GB2198164A - Fabricated beams of corrugated web - Google Patents

Abstract

A fabricated beam 1 having a corrugated web 6 secured to flange plates 2 and 3 by continuous full penetration welds. The corrugations of the web 6 increase the stiffness of the beam 1 and allow a corrugated web beam to be fabricated of thinner plates so as to have a lower weight for a given strength. The use of full penetration welds enables the maximum strength of corrugated web beams to be obtained. Alternative forms of web with optional web reinforcements (64 Fig 4) by forming individual box sections are shown. Also described are beam fabrication apparatus (Figs. 5-7) and beam fabrication methods (Figs. 8A-9), including automated weld line tracking and welding parameter control. <IMAGE>

Description

"Fabricated Beams, And Methods And Apparatus For Fabricating Beams" This invention relates to fabricated beams, and to methods and apparatus for fabricating beams. The invention relates more particularly but not exclusively to structural beams fabricateS of steel and suitable for use in large structures such as oil rigs and the like, together with procedures and plant for fabricating such beams.

In the past various forms of I-beam construction have been used depending on the size of the beam and its application.

Thus traditionally most steel I-beams have been made by rolling. However, this procedure is not practical for beams of large cross-section, eg up to 4 metres deep, and conventionally such beams have been manufactured by welding top and bottom flange plates to a web plate. Such welding results in considerable problems in maintaining correct alignment of the various plates and also in avoidance of localized distortions which can seriously limit the performance of the finished product. The problem of localized distortion is particularly acute with the larger sizes of beams produced by welding methods since it is necessary to use relatviely thick plates and there then arises a problem in producing reliable welded joints without distortion to the beam itself due to the very high temperatures that have to be used in the welding process.

The above problems can be particularly serious where weight saving is important and the beam is being used towards the limits of its design performance. In practice much of the performance under load of a conventionally designed I-beam does not depend n the strength of the connection between the web and the top and bottom flange plates so that in the past little attention has been paid to this part of the fabrication process.

More recently there has been proposed an I-beam construction using a corrugated web of relatively thinner metal in order to maintain load capacity but with a decrease in overall beam weight. Such a form of beam construction cannot readily be made by rolling but has the advantage of aa+itl ##fli#itating correct alignment of the flange plates due to the relatively large overall "thickness" of the web compared to the width of the top and bottom flange plates.There arises however the problem of variations in performance along the length of the beam particularly where the web is asymmetrically disposed with respect to the longitudinal centre lines of the flanges, and also as a result of variations in the strength and integrity of the welded joints which in turn arise from the lateral changes in direction of the web and from localized distortions resulting from the relatively unsophIsticated welding procedures used. In conformity with conventional procedures where, as noted above, no particular reliance is placed on the strength of the joint, the web and flange plates have conventionally been jointed simply by spot welding, onesided welding, or otherwise intermittent welding. As a result the performance of such known beams is substantially limited.

It is an object of the present invention to provide a fabricated beam, and a method and apparatus for fabricating such beams, which avoid or minimise the above disadvantages.

According to the present invention there is provided a fabricated beam comprising first and second mutually spaced flange plates with a corrugated web extending longitudinally along said beam between said flange plates, said web being in the form of a substantial plurality of generally planar plate portions interconnected along a generally zigzag path extending intermediate the side edges of said first and second flange plates, said web being connected to said first and second flange plates by substantially laterally symmetrical and substantially longitudinally continuous full penetration welds.

Preferably each joint between the web and one of said first and second flange plates extends from one side of the web to the other substantially symmetrically and runs substantially continuously along the length of the joints between the web and the flanges. With this form of full-penetration welding fabrication, variations in performance along the length of the beam, for example, at changes in direction along the web, are minimised and the performance of the beam is maximised by the substantial integration of the web with the flange plates which results in a greater effective web thickness than the actual web thickness and correspondingly greater contribution of the web to the total strength of the complete beam. The corrugated web gives the fabricated beam a strength comparable to that of a rolled beam with a much thicker web, and a correspondingly greater weight.

