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Correlations Between FrequencyContent Indicators of Strong GroundMotions and PGVF. Pavel a & D. Lungu aa Department of Reinforced Concrete Structures , TechnicalUniversity of Civil Engineering Bucharest , RomaniaAccepted author version posted online: 10 Jan 2013.Publishedonline: 14 Apr 2013.

To cite this article: F. Pavel & D. Lungu (2013) Correlations Between Frequency Content Indicatorsof Strong Ground Motions and PGV, Journal of Earthquake Engineering, 17:4, 543-559, DOI:10.1080/13632469.2012.762957

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Journal of Earthquake Engineering, 17:543559, 2013Copyright A. S. ElnashaiISSN: 1363-2469 print / 1559-808X onlineDOI: 10.1080/13632469.2012.762957

Correlations Between Frequency Content Indicatorsof Strong Ground Motions and PGV

F. PAVEL and D. LUNGUDepartment of Reinforced Concrete Structures, Technical University of CivilEngineering Bucharest, Romania

The frequency content of ground motions seems to be one of the most important parameters to explainthe structural damage experienced during worldwide strong earthquakes. The frequency content ofground motions can be characterized by various stochastic and/or deterministic indicators: the fre-quency bandwidth indicator (Cartwright & Longuet-Higgins) related to the power spectral densityfunction and, respectively, the control (corner) period Tc of the structural response spectra or themean period TM. Peak ground velocity (PGV) and the ratio PGA/PGV can be used as either dam-age potential parameters or frequency content indicators. A comparative analysis of stochastic anddeterministic frequency content indicators and of PGV is applied to a set of 30 strong ground motionrecords having peak ground acceleration (PGA) from 0.20.8 g and recorded on 4 continents duringthe last 70 years.

Keywords Earthquake Records; Stochastic Modeling; Frequency Content Indicators; DamagePotential; Response Spectra

1. IntroductionGround motions records show various frequency content, from wide and/or intermediatefrequency bandwidth ground motions (in hard and/or medium soil conditions) to narrowfrequency band ground motions (in soft soil conditions). The random frequency contentof the recorded strong ground motions generally depends on both magnitude and sourcemechanism as well as on local soil conditions and epicentral distance.

Probability-based assessment [Lungu and Cornea, 1987; Lungu et al., 1993] of the fre-quency content of the ground motion records can be done using the Power Spectral Density(PSD) and its related indicators: the dimensionless bandwidth indicators (Cartwright& Longuet-Higgins) and q (Vanmarcke), as well as fractile frequencies f10, f50, and f90(KennedyShinozuka indicators) below which 10%, 50%, and 90% of the total cumulativepower of the PSD occurs.

The best deterministic indicators of the frequency content of the ground motion recordsare the control periods of structural response spectra, historically introduced by Newmarkand Hall [1969, 1982]. The evolution of this concept during the years 19782010 is furtherdescribed in ATC [3-06, 1978]; Lungu et al. [1997]; Rathje et al. [1998]; Bommer et al.[2000]; and ASCE [7-10, 2010].

The amplitude of the ground motion can be usually described by the peak groundacceleration and/or by the peak ground velocity (PGV) which has received less attentionthan PGA. Due to the fact that PGV is less sensitive to the high frequency amplitudes

Received 19 June 2012; accepted 23 December 2012.Address correspondence to F. Pavel, Department of Reinforced Concrete Structures, Technical University

of Civil Engineering Bucharest, Bd. Lacul Tei, 122-124, RO 020396, Romania. E-mail: florin.pavel@utcb.ro

