Publications
141 results found
Tsaparli V, Kontoe S, Taborda D, et al., 2015, Numerical investigation of the effect of the irregular nature of seismic loading on the liquefaction resistance of saturated sand deposits, SECED 2015 Conference: Earthquake Risk and Engineering towards a Resilient World
Colombero R, Kontoe S, Foti S, et al., 2015, Numerical modelling of drop load tests, Soil Dynamics and Earthquake Engineering, Vol: 77, Pages: 279-289, ISSN: 1879-341X
Han B, Zdravkovic L, Kontoe S, 2014, Stability investigation of the Generalised-α time integration method for dynamic coupled consolidation analysis, Computers and Geotechnics, Vol: 64, Pages: 83-95, ISSN: 1873-7633
In this paper, the stability of the Generalised-α time integration method (the CH method) for a fully coupled solid-pore fluid formulation is analytically investigated for the first time and the corresponding theoretical stability conditions are proposed based on a rigorous mathematical derivation process. The proposed stability conditions simplify to the existing ones of the CH method for the one-phase formulation when the solid–fluid coupling is ignored. Furthermore, by degrading the CH method to the Newmark method, the stability conditions are in agreement with the ones proposed in previous stability investigations on coupled formulation for the Newmark method. The analytically derived stability conditions are validated with finite element (FE) analyses considering a range of loading conditions and for various soil permeability values, showing that the numerical results are in agreement with the theoretical investigation. Then, the stability characteristics of the CH method are explored beyond the limits of the theoretical investigation, assuming elasto-plastic soil behaviour which is prescribed with a bounding surface plasticity constitutive model. Since the CH method is a generalisation of a number of other time integration methods, the derived stability conditions are relevant for most of the commonly utilised time integration methods for the two-phase coupled formulation.
Kontoe S, Avgerinos V, Potts DM, 2014, Numerical validation of four analytical solutions and their use for equivalent-linear seismic analysis of circular tunnels, Soil Dynamics and Earthquake Engineering, Vol: 66, Pages: 206-219
The first part of this paper presents an extensive validation of four analytical solutions for the seismic design of circular tunnels. The validation is performed with a quasi-static Finite Element (FE) model which conforms to the assumptions of the analytical solutions. Analyses are performed for a wide range of flexibility ratios, slippage conditions at soil-lining interface, assuming both drained and undrained behaviour. Based on the numerical predictions the relative merits of the considered analytical solutions are discussed and recommendations are given for their use in design. The second part of this paper explores the use of equivalent linear soil properties in analytical solutions as an approximate way of simulating nonlinearity. The results of equivalent linear site response analyses are used as an input for the analytical solutions. The comparison of the analytical predictions with nonlinear numerical analysis results is very satisfactory. The results of this study suggest that analytical solutions can be used for preliminary design using equivalent linear properties and the corresponding compatible strain as an approximate way of accounting for nonlinear soil response.
Theodoulidis N, Klimis N, Savvaidis A, et al., 2014, Defining shallow structure properties by composing ambient noise and geological data for site response analyses: the case of Xanthi town (NE Greece), 2nd European Conference on Earthquake Engineering and Seismology
Taborda DM, Zdravkovic L, Kontoe S, et al., 2014, Computational study on the modification of a bounding surface plasticity model for sands, Computers and Geotechnics, Vol: 59, Pages: 145-160, ISSN: 0266-352X
The accurate simulation of complex dynamic phenomena requires the availability of advanced constitutive models capable of simulating a wide range of features of soil behaviour under cyclic loading. One possible strategy is to improve the capabilities of existing bounding surface plasticity models, as this framework is characterised by its modularity and flexibility. As a result, specific components of the formulation of this type of model may be adjusted to improve the reproduction of any aspect of soil behaviour deemed essential to the problem being analysed. In this paper, a series of computational studies are performed in order to establish the impact of expanding a bounding surface plasticity model for sands on its modelling capabilities and to suggest ways of mitigating the associated increase in complexity. Changes to three distinct aspects of the selected constitutive model are examined: the shape of the Critical State Line in p′ − e space, the expression used for calculating the hardening modulus and the form of the yield surface. It is shown that the introduced changes have the potential to increase significantly the ability to control how certain aspects of soil response, such as degradation of stiffness and flow liquefaction with limited deformation, are reproduced by the model. Moreover, this paper presents a systematic approach to the expansion of this type of constitutive model, establishing how alterations to the formulation of a model may be assessed in terms of improved accuracy and potential benefits.
