Tesis sobre el tema "Seismic performance-based assessment"

Severe seismic events in urban regions during the last two decades revealed that the structures constructed before the development of modern seismic codes are the most vulnerable to earthquakes. Sub-standard reinforced concrete buildings constitute an important part of this highly vulnerable urban building stock. There is urgent need for the development and improvement of methods for seismic performance assessment of existing reinforced concrete structures. As an alternative to current conventional force-based assessment methods, a performance evaluation procedure for structural members, mainly reinforced concrete columns is proposed in this study, by using an energy-based approach combined with the low cycle fatigue concept. An energy-based hysteresis model is further introduced for representing the inelastic response of column members under severe seismic excitations. The shape of the hysteresis loops are controlled by the dissipated cumulative energy whereas the ultimate strength is governed by the low cycle fatigue behavior. These two basic characteristics are obtained experimentally from full scale specimens tested under constant and variable amplitude displacement cycles. The first phase of the experimental program presented in the study constitutes of testing sub-standard non-conforming column specimens. The second phase of testing was conducted on standard, code compliant reinforced concrete columns. A total number of 13 specimens were tested. The behavior of these specimens was observed individually and comparatively according to the performance based objectives. The results obtained from the experiments were employed for developing relations between the energy dissipation capacity of specimens, the specimen properties as well as the imposed displacement history. Moreover, the measured rotation capacities at the plastic regions are evaluated comparatively with the limits proposed by modern displacement-based seismic design and assessment provisions.

Steel framed structures constitute a considerable proportion of residential and commercial structures in earthquake prone regions. In such structures, typically, masonry infills are implemented as walls and partitions. However, in common practice, the influence of the infill panels on the performance and resistance of the building is mostly ignored, not just at the design stage, but also during assessment. Despite the possible strength enhancement that infill panels can bring to the structure for modest earthquakes, they may put the building at high risk of heavy damage if their impact is overlooked, and the interaction not properly designed, as seen in the 2003 Bam earthquake and many other destructive seismic events. Following the performance-based seismic assessment methodology, the dissertation focuses on evaluating the seismic performance of existing masonry infilled steel frames. The seismic response of several building typologies, designed according to common practice, is assessed through nonlinear dynamic methods. Detailed three-dimensional numerical models of selected index buildings are developed, capable of simulating the impact of masonry infill walls along other critical elements such as the beam-column connections, according to available empirical and experimental data. In order to measure the seismic vulnerability, along with possible losses and life cycle costs, analytical fragility functions are derived for the structures, while considering the hazard characteristics of the location under study. The derived fragility functions will help enrich the limited library of existing function dedicated to both bare and infilled steel structures. The outcome is of great importance for insurance valuation, as well as managing disasters and performing strengthening if necessary.

This dissertation develops a new concept for performance-based monitoring (PBM) of instrumented buildings subjected to earthquakes. This concept is achieved by simultaneously combining and advancing existing knowledge from structural mechanics, signal processing, and performance-based earthquake engineering paradigms. The PBM concept consists of 1) optimal sensor placement, 2) dynamic response reconstruction, 3) damage estimation, and 4) loss analysis. Within the proposed concept, the main theoretical contribution is the derivation of a nonlinear model-based observer (NMBO) for state estimation in nonlinear structural systems. The NMBO employs an efficient iterative algorithm to combine a nonlinear model and limited noise-contaminated response measurements to estimate the complete nonlinear dynamic response of the structural system of interest, in the particular case of this research, a building subject to an earthquake. The main advantage of the proposed observer over existing nonlinear recursive state estimators is that it is specifically designed to be physically realizable as a nonlinear structural model. This results in many desirable properties, such as improved stability and efficiency. Additionally, a practical methodology is presented to implement the proposed PBM concept in the case of instrumented steel, wood-frame, and reinforced concrete buildings as the three main types of structural systems used for construction in the United States. The proposed methodology is validated using three case studies of experimental and real-world large-scale instrumented buildings. The first case study is an extensively instrumented six-story wood frame building tested in a series of full-scale seismic tests in the final phase of the NEESWood project at the E-Defense facility in Japan. The second case study is a 6-story steel moment resisting frame building located in Burbank, CA, and uses the recorded acceleration data from the 1991 Sierra Madre and 1994 Northridge earthquakes. The third case is a seven-story reinforced concrete structure in Van Nuys, CA, which was severely damaged during the 1994 Northridge earthquake. The results presented in this dissertation constitute the most accurate and the highest resolution seismic response and damage measure estimates obtained for instrumented buildings. The proposed PBM concept will help structural engineers make more informed and swift decisions regarding post-earthquake assessment of critical instrumented building structures, thus improving earthquake resiliency of seismic-prone communities.

