Publications
140 results found
Stafford PJ, Zurek BD, Ntinalexis M, et al., 2019, Extensions to the Groningen ground-motion model for seismic risk calculations: component-to-component variability and spatial correlation, Bulletin of Earthquake Engineering, Vol: 17, Pages: 4417-4439, ISSN: 1573-1456
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 .
Dong W, Stafford P, Ruiz-Teran A, 2019, Inverse form-finding for tensegrity structures, Computers and Structures, Vol: 215, Pages: 27-42, ISSN: 0045-7949
In this study we examine the topic of inverse form-finding, also referred to as topology finding, for tensegrity structures. Specifically, the problem addressed is given the specification of final nodal positions for a tensegrity, we seek to find appropriate connectivities, or topologies, that satisfy stability and connectivity constraints. Two new algorithms are presented in the paper. The first may be applied for generating prestress-stable tensegrity structures, while the second can be used to generate super-stable tensegrities. Numerical examples for both 2D and 3D tensegrities are provided to demonstrate that these new algorithms can produce desirable structures with nodal positions being the only prescribed piece of information. We also show that inverse form-finding of a specific Class k tensegrity can be formulated into a graph factorization problem. This is the first time that both the stability property and class can be specified among the few existing inverse form-finding methods. These new methods facilitate the design process in which a desired nodal geometry is prescribed, and viable structural configurations consistent with this geometry can be obtained.
Stafford PJ, 2019, Continuous integration of data into ground-motion models using Bayesian updating, Journal of Seismology, Vol: 23, Pages: 39-57, ISSN: 1383-4649
The development of empirically constrained ground-motion models has historically followed a cyclic process in which every few years, existing models are updated to reflect new data and knowledge that has become available. Ground-motion developers make use of their prior knowledge to identify appropriate functional forms for the models, but the actual regression analysis and model calibration is effectively performed from a fresh start with each update. With the anticipated increase in data availability coming in the future, this traditional approach will become increasingly cumbersome. The present article presents a framework in which Bayesian updating is used to continuously update existing ground-motion models as new data becomes available. This new approach is shown to provide similar results to the more traditional approach, but is far less data-intensive and will scale well into the future. The approach is demonstrated through an example in which an initial regression analysis is conducted on a portion of the NGA-West2 dataset representative of the information available in 1995. Model parameters, variance components and crossed random effects are then updated with data from every other event in the NGA-West2 dataset and the results from Bayesian updating and traditional regression analysis are compared. The two methods are shown to provide similar results, but the advantages of the Bayesian approach are subsequently highlighted. For the first time, the article also demonstrates how prior distributions of model parameters can be obtained for existing ground-motion models that have been derived using both classical, as well as more elaborate multi-stage, procedures with and without constrained parameters.
Georgiadis K, Ruiz-Teran AM, Stafford PJ, 2019, Investigation of under-deck cable-stayed footbridges under dynamic pedestrian loading, Pages: 1655-1662
Under-deck cable-stayed (UDCS) footbridges are slender structures that promote the axial behaviour. This allows designers to take advantage of the entire sectional areas and reduce the required construction materials. Besides their high structural efficiency and sustainability, they also possess a number of other advantages such as multiple construction possibilities and strong aesthetic characteristics, therefore becoming an attractive solution in urban infrastructure. However, due to their slenderness, they are more prone to vibrations. Recent closures of footbridges of this typology, indicate that fundamental aspects of their structural response still remained unclear. This paper presents a set of example bridges built with this typology and a detailed investigation of a benchmark case under the dynamic action of pedestrians. Results show that, although ULS is satisfied using a very high deck slenderness (1/100), the SLS of vibrations is the critical design criterion that governs the slenderness of the deck (leading to values of 1/60).