The first and second flange plates may be mutually spaced by an amount which is constant along the length of the beam such that the resultant beam is of constant depth, or alternatively the first and second flange plates may be mutually spaced by an amount which varies along the length of the beam such that the beam is curved or tapered from one part of the length of the beam to another to suit cantilever loading of the beam or otherwise longitudinally variable bending loads on the beam.

The beams of the present invention may be fabricated by substantially synchronous continuous full penetration welding along each web-to-flange joint from opposite sides of the web at the welded joint. By this method a substantially longitudinally continuous and laterally symmetrical welded joint can be obtained whilst substantially avoiding distortion.

Desirably the welding of each joint is monitored substantially continuous1 during the progress vf welding thereby further to ensure avoidance of variations in the joint and hence in the load capacity of the finished beam along its length. In particular where TIG (tungsten in gas) welding is employed, there are desirably monitored the welding wire feed rate and the welding head travel rate and preferably also one or more of inert gas supply rate, and the voltage and current of the electric arc.Preferably the welding is carried out using substantially constant welding wire feed rate, welding head travel rate along the line of each wed1 and vl.aae and current In a further aspect the present invention provides a manipulation and welding apparatus for the fabrication of a steel beam having a corrugated web as aforesaid, said apparatus comprising a body, a beam component support means mounted on said body for supporting an initially unwelded assembly of beam components comprising a corrugated web plate and at least one flange plate having one face thereof in contact with one corrugated edge of said web plate along a corrugated joint zone, between said corrugated web plate and said at least one flange plate and welding head support means having mounted thereon first and second welding heads in opposed spaced apart relationship, at least one of said beam component support means and welding head support means being formed and arranged to permit relative movement, in use of the apparatus, longitudinally and transversely of the beam component assembly with said welding heads being operatively moved along the respective weld lines under the influence of a drive control means connected thereto and arranged for providing relative displacement therebetween at a substantially constant head travel rate relative to the weld lines to be formed along the corrugated joint zone whilst maintaining said first and second heads substantially directly opposite each other on either side of said corrugated web plate.

Conveniently the welding head support means is formed and arranged for travel along said body relative to the beam component support means. The welding head support means is preferably also formed and arranged for varying the attitude of the welding head so as to maintain a generally predetermined attitude to a corrugated joint track during traversal thereof by the welding head means. Advantageously the apparatus included at least one of sensing means for tracking a corrugated joint zone and memory means for holding details of the track of a corrugated joint zone to be welded, and welding head travel control means for modulating the attitude and pathway of the welding heads in response to changes in direction of the corrugated joint zone.

As used herein in relation to web, joint, joint zone, path and the like, the term "corrugated" indicates having generally laterally symmetrical and preferably also longitudinally regular excursions to either side of the longitudinal central axis of the beam flanges.

Advantageously the fabrication apparatus of the present invention includes a tacking station for supporting the flanges securely against the web at right angles to the principal longitudinal plane of the web, and for securing the flanges to the web by means of welded tack joints as a preliminary step to forming the continuous full penetration welds.

Thus the method of the invention also advantageously included the preliminary steps of securely supporting the flanges to the web at right angles to the principal plane of the web, and securing the flanges to the web by means of welded tack joints.

Conveniently the web is supported generally horizontally and the flanges clamped to the opposed side edges thereof in a generally vertical position, for example, with the aid of hydraulic ram means. The welded tack joints are conveniently in the form of short spaced-apart welded fillet joints.

Adt'antageousl ea fabricated beam o-- the invention may be provided with stiffening means in the form of additional web portions, which conveniently may form 'box' sections in conjunction with individual corrugations of the principal web of the beam. Since these additional web portions generally function merely as stiffening means they do not require to be secured to the flanges with the same degree of integrity as the principal web so that conventional welded joints such as fillet welds may be employed instead of full penetration welds.