One of the major concerns in earthquake disaster resilience is understanding the risk posed by existing buildings that are not conformant with modern building codes. A related challenge is how, if necessary, to mitigate the risk through retrofit policies or other measures in a cost effective manner. For some types of buildings, such as unreinforced masonry, the risks are so obviously large, that mandatory laws have been enacted to assess and retrofit the buildings. However, in other cases, such as with non-ductile concrete buildings or older tall steel buildings, the risks and mitigation strategies are not as clear cut. This research addresses the risks posed by older seismically deficient steel buildings, which constitute a significant portion of tall buildings in western US cities with high seismic hazard. These buildings include many steel moment resisting frames (MRF), constructed during the late 1960's through mid-1990's, with the type of welded connections that experienced sudden brittle fractures during the 1994 Northridge earthquake. This work applies performance-based earthquake engineering (PBEE) tools to this potential seismic safety problem. San Francisco is selected as a case study city in order to permit engagement with the city’s ongoing earthquake safety initiatives. The performance of existing 1970s tall steel MRF buildings is evaluated through the development of archetype buildings. A series of studies that progressively explore the performance of individual archetype buildings, within a probabilistic framework, are carried out, including scenario-based, intensity-based and time-based assessments. Additionally, a method is proposed to extend such assessments to evaluate clusters of buildings and how their performance may impact the resilience of the community; going beyond individual building performance, towards more holistic seismic performance evaluations. The results of this body of research are communicated not only in terms of structural response, but also in terms of direct economic losses, downtime and recovery, which are more accessible to decision makers. The scenario-based and intensity-based evaluations are carried out to assess performance under an expected earthquake scenario, and design level shaking, respectively. The results indicate that, while the archetype buildings considered are expected to guarantee the life-safety of occupants, the associated economic losses and downtime entail a costly and slow recovery, which can, additionally, result in considerable indirect losses. The impact of adopting structural retrofit schemes, enhanced non-structural building components, and seismic mitigation measures is explored. The results indicate that, through a combination of these interventions, significant reductions, in both losses and downtime, under the earthquake ground motion shaking intensities considered, can be achieved. In order to benchmark the performance of 1970s steel MRFs versus modern design standards, a comparative time-based evaluation is carried out. The results indicate that the probabilities of collapse of the 1970s archetype buildings considered are well in excess of the 1% in 50 year target implicit in modern design standards. The results also illustrate that while modern designs result in performance that complies with the code intended collapse-safety margin, the level of damage control may be insufficient to enable a swift recovery and ensure the seismic resilience of these buildings. A methodology to assess the earthquake risk of existing tall buildings on the urban community is proposed. This method is implemented in a simple case study of a cluster of tall steel MRF buildings in downtown San Francisco. The results suggest that under a range of realistic earthquake scenarios, a considerable loss of occupancy and functionality is expected in buildings consistent with the 1970s archetype. Furthermore, permanent deformations in these buildings can result in large cordons around the damaged structures, which would prevent access to other buildings within a considerable area. The results of this research serve to inform the debate over the expected seismic performance of existing 1970s tall steel MRF buildings. This work provides an array of results from different types of assessment that can be informative to different parties including design practitioners, building owners, policy makers and the insurance sector.

Structural engineering is facing an extraordinarily challenging era. These challenges are driven by the increasing expectations of modern society to provide low-cost, architecturally appealing structures which can withstand large earthquakes. However, being able to avoid collapse in a large earthquake is no longer enough. A building must now be able to withstand a major seismic event with negligible damage so that it is immediately occupiable following such an event. As recent earthquakes have shown, the economic consequences of not achieving this level of performance are not acceptable. Technological solutions for low-damage structural systems are emerging. However, the goal of developing a low-damage building requires improving the performance of both the structural skeleton and the non-structural components. These non-structural components include items such as the claddings, partitions, ceilings and contents. Previous research has shown that damage to such items contributes a disproportionate amount to the overall economic losses in an earthquake. One such non-structural element that has a history of poor performance is the external cladding system, and this forms the focus of this research. Cladding systems are invariably complicated and provide a number of architectural functions. Therefore, it is important than when seeking to improve their seismic performance that these functions are not neglected. The seismic vulnerability of cladding systems are determined in this research through a desktop background study, literature review, and postearthquake reconnaissance survey of their performance in the 2010 – 2011 Canterbury earthquake sequence. This study identified that precast concrete claddings present a significant life-safety risk to pedestrians, and that the effect they have upon the primary structure is not well understood. The main objective of this research is consequently to better understand the performance of precast concrete cladding systems in earthquakes. This is achieved through an experimental campaign and numerical modelling of a range of precast concrete cladding systems. The experimental campaign consists of uni-directional, quasi static cyclic earthquake simulation on a test frame which represents a single-storey, single-bay portion of a reinforced concrete building. The test frame is clad with various precast concrete cladding panel configurations. A major focus is placed upon the influence the connection between the cladding panel and structural frame has upon seismic performance. A combination of experimental component testing, finite element modelling and analytical derivation is used to develop cladding models of the cladding systems investigated. The cyclic responses of the models are compared with the experimental data to evaluate their accuracy and validity. The comparison shows that the cladding models developed provide an excellent representation of real-world cladding behaviour. The cladding models are subsequently applied to a ten-storey case-study building. The expected seismic performance is examined with and without the cladding taken into consideration. The numerical analyses of the case-study building include modal analyses, nonlinear adaptive pushover analyses, and non-linear dynamic seismic response (time history) analyses to different levels of seismic hazard. The clad frame models are compared to the bare frame model to investigate the effect the cladding has upon the structural behaviour. Both the structural performance and cladding performance are also assessed using qualitative damage states. The results show a poor performance of precast concrete cladding systems is expected when traditional connection typologies are used. This result confirms the misalignment of structural and cladding damage observed in recent earthquake events. Consequently, this research explores the potential of an innovative cladding connection. The outcomes from this research shows that the innovative cladding connection proposed here is able to achieve low-damage performance whilst also being cost comparable to a traditional cladding connection. It is also theoretically possible that the connection can provide a positive value to the seismic performance of the structure by adding addition strength, stiffness and damping. Finally, the losses associated with both the traditional and innovative cladding systems are compared in terms of tangible outcomes, namely: repair costs, repair time and casualties. The results confirm that the use of innovative cladding technology can substantially reduce the overall losses that result from cladding damage.

