| Author: | Liu, Junzhi |
| Title: | Structural behaviour of hexagonal and octagonal shaped high strength steel stub columns under uniaxial compression |
| Advisors: | Chan, Tak-ming (CEE) |
| Degree: | Ph.D. |
| Year: | 2022 |
| Subject: | Steel, High strength -- Fatigue Columns, Iron and steel -- Design and construction Hong Kong Polytechnic University -- Dissertations |
| Department: | Department of Civil and Environmental Engineering |
| Pages: | xxx, 338 pages : color illustrations |
| Language: | English |
| Abstract: | Tubular members are gaining increasingly popularity due to its great potential in resisting torsional buckling and aesthetic appearance. The advancement of the high-strength steel (HSS) technology promotes the extensive applications of HSS in large-scale and high-rise buildings due to the comparably high strength-to-weight ratio as well as the low carbon footprint, resulting in lighter structural components with smaller dimensions. HSS hollow sections integrate the merit of hollow sections and HSS materials to increase the benefits. However, the material properties of high strength steel can not be simply represented by conventional mechanical response from normal mild steel. Moreover, HSS cold-formed steel structures, compared with hot-rolled sections and welded sections, are characterised with fast erection and less energy consumption. Compared with the conventional profile of tubular members such as rectangular hollow sections (SHS), square hollow sections (SHS), circular hollow sections (CHS), elliptical hollow sections (EHS), the application of the polygonal tubular sections is gaining increasing interests in recent years. In the polygonal section family, hexagonal and octagonal shaped sections have emerged with appealing appearance and great structural efficiency. These include hexagonal hollow sections (HexHS), irregular hexagonal hollow sections (IHexHS), octagonal hollow sections (OctHS) and irregular octagonal hollow sections (IOctHS). Compared with SHS/RHS and CHS, hexagonal and octagonal hollow sections provide flat surfaces allowing for easier connection construction with incoming members as an operation platform. In addition, the better local buckling resistance and enhanced confinement can be provided in comparison with the RHS/SHS. The aims of this thesis are to study the behaviour of the HSS HexHS, IHexHS and IOctHS through experimental and numerical investigations. Comprehensive experimental programmes have been implemented, including investigations on the material properties, residual stresses, imperfection measurements, cross-sectional behaviour through 76 tensile coupon tests, 74 strips with 898 strain readings for residual stress measurements and 18 stub column specimens of HexHS; 72 tensile coupon tests, 59 strips with 708 strain readings for residual stress measurements and 20 stub column specimens of IHexHS; and 50 tensile coupon tests, 55 strips with 660 strain readings for residual stress measurements and 13 stub column specimens of IOctHS. The obtained results for the ultimate resistances, deformation capacities, residual stress distribution, initial local geometric imperfection value failure modes, load-end shortening response were reported and discussed. In parallel with experimental tests, extensive numerical investigations were carried out through finite element modelling on stub column sections of the studied HSS HexHS, IHexHS and IOctHS. The obtained tested material properties accounting for the cold-forming effect induced by press-braking, stress-strain characteristics, initial local geometric imperfections, influence of the residual stress as well as the other influential factors were analysed. The developed finite element models were validated against the experimentally obtained results and observations of failure modes. Based upon validated numerical models, extensive parametric studies were conducted to generate a wider range of cross-sectional dimensions test data complementing to the test data pool. The parametric studies comprise 261 HexHS stub columns, 379 IHexHS stub columns and 150 IOctHS stub columns. The experimentally and numerically obtained tests results were used together to assess and evaluate the specifications codified in current design codes. It is known that HSS conventional cross-sections such as HSS RHS and CHS are covered by design codes of EN 1993-1-12 (CEN 2007), AISI/AISC 360-16 (AISC 2016) and AS 4100 (AS 2016). Design guidelines pertaining to the HSS HexHS, IHexHS, and IOctHS are not provided in existing structural steel design codes. The applicability of the existing design codes for conventional profiled sections to the HSS HexHS, IHexHS and IOctHS were evaluated and assessed. In addition to the design codes, the advanced design approaches of Direct Strength Method and Continuous Strength Method were also compared and assessed for their applicability. Reliability analysis concerning the design codes and the design approaches were carried out. |
| Rights: | All rights reserved |
| Access: | open access |
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