Electronic Thesis and Dissertation Repository

Thesis Format

Integrated Article

Degree

Doctor of Philosophy

Program

Civil and Environmental Engineering

Supervisor

Maged A. Youssef

Abstract

A major sustainability issue for reinforced concrete (RC) structures is the residual deformations caused by the yielding of the steel bars during extreme seismic events. Numerous efforts have been made to develop self-centering structures, which minimize these deformations and the associated seismic damage. Superelastic shape memory alloys (SE-SMA) can be utilized in concrete elements to achieve such behaviour. This thesis focuses on the use of SE-SMA bars in RC walls.

First, the thesis starts by conducting a fragility analysis to assess the seismic performance and vulnerability of ten and twenty-story SE-SMA RC walls. SE-SMA bars are used within the plastic hinge length of the walls and are assumed to replace all longitudinal steel bars or those reinforcing the boundary elements. The considered walls were found to possess an adequate margin of safety against collapse as compared to steel RC walls.

Due to the unique properties of SE-SMA material, the ductility and overstrength factors for SE-SMA RC walls are then evaluated. Nine-hundred and seventy-two walls were analyzed to investigate the effects of different design parameters on the ductility and overstrength factors. Suggested values for the design factors were then evaluated by conducting nonlinear time history analyses for three, six, and nine-story buildings.

The seismic performance of SE-SMA RC dual systems is evaluated. Incremental dynamic analysis is carried out under considering different seismic load events. Results allowed choosing a suitable SE-SMA layout for dual systems to achieve good seismic performance.

The seismic performance of RC core walls is significantly different from rectangular RC walls because of their ability to resist bidirectional and torsional loading. The seismic performance of reinforced concrete core walls under unidirectional and bidirectional seismic excitations, while accounting for variations in the torsional eccentricity, was examined. SE-SMA bars reduced not only the mean lateral displacements but also the floor rotations.

Finally, and to mitigate the seismic residual deformations and corrosion problems associated with steel RC walls, the seismic performance of walls reinforced with SE-SMA bars or hybrid (SMA-FRP) bars over the plastic hinge length and fiber-reinforced polymers (FRP) elsewhere is examined. The SMA-FRP bars resulted in a significant improvement in the wall capacity as compared to SE-SMA bars. Also, they resulted in lower seismic damage.

Summary for Lay Audience

Reinforced concrete shear walls are commonly used to resist lateral loads. Although they were able to prevent failure during major earthquakes, they had experienced severe damage and were permanently deformed. In most cases, such damage had led to demolishing the affected buildings. The thesis proposes the use of a novel material, superelastic shape memory alloy (SE-SMA), to mitigate such damage and achieve sustainable buildings. The use of SE-SMA in typical RC lateral load systems including: cantilever walls, dual systems, and core walls are examined and recommendations for their use are given. The thesis also introduces a new resilient lateral load system that can be used in areas where steel corrosion is expected to be a problemFirst, the thesis starts by conducting a fragility analysis to assess the seismic performance and vulnerability of ten and twenty-story SE-SMA RC walls. SE-SMA bars are used within the plastic hinge length of the walls and are assumed to replace all longitudinal steel bars or those reinforcing the boundary elements. The considered walls were found to possess an adequate margin of safety against collapse as compared to steel RC walls.

Due to the unique properties of SE-SMA material, the ductility and overstrength factors for SE-SMA RC walls are then evaluated. Nine-hundred and seventy-two walls were analyzed to investigate the effects of different design parameters on the ductility and overstrength factors. Suggested values for the design factors were then evaluated by conducting nonlinear time history analyses for three, six, and nine-story buildings.

The seismic performance of SE-SMA RC dual systems is evaluated. Incremental dynamic analysis is carried out under considering different seismic load events. Results allowed choosing a suitable SE-SMA layout for dual systems to achieve good seismic performance.

The seismic performance of RC core walls is significantly different from rectangular RC walls because of their ability to resist bidirectional and torsional loading. The seismic performance of reinforced concrete core walls under unidirectional and bidirectional seismic excitations, while accounting for variations in the torsional eccentricity, was examined. SE-SMA bars reduced not only the mean lateral displacements but also the floor rotations.

Finally, and to mitigate the seismic residual deformations and corrosion problems associated with steel RC walls, the seismic performance of walls reinforced with SE-SMA bars or hybrid (SMA-FRP) bars over the plastic hinge length and fiber-reinforced polymers (FRP) elsewhere is examined. The SMA-FRP bars resulted in a significant improvement in the wall capacity as compared to SE-SMA bars. Also, they resulted in lower seismic damage.

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