Nonlinear Finite Element Modelling of Reinforced Concrete Frames Retrofitted with Shape Memory Alloy Buckling Restrained Braces
Reinforced concrete buildings built prior to the enactment of modern seismic provisions are vulnerable when subjected to high-magnitude earthquakes since they lack the capacity to properly dissipate the energy associated with the ground excitation. Therefore, this research aims to investigate the benefits of Buckling-Restrained Braces (BRBs) as a retrofit technique for accommodating seismic demands in seismically deficient reinforced concrete frames, the dominant structural system of pre-1970s construction. The efficiency of Superelastic-Shape Memory Alloys (SE-SMA) as the core material of the BRB is also evaluated. Improvements in lateral strength capacity and residual displacements of the SMA-BRB retrofitted frames are assessed against a previously tested bare concrete frame and frames retrofitted with BRBs incorporating stainless steel and chrome-molybdenum steel core bars. Reverse cyclic finite-element modelling of the frames was conducted with VecTor2, and the numerical models were validated through experimental results present in the literature. The validated numerical models were further modified to address deficiencies in the original BRB design by including improvements in restraining of the buckling. The SMA-BRB provided lateral strength comparable to the modified steel BRB models with enhancements in ductility capacity. Notably, the SMA-BRB system did not accumulate additional residual displacements beyond those experienced by the bare frame alone. Therefore, the reduction in residual displacements, in comparison to conventional steel core BRB materials, illustrates one of the main benefits of SMA bars, leading to a viable and efficient alternative to increase the seismic performance and reduce damage in structural elements located in high seismic zones. Furthermore, nonlinear time-history analyses are conducted. Earthquake records that simulate design earthquakes for the cities of Montreal and Vancouver were selected for the dynamic loading. At the end of the thesis, an optimized BRB design is provided in which the full capacity of the core bars is achieved since localized buckling is minimized.
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