AU626030B2 - Structural member and process for forming same - Google Patents

Description

i OPI DATE 19/02/90 p AOJP DATE 29/03/90 APPLN. ID 39720 89 PCT NUMBER PCT/AU89/00313 INTERNATIONAL APPLICATION PUBLISHED UNDER THE PATENT COOPERATION TREATY (PCT) (51) International Patent Classification 4 (11) International Publication Number: WO 90/01091 EO4C 3/07, 3/10, B21D 5/08 Al (43) International Publication Date: 8 February 1990 (08.02.90) (21) International Application Number: PCT/AU89/00313 (81) Desig.ated States: AT, AT (European patent), AU, BB, BE (European patent), BF (OAPI patent), BG, BJ (OAPI (22) International Filing Date: 25 July 1989 (25.07.89) patent), BR, CF (OAPI patent), CG (OAPI paten), CH, CH (European patent), CM (OAPI patent), DE, DE (European patent), DK, FI, FR (European patent), GA Priority data: (OAPI patent), GB, GB (European patent), HU, IT (Eu- PI 9427 27 July 1988 (27.07.88) AU ropean patent), JP, KP, KR, LK, LU, LU (European pa- PJ 1534 18 November 1988 (18.11.88) AU tent), MC, MG, ML (OAPI patent), MR (OAPI patent), MW, NL, NL (European patent), NO, RO, SD, SE, SE (European patent), SN (OAPI patent), SU, TD (OAPI (71) Applicant (for all designated States except US): TUBE TECH- patent), TG (OAPI patent), US.

NOLOGY PTY LTD [AU/AU]; 134 Ingram Road, Acacia Ridge, QLD 4110 (AU).

Published (72) Inventor; and With international search report.

Inventor/Applicant (for US only) GOLEBY, Leslie, David [AU/AU]; 134 Ingram Road, Acacia Ridge, QLD 4110

(AU).

(74) Agent: G.R. CULLEN COMPANY; 8th Floor, 79 Eagle Street, Brisbane, QLD 4000 (AU).

626 (54).Title: STRUCTURAL MEMBER AND PROCESS FOR FORMING SAME (57) Abstract

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A structural member which comprises a pair of hollow end sections (58) and an intermediate web (59) characterized in that each hollow end section (58) is welded to the intermediate web (59) so as to form two weld lines or joins (60) extending along the structural member. Suitably the intermediate web (59) is predominantly planar and the structural member is formed from a unitary sheet of metal having opposed edges vhereby a respective edge is located adjacent said intermediate web and is welded thereto to form said weld lines or weld joins The invention also includes within its scope a process for forming the structural member including the following steps: passing substantially planar metal strip through a plurality of forming stations .42) to successively deform opposed free edges of the metal strip so as to provide a pair of substantially hollow end sections (58) wherein a respective free edge is located adjacent to an intermediate web (59) interposed between each substantially hollow end section and (ii) welding the respective free edge to the intermediate web to form two weld lines or joins (60) extending along the structural member.

:__11 i This invention relates to a structural member and a process for forming same.

Non hollow or solid structural members such as Ibeams, rolled steel joists (RSJ's) purlins and girts which are used for structural purposes in buildings such as factories, houses and office buildings have been found to be normally satisfactory in use and have a basic cross-sectional shape or profile which is very efficient in resisting bending movement.

These conventional structural members or beams are normally formed from hot rolling processes.

However, such conventional solid structural members or universal beams which are generally formed from hot rolling processes generally comprise two parallel flanges and a single flat or planar web wherein the flanges are substantially thicker than the web. Such conventional solid structural members have certain disadvantages and these include the following:exposed surface area to mass and strength ratios are high which lead to increased costs for both corrosion protection and fire proofing; (ii) flange widths to thickness ratios are generally limited to avoid reductions in load bearing section capacity due to local buckling considerations; (iii) web widths to thickness ratios are generally limited to avoid reductions in section load bearing capacity due to local buckling considerations; (iv) the hot rolling method of manufacture leads to i production of substantial mill scale and rust as well as 0 s ,D Af 2 providing a limited minimum thickness; and prime painting during manufacture is not a practical proposition.

There also have been used cold rolled structural members which include purlins and rectangular hollow sections and these are subject to certain disadvantages as described below.

