Papargyriou, Ioannis ORCID: 0000-0003-0834-3203 (2021) Performance-Based Evaluation and Design of Cold-Formed Steel Lateral Force-Resisting Systems for Multi-Storey Buildings. PhD thesis, University of Sheffield.
Abstract
Cold-formed steel (CFS) is becoming popular in building construction as it is more economical and lightweight compared to conventional hot-rolled steel whilst offering ease and speed of construction and greater flexibility in manufacture. However, due to the low element thickness it is more prone to buckling; hence, the design of elements and structures is more challenging, especially when called to resist lateral loads, like wind and earthquakes. While CFS strap-braced stud walls can be used to provide light steel frames with high lateral strength and stiffness, more research is needed to investigate their seismic performance. Furthermore, secondary moments due to P-Δ effects, amplified by the presence of additional vertical loading, are generally ignored in conventional design and can lead to premature failure of compressive studs and low ductility. In this research, the non-linear behaviour of CFS strap-braced stud walls is comprehensively examined to improve structural efficiency. By considering P-Δ effects, the key design parameters are identified, and a novel design framework is developed. CFS multi-storey frames are analysed numerically, and the efficiency of the proposed methodology is investigated by using local and global damage indices under seismic loading with different intensity levels. Finally, the work focuses on the development of new types of CFS moment-resisting beam-column joints, transferring bending moments through the flanges or both the webs and flanges, and design considerations are proposed to reach a balanced performance, combining high flexural capacity, deformability, ductility and rotational stiffness. The results of this study indicate that diagonal strap thickness and vertical loading had the most significant impact on critical seismic performance parameters, such as the lateral load and deformation capacity, ductility and energy dissipation. A case study 6-storey strap-braced frame, designed in accordance with Eurocode 8 specifications, exhibited very low ductility at some storey levels, below the target value of 4, while the design solution following the proposed methodology reached high ductility, preventing premature failure of the chord studs. The efficiency of Eurocode 8 and the proposed design solutions was studied and assessed under artificial and real spectrum-compatible ground motion records using non-linear dynamic analyses. The proposed design solution met all target performance levels and reached low damage index values. By contrast, Eurocode 8 design solution failed to meet the life safety (LS) and collapse prevention (CP) targets while sustaining extensive global damage even under low earthquake intensity levels of 0.20 g. The newly developed flange and web-flange connected joints proved to be an appropriate and efficient alternative solution to web-connected joints, exhibiting high bending moment capacity, ductility and energy dissipation while facilitating assembly. The results of this research have the potential to contribute to the development of more resilient CFS strap-braced systems in seismic regions.
Metadata
Supervisors: | Hajirasouliha, Iman and Pilakoutas, Kypros |
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Related URLs: | |
Keywords: | Cold-formed Steel (CFS); Strap-Braced Walls; Numerical Modelling; Lateral Load-Bearing Capacity; Ductility; Vertical load effect; Incremental Dynamic Analysis (IDA); Global Damage Index; Moment-resisting connections; Flange-connected joints |
Awarding institution: | University of Sheffield |
Academic Units: | The University of Sheffield > Faculty of Engineering (Sheffield) > Civil and Structural Engineering (Sheffield) |
Identification Number/EthosID: | uk.bl.ethos.842796 |
Depositing User: | Mr Ioannis Papargyriou |
Date Deposited: | 16 Nov 2021 11:57 |
Last Modified: | 01 Dec 2022 10:54 |
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