Effects of material nonlinearity on the global analysis and stability of stainless steel frames

© 2017 Elsevier Ltd In structural frames, second order effects refer to the internal forces and moments that arise as a result of deformations under load (i.e. geometrical nonlinearity). EN 1993-1-1 states that global second order effects may be neglected if the critical load factor of the frame αcris greater than or equal to 10 for an elastic analysis, or greater than or equal to 15 when a plastic global analysis is used. No specific guidance is provided in EN 1993-1-4 for the design of stainless steel frames, for which the nonlinear stress-strain behaviour of the material will result in greater deformations as the material loses its stiffness. A study of the effects of material nonlinearity on the stability of stainless steel frames is presented herein. A series of different frame geometries and loading conditions are considered. Based on the findings, proposals for the treatment of the influence of material nonlinearity on the global analysis and design of stainless steel frames are presented

The Continuous Strength Method for the design of stainless steel hollow section beam-columns

The Continuous Strength Method (CSM) is a deformation based design approach that provides accurate cross-section resistance predictions by making rational allowance for the interaction between cross-section elements, the partial spread of plasticity and the beneficial effects of strain hardening. The CSM can be used in conjunction with advanced analysis for the design of members and frames, but, for hand calculations, member-level stability checks are currently limited to stainless steel hollow section columns failing by flexural buckling. Extension to the design of stainless steel members subjected to combined compression and bending moment is presented in this paper. The analysis is based on numerical results and existing experimental data collected from the literature on stainless steel hollow section members, including members with stocky and slender cross-sections. Comparisons demonstrate that the adoption of the CSM design equations in conjunction with both current and revised interaction factors considerably improves the accuracy of beam-column capacity predictions for members with stocky cross-sections. The analysis on beam-columns with slender sections shows that similar resistance predictions are obtained using Eurocode 3 and the CSM. The reliability of the proposed approach is demonstrated through statistical analyses performed in accordance with EN1990

Una intervención en escritura académica durante la cursada virtual de Histología y Embriología, Facultad de Ciencias Veterinarias-Universidad de Buenos Aires.

En la asignatura Histología y Embriología de la carrera de Veterinaria de la Universidad de Buenos Aires se solicita a los alumnos cursantes resolver una serie de actividades escritas. Durante la cursada virtual del primer cuatrimestre de 2021 se implementaron cinco actividades de integración. El objetivo fue propiciar la integración de los contenidos de la materia y su adecuada expresión escrita. Las consignas propuestas solicitaban la producción de textos individuales y originales, con una elaboración adicional a la expuesta en las fuentes bibliográficas. Los docentes correctores realizaban una devolución formal de cada entrega, aplicando una rúbrica diseñada por los autores. Esta rúbrica permitía calificar en base a siete criterios: formato textual, registro, uso del lenguaje técnico de la materia, pertinencia y cobertura de los contenidos solicitados, relación y dominio de conceptos, aspectos formales y fuentes de investigación teórica. Cada criterio reunía varios parámetros analizables. La devolución constaba de comentarios puntuales sobre el texto y breves párrafos explicativos. Se analizaron los escritos de un grupo de estudiantes (n=23), entre un “momento inicial” de la intervención y un “momento final”. Mediante un instrumento adicional se evaluó la evolución para cada criterio (y parámetro) de la rúbrica.Se observó una evolución favorable en más del 40% de los estudiantes para los criterios: formato textual, registro (persona verbal), lenguaje (expresión), aspectos formales (sintaxis, puntuación) y bibliografía (calidad, formato). Entre el 30 y el 40% demostró evolución favorable en: registro (formal y tiempo verbal), lenguaje (precisión) y aspectos formales (conectores). Menos del 30% demostró evolución favorable en:pertinencia y cobertura, relación y dominio de conceptos y lenguaje técnico de la materia (léxico). Se concluye que la intervención tuvo un efecto favorable en la calidad de la escritura académica de los estudiantes

Effect of Corner Strength Enhancement on Shear Behaviour of Stainless Steel Lipped Channel Sections

During the cold-forming process of manufacturing, stainless steel sheets undergo plastic deformations, in particularly around corner regions of press braked sections. These plastic deformations lead to significant changes in material properties of stainless steel compared to its flat sheet properties. Consequently, yield strength and ultimate strength increments can be envisaged and this process is termed as cold working. Stainless steel exhibits significant level of strain hardening under plastic deformations. This is the main reason for these strength enhancements. In the structural design process of stainless steel sections, these strength increments are required to be considered to harness the benefits arising from it. Therefore, previous research proposed predictive models for these strength enhancements. In this context, the effect of corner strength enhancement on press-braked stainless steel lipped channel sections under shear was examined in this paper. 120 finite element models were developed. Different corner radii and section thicknesses were taken into account. Results highlighted that the effect of cold working on the shear capacity of stainless steel lipped channel sections is more significant in compact sections compared to slender sections where up to 9% increment was observed. Further analysis was conducted using 40 finite element models to highlight the inelastic reserve capacity available in compact stainless steel lipped channel sections in shear. From the results, it was concluded that when web slenderness is less than 0.25 more than 40% shear capacity increment can be achieved due to strain-hardening of stainless steel

Shear Behaviour of Cold-Formed Stainless Steel Lipped Channels with Reduced Support Restraints

