cold-formed steel structures: advances in research and design - apcmr

individual “element”. Each plate element is treated considering the stability theory of platesand the “effective width” concept for taking into account both elastic buckling phenomenaand post-buckling effects. As far as the distortional buckling is concerned, the codifiedprovisions, through the stiffener effectiveness evaluation, extend the methodologies originallyproposed only for local instability phenomena to the case of distortional buckling ofintermediate stiffened and edge stiffened elements (“flange distortional” buckling). Even ifthe current calculation models give comprehensive rules for the determination of “effectivesection” in the case of different load conditions, they require iterative calculations whichbecome enough complicated for more complex shape of cross section. Moreover, thisapproach ignores the interaction between plate elements and does not provide guidance ondistortional phenomena involving the transverse deformation of flange-to-web intersectionline (“lateral distortional” buckling).Significant advances in technology of manufacture lead to use members made ofhigher strength steels and having more complex and thin cross-sections. As inevitableconsequence, the design procedures must follow this development becoming more and morecomplex and cumbersome. These difficulties have stimulated the preparation of an ad hocsoftware to help the designers in their practical activities. This computer program, named“ColdForm”, represents the main issue of the book entitled “Design of Metallic Cold-FormedThin-Walled Members” [42].In particular, the ColdForm computer program was created in the late 1980s atUniversity of Naples, as a research tool for comparing the provisions on thin-walled steelcross-sections given by CNR 10022 Italian code [43], European code (ECCS-TW7/1 [44])and American code (AISI, 1986 [45]). Its first commercial version (ColdForm 2.0) wasdeveloped in 1993 with the sponsorship of ACAI (Italian Association of Steel Constructors).It was a Quick Basic version with a Windows-like appearance, which only allowed thechecking of CFS cross-sections according to Eurocode 3 provisions. The present release(ColdForm 3.0 or ColdForm 2001) is a Visual Basic version fully complying with Windowsstandards, as shown in Figure 8. In particular, Figure 8b shows the ColdForm window, inwitch the “Geometrical characteristic” output box appears. Figure 8c presents the evaluatedresistance window in the case of “Axial compression” together with the relevant “Effectivesections” window, while Figure 8d illustrates the check for “Combined compression andbending” window. Finally, the tabs in the “Internal actions” window are shown in Figure 8e.This version allows the analysis of both cold-formed steel members (according toENV 1993-1-3 [39] and AISI 1996 [40] provisions) and aluminium members (according toENV 1999-1-1 [46] provisions).The latest trend is to move towards approaches based on the evaluation of elasticbuckling “load” through a “whole section” analysis. In fact, different user-friendly numericaltools (CU-FSM [47], THIN-WALL [48]), able to capture the elastic buckling load of thewhole section through the Finite Strip Method (FSM), are currently available for designers.According to this approach and following the “direct strength method” [49], the nominalstrength can be “directly” determined starting from the values of elastic buckling load andyield load using appropriate “strength” curves. This procedure has several advantages: (1) thereliability of the method is shown to be comparable to the current specifications[49,50,51,52]; (2) the interactions between the plate elements are taken into account; (3) allthe buckling phenomena (local, distortional and global) are considered; (4) the calculationsare very simple and do not require iterations, also in the case of sections having complexshapes for which the current specifications do not provide provisions; (5) the finite stripanalyses provide a simple approach also when the CFS members interact with other materialsor constructive components, as in the case of purlins stabilised by cladding or wall studsstabilised by sheathings [53]. As consequence of these advantages, the inclusion of whole

section and direct strength approaches as alternative design procedures in design standardsshould be strongly considered. In reality, the possibility of using numerical procedures isgiven in the final version of prEN 1993-1-3 [54]. However, further investigation on the newmethodology appears to be necessary, as shown in [51,55]. In particular, future researchincluding studies on: (1) the definition of the applicability field in terms of cross-sectionshape and dimension limitations; (2) the applicability and reliability of the method in the caseof members subjected to combined bending and axial load or bending and shear; (3) thepossibility to apply this approach for members with significant shift of the effective centroidin the post-buckling regime.a–The cover of the book including ColdForm 2001.b–The “ColdForm” window.c–Evaluated resistence and “Effective section” windows for “Axial compression”.d–“Combined compression and bending” window.e–“Internal actions” windows.Fig. 8 – ColdForm 2001 computer program.

