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

结构工程面临的一个巨大挑战是，开发出能够抵御极端自然灾害（如飓风或地震）的建筑系统，并将损害降到最低或没有损害。这样的建筑系统可以在极端事件发生后立即入住，并将经济损失降到最低，有助于持续的国家繁荣和福利。随着建筑物中无粘结、后张拉剪力墙（upsw）的发展，在解决这一挑战方面取得了进展；然而，设计这种剪力墙的限制问题仍然存在。本研究将探索结构剪力墙的创新概念，以抵抗建筑物中的横向荷载，并在极端事件中实现无损伤。该概念由耦合、无粘结、后张拉的钢筋混凝土墙组成，这些墙通过曲面与基础相互作用。当墙体沿着底部曲面滑动时，横向变形将通过钟摆式运动来调节。横向阻力将由沿曲面和垂直无粘结后张索的摩擦提供。后张索也将有助于恢复墙的初始配置。这些耦合摆墙的能量耗散将通过结合连接装置来提供，这些连接装置使用弹性屈曲并在墙变形期间释放累积的弹性能量。因此，系统响应将利用产生的变形，而不是试图约束它们，就像在传统系统中那样。其结果将是与无损伤结构建筑系统设计相关的新技术，以及利用系统几何形状和变形来增强弹性和可持续建筑的新思路。与研究工作并行的是互补的教育和外展组成部分，包括培训两名博士生、为本科生提供研究经验、为本科生、研究生和实践者提供一个包含教程和研究成果的项目网站，以及为初高中学生提供外展活动。这些教程以及该项目的数据也将在美国国家科学基金会支持的自然灾害工程研究基础设施数据库（https://www.designsafe-ci.org）中公开提供。本研究的核心思想是一种新的设计理念，设想不受传统材料失效极限状态的限制。这一理念将通过耦合upsw的新概念得到验证。通过利用耦合系统变形引起的非线性运动行为来解决摇摆upsw的材料响应限制。因此，该项目的目标是为upsw的新概念开发可行的理论和技术，使upsw能够不受材料失效极限状态的影响而无损伤地工作。这一目标将通过两个独特而互补的特征来实现：(1)单个墙体沿着圆形路径滑动，在基础界面处没有分离；(2)通过具有可控弹性失稳的装置沿着垂直墙体接缝连续耗散能量。这个概念将被指定为一个钟摆UPSW系统，因为它围绕墙上的一个固定点旋转。接下来的方法将是将摆式upsw的面内响应表征为可行的横向抗载荷元件，开发和表征弹性元材料和元结构的使用，通过弹性不稳定性耗散能量，并表征摆式upsw与弹性多稳定结构耦合作为连接器的响应。分析，数值（有限元素）和实验方法的结合将被使用。这项研究将导致系统几何和变形的基本整合，以设计具有弹性和可持续的抗侧向荷载结构。这项研究将促进新的设计概念，利用变形来实现最佳性能，而不是将性能目标设定为目标材料极限状态。该研究也将有助于在大型结构系统中使用非线性弹性不稳定性。与无损伤结构系统、摩擦模型和弹性耗能装置相关的理论和方法也将得到发展。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

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.