This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).
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 the University of California, Davis (lead institution) and Santa Clara University (subaward), and the University of California, San Diego (subaward). This project will utilize the NEES equipment site at the University of California, Davis.
Hundreds of billions of dollars and thousands of lives are at risk when a major earthquake shakes a metropolitan area. Building damage or collapse is one of the primary contributors to the risk. Huge investments are being made to improve performance of new and old structures by including structural or mechanical energy dissipation devices such as dampers (huge shock absorbers) and even complex computer controlled actuators to counteract effects of earthquake shaking. Geotechnical and structural engineers, however, generally understand that a lot of the damaging shaking energy can be effectively dissipated just by allowing the foundations to absorb the energy. Energy that would otherwise damage a building can be dissipated through friction at the soil-foundation interface as well as by radiation back into the ground. Civil engineers understand this today, but they are reluctant to design buildings with foundations that rock (just a little) due to: (i) the understandable perception that geotechnical material properties are less certain than structural material properties and (ii) the partition between structural and geotechnical responsibility in our traditional engineering design process. (Presently, structural engineers design the part of the building above the ground and geotechnical engineers design the foundations, and there is minimal interaction between the two.)
While it is clear that the bearing capacity of shallow foundations is very sensitive to uncertain soil properties, the moment capacity of typical shallow foundations is much more predictable than the bearing capacity. Rocking has the added benefit of introducing a natural self-centering tendency; imagine tilting a refrigerator a few degrees, and then letting go ? the refrigerator will rock back and forth a little, but it will eventually end up standing vertical (this is what we mean by ?self-centering?. Geotechnical and structural engineers would need to work together to ensure that rocking movement of a foundation, for example, is compatible with the movement of the rest of the building. This work will bring together leaders in structural and geotechnical engineering from universities and private engineering firms to figure out how to perform the collaborative holistic building design that allows us to design buildings that can move with a rocking foundation and hence allow us to take advantage of cost effective energy dissipation in the foundation. A strong technology transfer team that includes practicing engineers will work with the academics in this project to help ensure that innovative concepts are not impractical. Teaming with construction and practicing engineers actively involved in building code revision will also help speed our results toward adoption by the profession.
Avoiding over-designed, over-conservative footings and reducing requirements for energy dissipation mechanisms within the superstructure will save construction costs and can improve performance. There is almost no experimental data available to indicate how rocking foundations will dynamically interact with a yielding structural system. This proposal will fill this gap by performing experiments on a NEES centrifuge facility. Computer simulations validated by experiments will be used to generalize findings over a larger range of prototype situations.
Although our work focuses on buildings, the use of inelastic soil-foundation behavior incorporating energy dissipating and self-centering is applicable to a large array of bridges, towers, and taller buildings. Improved performance will lead to a reduction in economic and human losses associated with earthquakes. An effort to recruit new engineers by inviting groups of students in MESA (an organization that helps educationally disadvantaged students succeed in Math, Engineering, and Science) programs at local community colleges learn about civil engineering will help grow a diverse engineering workforce. Data from this project will be archived and made available to the public through the NEES data repository.
