Steel Construction - SSAB

3Volume 5August 2012, p. 158-167ISSN 1876-0520

Reprint

Steel Construction

Cold-formed high-strength tubes for structural applicationsPekka O. Ritakallio

Design and Research

2

Articles

© Ernst & Sohn Verlag für Architektur und technische Wissenschaften GmbH & Co. KG, Berlin · Steel Construction 5 (2012), No. 3

1 Introduction

Many examples in nature show theexcellent properties of the tubularshape with regard to loading in com-pression, torsion and bending in alldirections. Furthermore, the closedshape reduces the area to be pro-tected and extends the corrosion pro-tection life. These excellent proper-ties are combined with an attractiveshape for architectural applications [1].Tubular materials enable steel struc-tures that are both architecturally andaesthetically impressive and also effi-cient structures from an engineeringpoint of view [2]. Increased strengthopens up the chance to reduce wallthicknesses and the weight of the struc-ture, see Fig. 1 [3].

Reduced wall thickness and lessweight usually bring benefits: – Easier processing– Lower transportation costs or in-

creased payloads– Possibility of realizing structures

that are not feasible with lower-strength steels

– Reduction in environmental impactand life cycle cost

Over the course of the last 30 yearswe have experienced a continuoustransition towards higher-strengthstructural tubes, see Fig. 2 [4]. Duringthe 1980s grade S275 dominated. Inthe 1990s grade S355 gradually tookover and has been dominant since

Pekka O. Ritakallio*

Cold-formed high-strength tubes forstructural applications

Cold-formed hollow sections are the dominant tubular construction material. The applic-ability of cold-formed tubes is sometimes questioned because of doubts about low-tem-perature ductility, deformation capacity of welded joints, suitability for welding in thecold-formed corner, poor fatigue behaviour of the corner or suitability for hot-dip galva-nizing. It is also claimed that by choosing hot-finished tubes, such risks can be automati-cally avoided. This study confirms that appropriate tube manufacturing yields cold-formedEN 10219 tubes in grades S355J2H to S460MH with a performance equal to or better thanhot-finished tubes. Properly made cold-formed high-strength tubes are available for fab-ricating efficient lightweight structures and can be safely used even at low temperatureswithout the aforementioned doubts.

DOI: 10.1002/stco.201210020

Selected and reviewed by the ScientificCommittee of the 12th Nordic SteelConstruction Conference, 5–7 Septem-ber 2012, Oslo, Norway* E-mail: [email protected]

Fig. 1. Weight-saving potential of steel for tension and bending [3]

Fig. 2. Evolution of structural tube strengths [4]

Yield strength [MPa]

09_158-167_Ritakallio (SC3)_000-000_Steel Constr. (3sp).qxd 01.08.12 11:18 Seite 158

3Reprint: Steel Construction 5 (2012), No. 3

P. O. Ritakallio · Cold-formed high-strength tubes for structural applications

then. Right now we are again witness-ing a transition and grade S420MH isanticipated to take over as the stan-dard material. This evolution is notincidental. It is due to progress in steel-making, tube manufacturing, work-shop fabrication, welding technologyand design.

2 Structural tubes

From a global perspective we are deal-ing with a diversity of quality. Accord-ing to Packer and Chiew [5], structuraltubes for steel construction are manu-factured in diverse locations aroundthe world, to a variety of standards,by either a hot-finishing or seamlessprocess or, more commonly, by cold-forming. The implications of using ma-terial produced to a particular stan-dard in various statically loaded ordynamically loaded applications areoften not fully appreciated. Problemsregarding surface finish, corner crack-ing and hot-dip galvanizing have beenencountered in North America andAsia with certain cold-formed squareand rectangular hollow sections. Dueto these observations these productsare now subject to constraints forseismic applications. This has also ledto a fundamental re-appraisal of thecold-formed manufacturing specifica-tion in North America.