Teslim-Balogun A, Malaga-Chuquitaype C, Stafford PJ, 2019, A Numerical Study on the Structural Response of Steel Structures under Post-Blast Travelling Fires, Structures Congress - Blast, Impact Loading, and Research and Education, Publisher: AMER SOC CIVIL ENGINEERS, Pages: 59-69
Shi Y, Stafford PJ, 2018, Markov-chain Monte Carlo ground-motion selection algorithms for conditional intensity measure targets, Earthquake Engineering and Structural Dynamics, Vol: 47, Pages: 1468-1489, ISSN: 0098-8847
Two new algorithms are presented for efficiently selecting suites of ground motions that match a target multivariate distribution - or conditional intensity measure target.The first algorithm is a Markov-chain Monte Carlo (MCMC) approach in which records are sequentially added to a selected set such that the joint probability density function (PDF) of the target distribution is progressively approximated by the discrete distribution of the selected records.The second algorithm derives from the concept of the acceptance ratio within MCMC but does not involve any sampling.The first method takes advantage of MCMC's ability to efficiently explore a sampling distribution through the implementation of a traditional MCMC algorithm.This method is shown to enable very good matches to multivariate targets to be obtained when the numbers of records to be selected is relatively large.A weaker performance for fewer records can be circumvented by the second method which uses greedy optimization to impose additional constraints upon properties of the target distribution.A preselection approach based upon values of the multivariate PDF is proposed that enables near-optimal record sets to be identified with a very close match to the target.Both methods are applied for a number response analyses associated with different sizes of record sets and rupture scenarios.Comparisons are made throughout with the Generalized Conditional Intensity Measure (GCIM) approach.The first method provides similar results to GCIM, but with slightly worse performance for small record sets, while the second method outperforms method one and GCIM for all considered cases.
Elghazouli AY, Bompa DV, Xu B, et al., 2018, Performance of rubberised reinforced concrete members under cyclicloading, Engineering Structures, Vol: 166, Pages: 526-545, ISSN: 0141-0296
This paper presents an experimental investigation into the cyclic behaviour of reinforced concrete members incorporating a significant proportion of recycled rubber particles as a replacement for mineral aggregates. Tests were carried out on thirteen large scale members of circular cross-section, with and without external confinement, and with different proportions of rubber content and axial loads. The specimens were subjected to inelastic lateral cyclic displacements and predefined levels of co-existing axial loading. After describing the testing arrangement and specimen details, the main results and observations are provided and discussed. The test results enable a direct comparative assessment of the key response characteristics of the specimens, with focus on stiffness properties and strength interaction, as well as ductility and energy dissipation. It is shown that rubberised reinforced concrete members can offer a good balance between bending capacity and ductility in comparison with conventional reinforced concrete members, particularly for low levels of axial loads. In the presence of relatively high axial loading and when a significant proportion of rubber content is used, external confinement such as through FRP sheets as employed in this study, can be adopted to recover the required capacity and to provide highly stable hysteretic response. The implications of the findings on the use of rubberised reinforced concrete members in practice, and procedures that can be used to determine the main design parameters, are also highlighted within the discussions.
Skiada E, Kontoe S, Stafford P, et al., 2018, Ground surface amplification for canyon topographies excited with bi-directional earthquake records, 16th European Conference on Earthquake Engineering
Ulmer KJ, Upadhyaya S, Green RA, et al., 2018, A Critique of b-Values Used for Computing Magnitude Scaling Factors, Geotechnical Earthquake Engineering and Soil Dynamics V, 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.
Lee RL, Bradley BA, Graves RW, et al., 2018, Investigation of Systematic Ground Motion Effects through Ground Motion Simulation of Small-to-Moderate Magnitude Earthquakes, Geotechnical Earthquake Engineering and Soil Dynamics V, 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.
Ramos-Moreno C, Ruiz-Teran AM, Stafford PJ, 2018, Serviceability response of a bench-mark cable-stayed footbridge: comparison of available methods, Footbridge 2017
In previous Footbridge Conferences, the focus of researchers has been on the representation of pedestrian actions (vertical and lateral) to design footbridges, on the proposal of methodologies for the analysis in service of these structures and on the description of the serviceability response of particular footbridges. Nonetheless, none of these research works have been focused on the magnitude of the serviceability response of footbridges according to its structural type.This paper characterises the response of footbridges with stayed cables as main structural type. Based on a compiled dataset of cable-stayed footbridges (developed for this research work), the paper presents the geometrical and structural characteristics of a footbridge that can be regarded as representative of this structural type. Considering the best methodologies available for the assessment of its response in vertical and lateral direction, the paper describes the magnitude of the serviceability performance of this bridge under a wide range of pedestrian scenarios. This description familiarises designers at early stages of their design with the order of magnitude of the serviceability response of cable-stayed footbridges with an arrangement similar to that commonly used for this structural type.
