Design procedures for cold-formed stainless steel equal-leg angle columns

Significance 

Driven by economic factors and social awareness, the world steel industry is trying over the last few years to establish a coherent model that encompasses low-carbon, sustainable and circular economies. Many research and innovation projects demonstrate the potential of newly developed steel grades and their benefits in lightweight structural applications. Given its entire life cycle, stainless steel has one of the lightest impacts on Earth of all known engineering materials. And at the end of its life, stainless steel can be recycled to create a new stainless steel that is as strong and durable as the original. Its application in engineering structures has been underpinned by active scientific research projects. Specifically, efforts have been directed to generate structural design rules and protocols to facilitate the development of international design rules for cold-formed stainless steel (CFSS) structures.

To meet these challenges, associated professor Jelena Dobrić, assistant professor Aljoša Filipović, Professor Dragan Buđevac and Professor Zlatko Marković of the University of Belgrade, Faculty of Civil Engineering in collaboration with Nancy Baddoo, an associate director of the Steel Construction Institute in the United Kingdom, performed a comprehensive investigation addressing cold-formed stainless steel equal-leg angle columns with pin-ended boundary conditions. The investigation included experiments and geometric and material nonlinear finite element (FE) failure analyses. Comprehensive FE quantitative parametric studies were performed to generate reliable data over a wider range of column slenderness, including both slender and non-slender equal-leg angle sections for the three most significant stainless steel families − austenitic, duplex and ferritic. The current European and Australian/New Zealand specification approaches involving local buckling, flexural-torsional buckling and flexural buckling were evaluated by a reliability-based method and the potential for their improvement for CFSS angle columns was thoroughly investigated and discussed. The research outcomes were fully reported in the recently published paper in the journal Thin-Walled Structures.

Based on the obtained results, the authors clearly demonstrated shortcoming to the existing European column buckling curve proposed in EN1993-1-4 and the need to revise its length plateau. For minor-axis flexural buckling, the buckling curve c in conjunction with the non-dimensional limiting slenderness of 0.2 may be used for ferritic and duplex grades for all cross-section classes. Following analysis of the assembled austenitic dataset, a new buckling curve for cold-formed austenitic equal-leg angle columns, of the same form as the existing European curves, was proposed, with the higher imperfection factor equal to 0.92 and with a reduced limiting slenderness of 0.15, with the aim of offering safe, but efficient predictions. The flexural-torsional buckling column resistance may be safely but quite conservatively predicted by using buckling curve b in conjunction with non-dimensional limiting slenderness of 0.2. The results of the statistical study also showed that this buckling curve results in significantly high data scatter for all three stainless steel grades. In addition, it was shown that the current AS/NZS codified design procedure safely and accurately quantifies column compressive capacities, especially for minor-axis flexural buckling failure. Similar to Eurocode 3, the design procedure addresses flexural-torsional buckling with significantly conservative predictions of the column ultimate strengths.

In summary, a detailed non-linear numerical investigation of the structural responses and ultimate resistances of pin-ended CFSS equal-leg angle columns was reported and the new design guidelines were proposed per stainless steel grades. The applicability of proposed recommendations was verified via reliability analysis. The overall research findings fill the existing gap created by the lack of experimental results and explicit design guidelines for CFSS equal-leg angle columns. In a statement to Advances in Engineering, Professor Jelena Dobrić said the new design recommendations would ensure the safe and robust design of cold-formed stainless steels angle columns for a wide range of structural applications.

Design procedures for cold-formed stainless steel equal-leg angle columns - Advances in Engineering

About the author

Dragan Budjevac, Ph.D., MSc, B.Civ.Eng, is a Professor Emeritus at the Faculty of Civil Engineering, University of Belgrade, Serbia. He was awarded the prize from the Chamber of Commerce of City of Belgrade for MSc and PhD theses, both in the field of steel structures. He was the mentor on more than 300 final examination works, 8 MSc theses and 4 doctoral theses.

Professor Budjevac is the author and co-author of 30 books and monographies in the field of steel structures and steel bridges; he published over 200 professional papers, which he presented through the different congresses and symposia, domestic magazines and international journals. Several areas could be identified, from his vast sphere of interest, to which Mr. Budjevac has dedicated his expert publications: design of cold-formed structures, fire resistance of steel structures, aluminum structures, implementation of steel structures in buildings, composite structures, Eurocode 3 implementation and project and design management.