In Europe we have harmonizedstandards for two main types of prod-uct: – EN 10210-1&2 – Hot-finished struc-

tural hollow sections of non-alloyand fine-grain steels

– EN 10219-1&2 – Cold-formedwelded structural hollow sectionsof non-alloy and fine-grain steels

The manufacturing methods for theseproducts are different. Consequently,the dimensions, tolerances and cross-sectional properties are slightly differ-ent, too.

“Hot-finished” stands for a man-ufacturing method where the finalforming process of the tube is carriedout hot, with final deformation> 700 °C, or where the tube is cold-formed and then subsequently fullbody heat-treated at a temperature> 550 °C. Normalized and normalizedrolled tubes are regarded as hot-fin-ished provided the tubes are processedor heat-treated in the normalizing tem-perature range.

“Cold-formed” stands for a man-ufacturing method where the mainforming process of the tube is carriedout at ambient temperature and theproduct is supplied without additionalheat treatment (except the weld seammay be heat-treated). Cold-formed hol-low sections are the dominant tubu-lar construction material (by a roughestimate 80–90 % of the volume).Economical and environmental con-straints favour cost competitivenessand higher strength. The cold-form-ing route is naturally economical andcan mostly adapt to higher strength,too.

The applicability of cold-formedtubes is sometimes questioned or lim-ited due to doubts about:– Low-temperature ductility– Deformation capacity of welded

joints – Suitability for welding in the cold-

formed corner – Poor fatigue behaviour – Suitability for hot-dip galvanizing

It is also claimed that choosing hot-finished tubes means it is possible toavoid the above risks because theseproducts have inherently better grainstructure and superior mechanicalproperties compared with their cold-formed counterparts [5]. In otherwords, there are claims that cold-formed tubes do not offer an accept-able level of structural safety and reli-ability.

The manufacture of high-qualitycold-formed tube comprises three cru-cial steps:1. Integrated steelmaking – ladle re-

fining – slab casting– appropriate chemistry of the steel

2. Hot rolling – controlled coolingand coiling– appropriate microstructure and

mechanical characteristics of theflat steel

3. Tube manufacturing – cold form-ing – welding – (weld normalizing)– shaping– appropriate dimensions and

structural properties and suitabil-ity for shop fabrication, down-stream processing and structuraluse

Thus, the quality of tube is not pureserendipity. It is a result of the ade-quate processing of the steel and man-ufacturing of the tube.

The aim of this paper is to high-light:– The fundamental reasons for the

doubts listed above regarding cold-formed tubes.

– The importance of the proper man-ufacturing of structural hollow sec-tions.

– The reliability and performance ofappropriate cold-formed structuralhollow sections.

3 Low-temperature ductility

Kosteski et al. [6] carried out a com-prehensive study of the low-tempera-ture impact properties of rectangularhollow sections from different sourcesand demonstrated the diversity of qual-ity while comparing:1. Products from various manufactur-

ers: North America, South Amer-ica, Japan and Europe

2. Product properties in various partsof the cross-section

3. Product properties in various ori-entations in the cross-section

Some of the observations from Koste -ski et al. [6] are shown in Fig. 3.

Comparison with European stan-dards EN 10210 and EN 10219 en-ables the following conclusions: – Hot-finished hollow section (d) is

quite uniform and conforms toEN 10210 grade S355J2H in all lo-cations over the cross-section.

– Cold-formed hollow section (c) isquite heterogeneous and does not conform to EN 10219 gradeS355J2H in any location over thecross-section.

– Stress-relieved hollow section (g) isextremely heterogeneous but con-forms to EN 10219 grade S355J2Hin all locations over the cross-sec-tion.

– Cold-formed product (h) is ratheruniform and conforms to EN 10219grade S355J2H in all locationsover the cross-section.

The study of Kosteski et al. [6] en-ables important conclusions:1. The products available on the mar-

ket are rather diverse.2. The product properties do not cor-

relate with the method of manu-facture.

3. Grade S355J2H rectangular hol-low sections with impact proper-ties conforming to EN 10210 or


4 Reprint: Steel Construction 5 (2012), No. 3


EN 10219 in any location and inany orientation are technically pos-sible and available on the Euro-pean market.

