Collaborative research: An innovative gap damper to control seismic isolator displacements in extreme earthquakes

• Principal investigators: Keri Ryan, University of Nevada, Reno, Justin Marshall, Auburn University
• Other project personnel: Hamed Zargar, graduate student, University of Nevada, Reno, Taylor Rawlinson, graduate student, Auburn University
• Sponsored by: National Science Foundation Award No.: CMMI-1101105, National Science Foundation Award No.: CMMI-1100922
• Project dates: July 1, 2011 to June 30, 2014
• Project number in project warehouse: 1080
• Project videos: Concept and Design,  Test and Preliminary Results

Project summary

The main objective of this project is to develop and test a phased damping device, or “gap damper”, to act alongside a base isolation system for buildings or bridges. The gap damper provides additional energy dissipation to the system to control the displacement demand of the isolation system in extreme earthquakes without affecting the response of the isolation system in a design earthquake. This will be accomplished through a mechanism that can trigger additional energy dissipation at a threshold level of displacement.

Several concepts were considered to develop phased damping, and one of these was chosen for prototype development and testing.

The final design chosen involves a protruding tube element extending downward from the isolated slab but not extending all the way to the basement floor. On the basement floor, lies a bumper system that is attached to the supplemental damping devices. At a specified distance, the tube “isolation nub” contacts the bumper system during an extreme event and activates the secondary energy dissipation. This design allows one or more gap dampers to be located anywhere under the building, utilizing the dampers in both tension and compression for maximum energy dissipation. In addition, by placing the dampers at the corners of the bumper system, bi-directional behavior is possible and the system will resist rotation due to eccentric impacts. The concept could be implemented “pure viscous” device, solely utilizing linear viscous dampers for secondary energy dissipation, or with and additional friction device for a two-phased viscoplastic model also favored in the analytical study.

The pure viscous and viscoplastic device setup were both tested at Auburn University (AU) in summer of 2013 to examine feasibility in the shake table study. The Auburn University test setup is shown in the image above. In April of 2014, shake table tests were completed at the University of Nevada, Reno to assess the performance of the gap damper in a building structure. The pure viscous gap damping device was implemented on a ¼ scale, 3-story isolated steel frame. These shake table tests extended the investigation to biaxial input and also to realistic velocities. Tests were conducted with and without the gap damper to validate the ability of the damper to control isolator displacements, and to understand how the activation of the damping affects the structure accelerations.