Vertical Design Spectra Research Articles

Hazard consistent vertical design spectra for active regions of India

According to the current Indian Standard earthquake-resistant design code (IS 1893, 2016), the vertical design spectrum is assumed as two-thirds of the horizontal spectrum. However, a previous investigation of the Indian ground motion records suggests that the vertical spectra exceeded the horizontal in many instances, which would render the previous consideration inadequate. Therefore, the current study aims at developing an appropriate recommendation for obtaining vertical design spectra, through development of hazard consistent vertical design spectra for the active regions of India. The vertical design spectrum is generated through scaling of a weighted average vertical-to-horizontal ratio (V/H) ground motion prediction equation (GMPE) to the horizontal component of the uniform hazard spectrum. The uniform hazard spectrum is obtained for the two active regions of India– the Western Himalayas and the North East India through probabilistic seismic hazard analysis and the weighted average V/H model is obtained by combining the V/H GMPE developed for India with several global models. Based on the proposed relations, a structural engineer can obtain site-specific vertical design spectra with ease and accuracy.

Selection and Modification of Ground Motion Prediction Equations for Makran Subduction Zone, Southeast Iran

The Iranian Plateau is considered mostly as a shallow crustal area, except the Makran region in southeast Iran where subduction events can occur. Because of the tectonic characteristics of the Makran subduction zone, different categories of ground motion prediction equations (GMPEs) are required for seismic hazard assessment, including GMPEs for shallow crustal events and subduction zone earthquakes (both in-slab and interface events). To show the applicability of candidate GMPEs, a selected dataset consisting of 314 records from 80 earthquakes is used for statistical analyses and modification of the candidate GMPEs. The earthquakes in the studied area are classified into two groups: shallow (events with focal depth less than 40 km; including 67 events and 210 records) and in-slab (events with focal depth more than 40 km; 13 events and 104 records). There are no recorded instrumental data in the region for the interface earthquakes. About ten GMPEs (developed based on local, regional, and global data) for shallow earthquakes are initial candidates for selection and modification in the studied region. In addition, four relationships are used in the statistical analyses for in-slab events. Different statistical analyses have been applied to show the performance of GMPEs and their applicability for the region. The results show that the modification term applied in the GMPEs improved the applicability of the relations significantly. The results are very important for the assessment of seismic hazard in the Makran region and other neighborhood countries, i.e., Oman and United Arab Emirates. Finally, a new model for vertical-to-horizontal spectral ratio has been proposed for the studied region that helps us to obtain vertical design spectra from horizontal spectra and their predominant scenarios resulting from seismic hazard analyses.

24 January 2020 Sivrice (Elazığ) earthquake damages and determination of earthquake parameters in the region

The 24 January 2020 (Mw=6.8) earthquake with epicentre in Elazig (Sivrice) on the East Anatolian Fault Zone caused loss of life and property. The information was given about the seismotectonic setting and regional seismicity along this fault zone and aftershock activity and ground motion data of this earthquake. Earthquake parameters were obtained for five different earthquake stations which were closer to the epicentre. Horizontal and vertical design spectra were obtained for the geographic locations for each earthquake station. The obtained spectra for the earthquake epicentre were compared with selected appropriate attenuation relationships. The damages after earthquake were evaluated via geotechnical and structural aspects. This study also aims to investigate the cause-effect relationships between structural damage in reinforced-concrete and masonry structures, respectively. The lack of engineering services was effective on the amount of damage in masonry structures. Insufficient reinforcement and concrete strength, dimensions and inadequate detailing increased the amount of damage in reinforced-concrete structures. Importance should be given to negative parameters that may weaken the defence mechanisms of structures for earthquake-resistant structural design.

Investigating properties of vertical design spectra in Japan by applying differential evolution to KiK-net data

The vertical design spectrum plays an important role in seismic design whether of critical or ordinary structures. However, many studies focused on the vertical to horizontal response spectral ratio and less researchers investigated the properties of vertical design spectra directly. In this study, differential evolution and simulated annealing are firstly examined to determine an appropriate method to estimate the characteristic parameters of the vertical design spectra. Then, the properties of the vertical design spectra in Japan are investigated by applying differential evolution to about 10000 KiK-net seismic data. Compared with epicentral distance, the influence of earthquake magnitude is more obvious which shows up as the linear correlation between the corner period and earthquake magnitude. Moreover, we propose a loglog exponential formula which relates the corner period of vertical design spectra to that of horizontal design spectra, and the formula may be used in other regions.

