Behavior and design of cold-formed steel elliptical and semi-oval hollow sections structural members

Abstract

Tubular members have gained popularity in recent years, particularly for exposed steelwork for aesthetic purposes. The closed nature of tubular sections brings quantities of merits to the structures, such as high resistance to compression and bending due to the high torsional stiffness, ability to provide permanent formwork for concrete infilled structures, aesthetic appearance as well as easy structural adjustment for innovative architectural forms. The typical tubular hollow section family comprises square, rectangular and circular hollow sections. With the advancement of structural steel manufacturing industry and the rapid development of cold-forming technology, the family of structural hollow sections has expanded and novel tubular sections with aesthetic appearance and prominent structural efficiency, such as elliptical and semi-oval hollow sections, have recently emerged. The aims of this thesis are to study the behavior of cold-formed steel elliptical and semi-oval hollow sections structural members through experimental and numerical investigation, and to develop design guidelines for these innovative sections. Comprehensive experimental investigation on the material properties, cross-section and member behavior was conducted through 65 tensile coupon tests, residual stress measurements on 2 sections, 11 stub column tests, 40 beam tests, 41 pin-ended column tests and 79 beam-column tests. Eight cross-section series of cold-formed steel elliptical and semi-oval hollow sections, including four on elliptical section and four on semi-oval section, were included in the test program. The key results, including the ultimate load-carrying capacities, failure modes and load-displacement responses, were reported and discussed. Extensive numerical studies were carried out on cold-formed steel elliptical and semi-oval hollow sections structural members, including stub columns, beams, pin-ended columns and beam-columns. Accurate finite element models with discreet selection of element type and mesh size as well as the consideration of strength enhancement effect, residual stresses and geometric imperfections were developed. Upon validation of the finite element models against the test results, extensive parametric studies on 96 stub columns, 433 beams, 480 pin-ended columns and 1152 beam-columns were performed. The feasibility of the existing design rules for the structural design of cold-formed steel elliptical and semi-oval hollow section members was evaluated. The experimental and numerical results were compared with the design strengths predicted by the existing design rules with certain assumptions and design methodologies that proposed by previous researchers. The results showed that the current design rules are not capable to provide accurate and reliable predictions for cold-formed steel elliptical and semi-oval hollow section members. New design rules and modified design methods are proposed in this study in order to improve the accuracy of the design strength predictions. The reliability of the existing and newly proposed design rules was examined through reliability analysis.