Ruukki’s current standard quality“Ruukki double grade S420MH/S355J2H” conforms to EN 10219-1&2grades S420MH and S355J2H and ful-fils the corresponding Charpy-V re-quirements both on the flat face and incorner area as well, see Figs. 4 to 6.

The manufacturing method, hot-finished or cold-formed, is not thefundamental factor that dictates thelow-temperature toughness. The ba-sic reason is related to other factorsin steelmaking and tube manufactur-ing. Hence, the quality of the productvery much depends on the supplier.Properly manufactured grade S355J2Hand grade S420MH rectangular hol-low sections with impact propertiesconforming to EN 10219 in any loca-tion of the cross-section and in anyorientation are technically possibleand available on the European market.

4 Welding in the cold-formed corner area

Rectangular hollow sections are wellsuited to the manufacture of welded

structures. For historical reasons, thereare concerns regarding the possiblestrain ageing caused by welding andhence the reduction in impact tough-ness of rectangular hollow sectioncorners. Consequently, Eurocode 3 in-cludes restrictions on welding in thecorner area [7].

EN 1993-1-8 section 4.14 “Weld-ing in cold-formed zones”, states thefollowing [7]:

“Welding may be carried outwithin a length 5t either side of acold-formed zone provided that oneof the following conditions is fulfilled:– the cold-formed zones are normal-

ized after cold-forming but beforewelding

– the r/t-ratio satisfy the relevantvalue obtained from Table 4.2. inEN 1993-1-8”

The requirements for the corner pro-file of EN 10219 hollow sections [8]are given in Table 2.

A comparison of Tables 1 and 2illustrates that rectangular hollowsections according to EN 10219 donot automatically satisfy the require-ments of EN 1993-1-8 for welding inthe cold-formed corners.

Verification of reliable weldingin cold-formed corners of rectangularhollow sections was the subject of adetailed study by Puthli and Herion[9], [10]. Their study focused on cold-formed rectangular hollow sectionsproduced by selected European man-ufacturers to European standard EN10219 and included the influence of:

Fig. 3. Charpy-V impact properties of hollow sections from various manufacturers[6]

Fig. 4. Charpy-V impact toughness of cold-formed hollow section, EN 10219 –Ruukki double grade S420MH/S355J2H – 60 × 60 × 5 mm



– chemical composition – corner radius – welding parameters – steel grades – service temperature

The characterization and testing ofthe tubular cross-sections was verydetailed. Welding in the corner wastested to clarify the influence of weld-ing on the Charpy-V impact tough-ness in the corner area. The testingincluded base material from the flatface, cold-formed corner as suppliedand the corner as welded. The posi-tion of the notch in the welded cor-ner specimen is shown in Fig. 7.


Fig. 5. Charpy-V impact toughness of cold-formed hollow section, EN 10219 –Ruukki double grade S420MH/S355J2H – 120 × 120 × 8 mm

Fig. 6. Charpy-V impact toughness of cold formed hollow section, EN 10219 –Ruukki double grade S420MH/S355J2H – 250 × 250 × 12.5 mm

Table 1. Conditions for welding cold-formed zones and adjacent material, EN 1993-1-8 Table 4.2 [7]

r/tStrain due to cold

forming (%)

Maximum thickness (mm)

Generally Fully killedAluminium-killed

steel(Al ≥ 0.02 %)

Predominantly static loading

Where fatigue predominates

≥ 25 ≤ 2 any any any≥ 10 ≤ 5 any 16 any≥ 3.0 ≤ 14 24 12 24≥ 2.0 ≤ 20 12 10 12≥ 1.5 ≤ 25 8 8 10≥ 1.0 ≤ 33 4 4 6

ThicknessT [mm]

External corner profile C1, C2 or R*

T ≤ 6 1.6 T to 2.4 T

6 < T ≤ 10 2.0 T to 3.0 T

10 < T 2.4 T to 3.6 T

* The sides need not be tangential to thecorner arcs.

