A drift-correlated ground motion intensity measure: application to steel frame buildings

Estimations of seismic risk in urban areas should include quantifications of the expected damage to civil structures subjected to earthquakes. In buildings, this quantification depends on the maximum inter-story drift (MIDR), among other aspects. In this study, the correlation between several intensity measures (IMs) and the maximum inter-story drift of steel structures was investigated. Three steel frame buildings of 3, 7 and 13 stories were used as a testbed. These buildings were modelled as 2D framed structures. For the seismic hazard, forty strong ground motion pairs were selected (80 individual horizontal components) from the Italian database. These records were scaled to a specific peak ground acceleration (PGA) and matched to a design spectrum from Eurocode 8. Nonlinear dynamic analysis was used to estimate the seismic response of the structures. Thus, 720 nonlinear dynamic analyses (NLDA) were performed [3 structures × (80 as recorded accelerograms + 80 scaled records + 80 matched records)]. Preliminary results indicate that PGA and MIDR show the worst correlation. A higher correlation was observed for peak ground velocity, root-mean-square velocity and specific energy density intensity-based measures. Finally, a new IM, which is highly correlated with MIDR, is proposed. This IM is called IΔ-PGV and considers both the PGV and the significant duration.Peer ReviewedPostprint (author's final draft

Étude de la réhabilitation sismique d'un pont avec des isolateurs en caoutchouc à basse température par le biais de surfaces de fragilité

Abstract : In Quebec, Canada, due to aging and deficient seismic detailing, bridges are susceptible to important damage in the occurrence of a strong earthquake. To enhance the seismic performance of the provincial bridge inventory, the replacement of typical bearings with natural rubber isolators has shown to be a potentially efficient retrofitting measure. However, variations in the mechanical properties of the isolators due to environmental conditions can affect the seismic performance. For instance, rubber undergoes substantial stiffening when exposed to low temperatures, as those typically observed during winter in eastern Canada. In bridge-type structures, the thermal stiffening of isolators increases the forces transmitted to the substructure, which in turn becomes more prone to damage. A more detailed consideration of the thermal effects on the seismic performance of typical provincial bridges is thus necessary. In this study, fragility surfaces are used to assess the vulnerability of a typical bridge in Quebec when retrofitted with natural rubber isolators under the concomitant actions of earthquakes and low temperatures. Bridges are composed of several different components with distinguished behaviors and complex interactions under seismic excitation. Owing to the importance of the contribution of different components to the bridge fragility, the first part of this study focuses on the construction of multivariate probabilistic seismic demand models (PSDM). The validity of the commonly adopted assumptions has been criticized and their impact on fragility estimates is not fully understood. A multivariate PSDM approach is thus developed coupling the multiple-stripe analysis and Gaussian mixture models. The novel approach concomitantly captures the complexity of the dynamic response of multicomponent structures and models their uncertainties and correlation. The proposed approach is then used to assess the potential bias introduced by poor modeling on fragility and risk estimates of a real as-built case-study bridge. This PSDM strategy then is adopted to translate the uncertainty and the correlation of the response of the case-study bridge components when retrofitted. Fragility surfaces based on logistic regression depict the effects of thermal stiffening of isolators on the performance of the bridge in both component- and system-level. A beneficial combination is revealed between the decoupling effect provided by isolators and the lateral restraining action of the abutment wing walls depending on the provide clearances. The derivation of fragility surfaces for isolated bridges in cold regions sheds new light on the challenges of retrofitting structures exposed to multiple extreme environments (e.g., seismic and thermal). Overall the presented results can facilitate seismic vulnerability modeling and retrofit assessment of these complex systems and afford valuable practical impacts. The insights and methodological advances can prompt research and applications well beyond the case study structures considered in the thesis, and have broad impacts.Au Québec, Canada, en raison du vieillissement et de détails insuffisants de dimensionnement sismique, les ponts sont susceptibles de subir des dommages importants en cas de fort séisme. Pour améliorer la performance sismique de l'inventaire des ponts de la province, le remplacement des appareils d'appui classiques par des isolateurs en caoutchouc naturel s'est avéré une mesure de réhabilitation potentiellement efficace. Cependant, les variations des propriétés mécaniques des isolateurs dues aux conditions environnementales peuvent affecter la performance sismique. Par exemple, le caoutchouc subit un raidissement important lorsqu'il est exposé aux basses températures, comme celles typiquement observées pendant les hivers dans l'est du Canada. Dans les ponts, le raidissement thermique des isolateurs augmente les forces transmises à la sous-structure, qui devient alors plus susceptible d'être endommagée. Une étude plus détaillée des effets thermiques sur la performance sismique des ponts provinciaux typiques est donc nécessaire. Des surfaces de fragilité sont donc utilisées pour évaluer la vulnérabilité d'un pont typique au Québec réhabilité avec des isolateurs en caoutchouc naturel sous les actions concomitantes des séismes et des basses températures. Les ponts sont composés de plusieurs éléments différents ayant des comportements distincts et des interactions complexes sous une excitation sismique. En raison de l'importance de la contribution de plusieurs composants à la fragilité du pont, la première partie de cette étude se concentre sur la construction de modèles probabilistes multivariés de demande sismique (PSDM). On a critiqué la validité des hypothèses couramment adoptées et leur impact sur les estimations de fragilité n'est pas entièrement compris. Une approche PSDM multivariée est donc développée en couplant l'analyse de bandes multiples et les modèles de mélange gaussien. La nouvelle approche capture de manière concomitante la complexité de la réponse dynamique et modélise les incertitudes et la corrélation. On évalue ensuite le biais potentiel introduit par une mauvaise modélisation sur les estimations de fragilité et de risque d'un pont réel tel que construit. Cette stratégie PSDM est ensuite adoptée pour traduire la réponse des composants du pont de l'étude de cas lorsqu'il est réhabilité. Les surfaces de fragilité basées sur la régression logistique décrivent les effets du raidissement thermique des isolateurs sur les performances du pont, tant au niveau des composants que du système. Une combinaison bénéfique est révélée entre l'effet de découplage des isolateurs et l'action de retenue latérale des murs en fonction des écarts fournis. La dérivation des surfaces de fragilité pour les ponts isolés dans les régions froides jette un nouvel éclairage sur les défis de la réhabilitation des structures exposées à de multiples environnements extrêmes (sismiques et thermiques). Dans l'ensemble, les résultats présentés peuvent faciliter la modélisation de la vulnérabilité sismique et l'évaluation de la réhabilitation de ces systèmes complexes et avoir des répercussions pratiques importantes. Les idées et les avancées méthodologiques peuvent susciter des recherches et des applications bien au-delà des structures étudiées dans la thèse, et en avoir un large impact

