Experimental and Numerical Investigation of Local Stability of Flexural Cold Formed High Strength Steel Hollow Section Profiles

Cold-formed hollow sections are the leading tubular profiles used in structural design. High strength combined with stiff form of welded hollow section enables creation of robust and lightweight structures. Because of favorable ratio between load bearing capacity and weight, high strength steels (HSS) rapidly conquering the position in steel structures market as well as gaining the attention of researchers. Nominally HSS resistance to both, stress and strain, is doubled (considering the ordinary steel as the reference), though the elastic deformation range is remaining narrow. Analysis of nonlinear effects and slenderness of the internal parts of cross-section through the bending zone of the flexural member, demands for consideration of interaction between bending and local stability of the web. This paper presents an experimental and numerical analysis of deformation behavior of cold-formed hollow sections made of high strength steels, based on strain monitoring approach. In-plane bending tests, in four-point bending configurations, on HSS sections in grades S700MLH, S900MH were conducted. It was found that both grades HSS cross-sections, having the same aspect ratio, exhibit comparable global and local failure modes. The experimental results were simulated by means of non-linear finite element approach with the aim to develop validated numerical models to predict deformation behavior of HSS tubular profiles in flexure. Moreover, the innovative digital image correlation technique used for the nondestructive strain monitoring is presented and its advantageous applicability for the analysis of HSS profiles local deformation behavior is discussed using the obtained test results. Gathered experimental results and numerical simulation outputs were discussed to clarify non-linear effects characteristic of deformation behavior of the hollow section profiles. Particular attention was paid to the distinct deformation response at the loading points and the resemblance of the failure mode observed during the tests.

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