Elliptical hollow sections

As the construction industry continues to evolve, innovative products and design techniques are being developed to respond to the ever increasing demands on both the efficiency and aesthetics of civil engineering structures. A recent advance has been the introduction of high strength, hot-rolled and cold-formed oval hollow sections for structural application. The fundamental test data and verified structural design guidance to enable their safe and efficient use in construction has been developed at Imperial College London.

Structural elliptical hollow sections represent a recent and rare addition to the range of cross-sections available to structural engineers and architects. Their emergence is also timely given the increasing application of hollow sections in construction and the current trend towards the use of bare steelwork to express structural form. However, despite widespread interest in their application on the basis of both architectural appeal and structural efficiency, a lack of verified design guidance is inhibiting uptake. Analytical and experimental studies on elliptical hollow sections are being undertaken together with numerical modelling in order to evaluate design rules for the recently introduced structural sections.

Laboratory testing has been carried out in various structural configurations – pure compression, pure in-plane bending, and combined compression and bending. In addition to the basic geometry (including initial geometric imperfections) and material properties, full load-deformation histories were recorded. Numerical models, using the finite element package ABAQUS, were created and validated against the test results, before a series of sensitivity and parametric studies were conducted. The models included features such as curved geometry, nonlinear material properties and initial geometric imperfections. For stub column behaviour, ultimate load was generally well predicted by the numerical models, but prediction of deformation at ultimate load was less accurate. For pure bending and combined compression and bending behaviour, the full bending moment-deformation history was consistently well predicted.

Comparison of the test and finite element results against the proposed design rules has demonstrated broadly acceptable agreement. Analysis has also be performed on concrete-filled elliptical hollow sections. Flexural buckling and lateral torsional buckling have also been investigated. Additional analysis on the basis of further testing and modelling is continuously being undertaken.