Évaluation de la fragilité sismique des barrages poids en utilisant des fonctions multivariées basées sur des méta-modèles

Les conséquences de la rupture d’un barrage peuvent être considérables, en termes de pertes humaines, économiques et environnementales. De plus, la sécurité des barrages et des aménagements hydroélectriques est une préoccupation majeure au Québec étant donné que plus de la moitié de la population vit dans des zones potentiellement inondables. Il y a environ 933 grands barrages au Canada et 333 ou un peu plus sont situés au Québec. Parmi eux, beaucoup d’entre eux ont été construits il y a plus de 50 ans. Au cours de cette période, d’importants progrès ont été réalisés dans les méthodes d’évaluation des risques naturels. Bien que la défaillance totale d’un barrage en béton à la suite d’un tremblement de terre soit rare, les tremblements de terre sont une cause majeure de dommages à différents degrés de gravité. Par conséquent, le vieillissement et ses problèmes associés, combiné aux nouvelles méthodes d’estimation des charges sismiques ont entraîné la nécessité de revoir et d’améliorer les méthodes d’analyse sismique pour les barrages. Au cours des dernières décennies, les outils probabilistes sont devenus de plus en plus populaires pour l’évaluation sismique des barrages. Cependant, de telles méthodes nécessitent souvent un grand nombre d’analyses dynamiques non linéaires de modèles complexes par éléments finis. Par conséquent, le compromis entre l’exactitude du modèle numérique et la quantité de calcul rend ce type d’analyse non viable. Toutefois, l’évaluation sismique des barrages peut être améliorée en incluant les incertitudes liées aux paramètres sismiques et aux paramètres de modélisation et accélérée en réduisant l’importante quantité de temps de calcul avec l’utilisation de techniques d’apprentissage automatique pour développer des modèles de substitution ou des méta-modèles qui serviront prédire la réponse du barrage. L’objectif principal de la recherche est de mettre au point une méthode d’évaluation de la sécurité sismique des structures de type barrage-poids grâce à une analyse de fragilité, effectuée avec la mise en oeuvre de méta-modèles et en identifiant correctement le scénario sismique susceptible d’être présent sur le site du barrage. La méthodologie est appliquée à un barrage-poids situé dans l’est du Canada, dont la fragilité est évaluée par comparaison avec les études antérieures et directives de sécurité actuelles. On observe que la procédure plus précise présentée ici pour choisir les accélérogrammes produit des estimations moins conservatrices de la fragilité pour le barrage. Nous avons trouvé que la surface de réponse polynomiale de 4ème ordre est le méta-modèle le plus performant, et elle a été utilisée pour générer des fonctions de fragilité multivariées pour tenir compte de la variation des paramètres les plus critiques du modèle influençant la fragilité sismique du barrage. A partir de l’analyse de ces modèles, des recommandations pratiques de conception ont pu être formulées et il a été observé que le paramètre de modélisation affectant le plus l’analyse de la fragilité est la cohésion entre le béton et la roche.Abstract: The consequences of dam failure can be substantial, in terms of casualties, economic and environmental damage. Moreover, the safety of dams and hydroelectric developments is a major concern in Quebec given that over half the population lives in potential flood zone. There are about 933 large dams in Canada and 333 or slightly more are located in Quebec. Among them, many have been built more than 50 years ago. During that time, important advances in the methodologies for evaluating the natural hazards have been made. Although total failure of a concrete dam following an earthquake is rare, earthquakes are a major cause of damage at different degrees of severity. Consequently, the combination ageing and its associated problems with new methods for estimating seismic loads, have resulted in the need to review and upgrade the methods of seismic analysis for dams. In recent decades, probabilistic-based tools, have become increasingly popular for the seismic assessment of dams. However, such methods often require a large number of nonlinear dynamic analysis of complex finite element models. As a result the trade-off between the accuracy of the numerical model and the computational burden render unviable this type of analysis. However, the seismic assessment of dams can be enhanced by including seismic and modeling parameters uncertainties and expedited by reducing the substantial computational time with the use of machine learning techniques to develop surrogate or meta-models to predict the response of the dam. The proposed research addresses direct gaps in the seismic performance assessment of dams, while also shedding new light on the use of machine learning to support fragility modeling of complex systems like dams. Accordingly, the main objective of this research was to develop a method for assessing the seismic safety of gravity dam-type structures through a fragility analysis, conducted with the implementation of meta-models and by properly identifying the seismic scenario likely to be present at the dam site. The methodology is applied to a case study gravity dam located in eastern Canada, whose fragility is assessed through comparison with previous studies and current safety guidelines. It is observed that the more accurate procedure presented herein to select ground motions produces less conservative fragility estimates for the case study dam. Likewise, the 4th order polynomial response surface came up as the best performing meta-model, and it was used to generate multivariate fragility functions to account for the most critical model parameter variation influencing the dam seismic fragility. From the analysis of these models, practical design recommendations could be formulated and it was observed that the modelling parameter affecting the fragility analysis the most was the concrete–rock cohesion