In particular purlin sections which are generally of C or Z shape have flange widths to thickness ratios and web width to thickness ratios which are severely limited by local buckling considerations.

Rectangular hollow section (RHS) have also been proposed as structural members wherein each wall of the rectangle was of substantially the same thickness. However, these conventional structural members were inefficient in regard to bending movement considerations and wall widths to thickness ratios were generally limited to avoid reductions in load bearing capacity due to local buckling considerations.

Structural members have also been proposed including a pai:: of hollow flanges which are separated by an intermediate web. Thus, for example, in U.S. Patent 3,342,007 to Merson, a structural member was proposed which was manufactured from a single piece of steel sheet by cold roll forming wherein there was provided triangular hollow flanges separated by a planar web. Each triangular hollow flange included a horizontal side and a pair of sloping sides or flanges and the free ends of the single piece of steel sheet were comprised of ends of each of the sloping sides which 0 CC-, 3 abutted the other adjacent sloping side.

In addition the structural members described in both the abovedescribed Merson and Lanternier specifications had markedly reduced load bearing capacities for concentrated loads.

U.S. Patent 3,517,474 to Lanternier also described a flanged structural assembly including a pair of hollow flanges which were rectangular or trapezoidal and an intermediate planar web. The hollow flanges and the web were all separate components and the web was welded to the hollow flanges. Each flange included a pair of free ends or edges which were bent or folded and which converged to the middle part of a top flange or wall of the hollow flanges.

U.S. Patent 426,558 to Ditheridge also described a structural member having a pair of hollow flanges and an intermediate planar web which was of an integral construction.

Although no method of manufacture is described it would seem that Ditheridge refers to wrought steel or iron beams or sills which are formed in a mould.

However, in regard to the structural members described in the abovementioned U.S. Patents it was considered that these structural members would have markedly reduced load capacities due to local buckling considerations. This would seem to be the case especially of U.S. Patent 3,342,007 to 25 Merson wherein the free ends of the single piece of steel sheet comprising one end of each sloping side abutted the other sloping side. This would also have applied to Lanternier. B cc C- 4 The flanged structural assembly of Lanternier in not being formed from a single piece of metal strip would also have been relatively expensive to produce because it was formed from three components. Also the manufacturing step of folding the free edges of each rectangular or hollow flange as described above would seem to complicate manufacture and increase the cost thereof.

It is therefore an object of the present invention to provide a structural member and a method of manufacture of same that alleviates the abovementioned disadvantages associated with the prior art.

According to one aspect of the present invention there is provided a structural member formed from a single strip of metal by a continuous cold rolling process, the structural member comprising:an intermediate web member and hollow flanges extending longitudinally of the intermediate web member; characterised in that the hollow flanges are formed by continuous seam welding of the respective free edges of the previously shaped hollow flange portions to the surface of the intermediate web member adjacent respective junctions with the web member; and that the free edges of the hollow flange portions are welded perpendicular to the surface of the intermediate web member by high frequency electrical induction or resistance welding. 1 The hollow flanges may be of any suitable shape and .7 4' c,4]

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1 :i thus may be circular, rectangular, triangular or polygonal.

It is also not necessary that each hollow flange have a similar shape so that it is within the scope of the invention to have differently shaped hollow flanges such as one being rectangular and the other being circular.

While it is preferred that each hollow flange be substantially of the same size this is not strictly essential and thus it is possible, having regard to the scope of the invention, that the hollow flanges be different in size as well as shape.

15 oooo oooo 20 i o i mo 'ooo -l 2 According to another aspect of the invention there is provided a process for forming, in a substantially continuous roll forming operation, elongate, structural member comprising spaced hollow flange member separated by an intermediate web member, the process including the steps of:passing a planar continuous strip of metal through a roll forming mill to successively deform opposed free edge portions of the metal strip to form spaced parallel hollow flange portions of predetermined cross-sectional shape, the hollow flange positions extending longitudinally of the intermediate web member; characterised in that a continuous seam weld is formed between each of the free edges of respective hollow flange portions and the surface of the intermediate web member adjacent the junction of the web mrmber and respective hollow flange portions; and that the free edges of the hollow flange portions are welded perpendicular to the surface of the f JJ cc- 1I-p

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i I ~L 6 iIII1II 1. 6 intermediate web member by high frequency electrical inductions or resistance welding.