5. FURTHER DEVELOPMENTSFurther studies representing the natural extension of the current research activities onthe behaviour of CFS structures have been planned at the University of Naples.The preliminary calibration study on the numerical modelling of CFS memberspresented in Section 2 will be used as a basis for a wide numerical study of the bendingbehaviour of C-sections. In particular, the reliability of the codified analysis methodologieswill be investigated, with systematic variation of the size of the edge-stiffening lip. Theultimate objective is to gain an insight into current available design methodologies andpossibly improve them. In fact, as discussed in Section 4, current codified provisions oftenpresent systematic error in prediction the load bearing capacity of such type of sectionsbecause the web-flange interaction in the distortional failure mode is neglected.The complex behaviour of CFS lightweight low-rise buildings laterally braced bypanels under seismic actions requires the setting-up of an additional research activity aimingat the development of useful and practical analysis and design methodologies. Consequently,on the basis of the results coming from the experimental studies illustrated in Section 3, thenext research activity will be articulated in the following two main phases: (1) developmentof reliable mechanical models, in order to capture the complex hysteresis response of shearwalls stud-panels systems; (2) evaluation of the deformation demand for stud shear wallssystems, on the basis of a realistic and sufficiently wide database of acceleration records.The development of the first phase of the research will benefit of the long experiencethat has been matured [56,57,58] in both the modelling of the hysteresis behaviour of singlestructural components and studying its influence on the global response of the structure. Thedefinition of the deformation demand to small buildings made of the stick-built constructionsystem represents the scope of the second phase of this research. It will be carried outaccording to the suggestions given in the document FEMA 350 [59]. It is deemed important toemphasise the need to perform an analytical-numerical study aiming at evaluating thedeformation demand to steel stud shear walls systems. In fact, such a structural systemexhibits a peculiar hysteresis behaviour, with a strong pinching of hysteresis loops, whichreduces the energy absorption capacity.6. REFERENCES[1] Pekoz, T., Possible future developments in the design and application of cold-formedsteel. Keynote lecture. In Proceedings of the 4 th International conference Light-weightsteel and aluminium structures (ICSAS’99), Espoo, Finland, 1999.[2] Yu, W.W., Cold Formed Design (3rd Edition). John Wiley & Sons. New York, 2000.[3] Schuster, R.M., Residential applications of cold-formed steel members in NorthAmerica. In Proceedings of the 5 th International Structural Stability ResearchConcilium – SSRC. Chicago, 1996.[4] Gad, E.F., Chandler, A.M., Duffield and C.F., Stark, G., Lateral behaviour ofplasterboard-clad residential steel frames. Journal of Structural Engineering, ASCE,No.125(1): 32-39, 1999.[5] Burstrand, H., Ligth-gauge steel framing leads the way to an increased productivity forresidential housing. Journal of constructional steel research, Elsevier, No.46(1-3):Paper No.213, 1998.[6] Davies, J.M., Light gauge steel framing for housing construction. In Proceedings ofthe 2 nd International conference on thin-walled structures, Singapore, 1998.

[7] Lawson, R.M. and Ogden, R.G., Recent developments in the light steel housing in theUK. In Proceedings of the 9 th North steel conference of construction institute,Helsinki, 2001.[8] Di Lorenzo, G. and Landolfo, R., Shear experimental response of new connectingsystems for cold-formed structures. Journal of constructional steel research, Elsevier,No.60: 561-579, 2004.[9] Shafer, B.W. and Pekoz, T., Local and distortional buckling of cold-formed steelmembers with edge stiffened flanges. In Proceedings of the 4 th Internationalconference Light-weight steel and aluminium structures (ICSAS’99). Espoo, Finland,1999.[10] Kesti, J. and Davies, J.M., Local buckling of thin-walled short columns. Thin-walledstructures, Elsevier, No.34(2): 115-134, 1999.[11] Young, B. and Rasmussen, K.J.L., Local, distortional, flexural and flexural-torsionalbuckling of thin-walled columns, In Proceedings of the 4 th International conferenceLight-weight steel and aluminium structures (ICSAS’99). Espoo, Finland, 1999.[12] Landolfo, R., Coupled instabilities in non linear materials. In Proceeding of the 3 rdInternational conferences on coupled instabilities in metal structures (CISMS 2000),Lisbon, 2000.[13] Rondal, J., Cold formed steel members and structures – general report. Journal ofconstructional steel research, Elsevier, No.55: 155-158, 2000.[14] Davies, J.M., Recent research advances in cold-formed steel structures. Journal ofconstructional steel research, Elsevier, No.55: 267-288, 2000.[15] Hancock, G.J., Cold-formed steel structures. Journal of constructional steel research,Elsevier, No.59: 473-487, 2003.[16] Landolfo, R., Advances in Italian cold-formed steel structures research. InProceedings of the International workshop on thin-walled structures, Loughborough,UK, 2004.[17] Mazzolani, F.M., Thin-walled metal constructions: research, design and codification.In Proceeding of the 50 th Anniversary conference of SSRC, Bethlehem, 1994.[18] Mazzolani, F.M., Cold-formed thin-walled constructions: recent developments. InProceedings of the Eurosteel ’95, Atene, 1995.[19] Landolfo, R. and Mazzolani, F.M., Behaviour of 3rd generation trapezoidal steelsheetings. In Proceedings of the International workshop needs in testing metals heldby RILEM, Naples, 1990.[20] Landolfo, R. and Mazzolani, F.M., Ultimate behaviour of trapezoidal steel sheets inbending. In Proceedings of the 12 th International specialty conference on cold-formedsteel structures, University of Missuri-Rolla, 1994.[21] De Martino, A., Ghersi, A., Landolfo, R. and Mazzolani, F.M., Bending behaviour oflong-span steel sheeting: testing and simulation. In Proceedings of the Internationalconference Light-weight steel and aluminium structures (ICSAS’91), Singapore, 1991.[22] De Martino, A., Ghersi, A., Landolfo, R. and Mazzolani, F.M., Calibration of abending model for cold-formed sections. In Proceedings of the 11 th Internationalspecialty conference on cold-formed steel structures, University of Missuri-Rolla,1992.[23] Ghersi, A., Landolfo, R. and Mazzolani, F.M., Buckling modes of double channelcold-formed beams. Thin-Walled Structures, Elsevier, No.19, 1994.[24] Calderoni, B., De Martino, A., Ghersi, A. and Landolfo, R., On the seismic resistanceof light gauge steel frames. In Proceedings of the 1 st International conference on theBehaviour of steel structures in seismic areas (STESSA ’94), Timisoara, Romania,1994.

