Ratio Of Spectral Acceleration Research Articles

Evaluation of vertical-to-horizontal spectral acceleration ratio for the 2023 Turkey-Syria seismic sequences

This paper aims to evaluate the vertical-to-horizontal, V/H, spectral acceleration ratios from the earthquake ground motions recorded during the February 6, 2023 Turkey-Syria seismic events, which include doublet events with moment magnitudes of Mw7.7 and Mw7.6 that struck the city of Kahramanmaraş and a considerable aftershock with Mw6.7 that mainly struck the city of Nurdağı. Statistics of the observed V/H spectral ratios computed from records that have peak ground acceleration larger than 0.1g showed that most records of the three earthquakes yielded spectral V/H ratios higher than 2/3, which is a typical value recommended by several seismic codes. Additionally, comparison of the observed V/H spectra with respect to the Ground Motion Predictive Models, GMPMs, for V/H ratios introduced by Bozorgnia and Campbell (2016), BC model, and Bommer et al. (2011), BAK model, revealed that both GMPMs mostly underestimate the V/H ratios at long spectral periods. Residual analysis showed that the capability of the BAK model for large source-to-site distances is more than that for small distances for which the ratios may be underestimated specially at long periods, while the estimations of the BC model do not significantly depend on the distance. Additionally, comparison of the observed V/H ratios with those computed based on the current 2018 edition of the Turkish seismic code indicated that the three considered earthquakes mostly yielded V/H ratios considerably higher than the code-based values in the long period range that could have higher damaging potential than those ratios in short period range.

Mean-to-median spectral acceleration ratios in Senior Seismic Hazard Analysis Committee Level 3 probabilistic seismic hazard analyses: An analysis of reported results

In many countries, seismic characterization of the site selected for a critical structure or industrial facility is required in terms of site-specific seismic ground motion hazard. For this purpose, a probabilistic seismic hazard analysis (PSHA), performed under the Senior Seismic Hazard Analysis Committee (SSHAC) protocol, is an extended practice for nuclear facilities. In the past decade, SSHAC Level 3 studies have been performed for sites in North America, Europe, Japan, Taiwan, and South Africa. When analyzing PSHA results, the mean-to-median spectral acceleration ratios given by the hazard curves can be interpreted as a measure of the degree of epistemic uncertainty associated with the results. In this article, results of 33 SSHAC Level 3 studies have been used to determine mean-to-median spectral acceleration ratios and the statistics of these ratios, as a function of spectral frequency and annual frequency of exceedance (AFE). The purpose was to develop a reference for the range of uncertainty that is typically captured in this kind of studies. It has been found that, for a given AFE, ratios corresponding to different sites are within a relatively small interval, especially for the spectral frequency band between 2.5 and 10 Hz, which is the band normally more relevant for the seismic design of nuclear installations. In this band, for 10−4 yr−1 AFE, a mean/median ratio of 1.40 would envelop practically all investigated sites.

Estimate of V/H spectral acceleration ratios for firm soil sites in Eastern Canada

This study aims to provide an estimate of vertical-to-horizontal (V/H) pseudo-spectral acceleration (PSA) ratios in the Eastern Canada seismic zone for firm soils (360 < Vs30 < 760 m/s) referred to as Site Class C in the National Building Code of Canada (NBC). According to previous studies, the 2/3 V/H empirical ratio prescribed in NBC is deemed overestimated for far-field areas and underestimated for near-field areas. In this study, the V/H PSA ratios were computed for 248 records from 67 historic earthquakes in the Eastern Canada region with a magnitude Mw ≥ 3.0 and an epicentral distance (Repi) < 150 km. Given the lack of available records for Site Class C in this region, sets of records from other site classes, mostly Site Class A (Hard rock), were selected and converted to the corresponding records on Site Class C. To this end, the equivalent linear method, using the Pressure-Dependent Modified Kondner Zelasko (MKZ) model of analysis in the frequency domain was selected using the software DEEPSOIL. Computed V/H PSA ratios were then calibrated with those obtained from available Ground Motion Prediction Equations (GMPEs) compatible with Site Class C of the studied region. The computed mean V/H PSA ratios were found to exceed the common value of 2/3 recommended in most codes, especially for short periods up to 1.3 sec, and new V/H ratios were proposed as a function of the fundamental period of the building. Finally, a profile of vertical acceleration design spectra (ADSver) was proposed for Site Class C in Montreal and compared with those obtained by ASCE/SEI 7–16 and ASCE 41-17 provisions.

