Ground Motion Selection and Modification (GMSM) Program

Nonlinear dynamic analysis of structures is becoming increasingly prevalent in engineering practice. Such analyses are often completed to meet building code or other regulatory requirements, but are also being used more frequently as part of performance-based earthquake engineering assessments. A recurring issue for both practicing engineers and the developers of regulatory documents is the selection of modification of input ground motions for these nonlinear dynamic analyses, and there is currently no consensus regarding appropriate methods. The engineering community is faced with numerous existing ground motion selection and modification (GMSM) methods, and the method choice can have a large impact on the results of nonlinear dynamic analysis.

Pilot studies have demonstrated that the particulars of a method can affect the predicted structural response by as much as a factor of three (re: COSMOS TS 2006). The chosen method can thereby lead to costly over-design of structures, or worse, dangerous under-design.

To address this issue, the Pacific Earthquake Engineering Research (PEER) Center has established the Ground Motion Selection and Modification (GMSM) Program. The mission is to provide practical guidance and tools to the engineering community regarding appropriate GMSM methods, that balances analysis effort (e.g., number of seismograms) with the precision of the results (e.g., expected structural response for an earthquake scenario). The GMSM Program strives to provide the engineering community with a basis, backed by research, for choosing appropriate GMSM methods. The end goal is to make GMSM into a quantitative, validated, and standardized step of an engineering analysis. This Program is envisioned to become a focal point of applied GMSM research that advances both the state of practice and knowledge of GMSM. This Program can then be a resource for other projects that need to solve GMSM issues.

In coordination with many others, the GMSM Program is conducting research that addresses this key issue regarding proper GMSM methods for use with nonlinear dynamic analysis. Findings will be published as both comprehensive PEER reports and more concise journal papers that will provide guidance for practicing engineers and will serve as resources for the developers of code and regulatory documents. The Program will host workshops and take part in technical conferences, to both increase awareness of GMSM issues and present Program findings and recommendations. The Program will also develop and support online tools through the PEER website, that will enable engineers to more easily apply the new guidance and utilize the recommended GMSM methods.

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