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. [DOI: 10.1193/1.3651317

Vector-Valued Probabilistic Seismic Hazard Assessment for the Effects of Vertical Ground Motions on the Seismic Response of Highway Bridges

The vertical ground motion component is disregarded in the design of ordinary highway bridges in California, except for the bridges located in high seismic zones (sites with design horizontal peak ground acceleration greater than 0.6 g). The influence of vertical ground motion on the seismic response of single-bent, two-span highway bridges designed according to Caltrans Seismic Design Code (SDC-2006) is evaluated. A probabilistic seismic hazard framework is used to address the probability of exceeding the elastic capacity for various structural parameters when the vertical component is included. Negative mid-span moment demand is found to be the structural parameter that is most sensitive to vertical accelerations. A series of hazard curves for negative mid-span moment are developed for a suite of sites in Northern California. The annual probability of exceeding the elastic capacity of the negative mid-span moment is as large as 0.01 for the sites close to active faults when the vertical component is included. Simplified approaches based on the distance to major faults or the median design peak acceleration show that there is a large chance (0.4 to 0.65) of exceeding the elastic limit if the current 0.6 g threshold is used for the consideration of vertical ground motions for ordinary highway bridges. The results of this study provide the technical basis for consideration of a revision of the 0.6 g threshold. [DOI: 10.1193/1.3464548

Preliminary ground motion model for subduction earthquakes based on NGA-Sub Japan database

This manuscript presents the preliminary ground motion model (GMM) for the subduction zone earthquakes based on the database collected from Japanese earthquakes within the frame of PEER Next Generation Attenuation: Subduction (NGA-Sub) project. The dataset used in the regression includes 5730 recordings from 56 subduction interface earthquakes with 5.16≤Mw≤9.13 and 4503 recordings from 27 intra-slab events with 5.2≤Mw≤8.32. Functional form of the model accommodates the differences in the depth and distance scaling for interface and intra-slab earthquakes. Both linear and non-linear site amplification factors and depth to the bedrock effects are incorporated in the model: linear site coefficient and depth to the bedrock scaling are estimated in regression; whereas the non-linear site amplification factors used in [1] are adopted. Magnitude dependent distance scaling and large magnitude scaling of the preliminary model is currently set equal to the BCHydro GMM [2], but will be re-evaluated using the global dataset of subduction events in the future. Median ground motions estimated by the preliminary model is approximately 20% higher than the median values given by the BCHydro GMM at the short period and 10% lower at the long periods

Turkey-Adjusted NGA-W1 Horizontal Ground Motion Prediction Models

The objective of this paper is to evaluate the differences between the Next Generation Attenuation: West-1 (NGA-W1) ground motion prediction models (GMPEs) and the Turkish strong ground motion data set and to modify the required pieces of the NGA-W1 models for applicability in Turkey. A comparison data set is compiled by including strong motions from earthquakes that occurred in Turkey and earthquake metadata of ground motions consistent with the NGA-W1 database. Random-effects regression is employed and plots of the residuals are used to evaluate the differences in magnitude, distance, and site amplification scaling. Incompatibilities between the NGA-W1 GMPEs and Turkish data set in small-to-moderate magnitude, large distance, and site effects scaling are encountered. The NGA-W1 GMPEs are modified for the misfit between the actual ground motions and the model predictions using adjustments functions. Turkey-adjusted NGA-W1 models are compatible with the regional strong ground motion characteristics and preserve the well-constrained features of the global models

Experimental evaluation of geomembrane/geotextile interface as base isolating system