Elghazouli AY, Bompa DV, Xu B, et al., 2018, Performance of Rubberised Reinforced Concrete Members under Cyclic Loading, 16th European Conference on Earthquake Engineering (16ECEE)
Bommer JJ, Dost B, Edwards B, et al., 2018, 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
Major efforts are being undertaken to quantify seismic hazard and risk due to production-induced earthquakes in the Groningen gas field as thebasis for rational decision-making about mitigation measures. An essential element is a model to estimate surface ground motions expected at anylocation for each earthquake originating within the gas reservoir. Taking advantage of the excellent geological and geophysical characterisationof thefield and a growing database of ground-motion recordings, models have been developed for predicting response spectral accelerations, peak groundvelocity and ground-motion durations for a wide range of magnitudes. The models reflect the unique source and travel path characteristics of theGroningen earthquakes, and account for the inevitable uncertainty in extrapolating from the small observed magnitudes to potential larger events.The predictions of ground-motion amplitudes include the effects of nonlinear site response of the relatively soft near-surface deposits throughoutthe field.
Green RA, Stafford P, Maurer BW, et al., 2018, Liquefaction hazard due to induced seismicity: Overview of the pilot study being performed for the Groningen region of the Netherlands, 11th U.S. National Conference on Earthquake Engineering, Publisher: Earthquake Engineering Research Institute
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
Models for the interfrequency correlations among Fourier spectral ordinates and variances of these ordinates are presented. These covariances among Fourier spectral ordinates can be used to generate accelerograms within a stochastic simulation framework that offer improvements over traditional approaches that make use of deterministic Fourier amplitude spectra combined with a random phase spectrum. The article demonstrates that the accelerograms generated in this new way result in response spectral ordinates that have variances that are very consistent with those predicted by empirical ground‐motion models. In addition, the interperiod correlations among response spectral ordinates obtained from the simulated motions are also consistent with empirically derived response spectral correlations. The study partitions the variance among Fourier spectral ordinates into between‐event, between‐site and within‐event components, and interfrequency correlation models, and variance models are derived for each component. The between‐event correlations are found to exhibit a mild degree of magnitude dependence. An important feature of the new correlation and variance models is that they can be used to generate accelerograms that are broadly consistent with conditional response spectra. This new approach has significant implications for response‐history analyses within earthquake engineering that make use of conditional spectra as a target.
Xu B, Bompa DV, Elghazouli AY, et al., 2017, Behaviour of rubberised concrete members in asymmetric shear tests, Construction and Building Materials, Vol: 159, Pages: 361-375, ISSN: 0950-0618
This paper deals with the experimental behaviour of rubberised concrete members subjected to asymmetric four-point shear loading. A detailed account of tests on 15 prismatic members using conventional concrete as well as rubberised concrete, with relatively high replacement ratios of both fine and coarse mineral aggregates with rubber particles, is given. The results enable direct assessment of strength and complete deformation characteristics including the post-peak response for ultimate behaviour governed both by shear and mixed-mode tensile-shear. After describing the material properties, mix designs and member details, the main observations from detailed measurements of the crack kinematics through a digital image correlation monitoring system, with focus on members developing shear-governed response, are reported. Complementary numerical studies are undertaken using nonlinear finite element procedures which are validated against tests developing shear-governed failures. In order to provide further insight into the key response characteristics, particularly those related to ultimate strength, a number of numerical sensitivity studies employing various constitutive parameters are also carried out. Moreover, comparative assessments in terms of shear resistance, toughness and force transfer across the cracked interfaces are performed and discussed. The detailed test measurements, coupled with the results obtained from the numerical simulations, permit the definition of expressions for representing the shear resistance as a function of the rubber content and concrete compressive strength.
Stafford PJ, Rodriguez-Marek A, Edwards B, et 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
Ground‐motion models for response spectral ordinates commonly partition site‐response effects into linear and nonlinear components. The nonlinear components depend upon the earthquake scenario being considered implicitly through the use of the expected level of excitation at some reference horizon. The linear components are always assumed to be independent of the earthquake scenario. This article presents empirical and numerical evidence as well as a theoretical explanation for why the linear component of site response depends upon the magnitude and distance of the earthquake scenario. Although the impact is most pronounced for small‐magnitude scenarios, the finding has significant implications for a number of applications of more general interest including the development of site‐response terms within ground‐motion models, the estimation of ground‐motion variability components ϕS2SϕS2S and ϕSSϕSS , the construction of partially nonergodic models for site‐specific hazard assessments, and the validity of the convolution approach for computing surface hazard curves from those at a reference horizon, among others. All of these implications are discussed in the present article.
