Choice of Intensity Measure in Incremental Dynamic Analysis

Incremental dynamic analysis (IDA) is a widely used method for assessing structural performance under earthquake excitations. It enables direct evaluation of the record-to-record variability in structural response through a set of ground-motion records. If the number of ground-motion records is large then, the method becomes computationally demanding. To facilitate its practical application, a precedence list of ground-motion records has been introduced, aiming at selecting the most representative ground-motion records for IDA analysis. In progressive IDA analysis, the IDA curves are computed progressively, starting from the first ground-motion record in the precedence list. After an acceptable tolerance has been achieved, the analysis is terminated. This approach may significantly reduce the computational effort for first-mode-dominated structures, since the seismic response can be computed only for a certain number of ground-motion records from the precedence list to achieve an acceptable level of confidence in the prediction of the summarized (16th, 50th, and 84th fractiles) IDA curves. The proposed implementation of incremental dynamic analysis, which is demonstrated using an example of a 4-story reinforced concrete frame, can also be used for the selection of ground-motion records from a very large set of records, provided that all the records properly represent the seismic scenario for a given site.

Seismic design practices and response analyses of infrastructures have conventionally used peak ground acceleration (PGA), velocity (PGV), displacement (PGD) or spectral intensities such as spectral acceleration (Sa) and displacement (Sd) as an intensity measure (IM) of an earthquake. Previous studies showed that the conventional IMs might not be always the most desirable parameters for correlating with seismic responses and damage of structures. The correlation between earthquake IMs and seismic responses of buildings were thoroughly investigated, whereas it is not sufficiently studied yet for nuclear power plant (NPP) structures. In this study, we perform a series of time-history analyses to identify the best IMs for seismic responses of NPP components. In particular, high-frequency and low-frequency ground motions are separately investigated. An advanced power reactor NPP in Korea, APR1400, is selected for numerical analyses where containment building, auxiliary building, and internal structure are modelled using OpenSees, a platform for earthquake engineering simulations. Seismic responses of these components are obtained in terms of the maximum drift ratio and floor spectral acceleration. A series of Pearson's correlation coefficients are calculated to recognize the correlation between each of 23 earthquake IMs and responses of NPP structures. The numerical results reveal that, for the high-frequency motions, the strong correlated IMs are specific energy density (SED), characteristic intensity, root-mean-square of velocity, and Arias intensity. The poor correlated IMs are the ratio of PGV/PGA, predominant period (Tp), mean period, and cumulative absolute velocity. In case of low-frequency ground motions, the best indicators are A95 parameter, PGA, sustained maximum acceleration, effective peak acceleration. On the other hand, the weak correlated parameters are SED, PGD, Sv(T1), Sd(T1), and Tp.

Journal of Earthquake and Tsunami, 2012

Intensity measure (IM) which describes the strength of an earthquake record plays an important role in the seismic performance assessment of structures. An improved IM that can reduce the variability in seismic demands helps reducing the number of records necessary to predict the seismic performance with sufficient accuracy. In this study, an improved RMS-based IM is developed based on the results obtained from incremental dynamic analyses of short-to relatively long-period frames under an ensemble of near-fault pulse-like earthquake records. It is observed that the root-mean-square value of pseudo spectral accelerations, (Sa) rms , is generally superior to that of spectral velocities, (Sv) rms , in seismic demand prediction under near-fault records. To compute (Sa) rms as IM, two appropriate period ranges are suggested for short- and moderated-to relatively long-period frames, respectively. Comparing the efficiency of (Sa) rms with several advanced IMs shows that (Sa) rms is more e...

2012

Accurate estimation of structural response for a given target hazard level requires a suitable set of ground-motion records that represents a pre-defined scenario event. With the aim of assessing the seismic performance of structural systems, this study presents a ground motion selection and scaling methodology. Given a relatively larger ground-motion database, the method uses the differences between individual records and corresponding estimations of a ground-motion prediction equation in order to determine the optimum subset of recordings. This way, the procedure provides a group of modified records whose median elastic spectral ordinate matches with the target intensity level without excessively manipulating the inherent aleatory variability in the selected recordings. Considering the sensitivity of overall structural response to the nonlinear behavior, the procedure approximately estimates the median and dispersion of inelastic structural response. The case study suggests that, ...

