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Interaction of geometric and material nonlinearities in stainless steel frames

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  • González de León, Isabel|||0000-0003-2667-9931
  • Arrayago Luquin, Itsaso|||0000-0002-0054-9322
  • Real Saladrigas, Esther|||0000-0003-1723-3380
Adequate mechanical properties make stainless steel an excellent construction material for structures. The current stainless steel European structural code EN1993-1-4 (2015) is largely based on provisions given for carbon steel EN1993-1-1 (2005) and does not establish specific design rules for the global analysis of stainless steel structures. Thus, the same classification criterion applies in both codes for sway and non-sway structures, as well as providing the same predicting expressions for the amplification of bending moments in basic structures, despite the considerable differences between the mechanical behaviour of these two materials. However, recent numerical research on stainless steel frames with H cross-sections by Walport et al. (2019) showed that the degradation of stiffness due to material nonlinearities considerably affects the response of stainless steel frames, causing greater deformations and increasing second order effects. In order to contribute to the optimal design of stainless steel structures, this paper investigates the influence of the nonlinear material response of stainless steel alloys on frame-type structures with Rectangular Hollow Sections based on the experimental results conducted by Arrayago et al. (2019), and the interaction of material and geometric nonlinearities., The authors acknowledge the funding from MINECO (Spain) under Project BIA2016-75678-R, AEI/FEDER, UE “Comportamiento estructural de pórticos de acero inoxidable. Seguridad frente a ac-ciones accidentales de sismo y fuego”. The first author would also like to acknowledge the financial support provided by FPI-MINECO PhD fellowship Ref. BES-2017-082958. The second author would like to acknowledge the financial support received funding from the European Union’s Horizon 2020 research and innovation pro-gramme under the Marie Sklodowska-Curie grant agreement No. 842395.




A stiffness reduction method for the in-plane design of stainless steel members and frames according with EN 1993-1-4

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  • González de León, Isabel|||0000-0003-2667-9931
  • Arrayago Luquin, Itsaso|||0000-0002-0054-9322
  • Real Saladrigas, Esther|||0000-0003-1723-3380
  • Mirambell Arrizabalaga, Enrique|||0000-0003-2612-9104
Current design standards for stainless steel such as ASCE 8-02 and EN 1993-1-4 prescribe provisions for the design of cross-sections and members that account for material nonlinearities and strain hardening, although these features are not considered in the global design of structures. Recent studies have highlighted the need of accounting for material nonlinearities in order to design efficient and safe stainless steel structures, and it is expected that the forthcoming versions of the standards will incorporate updated rules for the global design of these structures. To contribute to this field, this paper presents a Stiffness Reduction Method (SRM) for the in-plane design of stainless steel members and frames with stocky sections based on the prescriptions given in the next version of EN 1993-1-4. The proposed approach predicts the ultimate capacity and internal forces in stainless steel structures by performing a second-order elastic analysis in which the stiffnesses of the members are reduced by a set of factors defined in this paper to account for the effect of the spread of plasticity, residual stresses and member imperfections. The accuracy of the presented method is assessed for individual stainless steel structural members (columns, beams, and beam-columns) with different cross-sections and material properties, and for austenitic stainless steel portal frames, against numerical results obtained from nonlinear analyses conducted on finite element models. A comparison between the proposed approach and the Direct Analysis Method prescribed in the upcoming AISC 370 Specification is also provided, showing that the results are comparable in the two approaches., The research presented in this paper was developed in the frame of the Project BIA2016-75678-R, AEI/FEDER, UE “Comportamiento estructural de pórticos de acero inoxidable. Seguridad frente a acciones accidentales de sismo y fuego”, funded from the MINECO (Spain). The financial support received from the Spanish Ministry for Science, Innovation and Universities through the FPI-MINECO PhD fellowship Ref. BES-2017-082958 (I. González-de-León) and from the European Commission through the Marie Sklodowska-Curie grant agreement No. 842395 (I. Arrayago) is also gratefully acknowledged., Peer Reviewed