Elghazouli AY, Bompa DV, Xu B, et al., 2017, Inelastic behaviour of RC members incorporating high deformability concrete, fib Symposium 2017
Skiada E, Kontoe S, Stafford P, et 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.
Garcia-Troncoso N, Ruiz-Teran AM, Stafford PJ, 2017, Dynamic response of girder footbridges with supplemental damping, Footbridge 2017
Teslim-Balogun A, Malaga Chuquitaype C, Stafford PJ, 2017, Assessment of efficiency of intensity measures for performance-based travelling fire design, 39th International IABSE Symposium
Bommer JJ, Stafford PJ, Edwards B, et 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
The potential for building damage and personal injury due to induced earthquakes in the Groningen gas field is being modeled in order to inform risk management decisions. To facilitate the quantitative estimation of the induced seismic hazard and risk, a ground motion prediction model has been developed for response spectral accelerations and duration due to these earthquakes that originate within the reservoir at 3 km depth. The model is consistent with the motions recorded from small-magnitude events and captures the epistemic uncertainty associated with extrapolation to larger magnitudes. In order to reflect the conditions in the field, the model first predicts accelerations at a rock horizon some 800 m below the surface and then convolves these motions with frequency-dependent nonlinear amplification factors assigned to zones across the study area. The variability of the ground motions is modeled in all of its constituent parts at the rock and surface levels.
Bompa DV, Elghazouli AY, Xu B, et al., 2017, Experimental assessment and constitutive modelling of rubberised concrete materials, Construction and Building Materials, Vol: 137, Pages: 246-260, ISSN: 0950-0618
This paper focuses on examining the uniaxial behaviour of concrete materials incorporating rubber particles, obtained from recycled end-of-life tyres, as a replacement for mineral aggregates. A detailed account of a set of material tests on rubberised concrete cylindrical samples, in which fine and coarse mineral aggregates are replaced in equal volumes by rubber particles with various sizes, is presented. The experimental results carried out in this investigation, combined with detailed examination of data available from previous tests on rubberised concrete materials, show that the rubber particles influence the mechanical properties as a function of the quantity and type of the mineral aggregates replaced. Experimental evaluation of the complete stress-strain response depicts reductions in compressive strength, elastic modulus, and crushing strain, with the change in rubber content. Enhancement is also observed in the energy released during crushing as well as in the lateral strain at crushing, primarily due to the intrinsic deformability of the interfacial clamping of rubber particles which leads to higher lateral dilation of the material. The test results and observations enable the definition of a series of expressions to estimate the mechanical properties of rubberised concrete materials. An analytical model is also proposed for the detailed assessment of the complete stress-strain response as a function of the volumetric rubber ratio. Validations performed against the material tests carried out in this study, as well as those from previous investigations on rubberised concrete materials, show that the proposed models offer reliable predictions of the mechanical properties including the full axial and lateral stress-strain response of concrete materials incorporating rubber particles.
Skiada E, Kontoe S, Stafford P, et 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.
Malaga Chuquitaype C, Elghazouli AY, 2017, Design of Timber Structures, Seismic Design Of Buildings To Eurocode 8, Editors: Elghazouli, Pages: 213-234
Sadowski AJ, Rotter JM, Stafford PJ, et al., 2016, On the gradient of the yield plateau in structural carbon steels, Journal of Constructional Steel Research, Vol: 130, Pages: 120-130, ISSN: 0143-974X
New design methodologies are being developed to allow stocky steel members to attain and exceed the full plastic condition. For theoretical validation, such methods require a characterisation of the uniaxial stress-strain behaviour of structural steel beyond an idealised elastic-plastic representation. However, the strain hardening properties of carbon steels are not currently guaranteed by the standards or by any steel manufacturer. Assumptions must thus be made on what values of these properties are appropriate, often based on limited information in the form of individual stress-strain curves. There is very little consistency in the choices made.This paper first illustrates, using an example elastic-plastic finite element calculation, that a stocky tubular structure can attain the full plastic condition at slendernesses comparable with those defined in current standards and supported by experiment when using only a very modest level of strain hardening, initiated at first yield. It is then hypothesised that the yield plateau in the stress-strain curve for structural carbon steels, classically treated as flat and with zero tangent modulus, actually has a small but statistically significant positive finite gradient. Finally, a robust set of linear regression analyses of yield plateau gradients extracted from 225 tensile tests appears to support this hypothesis, finding that the plateau gradient is of the order of 0.3% of the initial elastic modulus, consistent with what the finite element example suggests is sufficient to reproduce the full plastic condition at experimentally-supported slendernesses.