Performance-Based Earthquake Engineering necessitates the development of simulation models that can predict the nonlinear behavior of structural components as part of a building subjected to seismic loading. For reliable seismic assessment of buildings, these models need to be calibrated with large sets of experimental data. This thesis advances the state-of-knowledge on the collapse assessment of concentrically braced frames (CBFs) designed in seismic regions. The thesis discusses the development of a database that includes extensive information from more than 300 tests of steel braces that have been conducted worldwide over the past 40 years. Statistical information of various properties of steel braces that can be used for quantification of modeling uncertainties is summarized and implications regarding the expected yield properties of various steel types as part of current design provisions are discussed. The steel brace database is utilized to develop drift-based and dual-parameter fragility curves for different damage states of steel braces. These curves can be used as tools for rapid estimation of earthquake damage towards the next generation of performance-based evaluation methods for new and existing buildings. Through extensive calibrations of an inelastic fiber-based steel brace cyclic model, modeling recommendations for the post-buckling behaviour and fracture of steel braces due to low-cycle fatigue are developed for three different brace shapes. The effectiveness of these recommendations is demonstrated through two case studies including concentrically braced frames (CBFs) subjected to earthquake loading. The emphasis is on the accurate assessment of the collapse capacity of concentrically braced frames with the explicit consideration of strength and stiffness deterioration of various structural components that are part of local story mechanisms that develop in CBFs after the steel braces fracture. The influence of modeling classical damping on the collapse capacity of CBFs is also discussed.
Le génie parasismique basé sur la performance des structures nécessite le développement des modèles de simulation qui peuvent estimer le comportement non-linéaire des composantes structurales faisant partie d'un bâtiment sujet ti aux efforts sismiques. Afin d'avoir une évaluation sismique fiable, les modèles doivent être étalonnés avec un grand inventaire de données obtenues expérimentalement. Cette thèse avance l'état des connaissances sur l'évaluation de l'effondrement des contreventements en treillis concentrique conçus dans les régions sismiques. Cette thèse adresse le développement d'une banque de données qui inclut plus de 300 essais effectués autour du monde sur des contreventements en acier depuis plus de 40 ans. Les données statistiques de plusieurs propriétés du contreventement en acier qui peuvent être utilisées pour la quantification des incertitudes de la modélisation sont résumées. Également les implications reliées aux propriétés limi d l'élasticité qui sont attendues selon le type d'acier sont présentées en fonction des règles d'actuelles de conception. La banque de données des contreventements en acier est utilisée afin de développer des drift-based et dual-parameter fragility curves courbes de fragilité à deux paramètres en fonction du déplacement horizontal relatif de l'étage pour différents degrés de dommage. Ces courbes servant à estimer efficacement et rapidement les dommages sismiques, amènt vers la prochaine génération des méthodes d'évaluation de la performance des structures. À travers une vérification approfondie de l'étalonnement du modèle non-linéaire cyclique à fibres du contreventement en acier des recommandations de modélisation du postflambement et de la rupture en fatigue oligocyclique sont développées pour trois différentes types de contreventement. L'efficacité de ces recommandations est démontrée à travers des études de cas incluantes des contreventements concentriques qui reprisent des efforts sismiques. L'accent est mis sur l'évaluation précise de la capacité de l'effondrement des contreventements en treillis concrentriques en prenant en compte explicitement le processus de dégradation de la capacité et de la rigidité des plusieurs composants structuraux qui font partie des mécanismes du dommage local qui s'évoluentdans différents étages d'une structure en contreventements concentriques en acier une fois que le contreventement s'est fracturé. L'effet de la modélisation de l'amortissement de la structure sur la capacité à l'effondrement des contreventements concentriques en acier est également considéré.

Recent advancements in numerical analysis and computational power have pushed the current bridge design specifications towards a more descriptive performance-based seismic design (PBSD) approach as compared to the conventional force-based method. One major attributes of this PBSD is to keep bridges operational and reduce the repair cost by limiting the global and local deformations of a bridge to acceptable levels under design loads. Shape memory alloy (SMA), with its distinct superelasticity, shape memory effect and hysteretic damping, is a promising material for the application in bridge piers to attain the objectives of PBSD. The objective of this research is to develop a performance-based seismic design guideline for concrete bridge pier reinforced with different types of SMAs. With the aim of providing a comprehensive design guideline, this study started with the experimental investigation of bond behavior of smooth and sand coated SMA rebar in concrete using pushout specimens. The test results were explored to evaluate the influence of concrete strength, bar diameter, embedment length, and surface condition. In addition, a plastic hinge length expression for SMA-RC bridge pier was developed which can be used for calculating the flexural displacement capacity and design of SMA-RC bridge pier. Using Incremental Dynamic Analysis (IDA), this study developed quantitative damage states corresponding to different performance levels (cracking, yielding, and strength degradation) and specific probabilistic distributions for RC bridge piers reinforced with different types of SMAs. Based on an extensive numerical study, the author proposed residual drift based damage states for SMA-RC pier. Based on the proposed damage states, a sequential procedure for the performance-based design of SMA-RC bridge pier is developed using a combination of residual and maximum drift. Finally, in order to elucidate the potential benefit and applicability of the proposed guideline, fragility curves and seismic hazard curves for different SMA-RC bridge piers are developed considering maximum and residual drift as engineering demand parameters. It is found that the SMA-RC bridge piers designed following the proposed design guideline have very low probability of damage resulting in a lower annual loss which will provide significant financial benefit in the long run.
Applied Science, Faculty of
Engineering, School of (Okanagan)
Graduate