Consistency Study on Observed Acceleration and Velocity Records

ABSTRACT We compare and analyze the consistency of observed acceleration and velocity data recorded by accelerometer and seismometer simultaneously in five aspects: time series, 5% damped response spectra, the variation and distribution characteristics of peak value ratios and spectral acceleration ratios, and correlation analysis. The results show that these two have good consistency, especially in medium-frequency bands and medium- and far-fields. In the research dataset of ground motion prediction equations (GMPEs), we propose the weight ratios of the observed acceleration and velocity records and verify that the empirical weighted ratios are reasonable and reliable and applicable to southwest China.

Local Geology Effects on Soil Amplification and Predominant Period in Düzce Basin, NW Turkey

Amplification and predominant periods of soils in Düzce Basin were investigated by analysing the data sets of last two major earthquakes and aftershocks of Kocaeli and Düzce earthquakes occurred in 1999 with a magnitude of Mw:7.4 and Mw:7.2, respectively. Two different methods named horizontal/vertical spectral acceleration ratio (HVSAR) and soil-to-rock Response Spectral Acceleration Ratio (RSAR) were used to determine soil amplifications for various periods in Düzce Basin. The data set includes 31 strong gorund motion records from five strong ground motion stations. It was found that the site amplifications at stations are directly related to the local geology underlying the stations. Averaging the residuals between the predicted and observed PGAs resulted in soil amplification from 1.33 to 2.33. The HVSAR method presented soil amplification values between 2.7 and 10 and predominant period values between 0.4 and 0.7 s. Soil amplification values from 1.5 to 14 and predominant periods from 0.5 to 0.8 s were obtained by the RSAR method. High site amplifications and predominant periods mainly depend on the thickness of lithological variances accompanied by low physical and geotechnical properties of alluvial deposits.

Investigation of pile‐induced filtering of seismic ground motion considering embedment effect

AbstractThe Foundation Input Motion (FIM) arising out of kinematic soil‐pile interaction forms an integral part of the seismic analysis of pile‐supported structures. Several studies in the recent past have recognized the importance of the filtering effect produced by pile foundations. This paper presents a comprehensive investigation of the influence of raft embedment on the Foundation Input Motion from piled rafts. A hybrid numerical methodology based on the finite element‐boundary element method is employed to rigorously model rectangular piled rafts in varying soil conditions. Analysis of transfer functions in the frequency domain suggests that the translational response is suppressed by increasing embedment of the raft. An increase in rocking response is also synchronous with this decrease in translational motion. A transient response analysis carried out using eight different earthquake time histories showed that the spectral acceleration curve is altered by the embedment effect. A set of simplified expressions are proposed to incorporate the embedment effects in the spectral acceleration ratio curve of a pile group. These proposed expressions have the potential to enable a quick estimation of the effect of embedment in the seismic design of pile‐supported structures.

Ground Motion Parameters and Resonance Effect During Strong Earthquake in Northern Thailand

Several previous investigations have suggested that ground motion as described by various parameters and resonance effects could have contributed to the damage observed during an earthquake. This paper presents a ground motion parameters study and site investigation in Northern Thailand during the Tarlay Earthquake of 2011. Ground motion parameters recorded at the closest seismic station to the earthquake rupture, i.e. Mae Sai Station (MSAA) are studied. Microtremor measurement was performed at the MSAA site. The horizontal to vertical spectral ratio (H/V) from the investigation are interpreted. Spectral acceleration ratios based on data from the MSAA are compared to determine the possibility of resonance during the earthquake. Spectral acceleration data based on recorded ground motion are compared to guideline design spectral acceleration to determine the critical period. Results show that during the Tarlay Earthquake, significant duration was 24 s. Within this duration, resonance was plausible within the frequency range of 1.82 to 2.1 The critical period ranged from 0.4 to 0.6 s, indicating that low-medium story buildings were most vulnerable. Results also show that horizontal ground motion was relatively dominant in the destruction of structural buildings during the earthquake.