A new formulation for a code‐based vertical design spectrum

SummaryConsideration of vertical seismic design loads is important for long‐span structural systems, short‐period structures, and for some nonstructural components in the buildings. To this end, seismic design codes utilize alternative approaches to define vertical design spectrum at different levels of complexity: either as a fraction of horizontal design spectrum or using a separate functional form having features different than the horizontal spectrum. In all cases, a consistency between the horizontal and vertical design spectral ordinates is sought. In this paper, we consider a set of modern seismic design codes, horizontal and vertical ground‐motion datasets, as well as ground‐motion predictive models (GMPMs) to assess the accuracy of code‐based vertical design spectrum expressions. We compute horizontal and vertical spectra for different earthquake scenarios (magnitude‐distance‐soil condition combinations) from the selected horizontal and vertical GMPMs for comparisons with their code‐based (idealized) counterparts. Besides that, we study the vertical spectrum behavior from observed ground‐motion data. Our observations suggest that the vertical design spectrum formulations by current codes do not fully explain the actual vertical spectral acceleration trends. We discuss the possible reasons behind the misrepresentation of vertical spectrum by the current code approach and introduce our own expressions to compute horizontal spectrum consistent vertical design spectrum from a comprehensive simulated dataset of correlated vertical and horizontal spectral ordinates.

Ground Motion Characterization for Vertical Ground Motions in Turkey—Part 1: V/H Ratio Ground Motion Models

Two approaches are used to develop the vertical design spectra in probabilistic seismic hazard assessment (PSHA): (i) performing PSHA for the vertical component using vertical ground motion models (GMMs), and (ii) utilizing the V/H ratio GMMs to scale the horizontal spectrum during or after the hazard calculations for the horizontal component. This study intends to develop a new framework for building a vertical ground motion logic tree that combines both vertical and V/H ratio GMMs in the PSHA analysis. For this purpose, the Turkish strong motion database (TSMD) (Akkar et al. in Journal of Seismology 14(3): 457–479, 2010) is updated with recordings from earthquakes that occurred between 2008 and 2015, including the Mw = 6.1 Elazig and Mw = 7.2 Van earthquakes. The updated TSMD contains 2698 recordings, with the earthquake metadata, source-to-site distance metrics for the recordings, measured shear wave velocity profiles for the recording stations, and spectral accelerations for horizontal and vertical components. Four candidate V/H ratio GMMs (proposed by Gulerce and Abrahamson in Earthquake Spectra 27(4): 1023–1047, 2011; Gulerce and Akyuz in Seismological Research Letters 84(4): 678–687, 2013; Akkar et al. in Bulletin of Earthquake Engineering 12(1): 517–547, 2014a; Bozorgnia and Campbell in Earthquake Spectra, 32(2): 951–978, 2016) are selected, and the model predictions are compared with the actual data in the updated TSMD using the analysis of the residuals and data-driven techniques. Analysis results showed that the median predictions of the V/H ratio GMMs proposed by Gulerce and Akyuz (2013), Akkar et al. (2014a), and Bozorgnia and Campbell (2016) are compatible with the V/H ratios in the Turkish strong motion dataset. The findings of this study and the compatibility analysis of the vertical GMMs with the updated TSMD are combined in the accompanying manuscript (Gulerce et al. in Pure and Applied Geopyhsics, 2019, submitted) to provide the complete framework of ground motion characterization for vertical ground motion component.