Han B, Zdravkovic L, Kontoe S, 2014, Analytical and theoretical investigations on the vertical seismic site response, 8th European Conference on Numerical Methods in Geotechnical Engineering (NUMGE), Pages: 1123-1128
Summersgill F, Kontoe S, Potts DM, 2014, A comparison of the mesh dependence of the nonlocal and local strain softening methods in a biaxial compression analysis, 8th European Conference on Numerical Methods in Geotechnical Engineering (NUMGE), Pages: 289-294
Rossetto T, D'Ayala D, Gori F, et al., 2014, The value of multiple earthquake missions: the EEFIT L'Aquila Earthquake experience, BULLETIN OF EARTHQUAKE ENGINEERING, Vol: 12, Pages: 277-305, ISSN: 1570-761X
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- Citations: 18
Pelecanos L, Kontoe S, Zdravkovic L, 2013, Numerical modelling of hydrodynamic pressures on dams, Computers and Geotechnics, Vol: 53, Pages: 68-82
This paper discusses several considerations related to appropriate numerical modelling of the reservoirhydrodynamic pressures on dams. The reservoir is modelled with 8-noded isoparametric displacementbased solid finite elements. The study includes both stiff and flexible dams with vertical and slopedupstream faces under ramp, harmonic and random acceleration loads. The numerical results were comparedand found to be in good agreement with available closed-form solutions. The same approach maybe used in analyses of other waterfront structures such as quay walls.
Han B, Zdravkovic L, Kontoe S, 2013, The stability of the Generalised-α time integration method for dynamic coupled consolidation problems, COMPDYN
This paper investigates the stability of the Generalised-α time integration method (the CH method) for a fully coupled solid-pore fluid formulation. Theoretical stability conditions are derived, which are shown to simplify to the existing ones of the CH method for the one–phase formulation when the solid-fluid coupling is ignored. Finite Element (FE) analyses considering a range of loading conditions are conducted to validate the analytically derived stability condition, showing that the numerical results are in agreement with the theoretical investigation. The CH method is a generalisation of a number of other tine integration schemes and hence the derived stability conditions are relevant for most of the commonly utilised time integration methods for fully coupled two-phase formulation.
Kontoe S, Christopoulos A, May R, 2013, Site response analysis for vertical ground motion, COMPDYN
This study initially considers a uniform soil layer subjected to vertically propagating harmonic P-waves. The response of the layer is calculated analytically, considering one-dimensional propagation, and numerically employing time domain coupled consolidation Finite Element analysis for a range of input frequencies. The computed amplification function is shown to significantly depend on the modelling of the fluid phase and the soil permeability. Subsequently, a ground profile corresponding to a downhole array in Dahan (Taiwan) is examined assuming undrained, drained and coupled consolidation behaviour. The numerical predictions are compared with the vertical recorded response during the 1999 Chi-Chi earthquake demonstrating a very good agreement for the coupled consolidation analysis and highlighting the limitations of the other two approaches (i.e. drained and undrained analyses).
