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