Viorel Ungureanu

Effect of imperfections on numerical simulation of instability behaviour of cold-formed steel members

The paper analyses the influence of imperfections on the behaviour of cold-formed steel members. Special attention is paid on the characterisation and codification of imperfections for non-linear FEM simulation. Based on the ECBL approach [2] and using an advanced non-linear inelastic analysis, the erosion of theoretical buckling strength, due to geometrical imperfections, in single and coupled instability modes is evaluated.

Recent research advances on ECBL approach.: Part I: Plastic–elastic interactive buckling of cold-formed steel sections

Abstract The objective of this two parts paper is to present some recent developments and applications of erosion of critical bifurcation load (ECBL) approach for the interactive buckling. Two different types of problems are analysed: (1) plastic–elastic interactive buckling which implements into the Ayrton–Perry interaction formula the plastic strength of the stub columns evaluated by means of local plastic mechanism analysis, and (2) elastic–elastic interactive buckling for members with perforations . The first part of the paper analyses the occurrence of local plastic mechanisms in cold-formed steel sections in compression, and how they can be implemented in the ultimate limit state analysis of the members. Actually, the failure of thin-walled cold-formed members in compression always occurs with a local plastic mechanism. Starting from this observation, the authors suggest to use in the interactive local-overall buckling analysis the sectional plastic mechanism strength instead of traditional ‘effective section’. The ECBL approach is used to implement the proposed interactive buckling model. Results are compared with those of other two recent methods, namely the direct strength method and plastic effective width approach. Relevant tests are used to evaluate the three methods. Comparisons with European and American design codes are also presented in the paper.

Design of cold-formed steel structures. : Eurocode 3 : design of steel structures. Part 1-3, Design of cold-formed steel structures

This book is primarily concerned with the design of cold-formed steel members and structures in building construction in Europe. For this reason it is mainly focused on the EN 1993-1-3, and the related parts of EN 1993 (e.g. EN 1993-1-1, EN 1993-1-5, EN 1993-1-8, etc.). Generally, the book contains the theoretical background and design rules for cold-formed members and connections, accompanied by design oriented flow charts and worked examples for common building application. The book was conceived primarily as a technical support for structural engineers in design and consulting offices, but it is expected to be of interest and useful for students and staff members of structural engineering faculties, as well as, for engineers working in steelwork industry. URI http://lib.hpu.edu.vn/handle/123456789/22866 Collections Technology [2729] Steel Bridges Conceptual and Structural Design of Steel and Steel-Concrete Composite Bridges ​ Lebet, Jean-Paul; Hirt, Manfred A. (Taylor and Francis, 2013) This book gives the professional systems engineer the tools to set up a proper and effective analysis of the resources, schedules and parts needed to successfully undertake and complete any large, complex project. This ... Design of Steel Structures: Eurocode 3 Design of Steel Structures. Part 1-1 General Rules and Rules for Buildings ​ ECCS European Convention for Constructional Steelwork (Ernst and Sohn, 2014) This book introduces the design concept of Eurocode 3 for steel structures in building construction, and their practical application. Following a discussion of the basis of design, including the limit state approach, the ... Finite Element Analysis and Design of Steel and Steel-Concrete Composite Bridges ​ Ellobody, Ehab (Butterworth-Heinemann, 2014) In recent years, bridge engineers and researchers are increasingly turning to the finite element method for the design of Steel and Steel-Concrete Composite Bridges. However, the complexity of the method has made the ... DSpace software copyright

Koiter asymptotic analysis of thin-walled cold-formed steel members

Abstract An imperfection sensitivity analysis of cold-formed steel members in compression is presented. The analysis is based on Koiter’s approach and Monte Carlo simulation. If the modes interaction is correctly accounted, than the limit load and the erosion of critical buckling load can be easily evaluated. Thousands of imperfection can be analysed with very low computational cost and an effective statistical evaluation of limit performance can be carried out. The analysis is done on pallet rack uprights in compression, based on an intensive experimental study carried out at the Politehnica University of Timisoara.

Experimental Evidence of Erosion of Critical Load in Interactive Buckling

AbstractThe paper starts with a selective review of some basic contributions related to local-overall buckling mode interactions in thin-walled steel members. Then, the results of an intensive experimental study carried out at the Politehnica University of Timisoara with the purpose of evaluating the erosion of a theoretical bifurcation load in the distortional-flexural buckling interaction range in pallet rack uprights are presented. Two different sizes of cross sections, with and without perforations, have been studied. To evaluate and quantify the erosion, the erosion of the critical bifurcation load approach is applied. This approach enables one to use the European buckling curves in the Ayrton-Perry format, expressing the imperfection factor (α) in terms of the erosion coefficient (ψ). It allows estimation of the member’s ultimate capacity, taking into account the interaction of sectional (local or distortional) and member (flexural, torsional, or flexural-torsional) instability modes. Test results a...

