Publications
140 results found
Bommer JJ, Dost B, Edwards B, et al., 2015, Developing an Application-Specific Ground-Motion Model for Induced Seismicity, Bulletin of the Seismological Society of America, Vol: 106, Pages: 158-173, ISSN: 1943-3573
A key element of quantifying both the hazard and risk due to inducedearthquakes is a suite of appropriate ground-motion prediction equations (GMPEs) thatencompass the possible shaking levels due to such events. Induced earthquakes arelikely to be of smaller magnitude and shallower focal depth than the tectonic earthquakesfor which most GMPEs are derived. Furthermore, whereas GMPEs formoderate-to-large magnitude earthquakes are usually derived to be transportable todifferent locations and applications, taking advantage of the limited regional dependenceobserved for such events, the characteristics of induced earthquakes warrant thedevelopment of application-specific models. A preliminary ground-motion model forinduced seismicity in the Groningen gas field in The Netherlands is presented as anillustration of a possible approach to the development of these equations. The GMPE iscalibrated to local recordings of small-magnitude events and captures the epistemicuncertainty in the extrapolation to larger magnitude considered in the assessment ofthe resulting hazard and risk.
Fox MJ, Stafford PJ, Sullivan TJ, 2015, Seismic hazard disaggregation in performance-based earthquake engineering: occurrence or exceedance?, Earthquake Engineering & Structural Dynamics, Vol: 45, Pages: 835-842, ISSN: 1096-9845
Seismic hazard disaggregation is commonly used as an aid in ground-motion selection for the seismic response analysis of structures. This short communication investigates two different approaches to disaggregation related to the exceedance and occurrence of a particular intensity. The impact the different approaches might have on a subsequent structural analysis at a given intensity is explored through the calculation of conditional spectra. It is found that the exceedance approach results in conditional spectra that will be conservative when used as targets for ground-motion selection. It is however argued that the use of the occurrence disaggregation is more consistent with the objectives of seismic response analyses in the context of performance-based earthquake engineering.
Stafford PJ, 2015, Extension of the Random-Effects Regression Algorithm to Account for the Effects of Nonlinear Site Response, Bulletin of the Seismological Society of America, Vol: 105, Pages: 3196-3202, ISSN: 0037-1106
The random-effects regression algorithm, made popular within engineeringseismology by Abrahamson and Youngs (1992), is arguably the most commonly usedapproach for developing empirical ground-motion models. The original presentation ofthis algorithm relates to the most simple application of a far more general mixed-effectsmodel formulation. In recent years, it has become increasingly common to incorporatenonlinear site response effects within empirical, or semi-empirical, ground-motion models,but the original random-effects algorithm does not apply to cases in which the randomeffects enter the model in a nonlinear manner. This article presents a more generalalgorithm for fitting mixed-effects models that can accommodate nonlinear site effects(among other effects). The presented algorithm deliberately mirrors that of Abrahamsonand Youngs (1992) but allows for the treatment of far more elaborate variance structures.
Bora SS, Scherbaum F, Kuehn N, et al., 2015, Development of a Response Spectral Ground-Motion Prediction Equation (GMPE) for Seismic-Hazard Analysis from Empirical Fourier Spectral and Duration Models, Bulletin of the Seismological Society of America, Vol: 105, Pages: 2192-2218, ISSN: 1943-3573
Empirical ground-motion prediction equations (GMPEs) require adjustmentto make them appropriate for site-specific scenarios. However, the process ofmaking such adjustments remains a challenge. This article presents a holistic frameworkfor the development of a response spectral GMPE that is easily adjustable todifferent seismological conditions and does not suffer from the practical problemsassociated with adjustments in the response spectral domain. The approach for developinga response spectral GMPE is unique, because it combines the predictions ofempirical models for the two model components that characterize the spectral andtemporal behavior of the ground motion. Essentially, as described in its initial formby Bora et al. (2014), the approach consists of an empirical model for the Fourieramplitude spectrum (FAS) and a model for the ground-motion duration. These twocomponents are combined within the random vibration theory framework to obtainpredictions of response spectral ordinates. In addition, FAS corresponding to individualacceleration records are extrapolated beyond the useable frequencies using thestochastic FAS model, obtained by inversion as described in Edwards and Fäh (2013a).To that end, a (oscillator) frequency-dependent duration model, consistent with theempirical FAS model, is also derived. This makes it possible to generate a responsespectral model that is easily adjustable to different sets of seismological parameters,such as the stress parameter Δσ, quality factor Q, and kappa κ0. The dataset used inBora et al. (2014), a subset of the RESORCE-2012 database, is considered for thepresent analysis. Based upon the range of the predictor variables in the selected dataset,the present response spectral GMPE should be considered applicable over the magnituderange of 4 ≤ Mw ≤ 7:6 at distances ≤200 km.
