Influencia de los requisitos de seguridad a la fatiga en el dimensionamiento de puentes mixtos de carretera

El fenómeno de fatiga es uno de los condicionantes más importantes en el diseño de puentes metálicos y mixtos bajo la acción cíclica de fuertes sobrecargas reales. Hoy en día, ha tomado mayor relevancia en el ámbito de puentes de carretera debido al aumento sustancial de la intensidad de tráfico y el peso de los vehículos. La evolución de las normativas actuales, que recogen su cálculo a partir del ELU de seguridad a fatiga, debe ir dirigida, hacia una mayor simplicidad de aplicación y un mayor rigor técnico. A partir del análisis de seis puentes mixtos de carretera proyectados recientemente (2007-2011) se pretende establecer una comparación, tanto cualitativa como cuantitativa, entre los métodos simplificados de la normativa española (antigua RPM/RPX 95 y actual EAE) y el Eurocódigo frente al Método del Daño Acumulado, caracterizado por ser más complicado de aplicar pero más riguroso. A través del análisis efectuado, se obtienen reglas prácticas sencillas y fiables para el dimensionamiento o verificación de elementos estructurales a fatiga según características principales como la tipología de la sección o la longitud de vano, entre otros. En conclusión, el trabajo que se propone desarrollar combina el análisis crítico de la base teórica con el estudio aplicado de casos reales y pretende sentar las bases para profundizar en esta área de gran interés para proyectistas. Fatigue is one of the most determining factors in the design of steel and composite bridges with dynamic loads subject to cyclic live loads. Nowadays, it has taken relevance in the field of roadway bridges due to considerable increase in the intensity of traffic and the weight of vehicles. The evolution of the current design codes, which include an analysis of the ultimate limit state of fatigue, should aim for greater ease of application and technical rigour. Based on the analysis of six composite road bridges designed recently (2007-2011), a comparison has been made, both qualitative and quantitative, between the simplified methods of the Spanish codes (current EAE and old RPM/RPX95) and Eurocode with regard to the Cumulative Damage Method, characterised for being more difficult to apply but more rigorous. Through an exhaustive analysis, a set of practical and reliable rules have been obtained for the sizing or verification of structural elements according to main characteristics such as the tipology of the cross section or the length of span, among others. In conclusion, the work developed combines the critical analysis of the theory with the applied study of real cases and sets out to lay the foundations for deepening into this area of great interest to designers.

Estudio de la adherencia de armaduras corroídas y su influencia en la capacidad resistente de elementos de hormigón armado