Vertical collapse safety margin assessment for steel frames against earthquake-induced loss of column

A quantifiable approach measuring the seismic structural collapse under sudden column removal is proposed using the interaction of the vertical collapse margin ratio (CMRV), the demand-to-capacity ratio (DCR) and the robustness (R). The assessment of CMRV needs the identification of the vertical maximum considered earthquakes. A classification of the ground motions based on the vertical-to-horizontal (V/H) ratios was used to obtain the vertical design spectrum. Six schemes of steel structures with various scenarios of sudden column removal were investigated to extract CMRV, DCR, and R. Then, a nonlinear regression analysis allows finding a general formulation of CMRV. A 15-story steel structure validates the proposed formulation of the CMRV. The two paths for estimating the minimum CMRV (CMRV, min) were the use of the recommended value of DCR and the minimum value of R inside the approximated CMRV expression, and the probabilistic distribution of CMRV, min from the analyses of different beam deformation states. The study of eighteen archetypes with 119 scenarios of sudden column removal reveals the value of the CMRV decreases when the V/H or/and DCR increase. The new maximum values of DCR with respect to R and its precise ranges are found with the use of the contour curves of CMRV, min.

A Study on the Damping Correction Factors for the Korean Standard Design Spectrum

In this study, we develop and propose damping correction factors for the Korean standard design spectra. The newly proposed Korean standard design spectra has been given only for 5% damping ratio. But in practice, engineers need design spectra for damping values other than 5%. To obtain design spectra for various damping values from the standard spectra, damping correction factors are derived. These factors modify the shape of design spectra in accordance with the damping ratio. Response spectra for various damping values are calculated from the earthquake records that had been used to calculate standard design spectra. They consist of 55 records from 18 earthquakes occurred in overseas intraplate regions and Korea. The regressed spectra for the damping values ranging from 0.5% to 50 % are compared with standard spectra at three regions acceleration, velocity and displacement sensitive regions. The regression analysis of these data rendered formula for damping correction factors. Finally, a single formula for damping correction factors is recommended that is valid for both horizontal and vertical design spectra and that is applicable to the entire range of periods. One thing to note that recommended damping correction factors is valid for the design spectrum of the rock grounds because the design spectra was developed based on the earthquake records of the rock ground.

Development of Korean Standard Vertical Design Spectrum Based on the Domestic and Overseas Intra-plate Earthquake Records

Development of Korean Standard Vertical Design Spectrum Based on the Domestic and Overseas Intra-plate Earthquake Records

Strong ground motion characteristics of the 2011 Van Earthquake of Turkey: Implications of seismological aspects on engineering parameters

The October 23 2011 Van Earthquake is studied from an earthquake engineering point of view. Strong ground motion processing was performed to investigate features of the earthquake source, forward directivity effects during the rupture process as well as local site effects. Strong motion characteristics were investigated in terms of peak ground motion and spectral acceleration values. Directiviy effects were discussed in detail via elastic response spectra and wide band spectograms to see the high frequency energy distributions. Source parameters and slip distribution results of the earthquake which had been proposed by different researchers were summarized. Influence of the source parameters on structural response were shown by comparing elastic response spectra of Muradiye synthetic records which were performed by broadband strong motion simulations of the earthquake. It has been emphasized that characteristics of the earthquake rupture dynamics and their effects on structural design might be investigated from a multidisciplinary point of view. Seismotectonic calculations (e.g., slip pattern, rupture velocity) may be extended relating different engineering parameters (e.g., interstorey drifts, spectral accelerations) across different disciplines while using code based seismic design approaches. Current state of the art building codes still far from fully reflecting earthquake source related parameters into design rules. Some of those deficiencies and recent efforts to overcome these problems were also mentioned. Next generation ground motion prediction equations (GMPEs) may be incorporated with certain site categories for site effects. Likewise in the 2011 Van Earthquake, Reverse/Oblique earthquakes indicate that GMPEs need to be feasible to a wider range of magnitudes and distances in engineering practice. Due to the reverse faulting with large slip and dip angles, vertical displacements along with directivity and fault normal effects might significantly affect the engineering structures. Main reason of excessive damage in the town of Ercis can be attributed to these factors. Such effects should be considered in advance through the establishment of vertical design spectra and effects might be incorporated in the available GMPEs.