In the process of the invention it is possible to initially subject the substantially planar metal strip to preforming operations wherein ancillary or additional structural features or embellishments may be imparted to the metal strip. These ancillary features include perforations, grooves, dimples, corrugations, protrusions and the like which may be considered appropriate having regard to the end use of the structural member or to increase load bearing capacity of the structural member.

The ancillary structural features made at the preforming stage may be either essentially unchanged or slightly or substantially modified by any subsequent forming 15 operations. Thus if desired further ancillary structural features or embellishments may be imparted to the structural S member of the invention after or during the forming operations.

operations.

i i oo •o go oo• e In carrying out the process of the invention the substantially planar metal strip may be successively deformed through a number of roll forming stations. Preferably each free edge portion may be successively or sequentially deformed so that the cross sectional profile of the metal strip is substantially W shaped after it passes through the forming stations. This is shown in detail in the drawings hereinafter. However, it will also be appreciated that other roll forming cross sectional profiles may be utilised such as for example the free edge portions of the metal strip being

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4bent inwardly through a number of different passes so as to form a substantially triangular hollow flange. This is also shown in the drawings hereinafter.

It is also possible in regard to the forming step that the desired end profile of the structural member be formed directly after passage of the metal strip through the final forming stations. However, it is also within the ambit of the invention that a basic cross-sectional shape e.g. two separate circles separated by a planar web be formed after passage through the final forming station which is then subsequently subjected to further shaping procedures to produce a number of different cross sectional profiles.

Another possible alternative is to produce the basic crosssectional shape of two separate circles separated by a planar web using different roll passes and then subjecting the basic shape to further shaping operations to produce a variety of cross sectional profiles.

In regard to the forming step, it is preferred to pass the metal strip through a plurality of cold roll forming stations.

2 After the forming step the strip or workpiece may be passed to a welding station. A number of welding methods could be used in a continuous welding process and these include the following: high frequency induction and/or electrical resistance welding; (ii) metal inert gas; (iii) tungsten inert gas; ~I i. i (iv) carbon dioxide shielded arc; atomic hydrogen gas arc; (vi) spot welding; (vii) electron beam welding; (viii) laser welding; or (ix) gas welding Of the above it is preferred, having regard to the process of the invention to use high frequency induction and/or electrical resistance welding as each of the other welding processes suffer from at least one serious limitation which precludes its use in a high speed continuous welding operation.

20 a 2V In high frequency electrical induction or resistance welding a high frequency alternating current is used to induce electrical currents in the areas requiring welding so that opposing weld seams where the free edge of the strip abuts the intermediate web) at two separate locations are heated to a point where fusion can occur.

At the welding station it is also within the scope of the process of the invention to apply one or more scarfing operations to the workpiece whereby any excess weld bead may be removed. As an alternative to scarfing to remove excess weld bead there also may be used weld bead flattening.

Finally, and if desired, the workpiece or shaped metal strip may be passed to a straightening and/or shaping station wherein shaping rolls mounted in a number of cold forming roll stands are used to produce the final desired

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r oo e 0 S. *t I k ft cross sectional profile. The shaping rolls may successively deform the welded section. However, it is possible to avoid the use of subsequent shaping rolls by direct forming the workpiece so that after passing through the welding station it is already in the desired final shape. In this case however straightening may be an integral part of the direct forming process.

Reference may now be made to a preferred embodiment of the invention as shown in the attached drawings wherein:- FIG 1 is a schematic view of apparatus used in the process of the invention including a forming section, edge preparation and welding section and a shaping and straightening section; FIG 2 is a side elevation of the forming section; FIG 3 is an end view of rolls S1-S2 shown in FIG 2; FIG 4 is an end view of rolls F2-F4 shown in FIG 2; FIG 5 is an end view of rolls F1-F2 shown in FIG 2; FIG 6 illustrates a typical set of rolls Fl; FIG 7 illustrates a typical set of rolls Sl; FIG 8 illustrates a typical set of rolls F4; FIG 8A illustrates another typical set of rolls F1 or F2; FIG 8B illustrates another typical set of rolls F3 or F4; or S2; FIG 8C illustrates another typical set of rolls S2 FIG 9 illustrates another preparation and welding section; side view of the edge 1- FIG 10 illustrates an end view of rolls WP1; FIG 11 illustrates an end view of rolls WP2; FIG 12 illustrates an end view of rolls EP1; FIG 13 illustrates a typical set of rolls WP1; FIG 14 illustrates a typical set of rolls EP2 FIG 15 illustrates a typical set of rolls EP1; FIGS 16, 17 and 18 illustrate alternative view of the welding section showing welding apparatus (FIG 16), welding rolls (FIG 17), and scarfing apparatus (FIG 18); FIG 19 illustrates a side view of the shaping and straightening section; FIG 20 illustrates a typical set of rolls designated as SH3; as SH1; FIG 21 illustrates a typical set of rolls designated 55 0*