Table 2. Tolerances on external cornerprofiles, EN 10219-2 Table 3 [8]

Fig. 7. Position of the notch crossingthe HAZ in the middle of the Charpy-V specimen, Fig. 4-1 [9]




Some observations from Puthliand Herion [9] are shown in Fig. 8.Apparently, cold-forming and ageingby welding has an insignificant effecton Charpy-V impact toughness inthese cases.

CIDECT has prepared a recom-mendation based on the study byPuthli and Herion [9], [10]:

“In respect of welding in coldformed areas of hollow sections madeof S275J2H, S355J2H and S460MLHsubjected to fatigue load followingrecommendation can be given: 1. According to EN 1993-1-8:2003

welding in the cold formed zonesof cold formed hollow sectionsaccording to EN 10219 is permit-ted, if the requirements given in

clause 4.14 in EN 1993-1-8:2003are fulfilled.

2. If the requirements for r/t given inTable 4.2 of EN 1993-1-8:2004 arenot fulfilled, the welding in thecold-formed zones is permitted,provided that – The minimum requirements for

the external corner profile ofEN 10219-2 are fulfilled

– The maximum nominal wall-thick-ness is not exceeding 12.5 mm

– Aluminium killed steels with thequality Grades J2H, K2H, MH,MLH, NH or NLH are used andthat the following maximum val-ues are kept: C ≤ 0.18 %, P ≤ 0.020 % and S ≤ 0.012 %”

The CIDECT recommendation is nowincluded in the July 2009 corrigendumto EN 1993-1-8, EN 1993-1-8:2005/AC, Eurocode 3: Design of steel struc-tures – Part 1-8: Design of joints, cor-rigendum July 2009 [11].

EN 10219 hollow sections satis-fying the EN 1993-1-8 criteria forwelding in the cold-formed corner areavailable on the European market.These materials can be welded with-out concerns regarding the possiblereduction in impact toughness of hol-low section corners. Ruukki’s EN10219 cold-formed hollow sections ingrades J2H, K2H, MH and MLH havenow fulfilled the current EN 1993-1-8 requirements for welding in thecold-formed zones for more than adecade.

5 Fatigue behaviour of the corners

The applicability of cold-formed tubesis sometimes questioned or limitedbecause of doubts regarding poor fa-tigue behaviour of the cold-formedcorner areas. It is also claimed that bychoosing hot-finished tubes, the afore-mentioned problems are automati-cally avoided. Bäckström et al. [12] andKokkonen and Björk [13] have stud-ied the fatigue strength of rectangularhollow section corners.

Bäckström et al. [12] studied rec-tangular hollow section corners byusing Ruukki’s cold-formed productsconforming to EN 10219 gradeS355J2H and good quality Europeanhot-finished products conforming toEN 10210 grade S355J2H. The re-sults are summarized in Fig. 9.

The fatigue strength of cold-formed test series CF-A seems to beclearly higher than the fatigue strengthof hot-finished series HF-A and thefatigue strength of cold-formed andconsiderably corroded series CF-B.The fatigue strength of series HF-Aand CF-B is about the same. Accord-ing to Bäckström et al. [12], thesmaller corner radius and the initialcracks of hot-finished sections causedby the manufacturing process seem todecrease the fatigue strength signifi-cantly at longer lives and at lower lev-els. Corrosion pits on the inside cor-ner surface of corroded cold-formedhollow sections seem to have thesame effect.

Kokkonen and Björk [13] studiedfatigue strength of hollow section cor-

Fig. 8. Charpy-V impact toughness of EN 10219 rectangular hollow sections fromselected European manufacturers, Puthli and Herion [9]




ners by using Ruukki’s EN 10219 hol-low sections in grades S355J2H andS460MH, see Fig. 10.

The conclusions of Kokkonenand Björk [13] include the following:

– “Transverse fatigue strength of cold-formed rectangular hollow sectioncorners fulfil the requirements(FAT 160) obtained in Eurocode 3and CIDECT design guides

– Fatigue class could be increased byavoiding the dents due to rollingscale in the corner”

The studies [12], [13] referred to aboveconfirm that the method of manufac-turing hollow sections, hot-finishedor cold-formed, is not the prime fac-tor dictating the fatigue strength ofthe material. The fundamental rea-sons are related to geometrical fac-tors and soundness of the surface.EN 10219 provides a good basis forhigh-performance hollow sections.Properly manufactured cold-formedrectangular hollow sections with fa-tigue strength equal to or better thanhot-finished EN 10210 hollow sections

are technically possible and availableon the European market.

