Imperial College London

DrPeterStafford

Faculty of EngineeringDepartment of Civil and Environmental Engineering

Reader in Engineering Seismology & Earthquake Engineering
 
 
 
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Contact

 

+44 (0)20 7594 7916p.stafford

 
 
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Assistant

 

Ms Ruth Bello +44 (0)20 7594 6040

 
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Location

 

321Skempton BuildingSouth Kensington Campus

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Summary

 

Publications

Publication Type
Year
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105 results found

Edwards B, Zurek B, van Dedem E, Stafford PJ, Oates S, van Elk J, deMartin B, Bommer JJet al., 2018, Simulations for the development of a ground motion model for induced seismicity in the Groningen gas field, The Netherlands, Bulletin of Earthquake Engineering, ISSN: 1570-761X

© 2018, The Author(s). We present simulations performed for the development of a ground motion model for induced earthquakes in the Groningen gas field. The largest recorded event, with M3.5, occurred in 2012 and, more recently, a M3.4 event in 2018 led to recorded ground accelerations exceeding 0.1 g. As part of an extensive hazard and risk study, it has been necessary to predict ground motions for scenario earthquakes up to M7. In order to achieve this, while accounting for the unique local geology, a range of simulations have been performed using both stochastic and full-waveform finite-difference simulations. Due to frequency limitations and lack of empirical calibration of the latter approach, input simulations for the ground motion model used in the hazard and risk analyses have been performed with a finite-fault stochastic method. However, in parallel, extensive studies using the finite-difference simulations have guided inputs and modelling considerations for these simulations. Three approaches are used: (1) the finite-fault stochastic method, (2) elastic point- and (3) finite-source 3D finite-difference simulations. We present a summary of the methods and their synthesis, including both amplitudes and durations within the context of the hazard and risk model. A unique form of wave-propagation with strong lateral focusing and defocusing is evident in both peak amplitudes and durations. The results clearly demonstrate the need for a locally derived ground motion model and the potential for reduction in aleatory variability in moving toward a path-specific fully non-ergodic model.

JOURNAL ARTICLE

Elghazouli AY, Bompa DV, Xu B, Ruiz-Teran A, Stafford Pet al., 2018, Performance of Rubberised Reinforced Concrete Members under Cyclic Loading, 16th European Conference on Earthquake Engineering (16ECEE)

CONFERENCE PAPER

Elghazouli AY, Bompa DV, Xu B, Ruiz-Teran AM, Stafford PJet al., 2018, Performance of rubberised reinforced concrete members under cyclic loading, ENGINEERING STRUCTURES, Vol: 166, Pages: 526-545, ISSN: 0141-0296

JOURNAL ARTICLE

Lee RL, Bradley BA, Graves RW, Rodriguez-Marek A, Stafford PJet al., 2018, Investigation of Systematic Ground Motion Effects through Ground Motion Simulation of Small-to-Moderate Magnitude Earthquakes, Pages: 494-503, ISSN: 0895-0563

© 2018 American Society of Civil Engineers. This paper presents results of ground motion simulations of small-to-moderate magnitude (3.5≤Mw≤5.0) earthquake events in the Canterbury, New Zealand, region over the past decade, for which centroid moment tensor solutions are available, and an investigation of systematic source and site effects determined via non-ergodic analysis. The simulations are carried out using the Graves and Pitarka methodology with the recently developed 3D Canterbury velocity model. In this study, 144 earthquake ruptures, modelled as point sources, are considered with 1924 quality-assured ground motions recorded at 45 strong motion stations located throughout the Canterbury region. The simulated ground motions, and also empirical prediction equations, are compared with observed ground motions via various intensity measures where the residuals are separated into between-event and within-event components to determine systematic source and site effects. Lastly, the causes of the biases are identified leading to recommendations which could improve the predictive capabilities of the simulation methodology.

CONFERENCE PAPER

Shi Y, Stafford PJ, 2018, Markov chain Monte Carlo ground-motion selection algorithms for conditional intensity measure targets, EARTHQUAKE ENGINEERING & STRUCTURAL DYNAMICS, Vol: 47, Pages: 2468-2489, ISSN: 0098-8847

JOURNAL ARTICLE

Skiada E, Kontoe S, Stafford P, Potts Det al., 2018, Ground surface amplification for canyon topographies excited with bi-directional earthquake records, 16th European Conference on Earthquake Engineering

CONFERENCE PAPER

Stafford PJ, Zurek BD, Ntinalexis M, Bommer JJet al., 2018, Extensions to the Groningen ground-motion model for seismic risk calculations: component-to-component variability and spatial correlation, Bulletin of Earthquake Engineering, ISSN: 1570-761X