The NGA-W1 Vertical-to-Horizontal Spectral Acceleration Ratio Prediction Equations Adjusted for Turkey

Online Material: Supplemental tables. Vertical ground motions are considered in the seismic design of critical structures such as nuclear power plants and dams. Results of a recent study revealed that the effect of vertical component ground motion on the seismic response of ordinary highway bridges is also significant, especially in near‐fault regions (Gulerce and Abrahamson, 2010; Gulerce et al. , 2012). In the probabilistic seismic‐hazard assessment (PSHA) environment, site‐specific vertical design spectra may be developed by computing the hazard independently for the vertical ground‐motion component, which in fact requires accurate prediction of vertical component ground‐motion intensity measures. However; new and updated vertical ground‐motion‐prediction equations (GMPEs) are not available for the western United States or for other active tectonic regions such as Turkey. Also, conducting separate vertical and horizontal component PSHAs may lead to inconsistent horizontal and vertical spectra due to the different distance and magnitude scaling and different standard‐deviation values of vertical GMPEs compared with horizontal GMPEs. The alternative approach is to use empirical vertical‐to‐horizontal spectral acceleration ratio (V/H ratio) prediction models to scale the horizontal spectrum that is developed using the results of horizontal component PSHA. Empirical V/H ratio predictive models may be built by developing separate vertical and horizontal GMPEs and then computing the ratio for a given magnitude and distance. In their studies, both Bozorgnia and Campbell (2004) and Bindi et al. (2009) used this approach on different sets of ground‐motion data. Recent predictive models derived by Bommer et al. (2011), Edwards et al. (2011), and Gulerce and Abrahamson (2011) were based on the directly calculated V/H ratios. However, datasets used by these developers, functional forms, and range of applicability of their models is considerably different. The database of Bommer et al. (2011) model includes 1267 ground motions from 392 earthquakes that occurred in Europe and surrounding regions within …

Determination of horizontal and vertical design spectra based on ground motion records at Lali tunnel, Iran

Most acceleration diagrams show high levels of unpredictability, as a result, it is the best to avoid using diagrams of earthquake acceleration spectra, even if the diagrams recorded at the site in question. In order to design earthquake resistant structures, we, instead, suggest constructing a design spectrum using a set of spectra that have common characteristics to the recorded acceleration diagrams at a particular site and smoothing the associated data. In this study, we conducted a time history analysis and determined a design spectrum for the region near the Lali tunnel in Southwestern Iran. We selected 13 specific ground motion records from the rock site to construct the design spectrum. To process the data, we first applied a base-line correction and then calculated the signal-to-noise ratio (RSN) for each record. Next, we calculated the Fourier amplitude spectra of the acceleration pertaining to the signal window (1), and the Fourier amplitude spectra of the associated noise (2). After dividing each spectra by the square root of the selected window interval, they were divided by each other (1 divided by 2), in order to obtain the RSN ratio (filtering was also applied). In addition, all data were normalized to the peak ground acceleration (PGA). Next, the normalized vertical and horizontal responses and mean response spectrum (50%) and the mean plus-one standard deviation (84%) were calculated for all the selected ground motion records at 5% damping. Finally, the mean design spectrum and the mean plus-one standard deviation were plotted for the spectrums. The equation of the mean and the above-mean design spectrum at the Lali tunnel site are also provided, along with our observed conclusions.

A Predictive Equation for the Vertical-to-Horizontal Ratio of Ground Motion at Rock Sites Based on Shear-Wave Velocity Profiles from Japan and Switzerland

Abstract Ratios of vertical-to-horizontal ( V / H ) ground motion are important for the computation of scenario-compatible vertical design spectra. They are therefore a crucial aspect of seismic hazard analysis. We characterize the V / H ratio at rock sites in terms of the recording site’s average quarter-wavelength velocity. A predictive equation is presented, which can be used for reconstructing the expected V / H ratio of the 5%-damped response and Fourier spectra for rock sites, given a known shear-wave velocity profile. The equation is based on the regression analysis of two datasets: one from Switzerland and one from Japan. The two datasets allow us to analyze well-characterized hard-rock sites in Switzerland using small earthquakes ( M w >2), while the magnitude range is increased up to events of M w 7.3 using strong-motion recordings from Japan’s KiK-net seismic network. It is shown that a correlation exists between the quarter-wavelength velocity at a given frequency and the V / H ground-motion ratio. Small differences, possibly due to velocity measurement bias or topographical and basin effects, existed when analyzing the individual regional datasets. Apart from near-source distances ( R V / H , no clear magnitude- or distance-dependence of the V / H ratios is present in either of the datasets of earthquake recordings. We show that the same correlation exists for response spectra and Fourier spectra of recorded ground motion. A similar correlation was derived for ambient vibrations recorded at Swiss station sites, resulting in larger values of V / H at a given frequency and thereby indicating that V / H is sensitive to the composition of the wave field. Finally, uncertainties in the V / H models are presented. We separate the sources of uncertainty into source and site-specific components and present the single-site sigma uncertainty measure for site-specific hazard analyses.