2015

Amplitude scaling and selection of ground-motion records are frequently used tools to obtain a group of accelerograms suitable for structural performance assessment for a given hazard level. To provide a suitable set of records to be used in nonlinear dynamic analysis either to estimate median structural response or to predict its full probability distribution, “n” scaled ground motions that best match with target spectrum are selected. Common concerns related with this approach are the use of appropriate definition of target spectrum according to the objective of nonlinear dynamic analysis and the number of required recordings, “n”, that yield unbiased structural response. This study uses scenario event spectrum, conditional mean spectrum, and conditional spectrum as alternative targets with 7, 11 and 15 records. Additionally, the adequate level of spectral match between ground-motion records and the target is also a critical issue as it could lead to biased results. This study use...

2021

This paper focuses on the probabilistic analysis of Intensity Measures (IMs) and Engineering Demand Parameters (EDPs) for earthquake excitations. Several statistical properties, which are desirable in IMs when they are used to predict EDPs, have been analyzed. The main sources of uncertainty involved in the calculation of the seismic risk have been considered in the analysis. Efficiency, sufficiency and steadfastness have been quantified for a set of IMs with respect to two EDPs: the maximum inter-storey drift ratio, MIDR, and the maximum floor acceleration, MFA. Steadfastness is a new statistical property proposed in this article. It is related to the ability of IMs to forecast EDPs for big building suites. This also means that efficiency does not significantly vary when different types of buildings are included in the statistical analyses. This property allows reducing the number of calculations when performing seismic risk estimations at urban level since, for instance, a large v...

arXiv (Cornell University), 2019

This paper aims to investigate the effects of motion duration on the structural seismic demands, seeking potential correlations between motion durations and structural responses at several seismic intensity levels. Three seismic levels with 100years, 475years, and 2475years earthquake return periods (RPs) are first considered for correlation computations. Spectrally matched ground motions are employed to isolate the contribution of duration from the effects of ground motion amplitudes and response spectral shape. Four single degree of freedom systems derived from four real reinforced concrete structures are studied, where both degrading and non-degrading equivalent SDOF systems are included for structural modeling. Results show a low positive correlation between motion duration and structural displacement demand but this correlation increases with an increase in earthquake RP. It is also investigated whether or not this small positive correlation has an impact on the incremental dynamic analysis curves. The spectrally matched ground motions are divided into two distinct groups in this case: short-and long-duration ground motions. The comparison of incremental dynamic analysis of these two groups at the collapse limit reveals that long-duration ground motions can cause up to a 20 percent decrease in the spectral acceleration demand of considered structural systems.

International Journal of Engineering, 2014

Incremental dynamic analysis (IDA) requires the analysis of non-linear response history of a structure for an ensemble of ground motions, each scaled to multiple levels of intensity and selected to cover the entire range of structural response. Recognizing that IDA of practical structures is computationally demanding, an approximate procedure based on the reduction of the number of ground motions is developed. A methodology based on data envelopment analysis (DEA), mathematical programming that can handle large numbers of variables and relations, is proposed to reduce the number of ground motions needed for the production of a reliable median IDA curve. The IDA curves computed by the exact and approximate procedures for two different sets of ground motions for the 9-storey SAC-Los Angeles building are presented. The results demonstrate that the approximate procedure, which uses a limited number of input ground motions, is accurate enough for practical application in building evaluation and design.

2014

Selecting sufficient number of appropriate ground motions compatible with regional tectonic condition is a major step in Incremental Dynamic Analysis method (IDA). This article is intended to compare and assess the nonlinear structural response of the selected four frames (two steel moment-resisting frames and two RC Special Moment Frames) through performing IDA method by use of the traditional and Conditional Spectrum methods. First, the CMS and CS approaches are briefly explained and discussed. The selected frames are dynamically nonlinearly analyzed using the traditional IDA and CS methods at four hazard levels (50%, 10%, 2%, and 1%). The plots of results obtained from the two approaches, in the form of mean curves, are compared and assessed. It is concluded that the CS method ends up with more reasonable results except in case where the frame poses structural instability as the result of using CS method. The necessity of performing more research work in this area is highlighted.

Asian Journal of Civil Engineering, 2020

In performance-based seismic engineering, the choice of ground motion goes hand in hand with dynamic analysis. This paper presents the relationship between the various intensity measures (IMs) parameter of ground motions that can be used in evaluating the behavior of structures. This is through the relationship between them and the ratio of the peak ground acceleration to the peak ground velocity (PGA/PGV). The PGA/PGV ratio has been used an empirical parameter to estimate ground motion frequency content and categorizes ground motion suites for performing nonlinear time history analyses of structures. Regression analyses are performed on data obtained from ground motion records with different PGA/PGV ratios. The regression analyses indicate that the best correlation IMs parameter with the PGA/PGV ratio in both near-and far-source earthquakes is the mean period (T m). Also, the relationships between PGA/PGV ratio and some IMs parameters in near-source earthquakes are stronger than it in far-source earthquakes.