Structural behaviour of cold-formed S700 high strength steel tubular members after exposure to fire
High strength steel tubular members have been increasingly used in civil engineering due to their exceptional mechanical strengths. Significant improvement of high strength steel design guidance at ambient temperature has been achieved in recent years. However, the structural behaviour and design of...
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| Other Authors: | |
| Format: | Thesis-Doctor of Philosophy |
| Language: | English |
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Nanyang Technological University
2022
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| Subjects: | |
| Online Access: | https://hdl.handle.net/10356/156784 |
| _version_ | 1811688011153276928 |
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| author | Zhong, Yukai |
| author2 | Zhao Ou |
| author_facet | Zhao Ou Zhong, Yukai |
| author_sort | Zhong, Yukai |
| collection | NTU |
| description | High strength steel tubular members have been increasingly used in civil engineering due to their exceptional mechanical strengths. Significant improvement of high strength steel design guidance at ambient temperature has been achieved in recent years. However, the structural behaviour and design of high strength steel members after exposure to fire remains unexplored. The primary aim of the present thesis is therefore to experimentally and numerically investigate the structural behaviour of cold-formed high strength steel tubular members after exposure to fire, and develop relevant post-fire design guidance.
A comprehensive experimental programme was firstly performed, which considered six tubular sections made from cold-formed S700 high strength steel. Specimens were heated to different levels of elevated temperature and then cooled down to ambient temperature. Material testing was conducted to obtain the post-fire material stress–strain curves, and initial geometric imperfection measurements were carried out to determine the imperfection magnitudes of the specimens. At cross-sectional level, 15 concentrically loaded stub column tests and 10 eccentrically loaded stub column tests were conducted to study the cross-section behaviour and residual resistances of cold-formed high strength steel tubular sections after exposure to fire. At member level, a total of 10 column tests and 10 beam-column tests were carried out to investigate the member buckling behaviour and residual load-carrying capacities of cold-formed high strength steel tubular section members after exposure to fire. A numerical modelling programme was carried out in parallel with the experimental programme. Finite element models were firstly established and validated against the test results, and then used to conduct a series of parametric studies to derive additional numerical results over a wide range of cross-section dimensions, member lengths and loading combinations. The obtained test and numerical data were used to evaluate the applicability of the current ambient temperature design codes for high strength tubular members to their post-fire counterparts, and to propose suitable amendments to the Eurocode design rules accordingly.
The evaluation results generally revealed that the current ambient temperature design codes lead to accurate and safe resistance predictions for concentrically and eccentrically loaded cold-formed high strength steel tubular sections after exposure to fire. For cold-formed high strength steel tubular column and beam-column members after exposure to fire, it was found that the design predictions were conservative, mainly due to the adoption of the conservative buckling curve and the lack of exploitation of the beneficial partial plasticity for Class 3 cross-sections. Modified Eurocode design approaches were proposed and shown to yield significant improvement of design accuracy and consistency over the original Eurocode design approaches for cold-formed high strength steel tubular members after exposure to fire. The reliability of the revised Eurocode design approaches has been confirmed through reliability analysis. |
| first_indexed | 2024-10-01T05:25:25Z |
| format | Thesis-Doctor of Philosophy |
| id | ntu-10356/156784 |
| institution | Nanyang Technological University |
| language | English |
| last_indexed | 2024-10-01T05:25:25Z |
| publishDate | 2022 |
| publisher | Nanyang Technological University |
| record_format | dspace |
| spelling | ntu-10356/1567842022-05-04T10:23:16Z Structural behaviour of cold-formed S700 high strength steel tubular members after exposure to fire Zhong, Yukai Zhao Ou School of Civil and Environmental Engineering ou.zhao@ntu.edu.sg Engineering::Civil engineering::Structures and design High strength steel tubular members have been increasingly used in civil engineering due to their exceptional mechanical strengths. Significant improvement of high strength steel design guidance at ambient temperature has been achieved in recent years. However, the structural behaviour and design of high strength steel members after exposure to fire remains unexplored. The primary aim of the present thesis is therefore to experimentally and numerically investigate the structural behaviour of cold-formed high strength steel tubular members after exposure to fire, and develop relevant post-fire design guidance. A comprehensive experimental programme was firstly performed, which considered six tubular sections made from cold-formed S700 high strength steel. Specimens were heated to different levels of elevated temperature and then cooled down to ambient temperature. Material testing was conducted to obtain the post-fire material stress–strain curves, and initial geometric imperfection measurements were carried out to determine the imperfection magnitudes of the specimens. At cross-sectional level, 15 concentrically loaded stub column tests and 10 eccentrically loaded stub column tests were conducted to study the cross-section behaviour and residual resistances of cold-formed high strength steel tubular sections after exposure to fire. At member level, a total of 10 column tests and 10 beam-column tests were carried out to investigate the member buckling behaviour and residual load-carrying capacities of cold-formed high strength steel tubular section members after exposure to fire. A numerical modelling programme was carried out in parallel with the experimental programme. Finite element models were firstly established and validated against the test results, and then used to conduct a series of parametric studies to derive additional numerical results over a wide range of cross-section dimensions, member lengths and loading combinations. The obtained test and numerical data were used to evaluate the applicability of the current ambient temperature design codes for high strength tubular members to their post-fire counterparts, and to propose suitable amendments to the Eurocode design rules accordingly. The evaluation results generally revealed that the current ambient temperature design codes lead to accurate and safe resistance predictions for concentrically and eccentrically loaded cold-formed high strength steel tubular sections after exposure to fire. For cold-formed high strength steel tubular column and beam-column members after exposure to fire, it was found that the design predictions were conservative, mainly due to the adoption of the conservative buckling curve and the lack of exploitation of the beneficial partial plasticity for Class 3 cross-sections. Modified Eurocode design approaches were proposed and shown to yield significant improvement of design accuracy and consistency over the original Eurocode design approaches for cold-formed high strength steel tubular members after exposure to fire. The reliability of the revised Eurocode design approaches has been confirmed through reliability analysis. Doctor of Philosophy 2022-04-23T07:38:58Z 2022-04-23T07:38:58Z 2022 Thesis-Doctor of Philosophy Zhong, Y. (2022). Structural behaviour of cold-formed S700 high strength steel tubular members after exposure to fire. Doctoral thesis, Nanyang Technological University, Singapore. https://hdl.handle.net/10356/156784 https://hdl.handle.net/10356/156784 10.32657/10356/156784 en This work is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License (CC BY-NC 4.0). application/pdf Nanyang Technological University |
| spellingShingle | Engineering::Civil engineering::Structures and design Zhong, Yukai Structural behaviour of cold-formed S700 high strength steel tubular members after exposure to fire |
| title | Structural behaviour of cold-formed S700 high strength steel tubular members after exposure to fire |
| title_full | Structural behaviour of cold-formed S700 high strength steel tubular members after exposure to fire |
| title_fullStr | Structural behaviour of cold-formed S700 high strength steel tubular members after exposure to fire |
| title_full_unstemmed | Structural behaviour of cold-formed S700 high strength steel tubular members after exposure to fire |
| title_short | Structural behaviour of cold-formed S700 high strength steel tubular members after exposure to fire |
| title_sort | structural behaviour of cold formed s700 high strength steel tubular members after exposure to fire |
| topic | Engineering::Civil engineering::Structures and design |
| url | https://hdl.handle.net/10356/156784 |
| work_keys_str_mv | AT zhongyukai structuralbehaviourofcoldformeds700highstrengthsteeltubularmembersafterexposuretofire |