Papaspiliou M, Kontoe S, 2013, Sensitivity of site response analysis on the number of ground motion records and implications for PSHA, Bulletin of Earthquake Engineering, Vol: available online, ISSN: 1573-1456
This paper investigates issues related to the number of ground-motion records required for the performance of site response analysis and the inclusion of the site-specific amplification function within probabilistic seismic hazard calculations (PSHA). It explores the minimum number of records required for a robust estimation of the median and standard deviation of the site amplification function, as well as the impact of the selected ground-motion suites on the results of PSHA. Site response analyses are performed using both equivalent linear and nonlinear methodologies. Although the median amplification was observed to be relatively easy to capture, the standard deviation was seen to fluctuate considerably, especially when suites of few records were used. It was observed that in the case of the nonlinear site response analysis 10 records provide relatively stable estimates of the hazard curves for the majority of periods, while in the case of the equivalent linear analysis 20 records or more are required to achieve a similar level of accuracy.
Mian J, Kontoe S, Free M, 2013, Assessment and Management of Risks Related to Earthquake-Induced Liquefaction, Seismic risk analysis and management of civil infrastructure systems, Editors: Tesfamariam, Goda, Cambridge, UK, Publisher: Woodhead Publishing Ltd
Tripe R, Kontoe S, Wong TKC, 2013, Slope topography effects on ground motion in the presence of deep soil layers, Soil Dynamics and Earthquake Engineering, Vol: 50, Pages: 72-84
An extensive investigation has been made into the interaction between topographic amplification and soil layer amplification of seismic ground motion. This interaction is suggested in the literature as a possible cause for the differences between topographic amplification magnitudes observed in field studies and those obtained from numerical analysis. To investigate this issue a numerical finite element (FE) parametric study was performed for a slope in a homogeneous linear elastic soil layer over rigid bedrock subjected to vertically propagating in-plane shear waves (Sv waves). Analyses were carried out using two types of artificial time history as input excitation, one mimicking the build-up and decay of shaking in the time histories of real earthquake events, and the other to investigate the steady-state response. The study identified topographic effects as seen in previous numerical studies such as modification of the free-field horizontal motion, generation of parasitic vertical motion, zones of alternating amplification and de-amplification on the ground surface, and dependence of topographic amplification on the frequency of the input motion. For the considered cases, topographic amplification and soil layer amplification effects were found to interact, suggesting that in order to accurately predict topographic effects, the two effects should not be always handled separately
Kontoe S, Pelecanos L, Potts DM, 2013, An important pitfall of pseudo-static finite element analysis, Computers & Geotechnics, Vol: 48, Pages: 41-50
Finite Element (FE) pseudo-static analysis can provide a good compromise between simplified methods of dynamic analysis and time domain analysis. The pseudo-static FE approach can accurately model the in-situ stresses prior to seismic loading (when it follows a static analysis simulating the construction sequence) is relatively simple and not as computationally expensive as the time domain approach. However this method should be used with caution as the results can be sensitive to the choice of the mesh dimensions. In this paper two simple examples of pseudo-static finite element analysis are examined parametrically, a homogeneous slope and a cantilever retaining wall, exploring the sensitivity of the pseudo static analysis results on the adopted mesh size. The mesh dependence was found to be more pronounced for problems with high critical seismic coefficients values (e.g. gentle slopes or small walls), as in these cases a generalised layer failure mechanism is developed simultaneously with the slope or wall mechanism. In general the mesh width was found not to affect notably the predicted value of critical seismic coefficient but to have a major impact on the predicted movements.
Mian JF, Kontoe S, Free M, 2013, Assessing and managing the risk of earthquake-induced liquefaction to civil infrastructure, HANDBOOK OF SEISMIC RISK ANALYSIS AND MANAGEMENT OF CIVIL INFRASTRUCTURE SYSTEMS, Editors: Tesfamariam, Goda, Publisher: WOODHEAD PUBL LTD, Pages: 113-138, ISBN: 978-0-85709-268-7
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- Citations: 5
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
Within PSHA, the effects of site response can be treated in a variety of different manners. Typically, there is an assumed hierarchy of accuracy for the alternatives, but the validity of this hierarchy has not been formally assessed. Site response can be modelled directly using empirical Ground Motion Prediction Equations (GMPEs) and the precision of the analysis is related to the published variance components of the model. An alternative approach is to conduct site-specific site response analyses, and this approach is commonly assumed to be the most accurate. Using equivalent linear (EQL) and non-linear (NL) site response analysis for two magnitude-distance (M-R) scenarios this study focuses on the total uncertainty associated with this computational demanding route. The spectral ordinates and the variability of the site response methods are further compared to the predictions of the Campbell and Bozorgnia (2008) GMPE for these two M-R combinations.