Lipped channel beams are commonly used in buildings for load-bearing components such as floor joists and roof purlins. The typical practice is to use one-sided web side plates (WSPs) to attach beams from their webs to the supports at the connections, through bolts. In such realistic conditions, it is not practical to use WSPs over the full height of the webs, thus only a part of the web height is restrained at the supports. This controls the mobilising of diagonal tension field in the web and also provides less restraint to the lateral movement of the web. Therefore, realistic support conditions affect the shear capacity due to the lack of restraint of the web at the supports. On the other hand, the current shear design rules are based on ideal support conditions which do not represent the true scenario. Therefore, it is critical to investigate the effect of reduced support restraints on the shear capacity since it has been given less attention in the literature. This paper presents the effect of reduced support restraints on the shear capacity of stainless steel lipped channel beams. Finite element models were developed to study the effect with regard to various influential parameters. From the finite element results, it was found that the shorter the WSP—the higher the shear capacity reduction, where about 50% shear capacity reduction was observed for 60% reduction in WSP height. Furthermore, it was concluded that compact sections exhibit more significant capacity reduction than slender sections when reducing the WSP height. Therefore, a reduction factor was introduced to the current direct strength method shear design rules considering the effect of reduced support restraints on the shear capacity

The continuous strength method for the design of stainless steel hollow section columns

The Continuous Strength Method (CSM) provides accurate resistance predictions for both stocky and slender stainless steel cross-sections; in the case of the former, allowance is made for the beneficial effects of strain hardening, while for the latter, design is simplified by the avoidance of effective width calculations. Although the CSM strain limits can be used in conjunction with advanced analysis for the stability design of members, for hand calculations, the method is currently limited to the determination of cross-sectional resistance only, i.e. member buckling resistance is not covered. To address this limitation, extension of the CSM to the design of stainless steel tubular section columns is presented herein. The proposed approach is based on the traditional Ayrton-Perry formulation, but features enhanced CSM cross-section resistances and a generalized imperfection parameter that is a function of cross-section slenderness. The value of the imperfection parameter increases as the slenderness of the cross-section reduces to compensate for the detrimental effect of plasticity on member stability that is not directly captured in the elastic/first yield Ayrton-Perry approach. The accuracy of the proposed approach is assessed against numerical results generated in the current study and existing experimental results collected from the literature. The presented comparisons show that the CSM provides consistently more accurate member buckling resistance predictions than the current EN 1993-1-4 design rules for all stainless steel grades. The reliability of the proposed approach is demonstrated through statistical analyses performed in accordance with EN 1990. Finally, the paper presents a framework through which the proposed approach can be developed for other cross-section types and materials

Influence of geometric and material nonlinearities on the behaviour and design of stainless steel frames

Material nonlinearity affects the stiffness and consequently the distribution of internal forces and moments in indeterminate structures. This has a direct impact on their behaviour and design, particularly in the case of stainless steel, where material nonlinearity initiates at relatively low stress levels. A method for accounting for the influence of material nonlinearity in stainless steel frames, including making due allowance for the resulting amplified second order effects, is presented herein. Proposals have been developed for austenitic, duplex and ferritic stainless steels. The method was derived based on benchmark results calculated through second order inelastic analysis with strain limits, defined by the Continuous Strength Method, using beam finite element models. A comprehensive set of frames was modelled and the proposed assessment of second order effects in the plastic regime was also verified against the results of four full-scale stainless steel frame tests. The proposed method is due to be included in the upcoming revision to Eurocode 3 Part 1.

Rotation capacity of cold-formed stainless steel RHS beams under cyclic loading

Stainless steel is a structural material with great potential in seismic design due to its ductile and strain hardening characteristics. However, no specific seismic design provisions exist for stainless steel, despite the remarkable differences with carbon steel. Moreover, research on the behaviour of stainless steel under cyclic conditions is scarce, not allowing designers to rely on accurate capacity models able to catch the actual member ductility under seismic excitation. Hence, the aim of this paper is to fill this lack and to provide simple provisions to estimate the total and stable part of the rotation capacity of stainless steel members with rectangular hollow section (RHS). A numerical study on 120 austenitic, ferritic and duplex beams under cyclic loading was performed following the ANSI/AISC 341 loading protocol. From the resulting skeleton curves, information on the ultimate strength and ductility (total and stable parts of the rotation capacity) were extracted. It was found that the ultimate bending moment resistance of RHS stainless steel beams under cyclic loading is accurately predicted by the Continuous Strength Method moment capacity, and that the rotation capacities can be related to the local slenderness by power functions calibrated from the numerical results. Finally, a tri-linear model that describes the full moment-rotation curves of stainless steel beams under cyclic loading is proposed using the calibrated equations, showing a good agreement with numerical moment-rotation curves, and which can be implemented in design software to define the behaviour of concentrated plasticity hinges

Experimental study on stainless steel tubular members under cyclic loading

Stainless steel is an excellent construction material due to its high ductility, strain hardening, durability and aesthetic characteristics. To date, most studies on stainless steel have been devoted to understanding its mechanical properties and the behaviour of individual structural members and simple structures under monotonic loading. As a result, next versions of stainless steel codes, traditionally based on carbon steel codes, will enable efficient structural designs under static forces. However, advances related to the performance of stainless steel structural members under cyclic forces are still scarce, and there are no specific rules for the seismic design of stainless steel structures in Eurocode 8 in spite of the notable differences between this material and other steels. On this basis, an experimental programme on austenitic stainless steel hollow section elements subjected to cyclic loading has been recently conducted. A total of nine specimens with different local and member slenderness values were tested under cyclic bending around their major axis following a cantilever loading scheme. This paper describes the experimental set-up adopted for the tests, including the loading scheme and instrumentation, and discusses the load–displacement, moment–rotation, degradation of stiffness and energy dissipation values obtained in detail. In addition to providing fundamental information on the response of stainless steel members under cyclic loading, the description of the set-up reported in this paper will assist researchers in planning similar experimental programmes, while the results will serve as a reference to validate numerical analyses of stainless steel members and frames subjected to cyclic loading