6 Hot-dip galvanizing

Hot-dip galvanizing is one of theprime corrosion protection methodsfor tubular structures. Corner crack-ing sometimes occurs while hot-dipgalvanizing square and rectangulartubes. According to Packer and Chiew[5], the appearance of corner cracksin cold-formed rectangular hollow sec-tions has been discussed since 1993.In the last decade the incidence hasincreased in North America and Asia,particularly during hot-dip galvaniz-ing. Complete structures made of gal-vanized rectangular hollow sectionshave even been condemned due tocracking, e.g. sign bridges. In Europethis phenomenon is deemed to be a“rare but important issue” [5].

The problem with corner crack-ing has been generally attributed toliquid metal embrittlement (LME) inassociation with very high residualstresses in the cold-formed rectangu-lar hollow section corners. Interac-tion of three conditions determinesthe occurrence of LME [14]:– Critical level of internal stress, e.g.

residual stress due to cold workingand welding

– Susceptible material, e.g. non-alu-minium killed steel, high yield-to-tensile ratio, pre-existing microc-racks as a result of forming or ad-verse chemical composition

– Liquid metal, especially with thepresence of impurities or additives

According to the study of Poag andZervoudis [15], the predominant fac-tor affecting cracking upon galvaniz-ing was the rectangular hollow sec-

Fig. 9. Fatigue strength of grade S355J2H rectangular hollow section corners as afunction of nominal normal stress amplitude, Bäckström et al. [12]

Fig. 10. Fatigue strength of hollow section corners according to Kokkonen andBjörk [13]; mean and characteristic lines for material S355 tests and a designvalue FAT 160 MPa are shown; note: specimen CD3 external corner radius 2t;specimen CD6 in grade S460MH

Fig. 11. Example of extreme cornercracking in a rectangular hollow sec-tion during hot-dip galvanizing [5]




tion itself. In the worst case, cornercracking can completely damage thestructure, see Fig. 11. But even moredangerous is hidden invisible crack-ing, which may reduce the strength ofthe structure.

Ruukki has undertaken internalstudies with both cold-formed andhot-finished rectangular hollow sec-tions in order to verify the influenceof hot-dip galvanizing and susceptibil-ity to LME and corner cracking. Theverification was done using Ruukki’sown cold-formed products conform-ing to EN 10219 grades S355J2H,S420MH and S500MH and goodquality European hot-finished prod-ucts conforming to EN 10210 gradeS355J2H.

The influence of hot-dip galva-nizing on the tensile test is shown inFigs. 12 and 13. Hot-dip galvanizinghas a minor influence on the strengthof the material up to grade S500MH.The influence is similar regardless ofmanufacturing method, hot-finishingor cold-forming.

Susceptibility to LME and cor-ner cracking was verified by using a“corner opening test”, i.e. a “three-point bending test” at controlled tem-peratures from +20 to –60 °C. Thetest is performed by flattening out thecorner and measuring the force–dis-placement curve. The test setup isshown in Fig. 14.

Fig. 15 illustrates an example of ahollow section susceptible to LME andcorner cracking. The material is ductileprior to hot-dip galvanizing in the as-supplied condition even at an ex-tremely low temperature of –60 °C. Buthot-dip galvanizing triggers the LME,and corner cracking starts to appeareven at room temperature, see Fig. 15.

The test results shown in Figs. 16and 17 confirm that properly manu-factured hot-finished and cold-formed hollow sections behave simi-larly and are not susceptible to LME.The test results in Fig. 18 confirmthat properly manufactured cold-formed hollow sections without sus-ceptibility to LME and corner crack-ing up to grade S500MH are avail-able on the market.

