Local and distortional buckling of perforated steel wall studs

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Doctoral thesis (monograph)
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101, [19]
Helsinki University of Technology Laboratory of Steel Structures publications, 19
The local and distortional buckling behaviour of flange and web-stiffened compression members was investigated. In particular, the behaviour of web-perforated sections was investigated both numerically and experimentally. Perforation reduces the perpendicular flexural stiffness of the web and thus particularly reduces the distortional buckling strength of the section. The main task of the research was to develop a design method for estimating the compression capacity of a perforated steel wall-stud under centric loading. The influence of the gypsum sheathing on the distortional buckling strength is also taken into account. It was shown that the method given in Eurocode 3 is quite rough and sometimes gives inaccurate results for estimating the elastic distortional buckling stress of both C-sections and intermediate stiffened plates. In the case of C-sections, the method developed by Lau and Hancock and the method developed by Schafer and Peköz correlate better with the results defined numerically. The Finite Strip Method (FSM) and Generalized Beam Theory (GBT) provided particularly good tools with which to analyze local and distortional buckling modes. It was also shown that interaction between different distortional buckling modes should be taken into account when analysing sections having both web and flange stiffeners. Distortional buckling stress of the web-perforated C-section with or without web stiffeners can be determined by replacing the perforated web part with an equivalent plain plate corresponding to the same perpendicular bending stiffness. Distortional buckling stress may be determined by some numerical method such as FSM or GBT. For the web-perforated C-section, an analytical method for the distortional buckling is also presented. Gypsum sheathing connections give rotational restraint to the wall–stud, thus improving distortional buckling strength. Some practical guidelines are given for calculating the rotational restraint. Buckling analysis showed that relatively small restraint may double the distortional buckling stress of the web-perforated section. Buckling analysis and experimental research showed that screw pitch also has a considerable effect on the distortional buckling stress. Using restraint values given by the connection tests, the predicted values for the gypsum board braced columns are in good accordance with the test results. In practical design, utilizing the gypsum board in the determination of the distortional buckling stress requires that the sheathing retains its capacity and stiffness for the expected service life of the structure. Furthermore, the connection characteristics should be carefully examined. Based on the results of the experimental and theoretical studies, design proposals were made for the design of compressed web-perforated steel wall studs. Some practical guidelines were also given for taking into account the gypsum sheathing. These design proposals are also valid for solid steel wall studs, especially for slender sections, which are sensitive to distortional buckling.
cold-formed steel, local buckling, distortional buckling, steel wall stud, perforation, gypsum board
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