Liquefaction-induced settlement can cause significant damage to structures and infrastructure in the wake of a seismic event. Predicting settlement is an essential component of a comprehensive seismic design. The inherent uncertainty associated with seismic events makes the accurate prediction of settlement difficult. While several methods of assessing seismic hazards exist, perhaps the most promising is performance-based earthquake engineering, a framework presented by the Pacific Earthquake Engineering Research (PEER) Center. The PEER framework incorporates probability theory to generate a comprehensive seismic hazard analysis. Two settlement estimation methods are incorporated into the PEER framework to create a fully probabilistic settlement estimation procedure. A seismic hazard analysis tool known as PBLiquefY was updated to include the fully probabilistic method described above. The goal of the additions to PBLiquefY is to facilitate the development of a simplified performance-based procedure for the prediction of liquefaction-induced free-field settlements. Settlement estimations are computed using conventional deterministic methods and the fully probabilistic procedure for five theoretical soil profiles in 10 cities of varying seismicity levels. A comparison of these results suggests that deterministic methods are adequate when considering events of low seismicity but may result in a considerable under-estimation of seismic hazard when considering events of mid to high seismicity.

Liquefaction-induced lateral spread displacements cause severe damage to infrastructure, resulting in large economic losses in affected regions. Predicting lateral spread displacements is an important aspect in any seismic analysis and design, and many different methods have been developed to accurately estimate these displacements. However, the inherent uncertainty in predicting seismic events, including the extent of liquefaction and its effects, makes it difficult to accurately estimate lateral spread displacements. Current conventional methods of predicting lateral spread displacements do not completely account for uncertainty, unlike a performance-based earthquake engineering (PBEE) approach that accounts for the all inherent uncertainty in seismic design. The PBEE approach incorporates complex probability theory throughout all aspects of estimating liquefaction-induced lateral spread displacements. A new fully-probabilistic PBEE method, based on results from the cone penetration test (CPT), was created for estimating lateral spread displacements using two different liquefaction triggering procedures. To accommodate the complexity of all probabilistic calculations, a new seismic hazard analysis tool, CPTLiquefY, was developed. Calculated lateral spread displacements using the new fully-probabilistic method were compared to estimated displacements using conventional methods. These comparisons were performed across 20 different CPT profiles and 10 cities of varying seismicity. The results of this comparison show that the conventional procedures of estimating lateral spread displacements are sufficient for areas of low seismicity and for lower return periods. However, by not accounting for all uncertainties, the conventional methods under-predict lateral spread displacements in areas of higher seismicity. This is cause for concern as it indicates that engineers in industry using the conventional methods are likely under-designing structures to resist lateral spread displacements for larger seismic events.

In the last three decades, seismic performance assessment of buried structures has evolved through the following stages : i) buried structures are not prone to seismically-induced damages, thus no need for detailed investigations, ii) eliminating soil-structure-earthquake interaction and use of seismically-induced free field ground deformations directly as the basis for seismic demand, thus producing conservative results, and finally iii) soil-structure and earthquake interaction models incorporating both kinematic and inertial interactions. As part of soil-structure and earthquake interacting models, simplified frame analysis established the state of practice and is widely used. Within the confines of this thesis, the results of simplified frame analysis based response of buried structures are compared with those of 2-D finite element dynamic analyses. For the purpose, 1-D dynamic and 2-D pseudo-dynamic analyses of free field and buried structural systems are performed for a number of generic soil, structure and earthquake combinations. The analyses results revealed that, in general, available closed form solutions are in pretty good agreement with the results of finite element analyses. However, due to the fact that dynamic analyses can model both kinematic and inertial effects
it should be preffered for the design of critical structures.