Thus according to the present invention it is possible to fabricate large structural I-beams having a depth of 2 metres or more with substantially greater strength for less weight than equivalent conventional flat web I-beams. By using lighter plate sections for a given strength of fabricated beam it is moreover easier to obtain reliable welded joints between the top and bottom flange plates and the central corrugated web, for example by requiring fewer passes of the welding heads than for the welding of a beam with an uncorrugated web.In addition the substantially automatic alignment of the top and bottom flange plates squarely with respect to the corrugated web when the flange plates are placed against the corrugated opposite edges of the web reduces the need for the use of complex jigs and supports in comparison to conventional fabrication methods and apparatus for producing beams with uncorrugated webs.

Further preferred features and advantages of the present invention will appear from the following detailed description of a preferred embodiment given by way of example and illustrated with reference to the accompanying drawings in which: Fig. 1 is a general perspective view of one form of fabricated I-beam in accordance with the present invention; Fig. 2 is a horizontal section of the beam of Fig. 1; Fig. 3 is a veritcal end elevation of the beam of Fig. II Fig. 4 is a horizontal section of another form of fabricated I-beam in accordance with the invention and which is provided with additional stiffening; Fig. 5 is a vertical end elevation of a fabrication apparatus of the invention in the form of a manipulation and welding apparatus; Fig. 6 is a corresponding view of a tacking station for use with the fabrication apparatus of Fig. 5;; Fig. 7 is a side elevation of the fabrication apparatus of Fig. 5; Figs. 8A and 8B are detail plan views illustrating part of the welding head tracking path; and ly. w is a schematic block diagram showing the welding control means.

Fig. 1 shows an I-beam 1 comprising a first or top flange plate 2, a second or bottom flange plate 3 and a corrugated central web 4 extending therebetween. The central web 4 is made up of a single plate 5 corrugated into a plurality of planar plate portions 6 interconnected with each other so that the web 4 extends along a generally zigzag 7 path substantially centrally between the side edges S, 9 of the top and bottom flans plates 2, 3 respectively.

In the case of a conventional I-beam having a depth of 2 metres, there would normally be employed top and bottom flange plates having a thickness of some 25mm. With a similar overall size of fabricated beam or girder in accordance with the invention and as illustrated in Fig. 1 the top and bottom flange plates 2 and 3 need only have a thickness of about 20 to 25mm and the central web 4 a thickness of about 12 to 15mm for s ccr#arab'-r beam strength. The substantially reduced plate thicknesses of the beam 1 thus result in a considerable reduction in weight compared to a conventional uncorrugated beam of similar strength.

In addition these reduced plate thicknesses considerably facilitate the fabrication of the beam of Fig. 1 and in particular the production of full penetration welded joints 10, 11 between the central web 4 and the top and bottom flange plates 2 and 3 respectively. Furthermore the relatively large overall width of the central web 4 (see Fig. 3) means that the top and bottom flange plates 2 and 3 can be much more readily maintained in square alignment with the central web 4 during the welding process than in the case of a conventional I-beam with an uncorrugated web.

It will be appreciated that various modifications and improvements may be made to the above design without departing from the scope of the present invention. Thus a different form of angular web extending along a different form of path could be used.

In particular the angle alpha (cG) between the web plate portions 61 which extend parallel to the longitudinal axis X - X of the beam 1 and those portions 62 which extend diagonally across said axis X - X could be varied.

Desirably the angle alpha (C) has a value in the range of 900 to 1500, preferably from 1200 to 1400, and most preferably about 1350. Also the parallelly-extending plate portions 61 could be omitted, the web consisting essentially of interconnected diagonally extending plate portions 62.

Fig. 4 is a view corresponding to Fig. 2 of a further embodiment of fabricated beam in accordance with the invention and in which the central corrugated web is in the form of a plurality of centrally disposed web portions 61a extending along the central longitudinal axis X - X of the beam 1, interconnected by a series of lateral excursions 63 to alternate sides of the central axis X - X. The lateral excursions 63 have a generally trapezoidal form made up of diagonally extending plate portions 62 interconnected by plate portions 61b which extend parallel to the central longitudinal axis X - X but offset therefrom.At an area A along the beam 1 which is subject to above average stressing in use, additional stiffening is provided in the form of an additional lateral web component 64 forming a lateral web excursion disposed in laterally opposed relation to one of the main web lateral excursions 63 so as to form together therewith a generally hexagonal prism-shaped box section 65.

