The broad research objective of this award is to assess and develop earthquake ground motion selection and modification (i.e., scaling) methods for the nonlinear response history analysis of building structures. To achieve this objective, the research will: (1) conduct a large number of small-scale shake-table experiments of re-configurable nonlinear multi-degree-of-freedom structural models; (2) investigate how different site conditions, hazard levels, and structure characteristics affect the accuracy and efficiency of the scaling methods; and (3) use the experimental ?benchmark? results to develop seismic design guidelines and procedures for structures with regular and irregular configurations. The shake-table tests will form the first experimental study on nonlinear dynamic response considering a wide range of building characteristics and ground motions. These deliverables will not only provide the evidence needed to develop consensus on how an appropriate suite of records should be selected and scaled in seismic design, but also establish the minimum number of records needed to retain accuracy in the median engineering demand estimates with minimum dispersion.
If successful, the project will represent a major advancement on the design of reliable earthquake-resistant buildings with ancillary contributions to engineering seismology, thus providing direct service to society by mitigating loss of life and property from future seismic events. Prominent practicing engineers and relevant professional organizations will be engaged to ensure rapid dissemination of the results. The workforce impact will include one Ph.D. student and several undergraduates, strongly focusing on underrepresented groups. The project team will include researchers from a predominately-undergraduate institution (Cal State - Sacramento). The researchers will also utilize the project to educate future engineers through K12 activities. To further enhance the broader impacts from the project, a new experiential learning module will be developed to demonstrate basic concepts in earthquake engineering using smaller versions of the nonlinear model structures on a portable shake-table.
Among the natural hazards affecting many parts of the U.S. and abroad, the social and economic impacts of earthquakes are immense as demonstrated by the recent major earthquakes around the World. To this end, this project contributed to the general public welfare by developing new knowledge to increase the reliability of the design of building structures against earthquakes. This contribution has the potential to mitigate loss of life and property and improve the performance of buildings during an earthquake, thus providing direct service to society. The outreach activities from the project also contributed to the development of public awareness about earthquake hazard. The seismic design of most building structures in the U.S. is based on significant nonlinear behavior, which means that the structure is allowed to experience damage under a large earthquake. The primary design objective imposed by current design Codes is to prevent loss of life rather than loss of property. In recent years however, new "performance-based" design considerations have been developed to control the level of damage during an earthquake. This new design methodology requires a set of ground motion records to be selected and modified (i.e., scaled) such that they can represent different levels of earthquake hazard at which the amount of damage is to be controlled [e.g., Service Basis Earthquake (SBE) where no damage is allowed; Design Basis Earthquake (DBE), where some damage is allowed but the structure can be repaired and put back to use]. The method used for scaling ground motion records to represent different hazard levels has a very large impact on the design outcome and uncertainty. For example, if a DBE ground motion set is weaker than intended, the actual damage from real earthquakes may be greater than permissible, even leading to possible collapse. The previous research in this area has been based solely on numerical simulations with no experimental data for the validation of the results. This has resulted in a lack of consensus and the use of mostly subjective choices for ground motion scaling by the seismic design community. Considering these issues, this project involved the first experimental investigation on ground motion scaling for use in the linear and nonlinear seismic design of building structures, resulting in new technical knowledge, physical resources, know-how, and human resources for the testing, analysis, and design of buildings under earthquake loads. The development of validated methods to improve the seismic design of building structures represents a major long-range and transformative, seminal rather than incremental advancement for achieving earthquake-resistant buildings. The main intellectual outcome from the project resides in its contributions to the area of earthquake-resistant buildings by: 1) experimentally investigating the effectiveness of different ground motion scaling methods in reducing the uncertainty in seismic design; and 2) determining how the effectiveness of the different scaling methods change with different structural properties. Dissemination of the project results is leading to community consensus on which scaling methods are best suited to achieve reliable seismic designs over a range of structural properties. Ultimately, this consensus is expected to transfer to industry practice through the adoption of the validated scaling methods by practicing engineers and can form the foundation for codified regulatory seismic design standards. Buildings designed using these results can reliably achieve the intended levels of damage by the designer, increasing confidence levels, and can prevent catastrophic collapse saving both life and property. The intellectual outcomes from the project also include the development of a one-of-a-kind, reusable, reconfigurable nonlinear building frame specimen for earthquake testing on a shake table. The reusable characteristic of this specimen made it possible for the current project to conduct an unprecedented experimental study consisting of more than 720 dynamic tests. As a broader technical outcome, the seismic demands from these tests can be used to evaluate various approximate analytical procedures for seismic design. The test specimens can also be used to investigate damage detection algorithms for nonlinear structures. Additionally, the test specimens can be used as educational aids in courses such as Earthquake Engineering and Experimental Structural Dynamics. The project played a significant role in the career development of the faculty investigator as a researcher and educator in earthquake engineering. Additional contributions and broader impacts of the project to human resource development in science, engineering, and technology included the involvement of the co-principal investigator from the United States Geological Survey, one assistant professor from the University of Notre Dame, one Ph.D. student, as well as six undergraduate students (one female) at Notre Dame. Four of these undergraduates have gone on to pursue advanced degrees in structural engineering. In addition, an assistant professor and an undergraduate student from the University of Texas at Tyler (a predominantly undergraduate institution with a fledgling Civil Engineering department) took part in the project. The project team also included industry participants who will ultimately help in technology transfer.