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25 FIG 22 illustrates an end view of rolls SH1; FIG 23 illustrates an end view of rolls SH2; FIG 24 illustrates an end view of rolls SH3; FIG 25 illustrates an end view of rolls SH4; FIG 26 illustrates an end view of rolls FIGS 27, 28 28A illustrate alternative flower sections that may be obtained in the forming step; and FIGS 29-35 illustrate alternative cross sectional profiles that may be obtained in accordance with the invention.

For comparative purposes, FIG' 36 illustrates a beam in accordance with the aforementioned Merson specification which is subject to local buckling; '4" *I V=fn 11 FIGS 37, 38 and 39 illustrate a structural member of the invention prestressed by appropriate means, wherein FIG 38 is a section along line B-B of FIG 37.

In FIG 1 there is shown flat metal strip 10 being passed through a forming section 11 having forming rolls Fl, F2, F3 and F4 as well as side rolls S1 and S2. There is also shown edge preparation and welding section 12 having rolls EPI, EP2 and WP1. Also shown is welder 13. Finally there is shown shaping and straightening section 14 having shaping rolls SHI, SH2, SH3 and SH4 and straightening rolls ST1. Also shown is structural member 15 having the desired cross sectional profile in accordance with the invention.

In FIGS 2-5 the shaping rolls F1-F2 as best shown in FIG 5 include adjusting screws or screw jacks 16, drive shafts 17 and drive unit 18. Also shown are upper rolls 19 and lower roll 20. Upper rolls 19 are each vertically adjustable by movement along adjusting screws 16. Also shown are bearing housings 21. Support stands 23 and 24 are also. shown.

Movement of rolls 19 along screw jacks 16 is caused by manual actuation of adjustment mechanisms 17A.

The forming rolls F3-F4 as best shown in FIG 4 include adjusting screws or screw jacks 25 for top rolls 26.

Shafts 27-28 are connected to a drive unit such as drive unit 18 shown in FIG 5. There are also shown side rolls 26A and lower roll 26B. Horizontal adjustment of side rolls 26A relative to workpiece 10 is caused by adjusters 29. There are also indicated direct coupling 30 and connection shafts 31 which engage with gearboxes 32 to move the top roll 26 along w c 12 screw jacks 25 in unison.

Actuation of vertical movement of rolls 26 is caused by manual adjustment wherein actuating spindle 32A is rotated by appropriate means.

The side rolls S1-S2. as best -shown in FIG 3 include roll stands 33, bearing housings 34, vertically oriented rolls lower roll 36 and roll shafts 37.

FIGS 6-8 shown sequentially the formation of strip and the development of the desired W cross sectional profile. The side edges of strip 10 are gradually bent inwardly as shown by the action of rolls 19 and 20 in FIG 6, rolls 35 and 36 in FIG 7 and rolls 26A, 26B and 26 in FIG 8.

In FIGS 8A, 8B and 8C there is shown a modified sequence of shapes that are applicable to roll stations F1 and F2, F3 and F4 and S1 and S2 respectively. These roll S* station. configurations are similar to those shown in FIG 3, 4 and 5 with the exception that rolls 19A and 20A in FIG 8A, rolls 26V and 26W in FIG 8B and rolls 35A and 36A have a different profile to the corresponding rolls 19 and 20 in FIG S 26 and 26B in FIG 4 and 35 and 36 in FIG 3.

FIGS 9-12 show the edge preparation and welding /section wherein strip 10 passes sequentially through rolls EP1, EP2 and WP1.