Papaspiliou MI, Kontoe S, 2012, Ground Motion Selection for the Integration of Site Response in Probabilistic Seismic Hazard Analyses, 15th World Conference on Earthquake Engineering
This paper examines issues related to ground-motion selection for the performance of site response analysis and the integration of the site-specific amplification function within probabilistic seismic hazard calculations. The, typically, deterministic modification of the probabilistically estimated rock ground motions to consider site effects often leads to nonconservative ground motions at the soil surface. In this paper a methodology proposed by Bazzurro and Cornell (2004b), which allows the transformation of a rock ground-motion prediction equation into a site-specific one by modifying both the median and standard deviation terms of the equation, is used and its sensitivity to different suites of ground-motion records is explored. Suites of 10, 15 and 20 records are used for the performance of the site response analysis in order to examine their impact on capturing the median site amplification and its standard deviation. Subsequently, their impact on the results of a probabilistic seismic hazard assessment is explored.
Pelecanos L, Kontoe S, Zdravković L, 2012, Numerical analysis of the seismic response of La Villita dam in Mexico, Pages: 120-130
This paper presents two-dimensional plane-strain static and dynamic finite element analyses of La Villita earth dam in Mexico, which has experienced a number of large earthquakes. Static analyses are employed to simulate the layered construction of the embankment, water impounding and consolidation, whereas dynamic analyses simulate the earthquake events. The static behaviour of the dam is well captured, as evidenced by the predicted and recorded crest settlement. The dynamic behaviour is satisfactorily captured by comparing the accelerations recorded at both the crest and downstream berm of the dam.
Kontoe S, Zdravkovic L, Menkiti CO, et al., 2012, Seismic response and interaction of complex soil retaining systems, Computers and Geotechnics, Vol: 39, Pages: 17-26
This paper examines the seismic response of a large and complex system comprising a Lock chamber and three neighbouring water saving basins (WSBs). The developed two-dimensional plane strain finite element model included the entire system in order to explore the interaction of the various structures. The first set of analyses was undertaken under static conditions to simulate the construction sequence and to establish the stress regime prior to the examined seismic event. Subsequently, dynamic time domain analyses were performed to examine the response of the system to seismic loading. The ground motion was applied into the finite element mesh employing a sub-structuring technique which enables economic modelling of large computation domains and accurate representation of the semi-infinite half-space. The paper explores some aspects of the numerical modelling of such complex systems, such as the impact on the predicted seismic response of the adopted constitutive model and the modelling of hydrodynamic effects. The discussion of the dynamic analyses results focuses on the main Lock structure, looking at the prevailing modes of deformation, the potential lift-off of the base of the Lock walls and the interaction of the main wall with the other retaining structures.
Guerreiro P, Kontoe S, Taborda D, 2012, Comparative study of stiffness reduction and damping curves, 15th World Conference on Earthquake Engineering
Papaspiliou M, Kontoe S, Bommer JJ, 2012, An exploration of incorporating site response into PSHA, Part I: Issues related to site response analysis methods, Soil Dynamics and Earthquake Engineering, Vol: 42, Pages: 302-315
This paper presents a series of analyses for the evaluation of the ground response of two NEHRP class D sites, subjected to shaking by a large number of strong ground-motion records. The two investigated sites have very distinct profiles, but they are characterised by almost identical Vs30 values. The site response analyses are performed using various methods of analysis and input parameters in order to explore the sensitivity of the ground response estimates and to identify the dominating parameters. Equivalent linear analysis is performed using different sets of dynamic soil properties curves, while nonlinear analysis is performed using different target dynamic soil curves, viscous damping formulations and fitting procedures for the constitutive model parameters. Particular focus is given to the sensitivity of the response when soil sites are subjected to high-intensity shaking, a subject of particular interest when the prediction of surface ground motions with low annual probabilities of exceedance is the target of probabilistic seismic hazard analyses (PSHA). The site response analysis results of this paper are incorporated into the probabilistic framework of Bazzurro and Cornell [1] in our companion paper in order to assess their impact on the final soil surface hazard calculation.