Influence of corrugation depth on lateral stability of cold-formed steel beams of corrugated webs

Abstract The beams of thin corrugated web afford a significant weight reduction compared with hot-rolled or welded ones. In the initial solutions, the flanges are made of flat plates, welded to the sinusoidal web sheet, requiring a specific welding technology. A new solution is proposed by the authors, in which the beam is composed by a web of trapezoidal cold-formed steel sheet and flanges of back-to-back lipped channel sections. For connecting flanges to the web self-drilling screws are used. The paper summarizes the experimental and numerical investigations carried out at the CEMSIG Research Centre (www.ct.upt.ro/centre/cemsig/) of the Politehnica University of Timisoara and, at the end, presents the influence of corrugation depth of web on the lateral stability of the beams.

Plastic mechanisms for thin-walled cold-formed steel members in eccentric compression

Abstract The Eurocode 3 concerning thin-walled steel members divides members subjected to compression into four classes, considering their ductility. The representatives of the class C4 are short bars, for which the load-capacity corresponds to the maximum compression stresses less than the yield stress. There are bars prone to local buckling in the elastic range and they do not have a real post-elastic capacity. The failure at ultimate stage of such members, either in compression or bending, always occurs by forming a local plastic mechanism. This fact suggests the possibility to use the local plastic mechanism to characterise the ultimate strength of such members. The present paper is based on previous studies and some latest investigations of the authors, as well as the literature collected data. It represents an attempt to study the plastic mechanisms for members in eccentric compression about minor axis and the evolution of plastic mechanisms, considering several types of lipped channel sections.

Experimental investigations on built-up cold-formed steel beams connected by resistance spot welding

This work was supported by a grant of the Romanian National Authority for Scientific Research and Innovation, CNCS/CCCDI - UEFISCDI, project number PN-III-P2-2.1-PED2016-1684 / WELLFORMED - Fast welding cold-formed steel beams of corrugated sheet web, within PNCDI III.

Behaviour of thin-walled cold-formed steel members in eccentric compression

Thin-walled cold-formed steel structures are usually made of members of class 4 cross-sections. Since these sections are prematurely prone to local or distortional buckling and due to the fact they do not have a real post-elastic capacity, the failure at ultimate stage of those members, either in compression or bending, always occurs by forming a local plastic mechanism. The present paper investigates the evolution of the plastic mechanisms and the possibility to use them to characterise the ultimate strength of short thin-walled cold-formed steel members subjected to eccentric compression about minor axis, particularly for members with lipped channel cross-section. Five different types of plastic mechanisms for members in compression with different eccentricities are identified and examined on the basis of FE numerical simulations. Preliminary results of experimental validation of numerical results are presented. The research is based on previous studies and some new investigations of the authors.Thin-walled cold-formed steel structures are usually made of members of class 4 cross-sections. Since these sections are prematurely prone to local or distortional buckling and due to the fact they do not have a real post-elastic capacity, the failure at ultimate stage of those members, either in compression or bending, always occurs by forming a local plastic mechanism. The present paper investigates the evolution of the plastic mechanisms and the possibility to use them to characterise the ultimate strength of short thin-walled cold-formed steel members subjected to eccentric compression about minor axis, particularly for members with lipped channel cross-section. Five different types of plastic mechanisms for members in compression with different eccentricities are identified and examined on the basis of FE numerical simulations. Preliminary results of experimental validation of numerical results are presented. The research is based on previous studies and some new investigations of the authors.

Conversion of a Temporary Tent with Steel Frame into a Permanent Warehouse

The paper is dealing with the problem of a functional conversion (involving both architectural and structural issues) applied to the case of an industrial building. As well known, temporary tents, designed according to the European Code EN13782, represent a remarkable stake on the building market and a fast and practical solution for some situations. It is exactly the case approached by the paper, where the investor has initially decided to erect on his platform a provisional shelter for agricultural machines and subsequent staff, built of a light steel structure covered by PVC roofing and cladding. This temporary tent has been acquired from a specialized supplier in form of a series product. After using the tent for a number of years, the investor has decided to convert the existing structure from architectural and structural point of view by switching to a permanent structure designed accordingly. Important changes were thus imposed both to the architectural part (technological flows, openings, facades) and especially to the structural part where this switch imposed a re-design to the codes of permanent structures (especially as far as climatic loadings are concerned). The required architectural change implied the building of a 70 cm high concrete plinth and replacing the PVC membrane temporary roofing and cladding by permanent 60 mm thick PUR sandwich panels. Together with a new system of openings this has led to renewed facades of the buildings. As for the structural change, the required conversion has imposed a thorough checking of the existing steel structure (very slender and typical to a tent) in view of transforming it into a permanent structure. The consolidation measures of the existing galvanized steel structure are described, together with the measures applied at infrastructure level in order to implement the required conversion.