© 2018, The Author(s). A bespoke ground-motion model has been developed for the prediction of response spectral accelerations, peak ground velocity and significant duration due to induced earthquakes in the Groningen gas field in the Netherlands. For applications to the calculation of risk to the exposed building stock, extensions to the model are required. The use of the geometric mean horizontal component in the ground-motion predictions and the arbitrary horizontal component for the building fragility functions requires the addition of component-to-component variability. A model for this variability has been developed that both reflects the strong horizontal polarisation of motions observed in many Groningen records obtained at short distances and the fact that the strong polarisation is unlikely to persist at larger magnitudes. The other extension of the model is the spatial correlation of ground motions for the calculation of aggregated risk, which can be approximated through simple rules for sampling the variance within site response zones. Making use of ground-motion recordings from several networks in the field and the results of finite difference waveform simulations, a Groningen-specific spatial correlation model has been developed. The new model also combines results from traditional variogram fitting approaches with a new method to infer spatial correlation lengths from observed variance reduction. The development of the new spatial correlation model relaxes the need to approximate spatial correlation through the sampling of site response, although the results obtained herein suggest that similar results could be obtained using either approach. The preliminary consideration of the numerical waveform modelling results in this study paves the way for significant extensions to be made for the modelling of spatial correlations and the decomposition of apparent spatial variability into systematic and random components within a fully non-ergodic framework

JOURNAL ARTICLE

Ulmer KJ, Upadhyaya S, Green RA, Rodriguez-Marek A, Stafford PJ, Bommer JJ, Van Elk Jet al., 2018, A Critique of b-Values Used for Computing Magnitude Scaling Factors, Pages: 112-121, ISSN: 0895-0563

© 2018 American Society of Civil Engineers. The objective of this paper is to explore the effects of relative density, effective confining stress, and liquefaction initiation criteria on the slope (or b-value) of the cyclic stress ratio versus number of uniform stress cycles to liquefaction curve in log-log space. The b-value is central to the computation of magnitude scaling factors (MSF) used in evaluating liquefaction potential and can be determined from cyclic laboratory tests such as cyclic triaxial (CTRX), cyclic simple shear (CSS), and cyclic torsional (CTS) tests. This paper provides a summary of b-values calculated from published test data representing multiple types of laboratory tests, sands, sample preparation methods, and liquefaction criteria. Trends between b-values and relative density are shown to be more ambiguous than is often assumed. Effective confining stresses and liquefaction criteria are also shown to have an effect on b-values.

CONFERENCE PAPER

Xu B, Bompa DV, Elghazouli AY, Ruiz-Teran AM, Stafford PJet al., 2018, Behaviour of rubberised concrete members in asymmetric shear tests, CONSTRUCTION AND BUILDING MATERIALS, Vol: 159, Pages: 361-375, ISSN: 0950-0618

JOURNAL ARTICLE

Bommer JJ, Dost B, Edwards B, Kruiver PP, Ntinalexis M, Rodriguez-Marek A, Stafford PJ, van Elk Jet al., 2017, Developing a model for the prediction of ground motions due to earthquakes in the Groningen gas field, NETHERLANDS JOURNAL OF GEOSCIENCES-GEOLOGIE EN MIJNBOUW, Vol: 96, Pages: S203-S213, ISSN: 0016-7746

JOURNAL ARTICLE

Bommer JJ, Stafford PJ, Edwards B, Dost B, van Dedem E, Rodriguez-Marek A, Kruiver P, van Elk J, Doornhof D, Ntinalexis Met al., 2017, Framework for a Ground-Motion Model for Induced Seismic Hazard and Risk Analysis in the Groningen Gas Field, The Netherlands, EARTHQUAKE SPECTRA, Vol: 33, Pages: 481-498, ISSN: 8755-2930

JOURNAL ARTICLE

Bompa DV, Elghazouli AY, Xu B, Stafford PJ, Ruiz-Teran AMet al., 2017, Experimental assessment and constitutive modelling of rubberised concrete materials, CONSTRUCTION AND BUILDING MATERIALS, Vol: 137, Pages: 246-260, ISSN: 0950-0618

JOURNAL ARTICLE

Elghazouli AY, Bompa DV, Xu B, Stafford PJ, Ruiz-Teran AMet al., 2017, Inelastic behaviour of RC members incorporating high deformability concrete, Pages: 2399-2406