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
Inelastic spectral displacement demand is arguably one of the most effective, simplified means of relating earthquake intensity to building damage. However, seismic hazard assessment is typically conducted using empirical ground-motion prediction equations (GMPEs) that only provide indications of elastic spectral response quantities, which an engineer subsequently relates to inelastic demands using empirical relationships such as the equal-displacement rule. An alternative approach is to utilize relationships for the inelastic spectral displacement demand directly within the seismic hazard assessment process. Such empirical relationships are developed in this work, as a function of magnitude, distance, building period and yield strength coefficient, for four different hysteretic models that are representative of a wide range of possible structural typologies found in practice. The new relationships are likely to be particularly useful for performance-based seismic design and assessment.
Skiada E, Kontoe S, Stafford P, et 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.
Bora SS, Scherbaum F, Kuehn N, et 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, ISSN: 1943-3573
The functional form of empirical response spectral ground-motion predictionequations (GMPEs) is often derived using concepts borrowed from Fourier spectralmodeling of ground motion. As these GMPEs are subsequently calibrated with empiricalobservations, this may not appear to pose any major problems in the prediction ofground motion for a particular earthquake scenario. However, the assumption that Fourierspectral concepts persist for response spectra can lead to undesirable consequenceswhen it comes to the adjustment of response spectral GMPEs to represent conditions notcovered in the original empirical data set. In this context, a couple of important questionsarise, for example, what are the distinctions and/or similarities between Fourier andresponse spectra of ground motions? And, if they are different, then what is the mechanismresponsible for such differences and how do adjustments that are made to Fourieramplitude spectrum (FAS) manifest in response spectra? The present article explores therelationship between the Fourier and response spectrum of ground motion by usingrandom vibration theory (RVT). With a simple Brune (1970, 1971) source model, RVTgeneratedacceleration spectra for a fixed magnitude and distance scenario are used. TheRVT analyses reveal that the scaling of low oscillator-frequency response spectral ordinatescan be treated as being equivalent to the scaling of the corresponding Fourierspectral ordinates. However, the high oscillator-frequency response spectral ordinatesare controlled by a rather wide band of Fourier spectral ordinates. In fact, the peakground acceleration, counter to the popular perception that it is a reflection of the highfrequencycharacteristics of ground motion, is controlled by the entire Fourier spectrumof ground motion. Additionally, this article demonstrates how an adjustment made toFAS is similar or different to the same adjustment made to response spectral ordinates.For this purpose, two cases: adjustments to the stres
Bommer JJ, Stafford PJ, 2016, Seismic hazard and earthquake actions, Seismic Design of Buildings to Eurocode 8, Second Edition, Pages: 7-40, ISBN: 9781498751605
Earthquake-resistant design can be considered as the art of balancing the seismic capacity of structures with the expected seismic demand to which they may be subjected. In this sense, earthquake-resistant design is the mitigation of seismic risk, which may be defined as the possibility of losses (human, social or economic) due to the effects of future earthquakes. Seismic risk is often considered as the convolution of seismic hazard, exposure and vulnerability. Exposure refers to the people, buildings, infrastructure, commercial and industrial facilities located in an area where earthquake effects may be felt; exposure is usually determined by planners and investors, although in some cases avoidance of major geo-hazards may lead to relocation of new infrastructure. Vulnerability is the susceptibility of structures to earthquake effects and is generally defined by the expected degree of damage that would result under different levels of seismic demand; this is the component of the risk equation that can be controlled by engineering design. Seismic hazards are the potentially damaging effects of earthquakes at a particular location, which may include surface rupture, tsunami runup, liquefaction and landslides, although the most important cause of damage on a global scale is earthquake-induced ground shaking (Bird and Bommer, 2004). The focus in this chapter is exclusively on this particular hazard and the definition of seismic actions in terms of strong ground motions. In the context of probabilistic seismic hazard analysis (PSHA), seismic hazard actually refers to the probability of exceeding a specific level of ground shaking within a given window of time.
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