Seismic Analysis, Behavior, And Design of Unbonded Post-Tensioned Hybrid Coupled Wall Structures

This dissertation focuses on the development of a new type of hybrid coupled wall structure for seismic regions. Coupling of concrete wall piers is achieved by posttensioning steel beams to the walls using unbonded post-tensioning tendons. Different from conventional hybrid coupled walls, the coupling beams of the new system are not embedded into the walls. Steel top and seat angles are used at the beam-to-wall connections for energy dissipation.

Unbonded post-tensioned hybrid coupling systems offer important advantages over conventional coupling systems, such as simplified construction, ability to undergo large lateral displacements with little damage, and self-centering capability. Analytical investigations are conducted on the nonlinear behavior of floor-level coupled wall subassemblages and multi-story structures under combined lateral and gravity loads. Both finite element and fiber element analytical models are developed. The effects of design parameters (e.g., amount of post-tensioning, beam/wall properties) on the behavior of the structures (e.g., strength, energy dissipation, deformation capacity) are investigated. Systems with precast concrete walls as well as monolithic cast-in-place concrete walls are considered. The behavior of the proposed coupled wall system is compared with the behaviors of uncoupled walls and conventional systems with embedded steel coupling beams. The analytical results are used to develop approximate procedures to estimate the nonlinear load-deformation behavior of the structures without sophisticated analytical models.

The results from eleven half-scale experiments of floor-level unbonded posttensioned hybrid coupled wall subassemblages are also summarized in this dissertation. The tests results are used to validate and improve the analytical models, evaluate critical structural components that can limit lateral strength and ductility, and make recommendations for practical applications. Finally, a performance-based seismic design approach is developed for unbonded post-tensioned hybrid coupled wall structures. Two prototype eight-story hybrid coupled wall systems are designed using the proposed procedures. Evaluations of the global and local behavior of the structures are conducted based on nonlinear static lateral load analyses as well as dynamic time-history analyses under selected ground motion records. The results from these analyses are ultimately used to critically evaluate the validity of the design approach and procedures in achieving the target design performance objectives for the structures.