The objective of this study is to evaluate the effect of the geomembrane/geotextile interface on the seismic response of small-to-moderate height structures. Three building models with first-mode natural frequencies changing between 2-4 Hz (representing two, three and four storey structures) were tested with and without the addition of geomembrane/geotextile interface using the shaking table test setup by employing harmonic and modified/ scaled ground motions. Experimental results showed that the geomembrane/geotextile interface significantly reduced the floor accelerations, especially at moderate-to-high ground shaking levels. The interaction between the first-mode natural frequency of the model and the predominant frequency of the input motion is significant, and the interface is most effective when these two frequencies are close to each other. This effect is more clearly seen when the harmonic motions are employed during the tests compared to the modified/scaled ground motions. The results of the tests with modified/ scaled ground motions were used to evaluate the efficiency of the composite liner system in reducing the spectral accelerations in the frequency domain. The results presented here document that the geomembrane/geotextile interface reduces the floor accelerations in a certain frequency range and underline the potential of this interface to be used as a base isolation material

Ground Motion Prediction Equations for the Vertical Ground Motion Component Based on the NGA-W2 Database

Empirical ground motion models for the vertical component from shallow crustal earthquakes in active tectonic regions are derived using the PEER NGA-West2 database. The model is applicable to magnitudes 3.0-8.0, distances of 0-300 km, and spectral periods of 0-10 s. The model input parameters are the same as used by Abrahamson et al. (2014) except that the nonlinear site response and depth to bedrock effects are evaluated but found to be insignificant. Regional differences in large distance attenuation and site amplification scaling between California, Japan, China, Taiwan, Italy, and the Middle East are included. Scaling for the hanging-wall effect is incorporated using the constraints from numerical simulations by Donahue and Abrahamson (2014). The standard deviation is magnitude dependent with smaller magnitudes leading to larger standard deviations at short periods but smaller standard deviations at long periods. The vertical ground motion model developed in this study can be paired with the horizontal component model proposed by Abrahamson et al. (2014) to produce a V/H ratio. For applications where the horizontal spectrum is derived from the weighted average of several horizontal ground motion models, a V/H model derived directly from the V/H data (such as Giilerce and Abrahamson 2011) should be preferred

Turkey-Adjusted NGA-W1 Horizontal Ground Motion Prediction Models

The objective of this paper is to evaluate the differences between the Next Generation Attenuation: West-1 (NGA-W1) ground motion prediction models (GMPEs) and the Turkish strong ground motion data set and to modify the required pieces of the NGA-W1 models for applicability in Turkey. A comparison data set is compiled by including strong motions from earthquakes that occurred in Turkey and earthquake metadata of ground motions consistent with the NGA-W1 database. Random-effects regression is employed and plots of the residuals are used to evaluate the differences in magnitude, distance, and site amplification scaling. Incompatibilities between the NGA-W1 GMPEs and Turkish data set in small-to-moderate magnitude, large distance, and site effects scaling are encountered. The NGA-W1 GMPEs are modified for the misfit between the actual ground motions and the model predictions using adjustments functions. Turkey-adjusted NGA-W1 models are compatible with the regional strong ground motion characteristics and preserve the well-constrained features of the global models

Seismic demand models for probabilistic risk analysis of near fault vertical ground motion effects on ordinary highway bridges

The influence of vertical ground motions on the seismic response of highway bridges is not very well understood. Recent studies suggest that vertical ground motions can substantially increase force and moment demands on bridge columns and girders and cannot be overlooked in seismic design of bridge structures. For an evaluation of vertical ground motion effects on the response of single-bent two-span highway bridges, a systematic study combining the critical engineering demand parameters (EDPs) and ground motion intensity measures (IMs) is required. Results of a parametric study examining a range of highway bridge configurations subjected to selected sets of horizontal and vertical ground motions are used to determine the structural parameters that are significantly amplified by the vertical excitations. The amplification in these parameters is modeled using simple equations that are functions of horizontal and vertical spectral accelerations at the corresponding horizontal and vertical fundamental periods of the bridge. This paper describes the derivation of seismic demand models developed for typical highway overcrossings by incorporating critical EDPs and combined effects of horizontal and vertical ground motion IMs depending on the type of the parameter and the period of the structure. These models may be used individually as risk-based design tools to determine the probability of exceeding the critical levels of EDP for pre-determined levels of ground shaking or may be included explicitly in probabilistic seismic risk assessments. Copyright (c) 2011 John Wiley & Sons, Ltd