This work adopts a probabilistic evaluation approach to investigate the effectiveness of isolation devices for bridges in terms of seismic performance, vulnerability and expected life-cycle cost-benefit. A novel procedure to evaluate a reliable structure-based IM for isolated bridges and an improved life-cycle cost analysis formulation with respect to the existing ones are the two main original contributions. This dissertation has an assessment approach, so for each step some assumptions on the design of intervention, types of modelling and analysis have been introduced. No design optimization is carried out since it was not the purpose of this work, however the assumptions are based on the state of the art and practice and they will be clearly explained together with the limitations that eventually result from them. In order to achieve the purposes, an existing bridge has been selected as case study to take into account the complexity of a real structure. Even though a single case study bridge can restrict the generality of the numerical results, the main contributions mentioned previously consist in procedures that are not conditioned on the case study and that can be readily applied to other bridges. Damage to bridges during an earthquake event can lead to significant service breaks in the transportation system, causing primarily difficulties to the emergency operations. The main consequences due to bridge failure are a potential huge human's life loss and in addiction a wide economic impact on the transportation network, represented mainly by direct repair costs of intervention and indirect costs due to the loss of functionality of the bridge during repair. With specific reference to the Italian transportation network, the majority of the bridges was built between 1960 and 1980, consequently these structures are to date suffering structural deterioration and a large number of them was built following antiquated design standards with deficient or missing design criteria against seismic actions, therefore the issue of retrofitting of bridges assumes a key role, and it needs to be addressed with also reference to the Life-Cycle Cost (LCC) analyses. Between all the several design and retrofit strategies for improving the resistance of bridges to earthquakes, the seismic isolation is nowadays an effective choice for the protection of bridges that has been adopted in bridge design or retrofit for over 35 years in the United States and more recently it has been increasingly adopted also in Italy, especially towards the application of elastomeric bearings and friction-pendulum devices. The modern design philosophies, based on probabilistic performance-based earthquake engineering (PBEE) approaches, provides useful tools to identify the best retrofits for non-seismically designed bridges not only in terms of vulnerability assessment but also in order to achieve goals such as risk mitigation or minimization of economic loss. A primary objective of this work is the effectiveness evaluation of seismic protection devices for bridges following the probabilistic Intensity Measure (IM) based approach developed by the Pacific Earthquake Engineering Research (PEER). In fact, if IM-based approaches are well established and widely studied for bridges and buildings, there has been a very limited research to date regarding the performance assessment of bridges for evaluating the effectiveness of seismic isolation devices. This matter is then considered an actual topic implying a number of additional issues with respect to the case of non-isolated bridges. The elastomeric bearings (ERB) and the friction pendulum system (FPS) are here considered as isolation solutions, and they are applied to an existing railway bridge as case study. The bridge has a continuous five-span steel truss deck with a total length of about 500 m carried by four concrete piers with height ranging from 50 to 130 m. Geometry, loads, structural materials and existing bearings are investigated in order to design and estimate the retrofit interventions in an executable manner which can actually be put into practice. The structural modelling is conducted by developing three-dimensional finite element (FE) models of three bridge configurations (as-built, with ERB and with FPS) and subjecting them to a suite of 80 recorded ground motions with a wide range of spectral properties that are appropriate for isolated bridges. The FE models are developed in OpenSees employing fibre beam column elements for bridge piers and bilinear hysteretic elements for isolation devices. The influence of isolation on the demand for various critical bridge elements is evaluated through the development Probabilistic Seismic Demand Models (PSDMs) with 'cloud' approach to derive analytical fragility functions by nonlinear time history analysis (NLTHA) of the models. Peak ground acceleration (PGA) and Spectral Acceleration (Sa) calculated at different periods are adopted and compared as intensity measures (IMs) in terms of efficiency and sufficiency. To deal with the issue of adopting a reliable structure-based IM for isolated bridges, a novel procedure is introduced for the evaluation of the most appropriate period Ts which makes Sa(Ts) a reliable IM by maximizing its correlation to different components of a complex structure. The proposal of a new property for the IM, additional to efficiency and sufficiency, is addressed. Moreover, after the definition of appropriate limit states, the analysis of vulnerability at component level is addressed, followed by the evaluation of the effectiveness of isolation in terms of total probabilities of failure after the convolution with a seismic hazard coherently evaluated with respect to the selected ground motion set. To prevent high level of damage, both isolation systems give better protection in small piers than high ones, while they give more benefits in high pier for slight level of damage. The ERB results to be the most efficient to reduce the expected damage in the piers' base, however in terms of probability of damage at 1/3 height of the pier the effect of the two isolation systems are comparable. The FPS isolation is more efficient for the small piers than higher ones, for all the limit states. Moreover, the ERB provides a more uniform effect on the piers and better results on high piers than FPS. As mentioned above, life-cycle cost (LCC) analysis for bridges has gained widespread interest in recent years. Nevertheless, the effect of adopting seismic isolation devices for existing or new bridges, needs to be correctly addressed in terms of costs. The lack of knowledge regarding the correct estimation of LCC in presence of these kinds of devices needs to be covered by research, since in literature there are only few examples on how the isolation systems are producing cost-effective solutions for bridge owners. In order to give a contribution in this direction, this work provides an insight regarding the damage restoration of bridge components. The nominal retrofitting costs (initial cost in case of intervention), restoration costs (due to the possible damages in bearings and piers) and indirect costs (due to the loss of functionality of the bridge during repair) are estimated in an executable manner. Finally statistical moments of seismic losses, such as the expected value and variance, are calculated for the three examined bridge configurations by different life-cycle cost formulations (Wen and Kang, 2001, Beck et al., 2002, Wen et al., 2003, Ghosh and Padgett, 2011). The proposal of an improved LCC formulation with particular attention to the issue of a correct evaluation of discount functions to commutate future costs into present values is presented. The benefits of isolation in terms of expected costs are calculated comparing the different solutions.