La verificación de la seguridad estructural, tanto de estructuras que permitan un cierto grado de deterioro en su dimensionado como de estructuras existentes deterioradas, necesita disponer de modelos de resistencia que tengan en cuenta los efectos del deterioro. En el caso de la corrosión de las armaduras en las estructuras de hormigón armado, la resistencia depende de múltiples factores tales como la sección del acero corroído, el diagrama tensión-deformación del acero corroído, la adherencia hormigón-acero corroído, la fisuración o desprendimiento del hormigón debido a la expansión de los productos de corrosión. En este sentido, la transferencia de las fuerzas a través de la superficie de contacto entre el hormigón y el acero, la adherencia, es uno de los aspectos más importantes a considerar y es la base del comportamiento del hormigón armado como elemento estructural. La adherencia debe asegurar el anclaje de las armaduras y transmitir la tensión tangencial que aparece en las mismas como consecuencia de la variación de las solicitaciones a lo largo de un elemento estructural. Como consecuencia de la corrosión de las armaduras, el desarrollo de la adherencia se altera y, por tanto, la transferencia de la tensión longitudinal. Esta Tesis Doctoral aborda el comportamiento en estado límite último de la adherencia en el hormigón estructural con armaduras corroídas. El objetivo principal es la obtención de un modelo suficientemente realista y fiable para la evaluación de la adherencia con armaduras corroídas en el marco de la verificación de la seguridad estructural de elementos de hormigón armado con armaduras corroídas. Para ello se ha llevado a cabo un programa experimental de ensayos tipo pull-out excéntricos, con diferentes probetas, unas sin corrosión y otras sometidas tanto a procesos de corrosión natural como a procesos de corrosión acelerada, con diferentes grados de deterioro. Este tipo de ensayo de adherencia representa de forma realista y fiable realista los esfuerzos de adherencia en la zona de anclaje. Por otra parte, para la realización de estos ensayos se ha puesto a punto, además del procedimiento de ensayo, un sistema de adquisición de datos entre los que se incluye el empleo de sensores de tipo fibra óptica con redes de Bragg embebidos en la armadura para determinar los parámetros representativos de la adherencia en el hormigón estructural con armaduras corroídas. Por otra parte, la recopilación de los datos de los estudios de adherencia con armaduras corroídas procedentes de la literatura científica, además de los resultados de la presente investigación, junto con la identificación de las variables relevantes en el comportamiento de la adherencia con armaduras sanas y corroídas ha servido para la obtención de una formulación realista y fiable para la evaluación conjunta de la adherencia con armaduras sanas y corroídas a partir de modelos de regresión múltiple. La formulación propuesta ha sido validada mediante criterios estadísticos y comparada con otras formulaciones propuestas en la literatura científica. Además se ha realizado un análisis de las variables influyentes de la formulación propuesta. También se ha obtenido un modelo numérico simple y eficiente, validado con alguno de los ensayos realizados en esta tesis, para simular la adherencia con armaduras sanas y corroídas. Finalmente, se presenta un procedimiento para realizar la evaluación de vigas deterioradas por corrosión mediante el método de los campos de tensiones que incluye la evaluación de la adherencia mediante la formulación sugerida en esta Tesis Doctoral. Las conclusiones alcanzadas en este trabajo han permitido evaluar la adherencia con armaduras corroídas de forma realista y fiable. Asimismo, se ha podido incluir la evaluación de la adherencia en el marco de la verificación de la seguridad estructural en elementos de hormigón armado deteriorados por corrosión. ABSTRACT Structural safety verification of both structures allowing a certain degree of deterioration in design and deteriorated existing structures needs strength models that factor in the effects of deterioration. In case of corrosion of steel bars in reinforced concrete structures, the resistance depends on many things such as the remaining cross-section of the corroded reinforcement bars, the stress-strain diagrams of steel, the concrete-reinforcement bond and corrosion-induced concrete cracking or spalling. Accordingly, the force transfer through the contact surface between concrete and reinforcement, bond, is one of the most important aspects to consider and it is the basis of the structural performance of reinforced concrete. Bond must assure anchorage of reinforcement and transmit shear stresses as a consequence of the different stresses along a structural element As a consequence of corrosion, the bond development may be affected and hence the transfer of longitudinal stresses. This PhD Thesis deals with ultimate limit state bond behaviour in structural concrete with corrode steel bars. The main objective is to obtain a realistic and reliable model for the assessment of bond within the context of structural safety verifications of reinforced concrete members with corroded steel bars. In that context, an experimental programme of eccentric pull-out tests were conducted, with different specimens, ones without corrosion and others subjected to accelerated or natural corrosion with different corrosion degrees. This type of bond test reproduces in a realistic and reliable way bond stresses in the anchorage zone. Moreover, for conducting these tests it was necessary to develop both a test procedure and also a data acquisition system including the use of an embedded fibre-optic sensing system with fibre Bragg grating sensors to obtain the representative parameters of bond strength in structural concrete with corroded steel bars. Furthermore, the compilation of data from bond studies with corroded steel bars from scientific literature, including tests conducted in the present study, along with the identification of the relevant variables influencing bond behaviour for both corroded and non-corroded steel bars was used to obtain a realistic and reliable formulation for bond assessment in corroded and non-corroded steel bars by multiple linear regression analysis. The proposed formulation was validated with a number of statistical criteria and compared to other models from scientific literature. Moreover, an analysis of the influencing variables of the proposed formulation has been performed. Also, a simplified and efficient numerical model has been obtained and validated with several tests performed in this PhD Thesis for simulating the bond in corroded and non-corroded steel bars. Finally, a proposal for the assessment of corrosion-damaged beams with stress field models including bond assessment with the proposed formulation is presented. The conclusions raised in this work have allowed a realistic and reliable bond assessment in corroded steel bars. Furthermore, bond assessment has been included within the context of structural safety verifications in corrosion-damaged reinforced concrete elements.