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[42] Ghersi, A., Landolfo, R. and Mazzolani, Design of metallic cold-formed thin-walledmembers, E & FN Spon, London, 2001.[43] CNR 10022, Profilati di acciaio formati a freddo – Istruzioni per l’impiego nellecostruzioni, 1984.[44] ECCS, European recommendations for the design of light gauge steel members,ECCS-TWG 7/1, Final draft, 1986.[45] AISI, Specification for the design of cold-formed steel structural members. AISI(American Iron and Steel Institute), Washington, DC, 1986.[46] ENV 1999-1-1, Eurocode 9: Design of aluminium structures - Part 1-1: Generalrules. CEN (European Committee for Standardization), Bruxelles,1998.[47] CU-FSM: Cornell University Finite strip method. Software e tutorials.http://www.ce.jhu.edu/bschafer/cufsm/index.htm.[48] Papangelis, J.P. and Hancock, G.J., Computer analysis of thin-walled structuralmembers. Computer and structures, Elsevier, No.56 (1), 1995.[49] Schafer, B.W. and Pekoz, T., Direct strength prediction of cold-formed steel membersusing numerical elastic buckling solution. In Proceedings of the 14 th Internationalspecialty conference on cold-formed steel structures, 1998.[50] Schafer, B.W., Local, distortional, and Euler buckling in thin-walled columns. Journalof Structural Engineering, ASCE, No.128(3): 289-299, 2002.[51] Schafer, B.W., Progress on the direct strength method. 16 th International specialtyconference on cold-formed steel structures, Orlando, Florida, 2002.[52] Quispe, L. and Hancock, G.J., Direct strength method for the design of purlins. 16 thInternational specialty conference on cold-formed steel structures, Orlando, Florida,2002.[53] Schafer, B.W. and Hiriyur, B., Analysis of sheathed cold-formed steel wall stud. 16 thInternational specialty conference on cold-formed steel structures, Orlando, Florida,2002.[54] prENV 1993-1-3, Eurocode 3: Design of steel structures – Part 1-3: General rules -Supplementary rules for cold formed thin gauge members and sheeting. CEN(European Committee for Standardization), Bruxelles, (final draft 27 sept. 2002).[55] Schafer, B.W., Advances in direct strength design of thin-gauge members. InProceedings of Advances in Structures Steel, Concrete, Composite and Aluminium(ASSCCA '03). Sydney. 2003.[56] Della Corte, G., De Matteis, G. and Landolfo, R., A mathematical model interpretingthe cyclic behaviour of steel beam-to-column joints. In Proceedings of the XVII CTACongress, Naples, 1999.[57] Della Corte, G., De Matteis, G. and Landolfo, R., Influence of connection modeling onseismic response of moment resisting steel frames. In F.M. Mazzolani (ed.), Momentresistant connections of steel building frames in seismic areas. London: E & FNSPON, 485-512, 2000.[58] Della Corte, G., De Matteis, G., Landolfo, R. and Mazzolani, F.M., Seismic analysisof MR steel frames based on refined hysteretic models of connections. Journal ofConstructional Steel Research, Elsevier, No.58, 2002.[59] FEMA 350, Seismic Design Criteria for New Moment-Resisting Steel FrameConstruction, Report n. 350, FEMA (Federal Emergency Management Agency), 2001.