.FIGS 10-12 show rolls WP1, EP2 and EP1 which are all very similar in structure to rolls F3-F4 described in FIG 4 and hence similar reference numerals are shown. However the top rolls of FIG 10, 11 and 12 are designated 26K, 26H and 26E respectively, the side rolls 26L, 261 and 26F and the *IC i 7 11' 0 H U y 13 bottom rolls are designated 26M, 26J and 26G. Each of rolls WP1, EP2 and EP1 are supported on roll stands 22.

FIGS 13-15 also show sequentially the development of the cross sectional profile of strip 10 after passing through rolls EP1, EP2 and WP1. The formation of the desired circular hollow end sections is shown from the W profile shown in FIG 13.

FIGS 16-18 show welding apparatus used in the invention and this includes a high frequency welder 13 having welding contacts Aa, Ab, Ba and Bb which contact each free edge 38 of strip 10 and web part 39 as shown.

In relation to use of high frequency welder 13 the parts 38 and 39 of strip 10 are forced into abutment.

However, it is emphasised that in the case of use of other o e welding means such as TIG or MIG parts 38 and 39 do not have S* to necessarily abut but be located closely adjacent thereto.

FIG 17 shows the operaton of the rolls of roll assembly WP1 in producing the desired abutment of parts 38 and 39.

FIG 18 shows the operation of scarfing means 40 to S remove excess weld bead as discussed above.

FIGS 19-21 show the operation of shaping rolls SH1, SH2, SH3, SH4 and SH5 and straightening rolls ST1.

The operation of a typical shaping roll is best shown in FIG 20 and this is very similar to the operation of forming rolls F3, F4 as described above, hence similar reference numerals have been utilised. However, the top roll j ii has been designated 41, side rolls 42 and bottom roll 43.

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14 All the rolls are supported on roll stands 44.

The operation of the straightening roll assembly ST1 is best shown in FIG 21 and this includes roll housing There are provided a pair of top and bottom rolls 46-47 and a pair of side rolls 48. The entire assembly 49 of rolls 46, 47 and 48 may be pivoted about a centre axis designated by X in the plane of the drawing by actuation of handle 50 which engages in gearbox 51. There are also provided adjusters 52 and 53 for vertical adjustment movement of rolls 46 and 47 in supporting slides 54 relative to workpiece 10. There are also provided adjusters 55 and 56 for horizontal adjustment movement of side rolls 48 relative to workpiece 10 in supporting slides 57.

The sequential series of events which take place in regard to the workpiece 10 are now shown in FIGS 22-26 which demonstrate that a workpiece 10 having a cross sectional profile as best shown in FIG 22 may be converted into a number of other shapes as shown in FIG 23, 24, 25 or 26 to finally produce triangular hollow flanges. These were converted from circular end sections shown in FIG 22.

Typical flow sections that may be obtained in accordance with the process of the invention wx..ch are different to the preferred W profile as described previously are shown in FIGS 27, 28 and 28A after passage of strip 10C th:rough a series of rolls as described above. FIG 27 illustrates a profile obtained wherein the web remains primarily planar during the forming process. On the other hand FIGS 2a and 28A show that this is not essential and that i ii ,i

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i other shapes may be obtained such as sequential being of the free edges of the strip inwardly or back upon themselves to produce triangular hollow end sections.

FIGS 29-35 show various possible cross sectional profiles of structural members that may be obtained in accordance with the invention. FIG 29 shows a preferred structural member having hollow triangular flanges 58 and web 59. Two weld seams 60 between end sections 58 and web 59 are also shown. For the sake of convenience similar reference numerals have been utilised in regard to the remainder of the structural members shown in FIGS 30-35. Differently sized hollow flanges 58A and 58B may be obtained in accordance with the invention as shown in FIG 32. There also may be provided grooves 61 as shown in FIG 35 if desired.

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,2 *eo o*o From the foregoing it therefore can be appreciated that structural members produced in accordance with the invention have a number of advantages when compared to the prior art. In this regard the structural member of the present invention combines the traditional advantages of cold formed hollow sections with a basic shape which is relatively efficient in resisting bending movement.

Therefore advantages attributable to the present invention when compared to conventional non hollow or solid structural members include the following;minimum thickness of sections not limited by a hot rolling process in being preferably formed by cold rolling; (ii) cold-rolling of strip during forming enhances yield; (iii) removal of mill scale and rust during forming may be cc- AA "Al f Is i i i 'r 16 carried out; and (iv) prime-painting during manufacture may also be carried out.