Response of soil–foundation–structure interaction of tall building (frame-wall) structural system under seismic effect

The unavailability of standards or validated analysis techniques of estimating the soil -foundation-structure interaction (SFSI) lead to either simplifying or ignoring this interaction. The structural and geotechnical engineers consider the foundation effect on the multi-story building design. Where both the structural and geotechnical analysis is usually conducted individually. The geotechnical engineer may simplify a multi-degree of freedom to a single degree of freedom oscillator, and on the other hand, structural engineers may ignore the soil-foundation-structure interaction SFSI orrepresent the nonlinear soil-foundation-Structure interaction with simple linear springs, where the nonlinear Interaction between the superstructure and the substructure is neglected. This study was carried out using experimental and numerical approaches toanalysis the Interaction of soil foundation structures under seismic effect. Experimental work was performed through a series of shaking table test events for different parametric studies such as building height, soil density, and foundation type under the impact of shaking waves representing the soil vibration of seismic effect. Numerical simulation was performed using two popular software packages i.e.ABAQUS and ETABS package to solve the three-dimensional problem of soil foundation structure response under seismic effect. The results obtained from the software will then be compared with those obtained by experimental work. Based on the literature review, the following parameters (which are believed to have an influence on the Soil Structural Interaction response) were investigated in this study:Building characteristics such as the height and mass,Soil properties including the dynamic stiffness, damping ratio, shear, angle of internal friction and shear wave velocity,Pile group configuration and the nonlinear interaction between piles and the Soil,Type of the foundation such as Raft, and Raft-Pile foundations.Characteristics of the input motion (earthquake type).The main purpose of the experimental tests was to investigate the effect of the parameters on the structure and compare the outcome of those tests with the predictions from the software programme to validate the numerical model for further dynamic studies. The experimental work was divided into four stages: Firstly, the fixed base stage. Secondly, the soil container stage. Thirdly, the soil-foundation-structure interaction (raft foundation). Fourthly, the soil-foundation-structure interaction (pile foundation). Comparing the results of the numerical model and the experimental measurements, it can be concluded that the employed numerical model is appropriate for the simulation of the soil-foundation - structure interaction under dynamic effect. The scale modelsdemonstrate some behaviour of the prototype in economical way without examining the prototype itself. Consequently, the proposed numerical model of raft foundation and pile foundation are valid and qualified method of simulation with sufficient accuracy which can be employed for further numerical dynamic soil-structure interactioninvestigations. to consider the amplification of lateral deflections of soil-foundation-structure interactions under the seismic effect of the shear wall – columns structural system, a simplified calculation method of soil-structure interactions moment has been proposed.The proposed procedure enables structural engineers to extract the response of soil structure interaction in more reliable ways to ensure the design safety and reliability

Proceedings of the Salford Postgraduate Annual Research Conference (SPARC) 2011

These proceedings bring together a selection of papers from the 2011 Salford Postgraduate Annual Research Conference(SPARC). It includes papers from PhD students in the arts and social sciences, business, computing, science and engineering, education, environment, built environment and health sciences. Contributions from Salford researchers are published here alongside papers from students at the Universities of Anglia Ruskin, Birmingham City, Chester,De Montfort, Exeter, Leeds, Liverpool, Liverpool John Moores and Manchester