Pulse-like ground motions: Statistical characteristics, and GMPE development for the Iranian Plateau

This research attempts to study the pulse-like ground motions, recorded on the Iranian plateau, and propose predictive equations for simulating the main features of this type of signal. In this regard, firstly, the statistical characteristics of pulse-like records of the Iranian database, containing 770 events and 1206 accelerograms, are statistically investigated. The probability density function of facing a pulse-like signal, for a given location, is obtained, and the main features of acceleration and velocity spectra of these signals are evaluated for the horizontal and vertical directions. Interestingly, the mean value of vertical to horizontal ratio of spectral acceleration of signals reaches above one in many cases. In the next part, a set of ground motion prediction equations are presented for simulating the major properties of velocity pulse itself, including the amplitude, period, and the occurrence time during the recorded time series. Besides to these equations, another set of GMPEs is proposed for generating the 5% damped spectral acceleration of the horizontal and vertical pulse-like ground motions simultaneously considering their component's correlation. These newly developed equations are compared and validated with the existing GMPEs of the Iranian plateau. All of the suggested equations are applicable for the magnitude between 4.0 and 6.5, the site-to-source distance of 2 km–100 km, the focal depth of 2–40 km, and the shear wave velocity of underlying soil varying between 200 m/s to 900 m/s.

Investigating Efficiency of Vector-Valued Intensity Measures in Seismic Demand Assessment of Concrete Dams

The efficiency of vector-valued intensity measures for predicting the seismic demand in gravity dams is investigated. The Folsom gravity dam-reservoir coupled system is selected and numerically analyzed under a set of two-hundred actual ground motions. First, the well-defined scalar IMs are separately investigated, and then they are coupled to form two-parameter vector IMs. After that, IMs consisting of spectral acceleration at the first-mode natural period of the dam-reservoir system along with a measure of the spectral shape (the ratio of spectral acceleration at a second period to the first-mode spectral acceleration value) are considered. It is attempted to determine the optimal second period by categorizing the spectral acceleration at the first-mode period of vibration. The efficiency of the proposed vector IMs is compared with scalar ones considering various structural responses as EDPs. Finally, the probabilistic seismic behavior of the dam is investigated by calculating its fragility curves employing scalar and vector IMs considering the effect of zero response values.

Basin Edge Effect on Seismic Ground Response: A Parametric Study for Duzce Basin Case, Turkey

In this study, edge effect on the spatial variation of surface ground motion was evaluated by conducting one (1D) and two-dimensional (2D) dynamic analyses on the numerical model of Duzce basin. Duzce is a province in northwestern Turkey and was hit by a devastating earthquake in November 1999. In order to estimate the seismic behavior of Duzce basin, 1D and 2D dynamic response analyses were carried out on its numerical model by using the seismic bedrock motion data derived from the deconvolution analysis of the N–S component of 1999 Duzce earthquake accelerogram. In addition, a series of different accelerograms and slope values were utilized to investigate the possible effects of change in strong ground motion intensity level and edge geometry on the dynamic response of soil layers over inclined bedrock. The finite element model for the edge section of the flat sedimentary basin was set up by using the 2D shear wave velocity profile, geotechnical and geological site conditions in Duzce. The variation of 2D/1D spectral acceleration ratios and aggravation factors with distance from basin edge was obtained for different period values. The results indicate that the aggravation factors reached their maximum values at a specific zone near basin edge and they generally converged to 1 regardless of the bedrock inclination or period values with increasing distance from the edge section. The highest aggravation factor values were calculated as 2.0–2.5 for the period interval of $$T=$$ 0.2–0.6 s. A relationship was proposed between the aggravation factor and basin edge geometry.

Vector-IM-based assessment of alternative framing systems under bi-directional ground-motion