The basic shape of the structural members of the invention also will be relatively efficient for the following reasons:the section consists of two hollow flanges connected by a single web; the structural members of the invention are thus similar to traditional universal beams which have two parallel flanges and single flat web with flanges substantially thicker than. the web; a single web is much more efficient than two webs as in traditional cold-formed hollow sections; .ft 5 because the flanges are hollow the flanges are effectively much thicker than the web. This is much more ;efficient than having equal flange and web thicknesses; flange width to thickness ratios are also less limited by local buckling and web buckling considerations than is the case with traditional universal beams; web width to thickness ratios are effectively reduced by the width of the hollow section flanges which in turn reduces the effect of web buckling considerations on load beam capacity; because of these benefits in local buckling and web buckling considerations, higher yield strength steels can be used to provide significant economic advantages;: and low exposed surface area to mass and strength ratios ii,, i 17 are obtained which assists in reducing costs for both corrosion protection and fire-proofing.

It should be noted that these advantages are inherently related to the ability to produce welded hollow flanges or both edges of the web. An open section of similar shape, i.e. a section where the free ends of the metal strip are not welded to the web to form two closed h-ollow sections, would have markedly reduced load capacities due to local buckling considerations. This is clearly applicable to the prior art referred to previously, i.e. U.S. Patent 3,342,007 and U.S. Patent 3,517,474.

The main advantage of the structural members of the invention from a manufacturing viewpoint is that the structural members can be produced in conventional tube rolling mill. That brings all the advantages that coldforming offers over hot-rolling, including a much lower investment in plant and greatly reduced energy requirements.

Structural members of the invention also have other advantages which are not offered by either universal beam sections or traditional cold-formed hollow section. It is possible to utilise the space inside the hollow flanges for location of building services. In the case of water reticulation, the use of non-destructive procedures to test weld quality can be relatively easily extended to test watertightness of the hollow flanges.

It is also possible to provide pre-tensioning cables inside the hollow flanges to provide greater load capacity and control of in situ beam deflection.

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As discussed previously it is clear that the advantage that the structural member of the invention has over the prior art is that the structural member of the invention has two integrally formed hollow flanges connections by a single web.

An open section of similar shape, i.e. a section where the ends of the metal strip were not welded to the web to form two closed hollow flanges, would have markedly reduced load capacities due to local buckling considerations.

It is important to note in U.S. patent 3,342,007 that this relates to an open section, in that the free edges of the strip merely abut the web section of the 'member.

Because this product is an open section it would have markedly lower load capacities than achieved by the present invention.

In the Merson specification that portion of the flange which is bent to abut the web of the member would form substantial local buckles at relatively low loads. This is illustrated hereinafter in FIG 36. This is due to this segment of the section acting primarily as an unstiffened compression element, when the member is subject to either bending or compressive loading. Due to the local buckling of this portion of the section, the member as a whole would suffer dramatically reduce load carrying capacity.

This can be demonstrated relatively easily by modern theoretical analysis techniques for cold-formed steel sections. Alternatively it could be demonstrated by experimental testing of the product described in the Merson specification.

I a L X 19 The local buckling problems associated with the Merson product are overcome in the structural members of the invention by the welding of the free edge of the flange section to the web at two separate locations, thereby creating two closed hollow flanges connected by a single web.

The closed hollow end flanges of the invention have a much greater resistance to local buckling than that afforded by the open section proposed by Merson. These web sections also have improved local buckling performance due to both reduce depth of web and the restraint offered to the web by the hollow flange sections.

It should also be noted that the assertions made in the Merson specification relating to resistance to concentrated loads would seem to be extremely dubious. It is -:105- claimed that load applied to the top flanges of the member I; will be transmitted equally by the sloping segments of the member to the web of the member. One sloping side of the flange member is said to abut to the other sloping side of the flange member so that load "will be equally borne by the :;4P sloped sides to the web, without setting up members which might tend to cause the structural member to sway to either side".

SThese claims however would seem to be unjustified.

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S. The concentrated load will tend to follow the stiffest load path. That sloping side which is continuous with the web L will carry a far greater proportion of the concentrated loads.