Buckling curves for cold-formed stainless-steel columns and beams

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  • Arrayago Luquin, Itsaso|||0000-0002-0054-9322
  • Rasmussen, Kim J.R.
This material may be downloaded for personal use only. Any other use requires prior permission of the American Society of Civil Engineers. This material may be found at https://ascelibrary.org/doi/10.1061/%28ASCE%29ST.1943-541X.0003084., This paper summarises the background information and methodology used to derive a set of buckling curves proposed for cold-formed stainless steel columns and beams, incorporated in the recently revised SEI/ASCE 8-21 Specification. The study is based on experimental and numerical data collected from the literature on cold-formed stainless steel columns and beams featuring ASTM grades 304, 2101, 430, 404 and 443. Since most of the investigated specimens exhibited slender cross-sections, both the Effective Width Method (EWM) and the Direct Strength Method (DSM) are considered to account for the effect of interaction between global and local buckling on member strength. Buckling curves for flexural buckling and lateral-torsional buckling codified in current international standards are assessed based on the SEI/ASCE 8 reliability requirements, and new curves are derived accordingly. The proposed new buckling curves include expressions to account for the post-yielding capacity of stainless steel columns and the inelastic buckling resistance of cold-formed stainless steel beams. In addition, a new local buckling strength curve for members in flexure is proposed in the format of the DSM and shown to provide equivalent design resistances to the EWM., Funding for this investigation was received from the European Union’s Horizon 2020 Research and Innovation Programme under the Marie Sklodowska-Curie Grant Agreement No. 842395 (Project NewGeneSS)., Peer Reviewed




Reliability of stainless steel frames designed using the Direct Design Method in serviceability limit states

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  • Arrayago Luquin, Itsaso|||0000-0002-0054-9322
  • Rasmussen, Kim J.R.
Steel structures can be consistently and efficiently designed using system-based design-by-analysis approaches such as the Direct Design Method. However, since direct design approaches lead to potentially lighter structural configurations, they can also result in larger deformations under service loads. Thus, greater attention may be required to serviceability limit states in structures designed using design-by-analysis approaches than for structures designed elastically at their ultimate limit state following current two-stage approaches, especially for materials showing highly nonlinear stress vs strain responses such as stainless steel alloys. With the aim of investigating the influence of allowing larger deformations in the ultimate limit state design of stainless steel structures, this paper presents an explicit analysis framework for assessing serviceability reliability at system level. Using this framework, the paper investigates the serviceability reliability of cold-formed stainless steel portal frames designed using the Direct Design Method for different load cases, including the gravity load and the combined gravity plus wind load combinations. The study considers six baseline frames covering the most common stainless steel families and international design frameworks (i.e., Eurocode, US and Australian frameworks), for which the reliability of vertical deflection and lateral drift serviceability limit states is investigated using advanced numerical simulations and First-Order Reliability Methods. From the comparison of the calculated average annual reliability indices and the relevant target reliabilities for the different design frameworks, it was found that the reliability of stainless steel frames appears to be adequate for the serviceability limit states investigated for the Eurocode, US and Australian frameworks., Peer Reviewed




System-based reliability analysis of stainless steel frames under gravity loads

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  • Arrayago Luquin, Itsaso|||0000-0002-0054-9322
  • Rasmussen, Kim J.R.
Current structural codes for steel and stainless steel structures such as AISC 360-16, AISC 370-21, AS/NZS 4100 and Eurocode 3 are based on the traditional two-step member-based design approach, in which internal actions are first obtained from a structural analysis, usually elastic, and the strength of each member and connection is subsequently checked using a structural design standard. However, the most recent versions of these standards already incorporate preliminary versions of the direct, or one-step, system-based design alternative, which is based on the design-by-analysis concept and allows evaluating the strength of structures directly from numerical simulations, although the standards in their current form do not provide reliability requirements for structural systems. Therefore, it is necessary to build a rigorous structural reliability framework to investigate acceptable target reliability indices for structural systems and to provide adequate system safety factors and system resistance factors. While this framework has been developed based on advanced Finite Element analysis for hot-rolled and cold-formed carbon steel structures in recent years in the form of the Direct Design Method (DDM), the framework does not exist for stainless steel structures. This paper presents an extension of the DDM to the analysis of stainless steel structures, in which system reliability calibrations are presented for six stainless steel portal frames under gravity loads covering the three most common stainless steel families and different failure modes using advanced numerical simulations. From the derived reliability calibrations, suitable system safety factors and system resistance factors are proposed for the direct design of stainless steel frames in the European, US and Australian design frameworks under gravity loads., This project has Received funding from the European Union’s Horizon 2020 Research and Innovation Programme under the Marie Sklodowska-Curie Grant Agreement No. 842395., Peer Reviewed




Stiffness of randomly sampled stainless steel frames under gravity and gravity plus wind load scenarios

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  • Arrayago Luquin, Itsaso|||0000-0002-0054-9322
  • Rasmussen, Kim J.R.
This file includes data on system vertical and lateral stiffness of stainless steel frames under gravity and gravity plus wind load scenarios obtained from the finite element simulations carried out on six stainless steel frames.




