatively to the manufacturing method shown in Fig.3, a beam in accordance with the present invention can be manufactured in a more traditional way, i.e. by simple translation, as illustrated in Fig.8 a) to e). The two first steps a) b) are similar to those of Fig.3. A starting H-section beam 210a is cut along its web 212a following a continuous cutting line 222a, thus creating two T-beams 220₁ and 220₂. The respective free web edge profile 222 of the two T-beams 220₁ and 220₂ thus results from the shape of the continuous cutting line 222a. The two T-beams 220₁ and 220₂ are then separated, as shown in Fig.8b, by distance sufficient to permit relative shifting in the axial direction. The peaks 224 of the upper and lower beams are brought into abutment as shown in Fig.8 c) and the coinciding peaks 224 may then be welded together.
Contrary to the manufacturing method shown in Fig.3, the simple axial shifting of the lower beam 220₁ to the right does not permit to obtain one beam extremity with continuous web. Excess material at the beam extremities is cut.
In the configuration of Fig.8 d), all adjoining peaks 224 have been welded together (materialised by dashes). Further, the openings in the web 212 at the beam extremities have been advantageously closed using welding and appropriate materials (as illustrated by the grey areas) so as to form a continuous web end portions. The resulting castellated beam is then shown in Fig.8 e) having continuous beam end portions of same length.

Claims

Method for manufacturing a beam with openings comprising the steps of:
a) providing two T-beams, each having a flange and a web, the web of each of said T-beams having a respective free edge describing an undulated line with peaks and bases, said peaks being remote from the respective flange and said bases being close to the respective flange, said peaks being further essentially flat and parallel to a common axis;

b) positioning the two T-beams in face-to-face relationship so that the peaks of their web edges come into contact and substantially coincide;

c) welding the two T-beams together along their coinciding peaks to form a beam with openings located in its web; wherein
the undulated web edge lines of said T-beams are designed in such a way as to comprise a curvilinear line portion each side of each flat peak, said curvilinear line portion having a slope progressively approaching the slope of the flat peak, characterised in that
said curvilinear line portions extend over an approaching distance
of 150 mm from the peak ends, as projected along the beam axis; and the undulated web edge lines are designed so that upon welding, the distance between facing curved line portions of two coinciding, joined peaks is not more than 20 mm over said approaching distance.
Method according to claim 1, wherein said two T-beams are cut out from a single H- or I-section beam according to a continuous cutting line along the web thereof.
Method according to claim 2, wherein said continuous cutting line defines said undulated line.
Method according to claim 3, wherein said continuous cutting line further defines flat end sections extending from each end of said undulated line to the respective beam extremity, one of the flat end sections being closer to one flange while the other is closer to the opposite of said single beam.
Method according to claim 4, wherein upon cutting the two T-beams are separated, one of the T-beams is turned over 180°, and the two T-beams are positioned according to step b).
Method according to claim 5, wherein step c) further includes welding the abutting flat end sections at one end of the formed beam and forming a continuous web portion at the opposite end of the beam.
Method according to claim 6, comprising the step of cutting off excess beam material so as to form beam end portions of same length and having a continuous web.
Method according to claim 1, wherein said two T-beams are cut out from two different H- or I-section beams.
Method according to any one of the preceding claims, wherein step c) further includes soldering together facing curvilinear line portions over a given length.
Method according to any one of the preceding claims, wherein the T-beams are cambered before welding in step c).
Method according to any one of the preceding claims, wherein the undulated web edge lines are designed so that said curvilinear line portions extend over an approaching distance of up to 200 mm from the peak ends.
Method according to any one of the preceding claims, wherein the undulated web edge lines are designed so that, upon welding, the distance between facing curved line portions of two coinciding, joined peaks is not more than 15 mm over said approaching distance.
Beam with openings having a web and two flanges, said beam consisting of two assembled T-beams, said T-beams each having a flange and a web, wherein the web of each of said T-beams has a respective free edge describing an undulated line with peaks and bases, said peaks being remote from the respective flange and said bases being close to the respective flange, said peaks being essentially flat and parallel to a common axis, and wherein said T-beams are joined by their peaks that are welded together, wherein the undulated web edge lines of said T-beams are designed in such a way as to comprise a curvilinear line portion each side of each flat peak, said curvilinear line portion having a slope progressively approaching the slope of the flat peak; characterised in that
the undulated web edge lines are designed so that said curvilinear line portions extend over an approaching distance of 150 mm from the peak ends, as projected along the beam axis; and the distance between facing curved line portions of two coinciding, joined peaks is not more than 20 mm over said approaching distance.
the beam according to claim 13, wherein the undulated web edge lines are designed so that said curvilinear line portions extend over an approaching distance of up to 200 mm from the peak ends .
The beam according to claim 13 or 14, wherein the distance between facing curved line portions of two coinciding, joined peaks is not more than 15 mm over said approaching distance.
The beam according to claim 13, 14 or 15, comprising studs on one flange.
The beam according to any one of claims 13 to 16, wherein said bases are flat and of same length as said flat peaks.
The beam according to any one of claims 13 to 17, wherein the proportion of continuous web within one unit pattern of the beam lies in the range of 5 to 20 %, preferably 6 to 13 %.
The beam according to any one of claims 13 to 18, wherein said two T-beams originate from a single beam or from two different beams.
The beam according to any one of claims 13 to 19, wherein said beam is pre-cambered.