Molkenthin C, Scherbaum F, Griewank A, et al., 2015, Sensitivity of Probabilistic Seismic Hazard Obtained by Algorithmic Differentiation: A Feasibility Study, Bulletin of the Seismological Society of America, Vol: 105, Pages: 1810-1822, ISSN: 0037-1106
Probabilistic seismic-hazard analysis (PSHA) is the current tool of thetrade used to estimate the future seismic demands at a site of interest. A modern PSHArepresents a complex framework that combines different models with numerous inputs.It is important to understand and assess the impact of these inputs on the modeloutput in a quantitative way. Sensitivity analysis is a valuable tool for quantifyingchanges of a model output as inputs are perturbed, identifying critical input parameters,and obtaining insight about the model behavior. Differential sensitivity analysisrelies on calculating first-order partial derivatives of the model output with respect toits inputs; however, obtaining the derivatives of complex models can be challenging.In this study, we show how differential sensitivity analysis of a complex frameworksuch as PSHA can be carried out using algorithmic/automatic differentiation(AD). AD has already been successfully applied for sensitivity analyses in variousdomains such as oceanography and aerodynamics. First, we demonstrate the feasibilityof the AD methodology by comparing AD-derived sensitivities with analyticallyderived sensitivities for a basic case of PSHA using a simple ground-motion predictionequation. Second, we derive sensitivities via AD for a more complex PSHA studyusing a stochastic simulation approach for the prediction of ground motions. The presentedapproach is general enough to accommodate more advanced PSHA studies ofgreater complexity.
Bommer JJ, Coppersmith KJ, Coppersmith RT, et al., 2015, A SSHAC Level 3 Probabilistic Seismic Hazard Analysis for a New-Build Nuclear Site in South Africa, EARTHQUAKE SPECTRA, Vol: 31, Pages: 661-698, ISSN: 8755-2930
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- Citations: 66
Stewart JP, Douglas J, Javanbarg M, et al., 2015, Selection of Ground Motion Prediction Equations for the Global Earthquake Model, EARTHQUAKE SPECTRA, Vol: 31, Pages: 19-45, ISSN: 8755-2930
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- Citations: 103
Stafford PJ, 2015, Variability and uncertainty in empirical ground-motion prediction for probabilistic hazard and risk analyses, Geotechnical, Geological and Earthquake Engineering, Vol: 39, Pages: 97-128, ISSN: 1573-6059
© The Author(s) 2015. The terms aleatory variability and epistemic uncertainty mean different things to people who routinely use them within the fields of seismic hazard and risk analysis. This state is not helped by the repetition of loosely framed generic definitions that actually inaccurate. The present paper takes a closer look at the components of total uncertainty that contribute to ground-motion modelling in hazard and risk applications. The sources and nature of uncertainty are discussed and it is shown that the common approach to deciding what should be included within hazard and risk integrals and what should be pushed into logic tree formulations warrants reconsideration. In addition, it is shown that current approaches to the generation of random fields of ground motions for spatial risk analyses are incorrect and a more appropriate framework is presented.