The influence of hot-dip galva-nizing on welded structures has been

verified by testing hollow section X-joints made of “Ruukki double gradeS420MH/S355J2H”, which conformsto grades S420MH and S355J2H. Thetests were carried out at Lappeen-ranta University of technology at atemperature of –40 °C [16]. Two ex-amples are shown in Fig. 19. In theas-supplied condition, the deforma-tion capacity of the X-joints exceedsthe minimum requirement by factorsof 9.8 (Fig. 19, left) and 2.4 (Fig. 19,right). Hot-dip galvanizing has a mi-

Fig. 12. Influence of hot-dip galvanizing on the tensile strength of hollow sections; left: European hot-finished hollow section,EN 10210 – S355J2H – 50 × 50 × 5 mm; right: Ruukki’s cold-formed hollow section, EN 10219 – S355J2H – 50 × 50 × 5 mm

Fig. 13. Influence of hot-dip galvanizing on the tensile strength of hollow sections;Ruukki’s cold-formed hollow section, EN 10219 – Optim S500MH – 90 × 80 × 4 mm

Fig. 14. Test setup for “corner opening test”; left: “initial position”, right: “finalposition”




Fig. 15. Corner opening diagram for hollow section susceptible to LME; left: prior to hot-dip galvanizing, right: hot-dip galvanized

Fig. 16. Corner opening diagram for European hot-finished hollow section, EN 10210 – S355J2H – 50 × 50 × 5 mm; left:prior to hot-dip galvanizing, right: hot-dip galvanized

Fig. 17. Corner opening diagram for Ruukki’s cold-formed hollow section, EN 10219 – S355J2H – 50 × 50 × 5 mm; left:prior to hot-dip galvanizing, right: hot-dip galvanized

Fig. 18. Corner opening diagram for Ruukki’s cold-formed hollow section, EN 10219 – Optim S500MH – 90 × 80 × 4 mm;left: prior to hot-dip galvanizing, right: hot-dip galvanized




nor influence on the strength and de-formation capacity of the X-joint.

The observations above confirmthat properly made cold-formed hol-low sections do not have a tendencyto LME and corner cracking and hot-dip galvanizing essentially does notalter the strength or ductility of thehollow sections. Welded structuresmade of properly manufactured cold-formed EN 10219 hollow sectionscan be safely protected against corro-sion by hot-dip galvanizing.

7 Conclusions

Tubular materials enable the con-struction of steel structures that areboth architecturally and aestheticallyimpressive and also efficient struc-tures from the engineering point ofview. Increased strength opens up thechance to reduce wall thicknessesand the weight of the structure. Cold-formed hollow sections are the domi-nant tubular construction material.Economical and environmental con-straints favour cost competitivenessand higher strength. The cold-form-ing route is naturally economical andcan mostly adapt to higher strength,too. The applicability of cold-formedtubes is sometimes questioned or lim-ited due to doubts regarding the qual-ity of the products.

The observations presented inthis paper allow the following conclu-sions to be drawn:– Hollow sections from different

sources exhibit diversity of quality

and thus also a wide scatter in theirstructural performance.

– The manufacturing method, hot-finished or cold-formed, is not thefundamental factor dictating theproperties of hollow sections. Thebasic reason is related to other fac-tors in steelmaking and tube manu-facturing. Hence, the quality of theproduct very much depends on thesupplier.

– The quality of hollow sections re-sults from adequate processing ofsteel and tube.

– High-quality cold-formed EN 10219hollow sections in grades S355J2Hto S460MH with a performanceequal to or better than hot-finishedtubes• are technically possible and avail-

able on the European market,• satisfy the requirements for low-

temperature ductility, deformationcapacity of welded joints andwelding in the corner,

• exhibit good fatigue behaviour,and

• are suitable for hot-dip galvaniz-ing.

High-quality cold-formed EN 10219hollow sections constitute a safe, reli-able and versatile high-performancestructural material for environmen-tally sound and competitive solutions.