This paper examines the seismic performance of steel buildings with alternative framing systems subjected to bi-directional ground-motion. Peak drifts of one-way (perimeter framing) and two-way (space framing) systems are assessed by means of scalar and vector-valued probabilistic methods. Extensive non-linear response history analyses over idealized 3D structures representing 6- and 9-storey buildings are performed under pairs of linearly scaled ground-motions. Both far-field and near-field non-pulselike acceleration series are considered. The spectral acceleration of the geometric mean of the two horizontal components (Sa,GM) is taken as the primary intensity measure (IM) while four other ground-motion parameters are employed to construct IM-vectors including: the spectral acceleration ratio (RT3,T1), the spectral shape parameter (Np), and two frequency content parameters (Tm and To). This paper shows that incorporating the vector 〈Sa,GM,Np〉 into the assessment of bi-directionally loaded 3D buildings yields up to 40% lower conditional standard deviations than a purely scalar formulation at large drift levels while the vector 〈Sa,GM,RT3,T1〉 is more efficient at smaller drifts. The effects of alternative framing systems on structural fragilities are found to differ depending on the number of storeys. For 6-storey structures, consistently higher capacities are observed in two-way layouts with respect to one-way systems but they are associated with increasing variabilities at larger demand levels. Conversely, the 9-storey two-way building experiences 5% lower mean capacities than its one-way counterpart. Finally, drift hazard curves are calculated by combining the building fragilities with idealized ground-motion hazard estimates. The results indicate that one-way buildings experience consistently lower drift exceedance rates regardless of the ground-motion type, especially for drift levels larger than 2% although the differences are larger for the 9-storey frames in comparison with their 6-storey counterparts. This study represents a first attempt to implement vector-valued analysis in the context of bi-directionally loaded structures and its results constitute an important step towards discerning the most favourable framing system at different seismic performance levels.

A Numerical Study on Comparison of 1D and 2D Seismic Responses of a Basin in Turkey

Local site conditions such as seismic bedrock depth, bedrock slope of the edge, geometry and characteristics of soil layers, topographical irregularities, etc. are the most important factors affecting earthquake ground motion in a specific site. The amplitude and frequency content of bedrock motion can be changed by local site effects, and this variation is denoted as an amplification or de-amplification. Among the several factors, basin edge effect plays an important role in the transformation of earthquake waves and increase of the surface motion duration and amplitude. The limited width of the soil layers or the edge geometry at the deep formations cause earthquake wave transformations, thus the amplitude of the surface ground motion may vary depending on its location. For this reason the frequency content of surface ground motion may differ from the calculated surface ground motion by one dimensional dynamic analysis. In this case two dimensional analysis is required. In this study, in order to compare the soil response under different strong ground motion, one and two dimensional dynamic analyses were performed by using the Dinar Basin model in Turkey. The acceleration time histories and absolute acceleration spectra were obtained for pre-selected points on the ground surface. The 2D/1D spectral acceleration ratios were calculated by dividing the absolute acceleration spectra obtained from two dimensional (2D) and one dimensional (1D) dynamic analysis. The variations of the spectral acceleration ratios (2D/1D) with distance from basin edge were evaluated for different period values. The calculated 2D/1D spectral acceleration ratios reached their maximum values at a certain zone (X/D<3) near basin edge for every interested period value. While approaching to center of basin models, especially at the zones after X/D=3 point it can be noticed that 2D/1D spectral acceleration ratios generally converged to 1 regardless of the edge bedrock slope values. The highest average spectral acceleration ratios were calculated when the relevant period values were between T=0.2~0.5 s. They took values varying between 2 and 3 for this period interval. A relationship between the results of 1D and 2D dynamic analyses was established. In addition, the approximate validity range of 1D and 2D dynamic analysis at the basin edges was investigated for the model.

Seismic Demand of the Liquefaction Potential with Equivalent Number of Cycles for Probabilistic Seismic Hazard Analysis

Equivalent number of cycles (Ncyc) is a significant factor in assessing liquefaction potential during earthquakes. However, the effects of Ncyc are considered a deterministic value by using a magnitude scaling factor, and the uncertainties of these effects have not been included in the current design practice. This paper calculates Ncyc within the soil mass by deconvolution analysis as a function of the period of soil layer from the ground surface (Ts) and the soil property (b) using a wide range of acceleration time histories. The predictive model of Ncyc is developed as variable dependent on earthquake magnitude, peak ground acceleration (PGA), and ratio of spectral acceleration, Ts and b. Then, the Ncyc model is combined with the ground-motion prediction equation of PGA and the prediction equation of seismic shear-stress reduction coefficient (rd) to obtain the prediction equation of the seismic demand of the liquefaction potential (K1cyc). The standard deviation of K1cyc is also modeled on the basis of the aleatory variability of PGA, rd, and Ncyc with correlations between these residuals. This predictive model of K1cyc is implemented in probabilistic seismic hazard analysis (PSHA) to show the impact of these uncertainties on design practice.