ITOI T, STAFFORD PJ, KANEKO M, et al., 2014, 21146 Stochastic Ground Motion Simulation for Probabilistic Seismic Risk Assessment, Summaries of technical papers of annual meeting, Vol: 2014, Pages: 291-292, ISSN: 1883-9363
Camara A, Nguyen K, Ruiz-Teran AM, et al., 2014, Comfort in Slender Bridges Subjected to Traffic Loading and Hammering Effects, 37th International IABSE Symposium
Molkenthin C, Scherbaum F, Griewank A, et al., 2014, A Study of the Sensitivity of Response Spectral Amplitudes on Seismological Parameters Using Algorithmic Differentiation, Bulletin of the Seismological Society of America, Vol: 104, Pages: 2240-2252, ISSN: 0037-1106
Response spectra are of fundamental importance in earthquake engineeringand represent a standard measure in seismic design for the assessment of structuralperformance. However, unlike Fourier spectral amplitudes, the relationship of responsespectral amplitudes to seismological source, path, and site characteristics is notimmediately obvious and might even be considered counterintuitive for high oscillatorfrequencies. The understanding of this relationship is nevertheless important forseismic-hazard analysis. The purpose of the present study is to comprehensively characterizethe variation of response spectral amplitudes due to perturbations of the causativeseismological parameters. This is done by calculating the absolute parametersensitivities (sensitivity coefficients) defined as the partial derivatives of the modeloutput with respect to its input parameters. To derive sensitivities, we apply algorithmicdifferentiation (AD). This powerful approach is extensively used for sensitivity analysisof complex models in meteorology or aerodynamics. To the best of our knowledge, ADhas not been explored yet in the seismic-hazard context. Within the present study, ADwas successfully implemented for a proven and extensively applied simulation programfor response spectra (Stochastic Method SIMulation [SMSIM]) using the TAPENADEAD tool. We assess the effects and importance of input parameter perturbations on theshape of response spectra for different regional stochastic models in a quantitative way.Additionally, we perform sensitivity analysis regarding adjustment issues of groundmotionprediction equations.
Rodriguez-Marek A, Rathje EM, Bommer JJ, et al., 2014, Application of single-station sigma and site-response characterization in a probabilistic seismic-hazard analysis for a new nuclear site, Bulletin of the Seismological Society of America, Vol: 104, Pages: 1601-1619, ISSN: 0037-1106
Aleatory variability in ground‐motion prediction, represented by the standard deviation (sigma) of a ground‐motion prediction equation, exerts a very strong influence on the results of probabilistic seismic‐hazard analysis (PSHA). This is especially so at the low annual exceedance frequencies considered for nuclear facilities; in these cases, even small reductions in sigma can have a marked effect on the hazard estimates. Proper separation and quantification of aleatory variability and epistemic uncertainty can lead to defensible reductions in sigma. One such approach is the single‐station sigma concept, which removes that part of sigma corresponding to repeatable site‐specific effects. However, the site‐to‐site component must then be constrained by site‐specific measurements or else modeled as epistemic uncertainty and incorporated into the modeling of site effects. The practical application of the single‐station sigma concept, including the characterization of the dynamic properties of the site and the incorporation of site‐response effects into the hazard calculations, is illustrated for a PSHA conducted at a rock site under consideration for the potential construction of a nuclear power plant.
