Steel Elliptical Hollow Sections Research Articles

Analytical modelling of plastic collapse in compressed elliptical hollow sections

The plastic collapse response of structural steel elliptical hollow section (EHS) profiles in compression is examined in this paper. As an initial step, a parametric study to identify the factors that determine which plastic mechanisms would arise has been carried out using finite element (FE) results from the current work and experimental data from the literature. All investigated EHS had a cross-sectional aspect ratio of two. The parametric study revealed four plastic collapse mechanisms and showed that the “split flip disc” plastic collapse mechanism is the most likely to appear in compressed EHS. Thus, the present work is focussed on this failure mechanism, for which an analytical model to describe the relationship between load and deformation is developed. Coupled with the consideration of the elastic, yielding and strain hardening characteristics of steel, the derived analytical model enables construction of the full load–deformation behaviour of compressed EHS to be established. The parameters controlling the shape and size of the plastic hinges have been investigated and found to be of key importance; hence, special care has been taken in their definition. Finally, the developed load–displacement curves have been compared with both finite element results and experimental data. The comparisons have revealed good agreement, confirming the ability of the analytical model to predict the collapse response of elliptical tubes.

Behaviour of Axially Loaded Concrete Filled Stainless Steel Elliptical Stub Columns

This paper presents the details of an experimental investigation on the behaviour of axially loaded concrete-filled stainless steel elliptical hollow sections. The experimental investigation was conducted using normal and high strength concrete of 30 and 100 MPa. The current study is based on stub column tests and is therefore limited to cross-section capacity. Based on the equations proposed by the authors on concrete-filled stainless steel circular columns, a new set of equations for the stainless steel concrete-filled elliptical hollow sections were proposed. From the limited data currently available, the equation provides an accurate and consistent prediction of the axial capacity of the composite concrete-filled stainless steel elliptical hollow sections.

Upper Bound Plastic Interaction Relations for Elliptical Hollow Sections

A family of interaction expressions are developed for steel elliptical hollow sections (EHSs) subjected to combinations of axial force, biaxial bending moments, torsion, and bimoments. The formulation is based on kinematically admissible strain fields within the context of the upper bound theorem of plasticity. The interaction relations derived successfully capture the effect of confining radial strains present at welded end sections, as well as sections that are free to deform in the radial direction away from end welded sections. The interaction expressions developed consist of a set of elliptical integrals which are cast in a dimensionless form applicable for EHS of general geometries. An iterative solution technique is developed to solve the resulting nonlinear relations. The applicability of the resulting interaction relations for conducting the cross-sectional check is illustrated through examples. A comparison with shell finite-element analysis results illustrates the validity of the interaction relations derived.

Flexural Buckling of Elliptical Hollow Section Columns

Complementary to recent studies on the cross-section behavior of elliptical hollow sections, investigations into the member response have also been performed and described in this paper. The first stage of these investigations involved a series of precise column buckling tests on hot-finished steel elliptical hollow sections. In total, 24 flexural buckling tests about the minor and major axes were carried out. Specimen sizes and lengths were carefully chosen in order to cover a wide range of both cross section and member slendernesses. The nondimensional column slenderness of the test specimens varied between 0.19 and 1.58. Measurements were taken of specimen geometry, global initial geometric imperfections, and tensile material properties. Key results from the tests including the full load-deformation histories have been presented and discussed. The test results have also been supplemented by 158 numerically generated results, allowing a wider range of geometries to be investigated. Design rules for the member buckling resistance of elliptical hollow section columns have been proposed and verified by means of reliability analysis. The results presented are the first member buckling tests on elliptical hollow sections, and represent part of the development of comprehensive structural design rules for these sections.

Plastic interaction relations for elliptical hollow sections

Interaction expressions are developed for steel elliptical hollow sections (EHS) subjected to combinations of axial force, biaxial bending moments and torsion. The formulation is based on the lower bound theorem of plasticity and the maximum distortional energy density yield criterion. The interaction expressions developed consist of a set of elliptical integrals which are cast in a dimensionless form and numerically evaluated to obtain a grid of internal force combinations lying on the yield surface sought. A series of trial functions are fitted to the grid of internal force combinations and a simplified and conservative interaction equation is selected. The interaction relation relates axial force, biaxial bending and twisting moment combinations for EHS sections of common geometries. Its applicability for conducting the cross-sectional interaction check in structural steel design problems is illustrated through a practical example.

Shear response of elliptical hollow sections

Following the introduction of hot-finished elliptical hollow sections to the construction industry, recent research has been performed to develop supporting structural design guidance. This paper focuses on shear resistance. Twenty-four shear tests were performed on hot-finished steel elliptical hollow section members. The shear tests were arranged in a three-point bending configuration with span-to-depth ratios ranging from 1 to 8. This enabled the study of cross-section resistance in shear and the interaction between shear and bending. Measurements were taken of cross-section geometry, local initial geometric imperfections and material properties in tension. Test results, including moment– rotation histories, are presented. Additional results were generated numerically. These results have been used to verify proposed design expressions for shear resistance and resistance to combined shear and bending. Further investigations into design criteria for shear buckling are currently under way.

Cross-section classification of elliptical hollow sections

Tubular construction is widely used in a range of civil and structural engineering applications. To date, the principal product range has comprised square, rectangular and circular hollow sections. However, hot-rolled structural steel elliptical hollow sections have been recently introduced and offer further choice to engineers and architects. Currently though, a lack of fundamental structural performance data and verified structural design guidance is inhibiting uptake. Of fundamental importance to structural metallic design is the concept of cross-section classification. This paper proposes slenderness parameters and a system of cross-section classification limits for elliptical hollow sections, developed on the basis of laboratory tests and numerical simulations. Four classes of cross-sections, namely Class 1 to 4 have been defined with limiting slenderness values. For the special case of elliptical hollow sections with an aspect ratio of unity, consistency with the slenderness limits for circular hollow sections in Eurocode 3 has been achieved. The proposed system of cross-section classification underpins the development of further design guidance for elliptical hollow sections.