Enhancing resilience and self-centering of reinforced concrete single and coupled shear walls with externally bonded fibre reinforced polymer composites

Single shear walls (SSWs) and coupled shear walls (CSWs) are crucial elements in seismic engineering for improving a structure's ability to withstand seismic activity. These structures are carefully designed to withstand the lateral forces of earthquakes while maintaining ductility and providing sufficient stiffness to transmit these forces to the foundation. Moreover, they can dissipate seismic energy by forming plastic hinges under cyclic ground motion loads. Designing effective shear walls requires meticulous attention to detail. A crucial design principle for taller shear walls is ensuring that flexural failure prevails over shear failure. In the design of CSWs, careful attention is given to coupling beams (CBs), which are essential conduits for transferring shear forces between the walls. These beams are engineered to avoid premature shear failure and thereby maintain their integrity and functionality. At the same time, they are strategically designed to accommodate plastic hinge formation at their ends, embodying the concept of a weak beam-strong column. Although the creation of plastic hinges in shear walls can absorb a significant amount of seismic energy, it can also result in residual displacement in these pivotal components. The lingering effects of these displacements can pose challenges to the structural integrity of buildings after an earthquake. Therefore, to enhance building serviceability and minimize costs related to earthquake damage, it is essential to develop an effective strategy that reduces residual displacements in existing shear walls. This thesis proposes an effective strengthening configuration for shear walls located in Vancouver and Montreal, which represent Canada's western and eastern seismic zones, respectively. The suggested approach is based on the use of Externally Bonded Fiber Reinforced Polymers (EB-FRP) to enhance self-centering capability, therefore minimizing residual displacement in the walls after seismic ground motions. The permanent displacement within shear walls was gauged by using the Residual Inter-story Drift Ratio (RIDR). Nonlinear Time History Analysis (NLTHA) utilizing RUAUMOKO 2D software was employed to assess RIDR within these walls. To comply with the seismic hazard requirements specified by NBCC 2020, 15 ground motions were selected for Vancouver and 11 for Montreal and then scaled to the required seismic hazard level (2% per 50 years). In each shear wall, the benchmark for residual displacement was established by selecting the average maximum RIDR value. In the following phase, three different strengthening strategies utilizing EB-FRP composites were implemented in the shear walls, and their resulting RIDR values were compared to the control values. To create prototypes that adhered to the specifications outlined in (NBCC 2020) and (CSA A23.3-19), in the first step, four CSW models of 15 and 20 stories were crafted in Montreal and Vancouver. The wall piers were strengthened using vertical and horizontal EB-FRP strips to increase their flexural and shear strength. Coupling beams were reinforced with additional FRP wraps and strips to increase their confinement and flexural strength, respectively. In the next step, four SSWs were designed and evaluated with the same height and location. The walls flexural capacity were strengthened with three different configurations of vertical EB-FRP sheets coupled with FRP wraps increasing their shear strength. The study found that all proposed strategies successfully reduced the residual displacement within the shear walls. Notably, using three layers of EB-FRP on the edge of the walls and wrapping the plastic hinge zones had the most significant impact on improving wall performance. Additionally, wrapping coupling beams and increasing their bending resistance in coupled walls effectively reduced residual displacement. Moreover, the results highlighted that integrating EB-FRP in CSWs was more effective than in SSWs. Additionally, it was observed that as the height of the wall increased, the proposed method's efficacy in reducing displacement decreased. Interestingly, the SSWs in Montreal showed near-elastic performance and did not require retrofitting. Conversely, the shear walls affected by the significant Cascadia earthquakes had the highest residual post-earthquake displacements.

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