The objective of this project is to develop a “Design Ground Motion Library” (DGML), which is a library of recorded acceleration time histories suitable for use by engineering practitioners for time history dynamic analysis of various facility types in the western United States, including buildings, bridges, utility structures, dams, base-isolated structures, and other common infrastructure facilities. The overall goal is to have a current and authoritative library of strong motion records endorsed by leading scientists and users within the professional seismological and engineering communities.

The evaluation of the performance of many structures during earthquake strong ground motions involves subjecting analytical models of the structures to acceleration time histories of recorded ground motions. Such evaluations are required for site-specific seismic evaluation and design of important structures and in research to improve the understanding and quantification of the relationships between ground motion characteristics and structure damage. Although ground motion databases contain large numbers of time histories recorded during historic earthquakes, guidance is lacking on which time histories are suitable for particular applications. This project identifies and collects in an electronic library suitable time histories and provides guidance on developing time history sets as well as on scaling these time histories for specific applications.

The DGML will be implemented in a bin structure driven by earthquake engineering applications. The bin structure will be constructed to provide access to records identified by parameters of importance in assessing the suitability of a record for intended applications. Design parameters typically include earthquake magnitude, source-to-site distance, faulting mechanism, near-fault characteristics (e.g. record location relative to the fault rupture and direction of rupture propagation). Design parameters and other parameters of importance also include various ground motion parameters that are either specified for design or otherwise are important in determining the response and performance of the structure. Ground motion parameters include peak acceleration, velocity, and displacement, elastic response spectra, duration of strong shaking, and various other parameters such as pulse characteristics of near-fault records, inelastic response spectra, energy measures of a time history, and other damage measures of a time history.

The work is divided into six tasks. Following Task 1, which is a review of previous relevant efforts and information, basic criteria for the DGML is developed in Task 2. These criteria pertain to the ground motion parameters and other information to be quantified for the DGML, criteria for time history inclusion or exclusion in the DGML, and criteria for the bin structure of the DGML. Consensus is to be achieved on these criteria among the researchers and practitioners on the project team and the expert reviewers from PEER-Lifelines Program and the California Strong Motion Instrumentation Program (CSMIP). Utilizing these criteria, the DGML is formed in Task 3. In Task 4, guidelines for utilizing the DGML for various applications are developed. The Guidelines cover the initial selection of time history record sets for different applications and the scaling of the records for actual usage. Again, consensus is to be achieved on the guidelines. In Task 5, the DGML, including utilization guidelines, is evaluated by trial usage for different applications and, subsequently, refined as needed. Task 6 includes required reports, and presentations, and papers.

The project team for this work provides multi-disciplinary expertise in both the utilization of time histories in seismic design and research into the characteristics of time histories that correlate with damage to buildings, bridges, and other facilities. The team includes geotechnical engineers, structural engineers, and seismologists in private practice and with the PEER Center.

Work on the project to date has included review of ground motion data bases and libraries, including a recently developed library of time histories for seismic analysis of nuclear power plants, review of PEER research and other research on the characteristics of ground motions that are most damaging to different types of structures, formulation of preliminary criteria for selecting and binning time histories for the DGML, binning of records using the criteria, and presentation of preliminary results at the PEER annual meeting. During the remainder of 2003 (to project completion by December 31, 2003), criteria will be finalized, binning of time histories completed, utilization guidelines prepared, trial usage of the library conducted, and the final report submitted.

A library of acceleration time histories for use in analysis of nuclear power plants was recently developed in work sponsored by the Nuclear Regulatory Commission (NRC) (publication NUREG CR/6728). The nature of the library developed in the NRC project is much different than the DGML being developed in this project, principally in that:

1. the time histories for the NRC project were randomly selected from magnitude and distance hazard bins, whereas the time histories for the DGML are selected to have characteristics representative of the hazard environment and their damage potential to structures as determined by an expert multi-disciplinary team
2. the selection of time histories from near-fault environments was deemphasized in importance in the NRC project because of the typical strategy of siting nuclear power plans far from active faults, whereas the selection of time histories from active-fault environments is emphasized in the DGML project because of their usage in most cases to facilities sited near active faults and exposed to high ground motions in the seismically active parts of the Western U.S, and
3. the DGML project will provide comprehensive guidelines for the development and scaling of time history sets for a wide variety of engineering applications.

There is no specific time frame for future project phases beyond the completion of the current project in December 2003. PEER-Lifelines Program envisions that future extensions of the project will include

1. incorporation of time histories from subduction zone earthquakes (the current project is restricted to time histories from typical western U.S. shallow crustal earthquakes), and
2. incorporation of time histories from seismological ground motion modeling processes to supplement the recorded time histories selected in the current project.

Principal project milestones include development of basic criteria for the DGML, formation of the DGML, development of utilization guidelines for the DGML, trial usage and finalization of the DGML and guidelines, and the draft report.

The end deliverable is an electronic DGML package and an accompanying report that includes guidelines and scaling rules for proper usage of the DGML, describes the limits of applicability of the DGML for various engineering applications, and identifies deficiencies of the DGML with recommendations for possible follow-up on studies.