The degree of support offered by the abutting join is very doubtful. In fact at ultimate loads it is unlikely that the ,j qc f i~ N' :7 c sloping side with abutting join will provide any support to concentrated loads. Further the comment on setting up moments and sway seems largely irrelevant. This would be clearly evident from appropriate experimental testing.

It should be noted that the above problems associated with the Merson specification could have been overcome by continuous welding of the free edge of the strip to the web of the section, instead of simply abutting the free edges. However such a welding operation would be difficult for the Merson section, because the two abutting joins are located on one side of the member. Welding of the section would induce substantial distortion in the finished section, which would have to be removed by some further straightening process.

It is important to emphasise that the preferred section is formed from a single unitary piece which is welded at two separate locations to form a basic cross-sectional S0 :shape of two separate circles connected by a single web. This basic cross-sectional shape consisting of two separate circles :2p: connected by a single web can then be shaped into a myriad of final section shapes.

The preferred section thus consists of two hollow 0 flanges of any shape connected by a single web. The triangular shape which is similar to Merson (though as previously noted, Merson is an open section and not a closed hollow section) is only one shape amongst a wise range of shapes which are included within the scope of the current invention.

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1 k< i^;c 21 Two preferred shapes of the present invention are the symmetrical triangular shape which equates to the current range of universal beams and a further symmetrical triangular shape which equates to the current range of hot-rolled channels.

As previously discussed it would also be possible to utilise the space inside the hollow flanges to provide for pre-stressing of the structural members by the installation of pre-tensioning members within the hollow flanges.

It is possible to improve substantially the load carrying capacity and utility of the structural members of the invention by the use of pre-tensioning techniques. The following advantages are attributable to the use of pretensioning members within, the hollow end sections:- Pre-stressing provides an economical *method of inducing positive camber into v sections of the invention acting as beams.

S* Camber is typically used in floor beams in multi-storey steel framed buildings to °oeAio° counteract the affect of deflection in the floor beams due to the loading of wet concrete applied during the construction •ego! stage; (ii) Universal beams are normally cambered by a method known as heating and shrinking whereby a section of the beam on one side is heated then cooled rapidly to induce a bend in the beam; iCC 01 c c. 73 >l

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III-_I~I-~LY-1I~- U- ri II_- ii: (iii) In addition the resistance of the section of the invention to deflection is improved by the pre-stressing of the section. The action of the pre-tensioning member provides a reduction in deflection for the pre-tensioned section, when compared with a section without pre-tensioning; (iv) Pre-tensioning also improves the performance of composite sections consisting of sections of the invention acting in conjunction with concrete. The ultimate load capacity of such composite sections is improved by the pre-stressing of the section of the invention; and Further advantages can be provided by filling the hollow end section with grout so that the pre-tensioning member is protected from the effects of fire. The pre-tensioning member can then be used to improve the load capacity of such composite sections in fire loading situations.

Thus from the foregoing it will be appreciated that the invention includes within its scope structural members of the invention pre-stressed by appropriate reinforcement means as will be discussed in detail hereinafter -rcC A A off 70 CC Preferred reinforcement means may comprise high i i i r ;a eltl i i; r: preparation and welding section; i. "ii

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23 tensile metal 'oars which are located within the hollow interior of the structural members of the present invention wherein the reinforcement means or pre-stressing members are located within one of the hollow flanges.

The pre-stressing members extend the full length of a structural beam of the invention within that hollow flange.

Because the pre-stressing members are located in only one of the hollow flanges any applied pre-stressing load will act eccentrically to the centreline of the section.

The high tensile metal bars may be manufactured with high capacity threads on both, ends and are suitable provided with high strength nuts, purpose built bearing plates and spherical washers. The bars are subsequently pre-tensioned to a pre-determined load with suitable means such as a hydraulic jacking system. Both the load measured at the jacking unit and the measured elongation in the pre-tensioning bar are used to control the amount of load actually applied. However, it will be appreciated by one skilled in the art that other .2C7: suitable pre-stressing member(s) attachment means may be used.

Once the desired load is achieved the nut is engaged to maintain the load and the jack released. Bearing plates are required to ensure that the highly concentrated loads created by pre-tensioning do not cause local failure in the hollow flanges. Spherical washers are preferably used to ensure that the pre-tensioning member is only subject to concentric load.