Modica A, Stafford PJ, 2014, Vector fragility surfaces for reinforced concrete frames in Europe, BULLETIN OF EARTHQUAKE ENGINEERING, Vol: 12, Pages: 1725-1753, ISSN: 1570-761X
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- Citations: 45
Stafford PJ, 2014, Source-Scaling Relationships for the Simulation of Rupture Geometry within Probabilistic Seismic-Hazard Analysis, BULLETIN OF THE SEISMOLOGICAL SOCIETY OF AMERICA, Vol: 104, Pages: 1620-1635, ISSN: 0037-1106
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- Citations: 12
Bompa DV, Ruiz-Teran AM, Stafford PJ, et al., 2014, Innovative Reuse of all Tyre Components in Concrete: Analytical study of deformable elements, Publisher: Imperial College London
Rathje EM, Wang Y, Stafford PJ, et al., 2014, Probabilistic assessment of the seismic performance of earth slopes, BULLETIN OF EARTHQUAKE ENGINEERING, Vol: 12, Pages: 1071-1090, ISSN: 1570-761X
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- Citations: 49
Stafford PJ, 2014, Crossed and nested mixed‐effects approaches for enhanced model development and removal of the ergodic assumption in empirical ground‐motion models, Bulletin of the Seismological Society of America, Vol: 104, Pages: 702-719, ISSN: 0037-1106
Limitations in the size of strong‐motion databases that are used for the development of empirical ground‐motion models has necessitated the use of the ergodic assumption. Several recent efforts, using different databases from around the world, have been made to estimate the single‐station standard deviation of spectral accelerations. The computed estimates have been found to be very stable globally, despite the various researchers using quite different approaches. This paper demonstrates that the multistage procedures that have been adopted by previous researchers can be replaced by the use of more elaborate mixed‐effects regression analyses. Additionally, the traditional use of additive random effects to capture source, path, and site effects is shown to have conceptual shortcomings that are addressed through the use of a more complex treatment of mixed‐effects models. A model for the residual variance (within‐event single‐station variance) is presented using these advanced approaches.
Camara A, Nguyen K, Ruiz-Teran AM, et al., 2014, Serviceability limit state of vibrations in under-deck cable-stayed bridges accounting for vehicle-structure interaction, Engineering Structures, Vol: 61, Pages: 61-72, ISSN: 0141-0296
Verification of the serviceability limit state of vibrations due to traffic live loads can be neglected in conventional types of concrete road bridges but becomes critical in the design of slender structures like under-deck cable-stayed bridges. The novelty of the work presented in this article is that an innovative vehicle-bridge interaction model is employed, in which realistic wheel dimensions of heavy trucks, road roughness profiles and the cross slope of the road are considered in nonlinear dynamic analyses of detailed three-dimensional finite element models. An extensive parametric study is conducted to explore the influence of the bridge parameters such as the longitudinal and transverse cable arrangement and the support conditions, in addition to the load modelling, road quality, the wheel size, the transverse road slope and the vehicle position and speed on the response of under-deck cable-stayed bridges. It has been observed that the vibrations perceived by pedestrians can be effectively reduced by concentrating the cable-system below the deck at the bridge centreline. The Fourier amplitude spectrum of the acceleration at critical positions along the deck proved that the response of under-deck cable-stayed bridges is not dominated only by contributions at the fundamental mode and, consequently, the conventional deflection-based methods are not valid to assess the users comfort. Instead, Vehicle-Bridge Interaction analyses are recommended for detailed design, considering the wheel dimensions if the pavement quality is bad and/or if the wheel radius is large. Finally, we verify through multiple approaches that the comfort of pedestrian users is more critical than that of vehicle users. However, the comfort of vehicle users is shown to be significantly affected when the road quality is poor.