A linearization-based system reliability method with application to geotechnical analysis

Los análisis de fiabilidad representan una herramienta adecuada para contemplar las incertidumbres inherentes que existen en los parámetros geotécnicos. En esta Tesis Doctoral se desarrolla una metodología basada en una linealización sencilla, que emplea aproximaciones de primer o segundo orden, para evaluar eficientemente la fiabilidad del sistema en los problemas geotécnicos. En primer lugar, se emplean diferentes métodos para analizar la fiabilidad de dos aspectos propios del diseño de los túneles: la estabilidad del frente y el comportamiento del sostenimiento. Se aplican varias metodologías de fiabilidad — el Método de Fiabilidad de Primer Orden (FORM), el Método de Fiabilidad de Segundo Orden (SORM) y el Muestreo por Importancia (IS). Los resultados muestran que los tipos de distribución y las estructuras de correlación consideradas para todas las variables aleatorias tienen una influencia significativa en los resultados de fiabilidad, lo cual remarca la importancia de una adecuada caracterización de las incertidumbres geotécnicas en las aplicaciones prácticas. Los resultados también muestran que tanto el FORM como el SORM pueden emplearse para estimar la fiabilidad del sostenimiento de un túnel y que el SORM puede mejorar el FORM con un esfuerzo computacional adicional aceptable. Posteriormente, se desarrolla una metodología de linealización para evaluar la fiabilidad del sistema en los problemas geotécnicos. Esta metodología solamente necesita la información proporcionada por el FORM: el vector de índices de fiabilidad de las funciones de estado límite (LSFs) que componen el sistema y su matriz de correlación. Se analizan dos problemas geotécnicos comunes —la estabilidad de un talud en un suelo estratificado y un túnel circular excavado en roca— para demostrar la sencillez, precisión y eficiencia del procedimiento propuesto. Asimismo, se reflejan las ventajas de la metodología de linealización con respecto a las herramientas computacionales alternativas. Igualmente se muestra que, en el caso de que resulte necesario, se puede emplear el SORM —que aproxima la verdadera LSF mejor que el FORM— para calcular estimaciones más precisas de la fiabilidad del sistema. Finalmente, se presenta una nueva metodología que emplea Algoritmos Genéticos para identificar, de manera precisa, las superficies de deslizamiento representativas (RSSs) de taludes en suelos estratificados, las cuales se emplean posteriormente para estimar la fiabilidad del sistema, empleando la metodología de linealización propuesta. Se adoptan tres taludes en suelos estratificados característicos para demostrar la eficiencia, precisión y robustez del procedimiento propuesto y se discuten las ventajas del mismo con respecto a otros métodos alternativos. Los resultados muestran que la metodología propuesta da estimaciones de fiabilidad que mejoran los resultados previamente publicados, enfatizando la importancia de hallar buenas RSSs —y, especialmente, adecuadas (desde un punto de vista probabilístico) superficies de deslizamiento críticas que podrían ser no-circulares— para obtener estimaciones acertadas de la fiabilidad de taludes en suelos. Reliability analyses provide an adequate tool to consider the inherent uncertainties that exist in geotechnical parameters. This dissertation develops a simple linearization-based approach, that uses first or second order approximations, to efficiently evaluate the system reliability of geotechnical problems. First, reliability methods are employed to analyze the reliability of two tunnel design aspects: face stability and performance of support systems. Several reliability approaches —the first order reliability method (FORM), the second order reliability method (SORM), the response surface method (RSM) and importance sampling (IS)— are employed, with results showing that the assumed distribution types and correlation structures for all random variables have a significant effect on the reliability results. This emphasizes the importance of an adequate characterization of geotechnical uncertainties for practical applications. Results also show that both FORM and SORM can be used to estimate the reliability of tunnel-support systems; and that SORM can outperform FORM with an acceptable additional computational effort. A linearization approach is then developed to evaluate the system reliability of series geotechnical problems. The approach only needs information provided by FORM: the vector of reliability indices of the limit state functions (LSFs) composing the system, and their correlation matrix. Two common geotechnical problems —the stability of a slope in layered soil and a circular tunnel in rock— are employed to demonstrate the simplicity, accuracy and efficiency of the suggested procedure. Advantages of the linearization approach with respect to alternative computational tools are discussed. It is also found that, if necessary, SORM —that approximates the true LSF better than FORM— can be employed to compute better estimations of the system’s reliability. Finally, a new approach using Genetic Algorithms (GAs) is presented to identify the fully specified representative slip surfaces (RSSs) of layered soil slopes, and such RSSs are then employed to estimate the system reliability of slopes, using our proposed linearization approach. Three typical benchmark-slopes with layered soils are adopted to demonstrate the efficiency, accuracy and robustness of the suggested procedure, and advantages of the proposed method with respect to alternative methods are discussed. Results show that the proposed approach provides reliability estimates that improve previously published results, emphasizing the importance of finding good RSSs —and, especially, good (probabilistic) critical slip surfaces that might be non-circular— to obtain good estimations of the reliability of soil slope systems.