He is also a member of the many scientific and expert organizations. For ten years he has been the technical director and CEO of the “Delta Invest” company, member of “Delta Holding”. For three years he has been the technical director of the UK Company “MACE” for Balkan region. As director of Delta Invest he won BPB International Trophy 2006. for best interior in the world with technical innovation at “Delta Sport” office building project. The same year he was pronounced among the 50 greatest builders by the Italian magazine “Materia”. He was elected the Manager of the year 2007. by the Serbian economy journalists. Beside lecturing and scientific activities, Dragan Budjevac plays an important role as the designer, consultant and reviewer of more than 500 different engineering structures.

About the author

Jelena Dobric BEng MSc PhD, is associate professor at University of Belgrade, Faculty of Civil Engineering (URL). She has significant lecturing experience in the courses and practical classes of bachelor and master programmes in Civil Engineering in the Department of material and structures. Over the past years, she has led a scientific research group exploring the structural behaviours of metallic structures, with a special interest in stainless steel. Her team developed new design guidance for the flexural buckling of stainless steel equal-leg angle columns considering cold-formed, hot-rolled and laser-welded products. Today, she is studying the behaviour of duplex stainless steel bolted connections under static load. She has strong academic knowledge and deep insight into world-wide technical regulations in the area of metallic structures.

She is a member of the stainless steel working group CEN/TC 250/SC 3/WG 4 and the committee of Serbian Institute for Standardization for steel, composite and aluminium structures. She also has specialized experience in the design and detailing of metallic and composite structures, she has participated as head designer or design team member in producing a large number of conceptual projects and detailed designs. She is a member of Serbian Chamber of Engineers for state licence exam and mentor for professional assignments in the field of steel and composite structures.

About the author

Nancy Baddoo is an Associate Director at The Steel Construction Institute (SCI) in the UK and Fellow of the Institution of Civil Engineers. She has worked on many research projects studying the structural performance of stainless steel as well as being active in disseminating design guidance through publications and seminars. For the last 10 years she has chaired the European technical committee responsible for the stainless steel Eurocode, EN 1993-1-4. She has taken a key role in developing the new American Institute of Steel Construction (AISC) stainless steel design specification, ANSI/AISC 370, and authored the AISC Design Guide 27 Structural Stainless Steel.

About the author

Aljosa Filipovic PhD, is assistant on a group of courses in the field of metal structures at the Department of Materials and Structures at the Faculty of Civil Engineering, University of Belgrade. His research work is mainly focused on the behavior of different types of stainless steel equal angles under axial compression. As an author and co-author, Aljoša published numerous papers in significant international journals and at international conferences. As a researcher, he participates in realization of a scientific project funded by the Ministry of Science, Education and Technological Development of the Republic of Serbia, project ID: TR-36048.

Aljoša Filipović is vice director of Institute of Materials and Structures. He actively applies acquired professional knowledge through development of various construction projects. He holds a professional license issued by the Serbian Chamber of Engineers.

About the author

Zlatko Markovic is Full professor at University of Belgrade – Faculty of Civil Engineering and Head of Institute of Materials and Structures. Also, he is President of Association of Structural Engineers of Serbia – ASES and President of committees of Serbian Institute for Standardization, for steel, composite and aluminium structures, as well as for actions on structures and earthquake.

He is representative of Serbia in the Steering Committee of International Conference Eurosteel and member of scientific committees of many international conferences such as: IABSE, Danube bridges etc. He is also member of Project team CEN/TC 250 SC4.T5 “Development of rules covering shallow floor construction, and other flooring types using precast concrete elements”.

Professor Zlatko Markovic wrote, as the author or co-author, more than 150 articles in the field of steel and composite structures (16 in peer review papers from SCI list, number of heterocitations over 260). Also, he wrote, as author or co-author, nine books and chapters of monographies. He has participated in many national and international scientific, technologic and research projects. Professor Markovic is an active designer and reviewer in the field of steel and composite structures. He took part in design and reviewing of huge number of structures.

Reference

Dobrić, J., Filipović, A., Baddoo, N., Marković, Z., & Buđevac, D. (2021). Design procedures for cold-formed stainless steel equal-leg angle columnsThin-Walled Structures, 159, 107210. https://doi.org/10.1016/j.tws.2020.107210

Go To Thin-Walled Structures

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