Acknowledgments

The author extends his very heartfeltthanks to Prof. Timo Björk, Lappeen-

ranta University of technology, andhis staff for performing and evaluat-ing the X-joint tests included in thisstudy.

References

[1] Wardenier, J., Packer, J. A., Zhao, X.-L., Vegte, G. J. van der: Hollow Sec-tions in Structural Applications, 2ndEd., CIDECT, Geneva: Bouwen metStaal, Netherlands, 1–3, 2010.

[2] Eekhout, M.: Tubular Structures inthe Architecture. 2nd Ed., CIDECT,Geneva, Switzerland: TU Delft, Nether-lands, 2010.

[3] Kömi, J.: Hot-Rolled Ultra-High-Strength Steels. Vuorimiesyhdistys, Fin-land, Materia 1/2012, pp. 50–52, 2012.

[4] Courtesy of Ruukki Metals Oy, Fin-land, 2010.

[5] Packer, J. A., Chiew, S. P.: Produc-tion standards for cold-formed hollowstructural sections”, Proceedings of the13th International Symposium onTubular Structures – ISTS13 (ed. BenYoung) Hong Kong, China, 15–17 Dec2010.

[6] Kosteski, N., Packer, J. A., Puthli, R.S.: Notch Toughness of Cold-FormedHollow Sections. Report 1B-2/03,CIDECT, Geneva, 2003.

[7] EN 1993-1-8, Eurocode 3: Design ofsteel structures – Part 1-8: Design ofjoints, 2005.

[8] EN 10219-2: Cold-formed weldedstructural hollow sections of non-alloyand Fine-grain steels – Part 2: Toler-ances, dimensions and sectional prop-erties, 2006.

[9] Puthli, R. S., Herion, S.: Welding inCold-Formed areas of rectangular Hol-

Fig. 19. Influence of hot-dip galvanizing on the force–displacement diagram of a hollow section X-joint at a temperature of–40 °C; left: 120 × 120 × 6/120 × 120 × 6 mm, right: 150 × 150 × 6/120 × 120 × 4 mm; material: EN 10219 – Ruukki doublegrade S420MH/S355J2H




low Sections. Report 1A-1/05, CIDECT,Geneva, 2005.

[10] Salmi, P. et al.: Design rules forcold-formed structural hollow sections”EUR 21973, European Commission,2006.

[11] EN 1993-1-8:2005/AC, Eurocode 3:Design of steel structures – Part 1-8:Design of joints, corrigendum, July2009.

[12] Bäckström, M. et al.: A new fatiguetesting method for the corners of struc-tural hollow Sections. Design andAnalysis of Welded High-Strength SteelStructures, Proceedings of Fatigue 2002,8th International Fatigue Congress,Stockholm, 2–7 June 2002, pp. 277–302.

[13] Kokkonen, J., Björk, T.: Fatigue ofhigh-strength cold-formed RHS corners,Report 7X-9/06, CIDECT, Geneva,2006.

[14] Galvanizing structural steelwork –An approach to the management ofliquid metal-assisted cracking. BCSA& GA Publication No. 40/05, 1st Ed.,British Constructional Steelwork Asso-ciation & Galvanizers Association,London, 2005.

[15] Poag, G., Zervoudis, J.: Influence ofvarious parameters on steel crackingduring galvanizing. AGA Tech Forum,Kansas, MO, USA, 2003.

[16] Björk, T.: Testing of Rectangularhollow section X-joints. Lappeenranta

University of technology, 2011 (to bepublished).

Keywords: Cold-formed hollow sections;low-temperature ductility; welded joints;welding in the corner; fatigue of the cor-ner; hot-dip galvanizing; liquid metalembrittlement

Author:Pekka O. Ritakallio, Lic.Tech. in Metallurgy andMaterials, MBA, Director, Tubular Products,Process Development, Ruukki Metals Oy, Finland, Harvialantie 420, FI–13300 Hameenlinna,Finland, [email protected]


Ruukki Metals OyHarvialantie 420 • Fl-13300 Hämeenlinna, FinlandPhone number +358(0)20 59 11 • Telefax +358(0)20 59 25 080

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