Such additional lateral web components a can be added as frequently as required for local stiffening along the fabricated beam.

In connection with the above it may be noted that since the main structural strength of the beam 1 depends on the welded joints 10 and 11 between the main web 6 and the top and bottom flange plates 2 and 3, the additional welded joint 66 between the additional web plate of the additional lateral web component 64 does not require to meet the same high standards as the full penetration welds 1 and 11 between the main web 6 and the flange plates 2 and 3. Thus the additional web formed by the additional component(s) 64 may be secured to the main body of the beam 1 by means of a joint 66 formed by conventional fillet welding.

Figs. 5 and 7 show manipulation and welding apparatus 20 of the invention comprising a body 21 mounting overhead beam component support means 22, which includes pivotal joint means 22a enabling the beam be= 1 to be swung through 1800 about a longitudinal horizontal axis A - X tn bring alternate ones of the top and bottom flange plates 2 and 3 into position adjacent welding head support means 23 at different times for respective welding operations. The welding head support means 23 is mounted so as to be movable alongside the beam support 22 parallel to the central longitudinal axis X - X of the beam or girder 1 supported on the beam support 22.

The welding head support means 23 are disposed at opposite sides of the beam support 22 and include displacable portions 24 at the ends of which 25 are mounted two welding heads 26. The welding head suports 23 include drive and control means 27 formed and arranged to displace the welding heads 26 laterally of the longitudinal beam axis X - X so as to allow the welding heads closely to follow the traversely oscillating joint 11 between the corrugated web 6 and the bottom flange plate 3. In addition the control means 27 are formed and arranged so as to ensure substantailly synchronized movement of the two welding heads substantially directly opposite each other at either side of the welded joints 10 and 11.

Each welding unit 28 also includes an inert gas supply line 29 formed and arranged to supply an inert gas such as argon to shield the electric arc forming the welded joints 10 and 11.

Advantageously each welding unit 28 is provided with sensor means 30 formed and arranged for monitoring welding parameters including welding wire feed rate, welding head travel rate, voltage, current and inert gas supply rate.

In the above described welding apparatus embodiment, it will be appreciated that the overhead system 22 for supporting the beam requires the top and bottom flange plates 2 and 3 to be temporarily secured to the main web 6. This is conveniently effected in a tacking station 31 disposed upstream of the welding station 20 to form tack welds prior to continuous full penetration welding.

At the tacking station 31 there is provided an overhead gantry type lifting system 32 for use in removing the beam structure 1 and possibly also bringing in and positioning the main web 6 on to a web support 33 on which the web 6 is laid on to one of its sides 34. The flange plates 2 and 3 are then positioned along each side edge 35 of the main web 6 and firmly clamped thereto at right angles with the aid of a hydraulic ram clamping system 36. Above the clamping system 36 is mounted a tack welding unit 37 mounted 38 so as to run along the length of the web side edge 35. The welding unit 37 includes 2 vertical displacement means 39 for raising and lowering the welding head 40 as it tracks along the joint zone 10 between the corrugated main web 6 and the flange plates 2 and 3.Conveniently a control means 41 of the displacement means 39 is pre-programmed with the geometry of the web corrugations and joint zones 10 and 11 as the welding units traverse along the length of the corrugated main web 6.

In use of the tacking station 31, the welding heads 37 at eac side sdge 35 of the corrllgEted main n web 6 are used to form a plurality of spaced apart fillet welds along the length of the joint zones 10 and 11, preferably at points along parallelly extending web portions 61 at either side of the maximum width of the corrugated web 6 so as to provide maximum stability and security against relative movement between the main web 6 and the flange plates 2 and 3. With such an arrangement, it is sufficient to provide tack welds from one side only of the corrugated beam structure 1 corresponding to just one pass with the system of Figure 6.

desirably the precise sltis or the tack welds along the length of the beam structure 1 are recorded so that when the tack welded beam structure 1 is subsequently passed to the main welding station 20 where continuous full penetration welding is carried out, the welding units 26 thereof can be powered up and powered down respectively at the beginning and end of each tack weld so as to provide the necessary energy to cut through the tack welds and also to provide the full penetration weld between the main web 6 and the flange plates 2 and 3 thereby maintaining the consistency and continuity of the welded joint along the length of the beam 1.It will of course be appreciated that the welding parameters monitored by the sensors 30 will differ at the tack weld positions from other points along the length of the beam and it will therefore be necessary to programme corresponding acceptance window parameters modulations into the control system of the main welding station 20. (See also the control procedures schematically outlined in Fig.