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544 F. Pavel and D. Lungu

of the ground motion, it can be used to characterize the damage potential of the seismicrecord. PGV has been linked [Akkar and Ozen, 2005] to the earthquake magnitude, strongground motion duration, frequency content of ground motions, and inelastic deformationdemands in SDOF (single degree of freedom) systems. Based on their results the authorsconsider PGV as a stable candidate for ground motion intensity measure in simplifiedseismic assessment methods. Yakut and Yilmaz [2007] presented a series of analyses onMDOF (multiple degree of freedom) systems from which it appears that PGA is a betterGMI (ground motion intensity) indicator than PGV . However, the conclusion of the authorsis Since PGA and PGV do not reflect the characteristics of the structure they appear to beinadequate intensity parameters. Fajfar et al. [1990] introduced a damage potential indi-cator for intermediate period structures based on PGV and strong ground motion duration,while Bommer and Alarcn [2006] and Booth [2007] introduced relations for estimatingPGV using random vibration theory. The relation between the Modified Mercalli Intensity(MMI) and the peak ground acceleration PGA and peak ground velocity was studied inWald et al. [1999].The ratio PGA/PGV can be used both as a frequency content indicatorof the strong ground motion and as a damage indictor as outlined in Zhu et al. [1988].Elnashai and Di Sarno [2008] divided the ratio into 3 categories from low ratio (PGA/PGV< 0.8) to high ratio (PGA/PGV > 1.2). The lower bound for potentially damaging PGVwas established in Bommer and Martinez-Pereira [2000] at a value of 20 cm/s.

In the present article, a comparative analysis of stochastic and deterministic frequencycontent indicators is applied to a set of 30 strong ground motion records having PGA from0.20.9 g. Also, the relation between PGV and the spectral acceleration (SA) of the selectedground motion is analyzed. Finally, the relation between PGV and the ratio PGA/PGV onone hand and a series of frequency content indicators is considered.

2. Characterization of the Ground Motion Frequency Content

2.1. Stochastic Indicators for the Frequency Content of Seismic RecordsThe definition of the stochastic frequency content indicators of the ground motion recordsare based on modeling the strong phase of the recorded accelerogram as a stationarystochastic process.

The duration D of the stationary part of the motion may be selected as the time intervalin which a significant fraction (say 70%, 80% or 90%) of the total cumulative power of theaccelerogram a(t) is released, i.e. D0.9 = t0.05 t0.95, D0.8 = t0.10 t0.90, etc.:

Cum. Power =

0

[a(t)]2dt. (1)

Consequently, the power spectral density (PSD) of accelerograms considered in the presentstudy was determined for the stationary part of the record modeled to be within the timeinterval t0.10 t0.90.

The dimensionless indicator proposed by Cartwright & Longuet-Higgins and definedin Clough and Penzien [2003] as a function of the spectral moments of the PSD for thestationary process of the ground acceleration:

0 =

1 22

04 1, (2)

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Frequency Indicators and Ground Motions Correlation 545

where i is the i-th moment of the PSD and

i =+

iSx () d. (3)

The guidance values for indicator in the case of actual ground motion accelerogramsmight be [Clough and Penzien, 2003]:

2/3 < < 0.85 for a wide frequency band process (white noise or band-limitedwhite noise);

0.85 < < 0.90 for an intermediary band process; > 0.90 for narrow frequency band processes (very high-frequency low-amplitude

signal associated with a low-frequency band-limited signal).

Several representative examples of ground motions from Romania are: the narrowest fre-quency band ground motions ever recorded in Romania at INCERC station in Bucharest(the NS comp. of the 1977 and 1986 seismic events) and the broadest frequency bandground motions recorded at Carcaliu in Dobrogea during the 1986 and 1990 Vrancea earth-quakes. Another interesting series of seismic motions was recorded at Cernavoda City Hallduring the same 1986 and 1990 events; these represent ground motions with a very stablepredominant period.

In the epicentral area of the Vrancea earthquakes and in the East of the CarpathianMountains (Moldova), the recorded ground motions are characterized by wide frequencybandwidth: the maximum ordinates of the response spectra are in the range T = 0 0.6 s.In the Bucharest region, the recorded ground motions can be divided into two categories[Lungu et al., 1992]:

seismic records characterized by spectral peaks in the long period range (T > 1.0 s)and specific to narrow frequency bandwidth processes; or

seismic records having the maximum spectral peaks in the short period range (T