Collaborative Research: Unbonded Post-Tensioned Rocking Walls for Seismic Resilient Structures

National Science Foundation
CMMI Division of Civil, Mechanical, and Manufacturing Innovation
NSF Grant No. CMMI-1041650
December 1, 2010 to November 30, 2014

This award is an outcome of the NSF 09-524 program solicitation "George E. Brown, Jr. Network for Earthquake Engineering Simulation (NEES) Research (NEESR)" competition and includes Iowa State University (ISU) as well as two University of Minnesota campuses: Twin Cities (UMN) and Duluth (UMD). This project will utilize the NEES facilities located at UMN and the University of Nevada at Reno.

The motivation for this research is that damage caused by earthquakes, and the subsequent economic losses, underscore the need to focus on developing earthquake resilient buildings. One method of achieving resilient buildings is to design them with self-centering structural systems to resist earthquake lateral loads. Using unbonded post-tensioning tendons, a cost-effective, self-centering wall system known as PreWEC (i.e., Precast Wall with two End Columns) was developed at ISU, which has been proven analytically and experimentally to have excellent seismic performance with minimal structural damage. In this system, as well as in single rocking walls (SRWs) designed with unbonded post-tensioning, the response is dominated by a rocking mode. However, the energy loss caused by the wall impacting the foundation during rocking has not been given consideration in design due to lack of knowledge on this subject. Significant evidence suggests that this mechanism alone may be sufficient to dissipate the seismic energy. Furthermore, the resilience of a building containing rocking walls is also dependent on the behavior of surrounding structural components, especially floors and gravity columns, and their interactions with the seismic resistant systems. To ensure a fully resilient structure, these interactions should be addressed by understanding the wall-floor connection responses. Principal Investigator is involved in the development of the American Concrete Institute Building Code, ensures that the appropriate research findings may be translated directly into practice with improved detailing recommendations for nonrectangular structural walls. As such, this project will improve the nation's infrastructure in seismic regions.

Intellectual Merit: In collaboration with E-Defence in Japan and researchers at the University of Auckland in New Zealand, the intellectual merit of this project is the development of seismic resilient building solutions utilizing the fundamental characteristics of seismic rocking of both SRWs and PreWECs. By involving an international, cross-disciplinary team of experts and two NEES facilities, the project will accomplish this goal by completing the following objectives:
  • Understand the fundamental characteristics of seismic rocking of self-centering walls through NEES/international tests, thereby identifying different energy dissipation sources (i.e., energy loss due to impact, viscous damping and hysteretic damping)
  • Develop suitable connections between rocking walls and floors, and quantify the wall-floor-column interactions using large-scale tests
  • Ensure safety of the rocking systems through sufficient anchorage of the unbonded tendons
  • Design seismic resilient structures
  • Improve numerical simulation of buildings designed with rocking walls and different floor systems
  • Formulate design guidelines
  • Educate students, practitioners, and others (e.g., policy makers) on the significance of the proposed study.

Broader Impacts: This award also has several broader impacts. First, it offers several unique opportunities for graduate and undergraduate students from diverse populations to participate and collaborate with an international team of researchers in a distributed NEES environment. Second, it promotes the participation of underrepresented students in civil engineering and introduces K-12 students to the new NEES collaboration model and benefits of rocking walls in seismic resistant design. The research team will contribute to Project Lead the Way (PLTW), a program designed to prepare middle and high school students for college-level engineering education by exposing them to engineering courses. UMD will pilot the proposed PLTW program at schools in northern Minnesota, including tribal schools. Next, a unique, team-oriented course module will be developed by integrating the research outcomes so that it can be used for instruction at the graduate and undergraduate levels. This module will be made available to the earthquake engineering community through NEEShub. Using the planned NEES collaboration within the project, the project team will also contribute to advancing NEES telepresence technologies. Finally, the proposed project will enhance research and education at the three participating institutions, which includes a predominantly undergraduate university. All anticipated project outcomes will ultimately produce new basic knowledge needed to design safer, more resilient buildings in seismic regions and thus contribute to seismic hazard mitigation in the United States and around the world. Data from this project will be archived and made available to the public through the NEES data repository. This award is part of the National Earthquake Hazards Reduction Program (NEHRP).