9.) As explained above, in the apparatus of the welding station 20 the welding heads 26 are driven substantially synchronously either side of the corrugated main web 6.

Accordingly, it will be appreciated the welding head travel rates are modulated suitably at the internal and external corners 42, 43 of the corrugated main web 6, including for example as shown in Fig. 8A, temporary changes of direction 44 along the line of travel (shown in dashed outline), in addition to the required changes in angular disposition (shown in chain line) of the welding head. In particular, to ensure that the welding rate remains constant around the corners 42, 43 of the corrugated web 6, the welding head's arm 24 will travel backwards along the arcuate path 44 (Fig.

8B) as it exits from the internal corners 42 to confirm the head's correct position with respect to the line of the joint, as shown in Fig. 8B, which is a detail view of Fig.

8A to an enlarged scale highlighting this relative movement of the head 26 about the arm pivot point which lies between the welding head and its support arm. At about the same time, the arm 24 of the opposite welding head will make a relatively rapid arcuate forward sweep around the corresponding external corner on the opposite side of the web 6 in order to keep the linear speed along the weld line substantially constant.

As previously outlined, welding takes place using two welding machines (one either side of the web 6) whose movements are substantially synchronised so that the welding heads are maintained substantially directly opposite each other along the length of the beam. It will be appreciated that there may be a tendency for one head to lag behind the other at the corners of the web corrugations, but a limited degree of such lag will however generally be acceptable in practice. Thus for example with a web thickness of 15mm and an inner radius at the internal corner side of 25 mm, a lag of up to 12mm may be allowed. As the web thickness reduces, the permissable lag will be correspondingly reduced.

Fig. 9 shows a simplified schematic logic diagram of the steps in the control procedure for fabricating a corrugated web beta, in accordance with 'nethod of the invention, and which is embodied in the fabrication apparatus of the invention.

While the above description relates to a fabricated beam 1 in which the opposite flanges 2 and 3 are mutually spaced by a distance which is constant from one end of the beam 1 to the other end, with the corrugated web 6 being of correspondingly constant depth, the invention also encompasses fabricated beams with non-parallel flanges to for. sin or m'#lt'"nlv tapered or curved beams (with correspondingly varying depths of corrugated flange) to provide beams whose bending strength can vary along their length to match local variations in bending loads, as for example in cantilevers. Appropriate modifications will be made in the fabrication methods and apparatus.

Other modifications and variations can be made within the scope of the appended claims.

Claims (20)

CLAIMS:

1 A fabricated beam comprising first and second mutually spaced flange plates, each of said first and second flange plates having opposite side edges, and a corrugated web extending longitudinally along said beam between said flange plates, said web being in the form of a substantial plurality of generallly planar plate portions interconnected along a generally zigzag path longitudinally extending intermediate said side edges of said first and second flange plates, said web being connected to said first and second flange plates by substantially laterally symmetrical and substantially longitudinally continuous full penetration welds.

2 A fabricated beam as claimed in claim 1 wherein said corrugated web is in the form of longitudinal plate portions extending longitudinally of the beam and obliquely extending plate portions alternating with said longitudinal plate portions.

3 A fabricated beam as claimed in claim 2 wherein said beam includes at least one additional web plate component formed and arranged so as to form together with said one or more of said plate portions of said elongate web, a substantially closed box section.