©Springer International Publishing AG 2018. This paper examines the inelastic behaviour of dissipative zones in structural members incorporating high deformability concrete materials in which mineral aggregates are partly replaced by rubber particles. An experimental study on three large-scale circular reinforced concrete column specimens, subjected to lateral cyclic displacements and co-existing axial loads, is described. The testing arrangement, specimen details, and main observations, are presented and discussed. The test results enable a direct assessment of the strength and ductility characteristics of the specimens. In particular, the study permits an evaluation of the comparative performance of structural members with and without rubber replacement, as well as the influence of external confinement. The results show that, in comparison with conventional reinforced concrete members, structural elements incorporating a significant proportion of aggregate replacement by rubber particles can offer a good balance between bending capacity and ductility, particularly for modest levels of co-existing axial loads. For column members required to sustain substantial gravity loads, favourable performance can be achieved in rubberised concrete members by means of strength enhancement through external confinement such as fibre reinforced sheets. Based on the experimental findings, the main material and response parameters are discussed and their influence on the overall structural behaviour are highlighted.

CONFERENCE PAPER

Sadowski AJ, Rotter JM, Stafford PJ, Reinke T, Ummenhofer Tet al., 2017, On the gradient of the yield plateau in structural carbon steels, JOURNAL OF CONSTRUCTIONAL STEEL RESEARCH, Vol: 130, Pages: 120-130, ISSN: 0143-974X

JOURNAL ARTICLE

Skiada E, Kontoe S, Stafford P, Potts Det al., 2017, Ground motion amplification for canyon topographies with different input motions, 3rd International Conference on Performance-based Design in Earthquake Geotechnical Engineering (PBD-III), Publisher: ISSMGE

It is widelyknown that topographic irregularities influence the surfaceground motions, typically with anenhancement of the response close to convex topographic features,such as ridges and slope crests. Several studies have investigatedthe ground motion at the surface of filled valleys and empty canyons, focusingmainly onthe geometry and the soil characteristics rather than the input excitation.Further investigation of the impact of the input excitation to the ground surface response is needed in order to modifyexisting ground motion prediction models to account for topographic effects. The response of canyons has been previously examined; but mainly focusing on simple wavelet input. This paper considers a fully weathered canyon (i.e., without any in-fill material) aiming to investigate the influence of the input excitationon the surface ground motion through a parametric time-domain finite element (FE) study. A two-dimensional plane-strain model of an idealisedcanyon is considered for vertically propagating SV waves, using both wavelets and recorded earthquakes as input excitation. The model consists of two step-like slopes with slope height (H), in a homogeneous linear elastic soil layer overlying rigid bedrock. Topographic aggravation is presented for several points along the canyon ground surface aiming to derive a pattern of its distribution considering input excitation with different characteristics.

CONFERENCE PAPER

Skiada E, Kontoe S, Stafford P, Potts Det al., 2017, Canyon topography effects on ground motion, 16th World Conference on Earthquake Engineering, Publisher: WCEE

It is broadly known that topographic irregularities effect ground motions, with a particular enhancement of the ground response close to convex topographic features such as ridges and slope crests. Although there are many studies investigatingthe ground motion in the vicinity of slope crests, the response at the toe has not been studied in great detail, as the toe ground motion is normally considered to be smaller than that of the crest. However, for canyon topographies further investigation of the ground motion at the slope toe, where a more complicated response is expected due to the interaction of the canyon sides, is needed. The response of semi-circular and semi-elliptical canyons has been previously examined; butmainly focusing on valleys filled with soft materials. This paper considers a fully weathered canyon (i.e., without any in-fill material) aiming to investigate the influence of a canyon’s width on the surface ground motion through a parametric time-domain finite element (FE) study. A two-dimensional plane-strain model of an idealised canyon is considered for vertically propagating SV waves, using wavelets as input excitation. The model consists of two step-like slopes with slope height (H), in a homogeneous linear elastic soil layer overlying rigid bedrock. The analyses focus first on the canyon slope areas, where the ground motion is altered depending upon the proximity to the topographic irregularity, identifying the main parameters that effect the response. Results are also presented for several points along the canyon ground surface showing that the distribution of topographic aggravation varies significantly with canyon width.

CONFERENCE PAPER

Stafford PJ, 2017, Interfrequency Correlations among Fourier Spectral Ordinates and Implications for Stochastic Ground-Motion Simulation, BULLETIN OF THE SEISMOLOGICAL SOCIETY OF AMERICA, Vol: 107, Pages: 2774-2791, ISSN: 0037-1106

JOURNAL ARTICLE

Stafford PJ, Rodriguez-Marek A, Edwards B, Kruiver PP, Bommer JJet al., 2017, Scenario Dependence of Linear Site-Effect Factors for Short-Period Response Spectral Ordinates, BULLETIN OF THE SEISMOLOGICAL SOCIETY OF AMERICA, Vol: 107, Pages: 2859-2872, ISSN: 0037-1106