Following pre-tensioning it is possible to fill the 24 hollow flange with grout. Filling with grout in this instance can be used to improve the resistance to load under fire and help prevent the pre-tensioning members from corrosion. Grout filling is not a necessary requirement of the preferred pre-tensioning method for the sections and both grout filled and unfilled cores are suitable.

It should be noted that high tensile cables could be used in lieu of high tensile metal bars and either single or multiple pre-stressing members could be used within the hollow flanges.

In FIGS 37-39 the structural member 64 of the invention has hollow flanges 65 and intermediate web 66.

Pre-stressing member 67 is shown attached to structural member 64 by bearing end plates 68 and spherical nut 69.

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Claims (17)

1. 2. A structural member as claimed in claim 1 wherein ee* S the cross sectional profile of one or both of the hollow flange portion is changed after the welding of respective free edges thereof to the surface of the web member.
2. 3. A structural member as claimed in claim 1 whercin the hollow flanges are of the same cross sectional shape.
3. 4. A structural member as claimed in claim 2, wherein the hollow flanges are of the same or different cross- sectional shapes A structural member as claimed in any preceding claim wherein the hollow flanges are of the same or different cross-sectional areas. S VCdcr a 1: I% :-tC~ P at ~~3FS 26
4. 6. A structural member as claimed in claim 2 or claim wherein at least one hollow flange having a symmetrical triangular cross-sectional shape.
5. 7. A structural member as claimed in any one of claims 1 to 5 wherein at least one hollow flange has a circular cross-sectional shape.
6. 8. A process for forming, in a substantially continuous roll forming operation, elongate, structural members comprising spaced hollow flange members separated by an intermediate web member, the process including the steps of:- passing a planar continuous strip of metal through a roll forming mill to successively deform opposed free edge portions of the metal strip to form spaced parallel hollow flange portions of predetermined cross-sectional shape, the :o hollow flange positions extending longitudinally of the intermediate web member; c h a r a c t e r i s e d in that, a continuous seam weld is formed between each of the free edges of respective hollow flange portions and the surface of the intermediate web member adjacent the junction of the web member and respective hollow flange portions; and that the free edges of the hollow flange portions are welded perpendicular to the surface of the intermediate web member by high frequency electrical induction or resistance welding.
7. 9. A process as claimed in claim 8, wherein one or both of the respective hollow flanges is subjected to further deformation in the roll forming mill after the welding step to change the cross-sectional profile of the one or both hollow 4J cj i 27 flanges. A process as claimed in claim 8 or claim 9 wherein the central region of the planar metal strip which forms the intermediate web is subject to deformation in the roll forming mill to form a transversely contoured intermediate web.
8. 11. A process as claimed in claim 10, characterised in that deformation of the central region of the metal strip occurs before the free ends of respective hollow flange members are welded to the surface of the intermediate web member.
9. 12. A process as claimed in claim 10 or claim 11 wherein the transversely contoured web member is subject to a further deformation step in the roll forming mill to form a planar intermediate web member.
10. 13. A process as claimed in claim 10, wherein the intermediate web member is transversely contoured in the roll forming mill after the step of welding the free edge of I respective hollow flange members to the surface of the intermediate web member.
11. 14. A process as claimed in claim 8 wherein the hollow flanges are initially formed with a circular cross-section.
12. 15. A process as claimed in claim 9 wherein one or both of the hollow flanges is formed with a triangular cross- section.
13. 16. A process as claimed in any one of claims 8 to wherein both hollow flanges are formed with identical cross- sectional areas. I
14. 17. A process as claimed in any one V ;laims 8 to 15 Cci 1 W' 1 L 28 wherein the hollow flanges are formed with differing cross- sectional areas.
15. 18. A process for forming a structural member substantially as hereinbefore described with reference to any one of FIGS 1 to 26.
16. 19. A structural member as claimed in any one of claims 1 to 7 further including at least one pre-stressing element located within a hollow flange of said structural member. A structural member substantially as hereinbefore described with reference to any one of FIGS 20 to 26, 29 to or 37 to 41.
17. 21. A structural member whenever made in accordance with the process of any one of claims 8 to 18. Ot 6* o• 6 eo i cc i c