Ultimate load of randomly sampled stainless steel frames under gravity plus wind loads

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  • Arrayago Luquin, Itsaso|||0000-0002-0054-9322
  • Rasmussen, Kim J.R.
  • Zhang, Hao
Data was generated using the general purpose finite element software ABAQUS and performing advanced nonlinear analyses. The database is comprised of ultimate load factors corresponding to different random samples of six different nominal stainless steel frames under gravity and wind load combinations. The values of the random variable assignments are given for each case.

The full details of the finite element model can be found in: Arrayago, I.; Rasmussen, K.J.R.; Zhang, H. System-based reliability analysis of stainless steel frames subjected to wind loads. "Structural Safety", July 2022, vol. 97, art. No. 102211. DOI: https://doi.org/10.1016/j.strusafe.2022.102211




Statistical analysis of the material, geometrical and imperfection characteristics of structural stainless steels and members

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  • Arrayago Luquin, Itsaso|||0000-0002-0054-9322
  • Rasmussen, Kim J.R.
  • Real Saladrigas, Esther|||0000-0003-1723-3380
Traditional member-based two-step design approaches included in current structural codes for steel structures, as well as more recent system-based direct-design alternatives, require building rigorous structural reliability frameworks for the calibration of partial coefficients (resistance factors) to achieve specified target reliability requirements. Key design parameters affecting the strength of structures and their random variations are generally modelled by nominal or characteristic values in design standards, which are combined with partial coefficients that need to be calibrated from measurements on real samples. While the statistical characterization of material and geometric properties of structural steels has been consolidated over the last decades, information about the characterization of structural stainless steels is virtually non-existent due to the limited pool of available data. Thus, this paper presents the basic ingredient for developing reliability frameworks for stainless steel structures and components by statistically characterizing the main random parameters affecting their strength through a comprehensive database collected from the literature. Based on the collected data, appropriate probabilistic models are proposed for geometric properties, material properties, imperfections and residual stresses of different stainless steel alloys and cross-section or product types. The data is equally applicable to member-based reliability analyses as described in existing codes and system-based analyses targeted at the direct-design of stainless steel structures by advanced analysis., This research project has received funding from the European Union’s Horizon 2020 Research and Innovation Programme under the Marie Sklodowska-Curie Grant Agreement No. 842395. The time dedicated by numerous authors of referenced papers to provide additional data and information is also much appreciated., Peer Reviewed




Influence of the imperfection direction on the strength of steel and stainless steel frames [Dataset]

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  • Arrayago Luquin, Itsaso|||0000-0002-0054-9322
  • Rasmussen, Kim J.R.
This file includes finite element simulation data (ultimate load factors) carried out on 60 steel and stainless steel frames, including regular and irregular frame configurations with different section sizes. Ultimate load factors corresponding to different initial imperfection combinations are included.




System-based reliability analysis of stainless steel frames subjected to gravity and wind loads

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  • Arrayago Luquin, Itsaso|||0000-0002-0054-9322
  • Rasmussen, Kim J.R.
  • Zhang, Hao
In the process of developing the next generation of design standards for steel structures, most relevant international structural codes including AISC 360, AISC 370, AS/NZS 4100 and Eurocode 3 already incorporate preliminary versions of system-based design-by-analysis approaches that allow a direct evaluation of the strength of steel and stainless steel structures from advanced numerical simulations. As a result, recent research works have focused on building rigorous structural reliability frameworks to investigate acceptable target reliability indices for structural systems and to develop new design methods in conjunction with adequate system safety factors and system resistance factors. Although design recommendations exist for the direct design of hot-rolled and cold-formed steel structures based on advanced finite element analysis, the extension of the method to other materials such as stainless steel is under development. This paper is part of a research effort to build a reliability framework for stainless steel structures subject to different load combinations and presents the results of system reliability calibrations carried out on six stainless steel portal frames subjected to combined gravity and wind loads. The study covers the most common stainless steel families and three international design frameworks (i.e., Eurocode, US and Australian frameworks). From the reliability calibrations derived, suitable system safety factors and system resistance factors are proposed for the direct design of stainless steel frames under combined gravity and wind loads using advanced numerical simulations., The project leading to this research has received funding from the European Union’s Horizon 2020 Research and Innovation Programme under the Marie Sklodowska-Curie Grant Agreement No. 84239., Peer Reviewed