Análise teórica-experimental de perfis de aço formados a frio devido à instabilidade por distorção na flexão

Apresenta-se neste trabalho um estudo teórico-experimental sobre a instabilidade de perfis formados a frio submetidos à flexão. A instabilidade distorcional se faz comum na presença de tensões de compressão atuando sobre perfis enrijecidos e fabricados com aços de elevada resistência mecânica. A parte teórica abrange os métodos de cálculo analíticos e numéricos para a análise de instabilidade distorcional de perfis de seção aberta formados a frio. Na parte experimental inclui-se o estudo de perfis formados a frio com seções do tipo U enrijecidos submetidos aos ensaios à flexão. Nestes ensaios variou-se a altura de alma e espessura de chapa procurando-se abranger maior número de condições geométricas para análise da estabilidade distorcional. Inclui-se também a análise de instabilidade numérica dos perfis do programa experimental através do método de resistência direta via método das faixas finitas. Com base nos resultados experimentais, numéricos e na análise teórica do problema, verificou-se o procedimento adotado pela NBR14762/2001 e efetuou-se comparação entre curvas de resistência propostas para o dimensionamento de perfis formados a frio à flexão. Foi verificado que o fenômeno de instabilidade distorcional pode ser o estado limite último crítico para o dimensionamento dos perfis formados a frio.

Subsidence activity maps derived from DInSAR data: Orihuela case study

A new methodology is proposed to produce subsidence activity maps based on the geostatistical analysis of persistent scatterer interferometry (PSI) data. PSI displacement measurements are interpolated based on conditional Sequential Gaussian Simulation (SGS) to calculate multiple equiprobable realizations of subsidence. The result from this process is a series of interpolated subsidence values, with an estimation of the spatial variability and a confidence level on the interpolation. These maps complement the PSI displacement map, improving the identification of wide subsiding areas at a regional scale. At a local scale, they can be used to identify buildings susceptible to suffer subsidence related damages. In order to do so, it is necessary to calculate the maximum differential settlement and the maximum angular distortion for each building of the study area. Based on PSI-derived parameters those buildings in which the serviceability limit state has been exceeded, and where in situ forensic analysis should be made, can be automatically identified. This methodology has been tested in the city of Orihuela (SE Spain) for the study of historical buildings damaged during the last two decades by subsidence due to aquifer overexploitation. The qualitative evaluation of the results from the methodology carried out in buildings where damages have been reported shows a success rate of 100%.

