Thesis supervisor: Sándor Ádány
Location of studies (in Hungarian): BME Department of Structural Mechanics Abbreviation of location of studies: BMETM
Description of the research topic:
Thin-walled structural members are applied in various structural engineering applications. One of the most typical appearance is the cold-formed steel (CFS) profiles, which are traditionally used as secondary load-bearing elements (e.g., purlins, rafters), but more and more used as primary load-bearing elements, too, e.g., as part of CFS trusses or CFS frames. Due to the production and installation technology, CFS members are typically mono-symmetrical or asymmetrical, they are connected by special fasteners (e.g., self-drilling screws), and subjected to loads with various eccentricities. Also, CFS members are used to form built-up members, and almost uniquely in structural engineering practice, the load bearing capacity sometimes is increased by simply placing CFS members one upon the other (e.g., overlaps in purlins, doubled trapezoidal sheets, etc.)
In general, thin-walled members has complex behaviour, mainly due to the thin nature of their elements. In the case of CFS, however, the complexity is further increased by the special CFS features, such as asymmetry or eccentricities. A classic engineering approach to complex problems is to interpret the behaviour as the superposition of simpler behaviour components. In other words, e.g., the displacements are decomposed into simpler yet practically meaningful deformation modes. Accordingly, in case of thin-walled members it is usual to distinguish global (G), distortional (D), local (L), in plane shear (S) and transverse extension (T) behaviour. A general displacement-deformation field therefore can be interpreted as the combination from G, D, L, etc., Also, it is sometimes meaningful to solve a problem within a specific (deformation) sub-space or in a combination of some spaces, e.g., to solve buckling in the G space (which might lead to flexural buckling, flexural-torsional buckling, lateral-torsional buckling), or in the L space (which might lead to local-plate buckling, shear buckling or web crippling, separated from other forms of buckling), etc.
Recently the constrained finite element method (cFEM) is introduced, which is a shell finite element method, but with modal decomposition ability. This means that cFEM is able to solve problems (like linear static analysis, linear buckling analysis, geometrically nonlinear analysis, etc.) in any deformation spaces, as well as it is able to identify any deformation of a thin-walled member (which might be the result of e.g. a buckling analysis), that is it is able to objectively tell how the actual deformation is superposed from the various components. cFEM has been proved to be applicable for the analysis of virtually any thin-walled member that can be modelled by rectangular shell finite elements (e.g. members with arbitrary supports, loading, members with holes, etc.).
The general aim of the proposed research is two-fold. One aim is the further development of the cFEM method, for example to make it applicable for structures built up from thin-walled members (e.g., cold-formed steel built-up members, trusses, frames). It might also be reasonable to define new (shell) elements, or introduce material nonlinearity, etc. Another aim is to investigate certain yet unresolved problems of thin-walled structural elements and structures, e.g., to study the behaviour of CFS trusses, CFS portal frames, built-up members, etc., in order to understand the influencing factors of the behaviour, as well as to work out proposals to improve the structures or to improve the design procedures. The primary tool of the research is the finite element method, both classic finite element method (FEM) by using advanced FEM analysis software, and the special cFEM. But analytical studies as well as experimental work might also be necessary.
The candidate doctoral student is expected to be familiar with advanced finite element analysis, including advanced nonlinear FEM analyses (e.g., Ansys). It is also essential to have programming skills, e.g. elementary programming in MatLab is a must.
Number of students who can be accepted: 1
Deadline for application: 2019-05-31
2024. IV. 17. ODT ülés Az ODT következő ülésére 2024. június 14-én, pénteken 10.00 órakor kerül sor a Semmelweis Egyetem Szenátusi termében (Bp. Üllői út 26. I. emelet).
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