Advancement of a Novel Self-Centring Concentrically Braced Frame (SC-CBF) structural steel system for seismically active zones

The self-centring concentrically braced frame (SC-CBF) system developed at University of Galway offers several advantages over traditional concentrically braced frames (CBFs). In this SC-CBF system, post-tensioning elements are used along the beams to create a rocking joint behaviour, which helps absorb seismic energy and reduce the overall seismic demand on the structure. However, a key feature is that this system enables the structure to return to its original position after a significant earthquake. Therefore, residual deformations that compromise the integrity of traditional CBFs can be eliminated. In this thesis, the feasibility of using the SC-CBF system in seismic regions is evaluated through experimental testing and numerical analysis. Additionally, guidelines and design procedures for the SC-CBF systems are developed. A series of laboratory experiments including material tests and shake table tests were conducted to investigate the behaviour of the novel SC-CBF system. A one-storey SC-CBF structure was designed, manufactured and seismically tested on a shake table. Test results have demonstrated that the SC-CBF system performs well under realistic earthquake conditions, achieving a peak drift ratio of 2.51% with negligible residual drift (below 0.06%). This indicates strong self-centring behaviour, allowing the structure to recover most of its deformation after seismic events. Steel samples were cut from the specimens and material testing was performed to characterise the material properties of the steel. Coupon tests consisted of monotonic tensile loading, low-cycle, and extremely low-cycle fatigue loading. These results were used to develop a numerical model in OpenSees. By validating the numerical results with testing data, the model was proven to accurately predict the behaviour of the SC-CBF under seismic loads. Both experimental and numerical analyses demonstrated that the SC-CBF returns to its initial vertical position after large earthquakes, while dissipating energy through braces and, hence, keeping non-dissipative structural elements safe. Furthermore, the design guidelines of SC-CBF buildings, suitable for both Force-Based Design (FBD) and Direct Displacement-Based Design (DDBD) methods, are proposed. Case studies were performed to compare the efficiencies of the structures designed using the two methods. This series of research work helps ensure that the SC-CBF system can be effectively adopted by the industry, leading to overall improved seismic performance and greater resilience in CBF steel structures, fostering the widespread adoption of this innovative structural solution.

Publisher

University of Galway

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Attribution-NonCommercial-NoDerivatives 4.0 International

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University of Galway Theses (PhD Theses)