Dissertação de mestrado em European Master in Building Information Modelling
Despite the mature state of BIM software in the context of structural design, particularly in concern to the desirable interoperability between BIM authoring tools and structural design software, there is still a technical/research gap in the scope of the exchange of competent data towards a seismic analysis of existing buildings (e.g. following the recommendations of Eurocode 8 – Part 3). This dissertation aimed to develop a BIM-based framework to facilitate the process of seismic analysis of existing reinforced concrete (RC) buildings, through a streamlined set of modelling rules and interoperability between Autodesk Revit (BIM authoring tool) and SeismoStruct (seismic analysis software). This is achieved through a visual programming script developed in Dynamo. The developed script is able to export geometry, sections, material properties, supports as well as the reinforcement data for structural columns and beams. Furthermore, as infill walls can play a significant contribution to the seismic capacity of the building, they are also considered in the framework. This is considered an important contribution of this framework, as infill walls are normally ignored in the usual design office during a seismic assessment of existing buildings. The interoperability script is able to query the necessary information from the BIM model and export it to an XML (Extensible Mark-up Language) that can be directly recognized by the seismic analysis software. The non-linear static analysis (i.e. pushover analysis) is then performed in Seismostruct. Based on the capacity curves obtained from the pushover analysis for the structure with and without infill walls, the conclusions about the effectiveness of infill wall in RC structures can be made. Upon preparation of the framework, its operational capacity was assessed on an academic-oriented example of a regular 4 storey building. Lastly, the developed framework/script was tested and evaluated on a case study based on a real building, with some degree of irregularity. The seismic capacity of the building was evaluated using pushover analysis, with an evaluation of the beneficial effects of consideration of infill walls. It was concluded that the framework operated in a suitable manner, allowing the quick translation of data from the BIM authoring tool towards the seismic analysis software, thus permitting the structural engineers to concentrate on design tasks rather than repetitive and error-prone activities of parsing information between software. Two special features are highlighted in concern to the original contributions of the developed framework/script: (i) it allows the easy consideration of infill walls in the BIM model and hence in the seismic calculation, thus allowing more realistic assessments; (ii) a method to input reinforcement data based on non-graphical data was proposed, facilitating the quickness of the input of information to the BIM model (and hence to the seismic analysis) as compared to the alternative need to model all reinforcement bars of the building.
Apesar do estado de elevada maturidade dos software BIM no contexto do projeto de estruturas, particularmente no que diz respeito à desejável interoperabilidade entre plataformas de modelação BIM e aplicações para análise/dimensionamento estrutural, há ainda lacunas técnicas importantes no contexto das trocas de informação competentes no contexto particular da análise sísmica de edifícios existentes (p.ex. em coerência com as recomendações do Eurocódigo 8 – parte 3). Nesta dissertação pretendeu-se desenvolver uma metodologia baseada em BIM para facilitar o processo de análise sísmica de edifícios existentes em betão armado (BA), através dum conjunto de regras de modelação e ferramenta de interoperabilidade entre Autodesk Revit (plataforma de modelação BIM) e SeismoStruct (aplicação de análise estrutural). Para isso, foi utilizado um código em linguagem de programação visual desenvolvido em Dynamo. O código desenvolvido é capaz de exportar geometria, secções, propriedades de materiais, apoios e dados sobre a armadura nos pilares e vigas. Além disso, tendo em conta que as paredes de enchimento podem ter um papel relevante no contributo para o desempenho sísmico dos edifícios, a sua existência é considerada de forma explícita na metodologia aqui proposta. Esta é considerada uma contribuição importante desta metodologia, uma vez que as paredes de enchimento são normalmente ignoradas na prática corrente de avaliação de desempenho sísmico de edifícios em contexto de gabinetes de projeto. O código de interoperabilidade proposto é capaz de analisar a informação necessária do modelo BIM e exportá-la no formato XML (Extensible Mark-up Language), que é reconhecido diretamente pelo software de análise sísmica utilizado. A análise não linear estática (i.e. análise pushover) é seguidamente realizada no SeismoStruct. Com base nas curvas de capacidade obtidas na análise pushover, e tendo em conta a análise de cenários com e sem paredes de enchimento, é possível tirar ilações sobre o comportamento sísmico dos edifícios e do papel dessas mesmas paredes. Durante a preparação da metodologia, a sua capacidade operacional foi validada num exemplo académico de um edifício regular de 4 pisos. Finalmente, a metodologia desenvolvida foi testada e avaliada num caso de estudo baseado em edifício real, com algum grau de irregularidade. A capacidade sísmica do edifício foi aferida com análise pushover, com avaliação dos benefícios da consideração das paredes de enchimento. Concluiu-se que a metodologia funcionou de forma adequada, permitindo a rápida transposição de dados da plataforma de modelação BIM para o software de análise sísmica, permitindo, portanto que os Engenheiros de Estruturas se concentrem em tarefas de projeto/engenharia, em vez de investirem tempo em tarefas repetitivas e suscetíveis a erro na troca de informação manual entre software. Relevam-se as duas características especiais que se afiguram como as contribuições mais originais da metodologia desenvolvida no presente trabalho: (i) permite a consideração facilitada das paredes de enchimento na análise sísmica a partir de informação do modelo BIM, conduzindo a análises mais realistas (em oposição à tendência corrente de ignorar as paredes de enchimento); (ii) é proposto um método de modelação das armaduras baseado em informação não gráfica, facilitando a rapidez da introdução de informação no modelo BIM (e consequentemente na análise sísmica), quando comparado com a potencial alternativa de modelar todas as armaduras do edifício.

碩士
國立中興大學
土木工程學系所
100
Modern highway bridges are commonly design to experience structural yielding during a seismic event. As the result, nonlinear deformations can be expected. However, the structure may turn to unstable if structural yielding occurs in too many parts of the bridge, leading to the collapse of the strucutre. Taiwan’s bridge design considers the nonlinear deformation of the ductility of the bridge, and the design approach commonly used in practices is based on the design of seismic forces. Additionally, inelastic deformation of the bridge is expected to disperse the energy of the earthquake and prevent the structure from collapsing. The design can also reduce the requirements of the ultimate strength when designing, and to achieve both the goal of economic and safety. In this study, a design approach suitable for preliminary design of bridge column is presented. A bridge designed following the approach is then evaluated using the finite element analysis software Midas. The performance assessment of the column follows the well developed Seismic Evaluation System (SERCB).

Italy is characterized by high seismicity and the recent earthquakes have highlighted the high vulnerability of the Italian real estate, mainly composed of historical and old masonry buildings. The greatest damages mostly occurred in the historical centres, where masonry buildings in aggregate are the prevalent structural typology. This circumstance has renewed the need of procedures for the seismic risk assessment and the unitary planning of strengthening interventions, according to a specific methodology appropriate for the masonry aggregates, in order to achieve safety standards and reduce the losses. Indeed, in the seismic vulnerability assessment, the identification of a determined building (i.e., structural unit) as an independent structure can become difficult, since it is often in adjacency to others and the same boundary walls are shared. Consequently, it is known that these systems do not have an independent structural behaviour, given the reciprocal interactions with adjacent structures during a seismic event (namely, the “aggregate effect”), and their analysis is naturally affected by several sources of uncertainties. Hence, this research project aims at understanding how the “aggregate effect” should be modelled for a more accurate assessment of the global seismic performance of the masonry buildings in aggregate, reducing the uncertainties related to too extensive knowledge process and providing tools for the definition of new guidelines for the masonry aggregates. To this end, a new procedure, referred to as “target structural unit approach”, is proposed, aiming at identifying the optimal portion of the aggregate that best represents the “aggregate effect” for the investigated building, i.e. the Minimum Unit of Analysis (M.U.A.).

