Analysis and design of pendulum precast concrete unbonded post-tensioned shear walls

This manuscript presents Part I of a broader study on the analytical formulation and design of a new class of precast concrete (PC) unbonded post-tensioned shear (UPTS) walls. A companion Part II paper presents the experimental validation of the system response. The innovative feature of this new class of PC-UPTS walls is that at their bases the wall is shaped with a circular profile. By shaping the base in a circular form, the wall glides rather than uplifts under lateral loads, and instead of relying on traditional methods like additional dampers or reinforcement, energy is absorbed through the contact friction that develops at the base interface. The circular profile at the base enables the wall to pivot about a single point like a pendulum under lateral loads, thereby designating this system as a pendulum PC-UPTS wall. This design aims to keep the structural wall damage-free while still effectively handling seismic or wind-induced loads. This paper addresses the design of the circular profile as a means for improving the energy dissipation capacity of PC-UPTS walls while remaining damage-free and without requiring additional energy dissipation devices or reinforcement across the base interface. Mechanics-based formulations were developed based on closed-form solutions derived from geometric system kinematics and results from these simulations were used in the design of the circular base interface geometry. The seismic design approach for pendulum PC-UPTS walls capitalizes on the dual benefits of high-strength post-tensioning steel and energy dissipation through contact friction. The contact friction between wall components acts as an energy dissipation mechanism, thereby reducing the impact of seismic loads and improving the overall resilience of the structure. In order to maintain these benefits and ensure a gliding response of pendulum PC-UPTS walls, analytical results suggest that friction coefficients less than 0.16 should be ensured in the response of these systems and the wall radius to width ratio should be maintained within 0.7 to 1.0 limits. This paper presents additional design recommendations for enhancing both the strength and energy dissipation capacity of pendulum PC-UPTS wall systems, thereby aligning it with performance-based seismic criteria for optimal safety and durability.