Collaborative Research: Self-Centering Pendulum Shear Walls in Buildings via Nonlinear Elastic Kinematics

George Washington University, Washington DC

Investigators

Abstract

A grand challenge in structural engineering is to develop building systems that can resist loads from extreme natural hazards, such as hurricanes or earthquakes, with minimum or no damage. Such building systems could enable immediate occupancy and minimum economic losses after an extreme event, contributing to continued national prosperity and welfare. Progress has been made towards addressing this challenge with the development of unbonded, post-tensioned, shear walls (UPSWs) in buildings; yet limiting issues for designing such shear walls remain. This research will explore an innovative concept for structural shear walls to resist lateral loads in buildings and perform damage free during an extreme event. The concept consists of coupled, unbonded, post-tensioned, reinforced concrete walls that interact with the foundation via a curved surface. Lateral deformations will be accommodated through a pendulum-type motion as the wall slides along the bottom curved surface. Lateral resistance will be provided by friction along the curved surface and the vertical unbonded post-tensioned cables. The post-tensioned cables also will help restore the wall to its initial configuration. Energy dissipation of these coupled pendulum walls will be provided by incorporating connecting devices that use elastic buckling and release accumulated elastic energy during the walls' deformations. The system response thus will leverage the resulting deformations rather than trying to constrain them, as in traditional systems. The result will be new technology related to the design of damage-free structural building systems, and a new way of thinking about leveraging system geometry and deformations for enhanced resilient and sustainable buildings. Parallel to the research effort will be complementary educational and outreach components, including the training of two Ph.D. students, research experiences for undergraduate students, a project website with tutorials and research findings for undergraduate and graduate students and practitioners, and outreach activities for middle and high school students. The tutorials, as well as data from this project, also will be made publicly available in the NSF-supported Natural Hazards Engineering Research Infrastructure Data Depot (https://www.designsafe-ci.org). The core idea of this research is that of a new design philosophy envisioned to be unrestricted by traditional material failure limit states. This philosophy will be verified through a new concept for coupled UPSWs. The material response limitations of rocking UPSWs will be addressed by harnessing the nonlinear kinematic behavior resulting from coupled system deformations. Thus, the project objective is to develop the enabling theory and technology for a new concept of UPSWs that can perform damage free and unrestricted by material failure limit states. This objective will be achieved through two unique and complementary features: (1) individual walls gliding along a circular path with no separation at the footing interface, and (2) continuous energy dissipation via devices with controllable elastic instabilities along vertical wall joints. This concept will be designated as a pendulum UPSW system, as it rotates about a fixed point on the wall. The approach to be followed will be to characterize the in-plane response of pendulum UPSWs as viable lateral load resisting elements, develop and characterize the use of elastic meta-materials and meta-structures for dissipating energy via elastic instabilities, and characterize the response of pendulum UPSWs coupled with elastic multi-stable structures as connectors. A combination of analytical, numerical (finite element), and experimental methods will be used. This research will lead to the fundamental integration of system geometry and deformations for the design of lateral load resisting structures that are resilient and sustainable. The study will promote new design concepts that harness deformations for optimal performance rather than performance objectives set to target material limit states. The research also will contribute to the use of nonlinear elastic instabilities in large-scale structural systems. Theory and methods related to damage-free structural systems, friction models, and elastic energy dissipation devices will also be advanced. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.