Nonlinear dynamic analysis of structures is becoming increasingly prevalent in code and regulatory documents prescribing design and analysis. A recurring challenge for both practicing engineers and developers of such documents is the selection and modification of ground motions for these nonlinear dynamic analyses. Nonlinear structural response is often highly sensitive to the selection and modification of input ground motions, and many ground motion selection and modification (GMSM) methods have been proposed. No systematic studies exist that provide impartial guidance to engineers regarding appropriate methods for use in a specific analysis application; thus engineers are left to make an important decision that is virtually uninformed.
The purpose of this report is to provide the engineering community with a foundation, backed by comprehensive research, for choosing appropriate ground motion selection and modification methods for predicting the median drift response of buildings. To this end, the approach taken in this report is (a) to select and scale ground motions using a wide variety of proposed methods, (b) to use these ground motions as inputs to nonlinear dynamic structural analyses, and then (c) to study differences in the resulting structural response predictions in order to identify what GMSM decisions are most crucial. By studying a large number of GMSM methods and analyzing a variety of structures, this report quantitatively compares many of the GMSM methods available to the engineering community.
This report presents the methodology developed by the GMSM Program and the results obtained using 14 ground motion selection and modification techniques (25 if variations of those 14 are considered separately) to analyze four reinforced concrete frame and wall buildings. The results show that for the classes of buildings considered here, one can improve the prediction of structural response by appropriately taking into account higher-mode and nonlinear properties (in addition to elastic first-mode properties) of the buildings when selecting and scaling ground motion records. This is often accomplished through selection based on appropriate spectral shape, or through use of inelastic methods. The specific results of this report are intended to provide practical guidance for those selecting and scaling ground motions for buildings, and the overall methodology provides a general framework for future evaluation of other ground motion selection and scaling techniques and other classes of engineered structures.
The PEER Ground Motion Selection and Modification Program plans to continue these types of evaluations in order to bring further quantitative rigor to the use of ground motions for the analysis of buildings, and also to initiate such research for a wider range of engineering problems (e.g., bridges, nuclear
structures, earthen dams, site response). This report should thus be considered as an initial building block toward future studies that will grow increasingly comprehensive.
Full List of PEER Reports: click here.