4 A fabricated beam as claimed in any of claims 1-3 wherein said flange plates are mutually parallel.

5 A method for the fabrication of a beam which comprises first and second mutually spaced flange plates, each of said first and second flange plates having opposite side edges, and a corrugated web having opposite side edges welded to said flange plates along its opposite side edges by full penetration welds, said corrugated web extending longitudinally along said beam and being in the form of a substantial plurality of generally planar plate portions interconnected along a generally zigzag path longitudinaly extending intermediate said side edges of said first and second flange plates, said method comprising the steps of supporting said first and second flange plates transversely of said corrugated web in abutment with said opposed side edges of said corrugated web and full penetration welding said flange plates and said web together so as to fabricate a beam, said method further comprising the steps of providing first and second welding heads at opposite sides of said corrugated web adjacent a said side edge of the corrugated web, and moving at least one of said beam and said welding heads relative to the other such that said welding heads are mxi-ta-ned suustan. atly directly opposite each other at respective sides of said side edge of the corrugated web whilst full penetration welding said side edge of the web to the respective flange plate in abutment therewith along said side edge of the corrugated web such as to form a substantially laterally symmetrical and substantially longitudinally continuous full penetration weld between said web side edge and said flange plate.

R A TnetǒA as olmi in claim S further including the preliminary step o- a welding said thirst and second flange plates to said corrugated web.

7 A method as claimed in claim 6 further including the steps of providing monitoring means for monitoring at least one TIG welding apparatus operating parameter selected from welding wire feed rate, welding head travel rate, inert gas supply rate and voltage and current of the electric arc.

8 A method as claimed in claim 7 further including the step of adjusting said at least one TIG welding apparatus operating parameter in response to excursions therof beyond predetermined operating limits as detected by said monitoring means.

9 A method as claimed in claim 6 in which said corrugated web is supported horizontally on one side during said tack welding step, and further including the step of rotating said beam assembly through 900 about its longitudinal axis subsequent to tack welding and prior to full penetration welding.

10 A manipulation and welding apparatus for the fabrication of a beam as claimed in any of claims 1-4, said apparatus comprising a body, a beam component support means mounted on said body for supporting an inItially unwelded assembly of beam components comprising a corrugated web plate having corrugated side edges and at least one flange plate having one face in contact with one said corrugated side edge of said corrugated web plate along a corrugated joint zone, and welding head support means mounting first and second welding heads in opposed spaced apart relationship, at least one of said beam component support means and welding head support means being formed and arranged to permit relative movement, in use of the apparatus, longitudinally and transversely of the beam component assembely with said welding heads being operatively moved along the respective weld lines under the influence of a drive control means connected thereto and arranged for providing relative displacement therebetween at a substantially constant head travel rate relative to the weld lines to be formed along the corrugated joint zone whilst maintaining said first and second heads substantially directly opposite each other on either side of the corrugated web plate.

11 Apparatus as claimed in claim 10 wherein the welding head support means is formed and arranged for travel along said body relative to the beam component support means.

12 Apparatus as claimed in claim 1 wherein tne weiding head support means is also formed and arranged for varying the attitude of the welding head so as to maintain a generally predetermined attitude to said corrugated joint zone during traversal thereof by the welding head means in use of the apparatus.

13 Apparatus as claimed in claim 12 including sensing means for tracking a corrugated joint zone and memory means for holding details of the track of a corrugated joint zone to be welded: anti welding head travel control means for modulating the attitude and pathway of the welding heads, in response to changes in direction of the corrugated joint zone.

14 Apparatus as claimed in claim 10 including a tacking station for securely supporting the flanges against the web at right angles to the principal plane of said corrugated web and for securing the flanges to the web by means of welded tack joints

15 Apparatus as claimed in claim 14 including support means formed and arranged for supporting the web horizontally and clamping means for clamping the flanges to the opposed side edges of the web in a generally vertical position, in use of the apparatus.

16 A fabricated beam substantially as hereinbefore described with reference to the accompanying drawings.

17 A method for fabricating a beam, substantially as hereinbefore described with reference to the accompanying drawings.

18 Apparatus for fabricating a beam, substantially as hereinbefore described with reference to the accompanying drawings.

19 A beam fabricated by the method of claim 17.

20 A beam fabricated by the apparatus of claim 18.