JOURNAL ARTICLE

Teslim-Balogun A, Málaga-Chuquitaype C, Stafford PJ, 2017, Assessment of efficiency of intensity measures for performance-based travelling fire design, Pages: 1652-1658

© 2018 Ingenta. Current fire design methods assume a uniform temperature distribution in building compartments, which is unrealistic for large compartments. In contrast, travelling fire models account for the non-uniform distribution of temperatures in large compartments. However, an adequate fire intensity measure (IM) is important to properly define the severity of the fire, especially within the context of a performance-based design. This paper presents an assessment of IM as related to various engineering demand parameters (EDP) in order to establish the most efficient IM for performance-based travelling fire design. Non-linear analyses were carried out on generalised steel frame models to determine their structural response. Regression analysis was also carried out and it was observed that the length of fire was the most efficient IM in the range of EDPs considered. The results will be useful in the performance-based fire design of steel structures.

CONFERENCE PAPER

Bommer JJ, Dost B, Edwards B, Stafford PJ, van Elk J, Doornhof D, Ntinalexis Met al., 2016, Developing an Application-Specific Ground-Motion Model for Induced Seismicity, BULLETIN OF THE SEISMOLOGICAL SOCIETY OF AMERICA, Vol: 106, Pages: 158-173, ISSN: 0037-1106

JOURNAL ARTICLE

Bora SS, Scherbaum F, Kuehn N, Stafford Pet al., 2016, On the Relationship between Fourier and Response Spectra: Implications for the Adjustment of Empirical Ground-Motion Prediction Equations (GMPEs), BULLETIN OF THE SEISMOLOGICAL SOCIETY OF AMERICA, Vol: 106, Pages: 1235-1253, ISSN: 0037-1106

JOURNAL ARTICLE

Fox MJ, Stafford PJ, Sullivan TJ, 2016, Seismic hazard disaggregation in performance-based earthquake engineering: occurrence or exceedance?, EARTHQUAKE ENGINEERING & STRUCTURAL DYNAMICS, Vol: 45, Pages: 835-842, ISSN: 0098-8847

JOURNAL ARTICLE

Skiada E, Kontoe S, Stafford P, Potts DMet al., 2016, Canyon Depth Effect on Surface Ground Motion, 1st International Conference on Natural Hazards & Infrastructure

Topographic effects are rarely accounted for in seismic design codes, despite their potential to significantly modify surfaceground motions. This paper investigates the influence of a canyon’s slope height on the surface ground motion through aparametric time-domain Finite Element (FE) study. A two-dimensional plane-strain model of an idealised canyon isconsidered for vertically propagating SV waves, using wavelets as input excitation. The model consists of two step-likeslopes with slope height (H), in a homogeneous linear elastic soil layer overlying rigid bedrock. The analysis results showthat the distribution of topographic aggravation at the ground surface varies significantly with normalized canyon depthover the input wavelength (H/λ) and it does not necessarily reach a maximum at a specific H/λ ratio, as has been suggestedin previous studies. The validity of this conclusion is investigated for different depths to bedrock and soil layer properties.

CONFERENCE PAPER

Stafford PJ, Sullivan TJ, Pennucci D, 2016, Empirical Correlation between. Inelastic and Elastic Spectral Displacement Demands, EARTHQUAKE SPECTRA, Vol: 32, Pages: 1419-1448, ISSN: 8755-2930

JOURNAL ARTICLE

Bommer JJ, Coppersmith KJ, Coppersmith RT, Hanson KL, Mangongolo A, Neveling J, Rathje EM, Rodriguez-Marek A, Scherbaum F, Shelembe R, Stafford PJ, Strasser FOet 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

JOURNAL ARTICLE

Bora SS, Scherbaum F, Kuehn N, Stafford P, Edwards Bet 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: 0037-1106

JOURNAL ARTICLE

Molkenthin C, Scherbaum F, Griewank A, Kuehn N, Stafford PJ, Leovey Het 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

JOURNAL ARTICLE

Stafford PJ, 2015, Variability and Uncertainty in Empirical Ground-Motion Prediction for Probabilistic Hazard and Risk Analyses, PERSPECTIVES ON EUROPEAN EARTHQUAKE ENGINEERING AND SEISMOLOGY, VOL 2, Vol: 39, Pages: 97-128

JOURNAL ARTICLE

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

JOURNAL ARTICLE

Stewart JP, Douglas J, Javanbarg M, Bozorgnia Y, Abrahamson NA, Boore DM, Campbell KW, Delavaud E, Erdik M, Stafford PJet al., 2015, Selection of Ground Motion Prediction Equations for the Global Earthquake Model, EARTHQUAKE SPECTRA, Vol: 31, Pages: 19-45, ISSN: 8755-2930

JOURNAL ARTICLE

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