碩士
中原大學
土木工程研究所
90
People paid much attention on the seismic capacity of buildings after the Chi-Chi earthquake happened. The 1999 year edition of “the Seismic Capacity Assessment for RC Building”, promoted by “Architecture & Building Research Institute, Minster of Interior”, was the most popular in Taiwan. By the trend of the world, the buildings with different functions are getting more complex in structural systems. The minimum requirement for buildings to not collapsed during the earthquake, won’t meet the demand of buildings nowadays. Thus this thesis use of the concept of ATC-40 performance-based earthquake assessment from America to proceed nonlinear statics analysis for buildings besides the design spectrum is the Taiwan’s data which can really responded the reaction of structures during Taiwan earthquakes. The story drift ratio and ductility of members are justified in the corresponding collapse ground acceleration and compared with the current method of seismic evaluation. Furthermore this study compared and discussed the results of the two methods with two existing buildings.

Cold-Formed Steel (CFS) is a material used in the fabrication of structural and non-structural elements for the construction of commercial and residential buildings. CFS exhibits several advantages over other construction materials such as wood, concrete and hot-rolled steel (structural steel). The outstanding advantages of CFS are its lower overall cost and non-combustibility. The steel industry has promoted CFS in recent decades, causing a notable increase in the usage of CFS in building construction. Yet, structural steel elements are still more highly preferred, due to the complex analysis and design procedures associated with CFS members. In addition, the seismic performance of CFS buildings and their elements is not well known. The primary objective of this study is to develop a method for the seismic assessment of the lateral-load resistant shear wall panel elements of CFS buildings. The Performance-Based Design (PBD) philosophy is adopted as the basis for conducting the seismic assessment of low- and mid-rise CFS buildings, having from one to seven storeys. Seismic standards have been developed to guide the design of buildings such that they do not collapse when subjected to specified design earthquakes. PBD provides the designer with options to choose the performance objectives to be satisfied by a building to achieve a satisfactory design. A performance objective involves the combination of an earthquake (i.e., seismic hazard) and a performance level (i.e., limit state) expected for the structure. The building capacity related to each performance level is compared with the demand imposed by the earthquake. If the earthquake demand is less than the building capacity, the structure is appropriately designed. The seismic performance of a CFS building is obtained using pushover analysis, a nonlinear method of seismic analysis. This study proposes a Simplified Finite Element Analysis (SFEA) method to carry out the nonlinear structural analysis. In this study, lateral drifts associated with four performance levels are employed as acceptance criteria for the PBD assessment of CFS buildings. The lateral drifts are determined from experimental data. In CFS buildings, one of the primary load-resistant elements is Shear Wall Panel (SWP). The SWP is constructed with vertically spaced and aligned C-shape CFS studs. The ends of the studs are screwed to the top and bottom tracks, and structural sheathing is installed on one or both sides of the wall. For the analysis of CFS buildings, Conventional Finite Element Analysis (CFEA) is typically adopted. However, CFEA is time consuming because of the large number of shell and frame elements required to model the SWP sheathing and studs. The SFEA proposed in this study consists of modeling each SWP in the building with an equivalent shell element of the same dimensions; that is, a complete SWP is modeled by a 16-node shell element. Thus, significantly fewer elements are required to model a building for SFEA compared to that required for CFEA, saving both time and resources. A model for the stiffness degradation of a SWP is developed as a function of the lateral strength of the SWP. The model characterizes the nonlinear behaviour of SWP under lateral loading, such that a realistic response of the building is achieved by the pushover analysis. The lateral strength of a SWP must be known before its seismic performance can be assessed. In current practice, the lateral strength of a SWP is primarily determined by experimental tests due to the lack of applicable analytical methods. In this investigation, an analytical method is developed for determining the ultimate lateral strength of SWP, and associated lateral displacement. The method takes into account the various factors that affect the behaviour and the strength of SWP, such as material properties, geometrical dimensions, and construction details. To illustrate the effectiveness and practical application of the proposed methodology for carrying out the PBD assessment of CFS buildings, several examples are presented. The responses predicted by the SFEA are compared with responses determined experimentally for isolated SWP. In addition, two building models are analyzed by SFEA, and the results are compared with those found by SAP2000 (2006). Lastly, the PBD assessment of two buildings is conducted using SFEA and pushover analysis accounting for the nonlinear behaviour of the SWP, to demonstrate the practicality of the proposed technology.