Site-Specific Design Spectra for Vertical Ground Motion

This paper contains ground-motion prediction equations (GMPEs) for the vertical-to-horizontal spectral acceleration (V/H) ratio, and the methods for constructing vertical design spectra that are consistent with the probabilistic seismic hazard assessment results for the horizontal ground motion component. The GMPEs for V/H ratio consistent with the horizontal GMPE of Abrahamson and Silva (2008) are derived using the Pacific Earthquake Engineering Research Center's Next Generation of Ground-Motion Attenuation Models (PEER-NGA) database (Chiou et. al. 2008). The proposed V/H ratio GMPE is dependent on the earthquake magnitude and distance, consistent with previous models, but it differs from previous studies in that it accounts for the differences in the nonlinear site-response effects on the horizontal and vertical components. This difference in nonlinear effects results in large V/H ratios at short spectral periods for soil sites located close to large earthquakes. A method to develop vertical design spectra dependent on the horizontal component uniform hazard spectrum that accounts for the correlation between the variability of the horizontal ground-motion model and the variability of the V/H ratio ground-motion model is proposed.

Smooth Spectra of Horizontal and Vertical Ground Motions

An improved method of constructing a smooth-response spectrum from peak values of ground acceleration, velocity, and displacement (pga, pgv, and pgd) is presented. Improved dynamic amplification factors are presented for applying damping adjustments to the spectral accelerations or to backcalculate pga, pgv, and pgd from spectral accelerations. Horizontal-to-vertical spectral ratios are analyzed for rock and soil sites to allow the construction of a vertical design spectrum from a given horizontal design spectrum.

THE VERTICAL-TO-HORIZONTAL RESPONSE SPECTRAL RATIO AND TENTATIVE PROCEDURES FOR DEVELOPING SIMPLIFIED V/H AND VERTICAL DESIGN SPECTRA

This paper presents the results of a study on the engineering characteristics of vertical ground motion. A ground-motion model for the vertical-to-horizontal ratio (V/H) of peak ground acceleration and 5%-damped acceleration response spectra was derived by using a database of 443 near-source accelerograms recorded from 36 worldwide earthquakes of M w 4.7-7.7. The recordings were all located within 60 km of the seismogenic rupture zone of worldwide shallow crustal earthquakes in active tectonic regions. We found no bias in the V/H estimates from independent analyses of vertical and horizontal response spectra. We also found V/H to be a strong function of natural period, local site conditions, and source-to-site distance; and a relatively weaker function of magnitude, faulting mechanism, and sediment depth. V/H exhibits its greatest differences at long periods on firm rock (NEHRP site category BC), where it has relatively low amplitudes, and at short periods on firm soil (NEHRP site category D), where it has amplitudes that approach 1.8 at large magnitudes and short distances. We propose a tentative simplified model for estimating V/H spectra and two relatively simple procedures for developing a preliminary vertical design spectrum that could be used for practical engineering appli-cations where site-specific spectra (e.g. from a seismic hazard analysis) are not available. Extensive vetting from the seismological and engineering communities will be needed be-fore such simplified spectra are officially accepted and adopted in codified procedures in the United States.

Vertical Seismic Response Spectra

Response spectra are derived from 30 historical vertical motion accelerograms recorded on hard or rock sites and used as a basis for a recommended design response spectra. Accelerograms were corrected for baseline and instrument errors using routine processing methods. Statistics are derived for the response spectra normalized to peak ground displacement, velocity, and acceleration. Effects of sample size are examined and a method for deriving confidence intervals for the statistical results is presented. Following approaches of previous investigators the results are used as a basis for recommendations of a smoothed design response spectra for vertical motion at hard or rock sites. The recommended vertical design spectra for rock sites are lower than recommendations of previous investigators for sites of intermediate hardness.