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 …

The Basin Edge Effect on Dynamic Response: Dinar Basin Model

Earthquake ground motion is affected from local soil conditions, geological structures as well as earthquake source properties. The amplitude and frequency content of the strong ground motion can be changed by local site effects. Local site conditions such as seismic bedrock depth, bedrock slope of the edge, geometry and characteristics of soil layers and topographical irregularities are the most important factors affecting soil amplification. One dimensional (1D) equivalent linear dynamic analysis method is the simplest approach to investigate local site effects. 1D approach becomes valid especially for the sites far from edges or in shallow and wide valley models. In narrow and deep basins, body waves transform into surface waves especially at the edges during earthquakes and two dimensional (2D) resonance modes occur, the frequency content and amplitude of strong ground motion may vary with the distance from basin edge to its center. In this study, to investigate the effects of basin edge on the variation of surface motion under different strong ground motion acceleration records, one and two dimensional dynamic analyses were performed by using the Dinar basin edge model and the results were compared. The variations of the spectral acceleration ratios (2D/1D) were evaluated for the different points on the ground surface with the changing distance from the valley edges. A relationship between the results of one and two dimensional dynamic analyses was established. Shear wave velocity profile and bedrock depth in Dinar were obtained from microtremor array measurements.

Seismic hazard assessment of Chennai city considering local site effects

Chennai city suffered moderate tremors during the 2001 Bhuj and Pondicherry earthquakes and the 2004 Sumatra earthquake. After the Bhuj earthquake, Indian Standard IS: 1893 was revised and Chennai city was upgraded from zone II to zone III which leads to a substantial increase of the design ground motion parameters. Therefore, a comprehensive study is carried out to assess the seismic hazard of Chennai city based on a deterministic approach. The seismicity and seismotectonic details within a 100 km radius of the study area have been considered. The one-dimensional ground response analysis was carried out for 38 representative sites by the equivalent linear method using the SHAKE91 program to estimate the ground motion parameters considering the local site effects. The shear wave velocity profile was inferred from the corrected blow counts and it was verified with the Multichannel Analysis of Surface Wave (MASW) test performed for a representative site. The seismic hazard is represented in terms of characteristic site period and Spectral Acceleration Ratio (SAR) contours for the entire city. It is found that structures with low natural period undergo significant amplification mostly in the central and southern parts of Chennai city due to the presence of deep soil sites with clayey or sandy deposits and the remaining parts undergo marginal amplification.

Expected Signature of Nonlinearity on Regression for Strong Ground-Motion Parameters

This study examines the response of soil profiles with nonlinear properties to several hundred synthetic seismograms, generated to represent rock ground motions from magnitude 6.4 and 7.0 scenario earthquakes. Two shear-wave velocity models (developed to represent Class CD and D sites with water table at 3 m) are tested. The computed ratios of peak ground acceleration (PGA) between the surface of the soil profile and the bedrock decreases with increasing PGA values. The transition from amplification to deamplification occurs at about 0.2–0.3 g. The spectral acceleration (SA) ratios, defined as the ratios of SA between the surface of the soil profile and the input, vary with the natural period of the oscillators. At short periods less than 0.3 sec, the behavior of the SA ratios is similar to the PGA ratios: amplification for lower input SA and deamplification for higher input SA level. At longer periods, the influence of the input SA level on SA ratio decreases, and deamplification is seldom observed. We define the mean trends of these calculations as rock motion modification curves (RMM curves). The use of these curves is as follows: a ground-motion relation on rock is multiplied by the RMM curve for that ground motion to obtain the expected ground-motion relation at the soil surface. This procedure is applied to six sets of empirical ground-motion relations. A majority of the empirical ground-motion relations are consistent with the RMM curves. In the best case, the comparisons indicate that the empirical soil site PGA and SA ground-motion relations are very close to the predicted curves at all epicentral distances. For both PGA and SA, the differences between the empirical and predicted curves are within one standard deviation of the empirical curves. It is quite encouraging that this physical model for soil behavior predicts the average characteristics of the surface motion, given the highly scattered nature of the data set.