Η παρούσα διατριβή έχει ως θέμα την σεισμική αποτίμηση υφισταμένου τριώροφου δομήματος οπλισμένου σκυροδέματος. Συγκεκριμένα γίνεται έλεγχος των μέτρων επέμβασης για το κτήριο αιθουσών διδασκαλίας του ΤΕΛ Ναυπάκτου. Για τον σκοπό αυτό χρησιμοποιούνται μη-γραμμικές αναλύσεις (στατικές και δυναμικές) με βάση τις αρχές των κανονιστικών κειμένων ΚΑΝ.ΕΠΕ και EC8 για την αποτίμηση και τον ανασχεδιασμό κατασκευών. Στο πρώτο κεφάλαιο γίνεται τεκμηρίωση του υφιστάμενου δομήματος. Δίνονται στοιχεία για την θέση, την γεωμετρία, τις κατασκευαστικές μεθόδους που εφαρμόστηκαν. Δίνονται τα αποτελέσματα των οπτικών και των ενόργανων ελέγχων και προσδιορίζεται η γεωμετρία του φορέα. Στο δεύτερο κεφάλαιο δίνονται οι παραδοχές και οι αρχές με βάση τις οποίες έγινε η εξιδανίκευση του φορέα για την πραγματοποίηση των μη γραμμικών στατικών αναλύσεων. Για τις αναλύσεις χρησιμοποιείται το πακέτο λογισμικού ANSRuop που έχει αναπτυχθεί στο Εργαστήριο Κατασκευών του Τμήματος. Το μοντέλο μονότονης και ανακυκλιζόμενης φόρτισης που χρησιμοποιείται είναι το γνωστό προσομοίωμα Τakeda με εννέα κανόνες υστέρησης. Προσδιορίζονται οι παραδοχές για τον υπολογισμό των διαθέσιμων αντιστάσεων σε όρους παραμορφώσεων και δυνάμεων που υιοθετούνται από τον ΚΑΝΕΠΕ και τον EC8 καθώς και τα κριτήρια που αποδέχεται το κάθε κείμενο για την επιθυμητή στάθμη αποτίμησης και ανασχεδιασμού του φορέα. Ακόμα γίνεται αναφορά στο μοντέλο προσομοίωσης του λικνισμού των θεμελίων για θεώρηση διαφόρων εδαφών. Εν συνεχεία στο τρίτο Κεφάλαιο γίνεται αναφορά στους στόχους σχεδιασμού που θέτει ο κάθε κανονισμός και στις στάθμες επιτελεστικότητας για τον κάθε κανονισμό. Γίνεται παρουσίαση των τεχνητών σεισμικών καταγραφών που λήφθηκαν υπόψη για την πραγματοποίηση των μη γραμμικών δυναμικών αναλύσεων. Οι καταγραφές είναι κανονικοποιημένες πάνω στο φάσμα του EC8 για τύπο εδάφους C που διαφέρει από το φάσμα σχεδιασμού κατά ΕΑΚ για την στάθμη επιτελεστικότητας «Προστασία ζωής και περιουσίας των ενοίκων » μόνο κατά τον εδαφικό συντελεστή S. Ακόμα δίνεται η μεθοδολογία που υιοθετήθηκε για την εκτίμηση της ικανότητας του κτηρίου έναντι των απαιτήσεων που θέτει ο κανονισμός και προτείνεται εναλλακτικά και από τα δύο κείμενα. Στα κεφάλαια 4 και 5 παρουσιάζονται τα αποτελέσματα των μη-γραμμικών αναλύσεων. Συνολικά πραγματοποιήθηκαν 56 μη-γραμμικές στατικές αναλύσεις και 84 μη-γραμμικές δυναμικές. Για τις μη-γραμμικές στατικές αναλύσεις παρουσιάζονται οι καταγραφές τέμνουσας βάσης μετατόπισης κορυφής ενώ τα αποτελέσματα των μη-γραμμικών δυναμικών αναλύσεων δίνονται με την μορφή των μέσων όρων των δεικτών βλάβης. Τέλος στο 6ο κεφάλαιο γίνεται προσπάθεια ερμηνείας των αποτελεσμάτων για τις αναλύσεις πρίν και μετά την δομητική επέμβαση.
The present project deals with a seismic assessment analysis of an existing reinforced concrete building. A fully performance-based procedure is adopted based on the principals of the draft Greek Retrofitting Code and the draft part 3 of the Eurocode 8 : Assessment and retrofitting of Buildings. The method is subjected on an existing building, which has been constructed, during early 70’ s, prior to the principals of the modern codes for earthquake resistant design. The building is located in the area of Nafpaktos. In the first chapter a summary of the characteristics of the existing building is given. Special data concerning the site, the geometry and the construction methods at the time in which the building was constructed. The results of the damage investigation according to the visual and the instrumental inspection are also given. The basic principals according to which the modelling and the non-linear analysis procedures took place is given in the 2nd chapter. For the analysis procedures the program ANSR University of Patras is used which has been developed in the Structural Laboratory of The Civil Engineering Department of the University of Patras. One-component, point-hinge macromodels are used for the RC members, to relate the end-moment to the chord rotation at member ends within each plane of bending. The M-θ relation in monotonic loading is taken bilinear, with a post-yield hardening ratio p computed assuming antisymmetric bending and using empirical expressions according to the Greek Retrofitting Code and Part-3 of the EC8 (according to the selected limit state). The hysteresis rules supplementing the bilinear monotonic M-θ curve are of the modified-Takeda type. Also the monotonic M-θ relation which is used for the modelling of the foundation uplift is given. In the 3rd chapter the performance objectives of the assessment procedure are given according to the appropriate levels of protection for the selected limit state. The synthetic accellerograms which are used for the Nonlinear dynamic procedure are compatible to the EC8 elastic spectrum for type soil C for the limit state of Significant Damage. Moreover the methodology of the determination of the target displacement according to the Annex B of the EC8-part 1 and the draft Greek Retrofitting Code. Finally in chapters 4 and 5 the results of the nonlinear static and dynamic analysis are presented. For the nonlinear static procedures the results are given in terms of base shear vs roof displacement and in terms of Spectral acceleration vs Spectral displacement for the determination of the target displacement. The results of the NonLinear dynamic procedures are given in terms of mean values of the damage index.