Structural performance of concrete-filled cold-formed stainless steel members

Abstract

The structural performance of concrete-filled cold-formed stainless steel members has been investigated in this study. The current design rules for concrete-filled steel tubular members are applicable to carbon steel only and these design rules may not be appropriate for stainless steel. The structural performance of concrete-filled cold-formed stainless steel members was investigated using stub column, beam and beam-column tests. Cold-formed ferritic stainless steel square and rectangular hollow sections of grade EN 1.4003 and cold-formed austenitic stainless steel circular hollow sections of grade EN 1.4301 were used to fabricate the composite members. Concrete of nominal cylinder compressive strengths 40, 80 and 120 MPa were filled into the stainless steel tubes.

The experimental investigation included material tests, stub column, beam and beam-column tests. The test program consists of one square hollow section, four rectangular hollow sections and four circular hollow sections. Tensile coupons were extracted from each hollow section and tested to determine the corresponding material properties. In addition, the material properties of cold-formed ferritic stainless steel at elevated temperatures ranged from 22 – 1000 °C were also obtained by coupon tests. Flexural behaviour of cold-formed ferritic stainless steel square and rectangular hollow sections under four-point bending was also investigated, and new slenderness limits for section classification are proposed. A total of 22 stub column tests were carried out on concrete-filled cold-formed ferritic stainless steel square and rectangular hollow sections, and another 18 stub column tests were also conducted on concrete-filled cold-formed austenitic stainless steel circular hollow sections. The test program for beams included 23 concrete-filled cold-formed ferritic stainless steel square and rectangular members and 18 concrete-filled cold-formed austenitic stainless steel circular members. The beam-column tests were conducted on concrete-filled cold-formed ferritic stainless steel square and rectangular sections and a total of 48 specimens were bent about minor axis to determine the structural behaviour under combined axial load and bending conditions.

Accurate finite element models were developed and verified against the experimental results. The finite element models were used to perform extensive parametric studies in order to provide complementary data to facilitate the development of design rules. The extensive parametric studies included 165 stub columns, 171 beams and 239 beam-columns, for concrete-filled cold-formed ferritic stainless steel square and rectangular hollow sections as well as 168 stub columns and 165 beams for concrete-filled cold-formed austenitic stainless steel circular hollow sections.

The experimental and numerical results as well as available data from the literature were used to assess the applicability of current design specifications, including the American specification, European code and Australian standard designated for concrete-filled carbon steel tubular members, to concrete-filled stainless steel tubular members. Improved design rules are proposed in this study. In addition, the material properties of ferritic stainless steel at elevated temperatures and the slenderness limits on classification of ferritic stainless steel hollow sections specified in the European code were also examined. The current design rules and proposed design rules were evaluated by reliability analysis.

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