Douglas J, Akkar S, Ameri G, et al., 2014, Comparisons among the five ground-motion models developed using RESORCE for the prediction of response spectral accelerations due to earthquakes in Europe and the Middle East, BULLETIN OF EARTHQUAKE ENGINEERING, Vol: 12, Pages: 341-358, ISSN: 1570-761X
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- Citations: 60
Elghazouli AY, Kumar M, Stafford PJ, 2014, Prediction and optimisation of seismic drift demands incorporating ground motion frequency content, BULLETIN OF EARTHQUAKE ENGINEERING, Vol: 12, Pages: 255-276, ISSN: 1570-761X
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- Citations: 13
Bora SS, Scherbaum F, Kuehn N, et al., 2014, Fourier spectral- and duration models for the generation of response spectra adjustable to different source-, propagation-, and site conditions, BULLETIN OF EARTHQUAKE ENGINEERING, Vol: 12, Pages: 467-493, ISSN: 1570-761X
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- Citations: 63
Camara A, Ruiz-Teran AM, Stafford PJ, 2013, Structural behaviour and design criteria of under-deck cable-stayed bridges subjected to seismic action, Earthquake Engineering and Structural Dynamics, Vol: 42, Pages: 891-912, ISSN: 0098-8847
Under‐deck cable‐stayed bridges are very effective structural systems for which the strong contribution of the stay cables under live loading allows for the design of very slender decks for persistent and transient loading scenarios. Their behaviour when subjected to seismic excitation is investigated herein and a set of design criteria are presented that relate to the type and arrangement of bearings, the number and configuration of struts, and the transverse distribution of stay cables. The nonlinear behaviour of these bridges when subject to both near‐field and far‐field accelerograms has been thoroughly investigated through the use of incremental dynamic analyses. An intensity measure that reflects the pertinent contributions to response when several vibration modes are activated was proposed and is shown to be effective for the analysis of this structural type. The under‐deck cable‐stay system contributes in a very positive manner to reducing the response when the bridges are subject to very strong seismic excitation. For such scenarios, the reduction in the stiffness of the deck because of crack formation, when prestressed concrete decks are used, mobilises the cable system and enhances the overall performance of the system. Sets of natural accelerograms that are compliant with the prescriptions of Eurocode 8 were also applied to propose a set of design criteria for this bridge type in areas prone to earthquakes. Particular attention is given to outlining the optimal strategies for the deployment of bearings.
Boehm M, Collen B, Baillie JEM, et al., 2013, The conservation status of the world's reptiles, BIOLOGICAL CONSERVATION, Vol: 157, Pages: 372-385, ISSN: 0006-3207
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- Citations: 599
Dorra EM, Stafford PJ, Elghazouli AY, 2013, Earthquake loss estimation for Greater Cairo and the national economic implications, Bulletin of Earthquake Engineering, ISSN: 1570-761X
Kumar M, Stafford PJ, Elghazouli AY, 2013, Seismic shear demands in multi-storey steel frames designed to Eurocode 8, Engineering Structures, Vol: 52, Pages: 69-87
Stafford PJ, 2013, Uncertainties in ground motion prediction in probabilistic seismic hazard analysis (PSHA) of civil infrastructure, Handbook of seismic risk analysis and management of civil infrastructure systems, Editors: Tesfamariam, Goda, Publisher: Woodhead Publishing
Ground-motion prediction equations are a critical element of any probabilistic seismic hazard or risk analysis. The total uncertainty in a typical risk analysis is commonly dominated by the uncertainty associated with ground-motion prediction. Within the fields of Engineering Seismology and Earthquake Engineering a lot of attention has been paid to identifying intensity measures that are efficient for predicting response measures, and this efficiency is of great relevance for seismic risk analysis and the development of well-constrained fragility curves. However, the epistemic uncertainties associated with ground motions are still not adequately dealt with, and such uncertainties contribute to the overall predictability of an intensity measure, and hence of an engineering demand parameter. The present chapter provides an overview of the uncertainties that exist within ground-motion prediction and emphasises some of the main components that are not dealt with in a robust manner in current risk analyses. The chapter also highlights recent advancements as well as likely future trends associated with the treatment of uncertainty in ground-motion prediction, with a particular emphasis upon how such uncertainties influence the development of ground-motion models.
Kumar K, Stafford PJ, Elghazouli AY, 2013, Influence of ground motion characteristics on drift demands in steelmoment frames designed to Eurocode 8, Engineering Structures, Vol: 52, Pages: 502-517
Bommer JJ, Stafford PJ, 2012, Estimating ground motion levels in earthquake damage investigations: a framework for forensic engineering seismology, International Journal of Forensic Engineering, Vol: 1, Pages: 3-20
Stafford PJ, 2012, Evaluation of structural performance in the immediate aftermath of an earthquake: a case study of the 2011 Christchurch earthquake, International Journal of Forensic Engineering, Vol: 1, Pages: 58-77
Lessi-Cheimarios A, Kontoe S, Stafford PJ, 2012, Comparison of the total uncertainty associated with alternative approaches to site response analysis, 15th World Conference on Earthquake Engineering
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