Papaspiliou M, Kontoe S, Bommer JJ, 2012, An Exploration of Incorporating Site Response into PSHA Part II: Sensitivity of Hazard Estimates to Site Response Approaches, Soil Dynamics and Earthquake Engineering, Vol: 42, Pages: 316-330
This paper examines the sensitivity of seismic hazard analyses to various site response analysis procedures. Site effects are incorporated in the hazard calculations using a probabilistic approach and specifically the methodology of Bazzurro and Cornell [1] for the transformation of a generic ground-motion prediction equation to a site-specific one. The paper explores the sensitivity of the median amplification function, its standard deviation and the resulting surface hazard curve, to different methods of site response analysis and model input parameters. The computed site-specific surface hazard curves are also compared with those obtained from a generic soil ground-motion prediction equation. For the two sites investigated, it is shown that the choice of equivalent linear or nonlinear analysis with different constitutive model parameters has a significant impact on the hazard results. The sandy site was seen to be more sensitive to the site response analysis approach employed than the clayey site.
Pelecanos L, Kontoe S, Zdravkovic L, 2012, Static and dynamic analysis of La Vilita dam in Mexico, 2nd International Conference on Performance-Based Design in Earthquake Geotechnical Engineering, Pages: 1045-1056
Zdravkovic L, Potts DM, Kontoe S, 2011, Effect of wall stiffness on ground deformations around deep excavations in stiff clay, XV European Conference on Soil Mechanics and Geotechnical Engineering, Pages: 1599-1604
Kontoe S, Zdravkovic L, Menkiti CO, et al., 2011, Seismic response of complex soil-structure systems, XV European Conference on Soil Mechanics and Geotechnical Engineering, Pages: 1491-1496
Avgerinos V, Kontoe S, 2011, Modelling the ovalisation of circular tunnels due to seismic loading using different approaches, 5th International Conference on Earthquake Geotechnical Engineering
Tripe R, Kontoe S, 2011, A numerical investigation into the interaction between topographic and soil layer amplification of earthquake motion, 5th International Conference on Earthquake Geotechnical Engineering, (5ICEGE)
Kontoe S, Zdravkovic L, Potts DM, et al., 2011, On the relative merits of simple and advanced constitutive models in dynamic analysis of tunnels, Geotechnique, Vol: 61, Pages: 815-829, ISSN: 0016-8505
This paper compares simple constitutive models that are widely used in engineering practice with more sophisticated methods in the context of a case study. In particular, four constitutive modelling approaches have been considered: a simple elasto-plastic constitutive model (modified Cam-clay), with and without Rayleigh damping; the same model coupled with a cyclic non-linear model that can simulate pre-yield hysteresis; and finally an advanced kinematic hardening model, which is an improved version of the Al-Tabbaa & Wood two-surface model. These four approaches are used to analyse the seismic response of a section of the Bolu tunnels during the 1999 Duzce earthquake. To shed light on the performance of the constitutive models, simple site response finite-element analyses were first undertaken for the studied site, paying particular attention to the calibration of the Rayleigh damping parameters. The results of these analyses, in terms of maximum shear strain, were then used as input to an analytical elastic method (extended Hoeg method) for calculating the thrust and bending moment acting in the tunnel lining. Finally the results of dynamic time domain plane-strain analyses, employing the four adopted constitutive modelling approaches, are compared against field observations and results obtained by the extended Hoeg method, to investigate the ability of the models, of ranging complexity, to mimic soil response under seismic excitation.
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