PREDICTION OF VERTICAL RESPONSE SPECTRA IN EUROPE

Equations for the prediction of vertical peak and absolute acceleration spectral ordinates in terms of magnitude, source-distance and site geology are presented. Comparison to similarly derived horizontal equations shows vertical spectral values to be 1/2-1/4 of the horizontal. The influence of site geology on vertical ground motion is reduced with respect to the horizontal. Ratios of peak vertical to peak horizontal ground acceleration in the near-field of thrust faults are magnitude and distance dependent, reaching values in excess of one very near the fault of large magnitude events. For strike-slip faults the ratio exceeds one for moderate events, decreasing for larger events, and is distance independent. Spectral acceleration ratios exceed one at short periods but are less than one at intermediate and long periods, irrespective of the source mechanism.

User perceptions of decision support system restriction: an experiment

This paper examines the seismic performance of steel buildings with alternative framing systems subjected to bi-directional ground-motion. Peak drifts of one-way (perimeter framing) and two-way (space framing) systems are assessed by means of scalar and vector-valued probabilistic methods. Extensive non-linear response history analyses over idealized 3D structures representing 6- and 9-storey buildings are performed under pairs of linearly scaled ground-motions. Both far-field and near-field non-pulselike acceleration series are considered. The spectral acceleration of the geometric mean of the two horizontal components (Sa,GM) is taken as the primary intensity measure (IM) while four other ground-motion parameters are employed to construct IM-vectors including: the spectral acceleration ratio (RT3,T1), the spectral shape parameter (Np), and two frequency content parameters (Tm and To). This paper shows that incorporating the vector 〈Sa,GM,Np〉 into the assessment of bi-directionally loaded 3D buildings yields up to 40% lower conditional standard deviations than a purely scalar formulation at large drift levels while the vector 〈Sa,GM,RT3,T1〉 is more efficient at smaller drifts. The effects of alternative framing systems on structural fragilities are found to differ depending on the number of storeys. For 6-storey structures, consistently higher capacities are observed in two-way layouts with respect to one-way systems but they are associated with increasing variabilities at larger demand levels. Conversely, the 9-storey two-way building experiences 5% lower mean capacities than its one-way counterpart. Finally, drift hazard curves are calculated by combining the building fragilities with idealized ground-motion hazard estimates. The results indicate that one-way buildings experience consistently lower drift exceedance rates regardless of the ground-motion type, especially for drift levels larger than 2% although the differences are larger for the 9-storey frames in comparison with their 6-storey counterparts. This study represents a first attempt to implement vector-valued analysis in the context of bi-directionally loaded structures and its results constitute an important step towards discerning the most favourable framing system at different seismic performance levels.

3673. Vacuum interlock system for molecular beam epitaxy: J W Robinson and M Ilegems, Rev scient Instrum, 49 (2), 1978 205–207

This paper examines the seismic performance of steel buildings with alternative framing systems subjected to bi-directional ground-motion. Peak drifts of one-way (perimeter framing) and two-way (space framing) systems are assessed by means of scalar and vector-valued probabilistic methods. Extensive non-linear response history analyses over idealized 3D structures representing 6- and 9-storey buildings are performed under pairs of linearly scaled ground-motions. Both far-field and near-field non-pulselike acceleration series are considered. The spectral acceleration of the geometric mean of the two horizontal components (Sa,GM) is taken as the primary intensity measure (IM) while four other ground-motion parameters are employed to construct IM-vectors including: the spectral acceleration ratio (RT3,T1), the spectral shape parameter (Np), and two frequency content parameters (Tm and To). This paper shows that incorporating the vector 〈Sa,GM,Np〉 into the assessment of bi-directionally loaded 3D buildings yields up to 40% lower conditional standard deviations than a purely scalar formulation at large drift levels while the vector 〈Sa,GM,RT3,T1〉 is more efficient at smaller drifts. The effects of alternative framing systems on structural fragilities are found to differ depending on the number of storeys. For 6-storey structures, consistently higher capacities are observed in two-way layouts with respect to one-way systems but they are associated with increasing variabilities at larger demand levels. Conversely, the 9-storey two-way building experiences 5% lower mean capacities than its one-way counterpart. Finally, drift hazard curves are calculated by combining the building fragilities with idealized ground-motion hazard estimates. The results indicate that one-way buildings experience consistently lower drift exceedance rates regardless of the ground-motion type, especially for drift levels larger than 2% although the differences are larger for the 9-storey frames in comparison with their 6-storey counterparts. This study represents a first attempt to implement vector-valued analysis in the context of bi-directionally loaded structures and its results constitute an important step towards discerning the most favourable framing system at different seismic performance levels.