Hybrid knowledge representation in a blackboard KBS for liquid retaining structure design

This paper highlights the importance of design expertise, for designing liquid retaining structures, including subjective judgments and professional experience. Design of liquid retaining structures has special features different from the others. Being more vulnerable to corrosion problem, they have stringent requirements against serviceability limit state of crack. It is the premise of the study to transferring expert knowledge in a computerized blackboard system. Hybrid knowledge representation schemes, including production rules, object-oriented programming, and procedural methods, are employed to express engineering heuristics and standard design knowledge during the development of the knowledge-based system (KBS) for design of liquid retaining structures. This approach renders it possible to take advantages of the characteristics of each method. The system can provide the user with advice on preliminary design, loading specification, optimized configuration selection and detailed design analysis of liquid retaining structure. It would be beneficial to the field of retaining structure design by focusing on the acquisition and organization of expert knowledge through the development of recent artificial intelligence technology. (C) 2003 Elsevier Ltd. All rights reserved.

Spin exchange and superconductivity in a t-J(')-V model for two-dimensional quarter-filled systems

The effect of antiferromagnetic spin fluctuations on two-dimensional quarter-filled systems is studied theoretically. An effective t-J(')-V model on a square lattice which accounts for checkerboard charge fluctuations and next-nearest-neighbor antiferromagnetic spin fluctuations is considered. From calculations based on large-N theory on this model it is found that the exchange interaction J(') increases the attraction between electrons in the d(xy) channel only, so that both charge and spin fluctuations work cooperatively to produce d(xy) pairing.

A failure criterion for fillet welds

The work constitutes a study of the strength of mild steel fillet welds subject to static loading, and the behaviour of flange welded beam-column connections under combined bending and shear. Tests are conducted on short welds in the as-welded and stress relieved conditions, and also on full-size beam-column connections. It is shown that welds under compression have a lower strength than when under tension. Failure of the fillet weld is initiated at the weld root, the important factor controlling the initiation being weld ductility. The greater the residual stress, the lower the weld ductility and ultimate strength. Thermal stress relieving increases strength by as much as 30%. Weld failure plane is rarely at the throat and varies from 0° to 45° depending upon loading condition. Failure plane average stresses are related by a circular function which is expressed in terms of externally applied forces at limit state. The tension weld of a flange-welded beam-column connection always fails before the compression weld. The shear load sharing between the welds is a complex function of elastic compression of the web, elastic/plastic deformation of the flanges, load/deformation characteristics, and the type of load application. Bearing forces between the compression flange and column face produce low level bearing stresses and frictional forces which make a negligible contribution to shear load resistance. Three modes of connection failure are possible; 'end mode', 'bending mode' and 'shear mode', with a sudden change taking place between the two latter.

Design of sway frames

The aim of the work presented in this thesis is to produce a direct method to design structures subject to deflection constraints at the working loads. The work carried out can be divided into four main parts. In the first part, a direct design procedure for plane steel frames subjected to sway limitations is proposed. The stiffness equations are modified so that the sway in each storey is equal to some specified values. The modified equations are then solved by iteration to calculate the cross-sectional properties of the columns as well as the other joint displacements. The beam sections are selected initially and then altered in an effort to reduce the total material cost of the frame. A linear extrapolation technique is used to reduce this cost. In this design, stability functions are used so that the effect of axial loads in the members are taken into consideration. The final reduced cost design is checked for strength requirements and the members are altered accordingly. In the second part, the design method is applied to the design of reinforced concrete frames in which the sway in the columns play an active part in the design criteria. The second moment of area of each column is obtained by solving the modified stiffness equations and then used to calculate the mlnlmum column depth required. Again the frame has to be checked for all the ultimate limit state load cases. In the third part, the method is generalised to design pin-jointed space frames for deflection limitatlions. In these the member areas are calculated so that the deflection at a specified joint is equal to its specified value. In the final part, the Lagrange multiplier technique is employed to obtain an optimum design for plane rigidly jointed steel frames. The iteration technique is used here to solve the modified stiffness equations as well as derivative equations obtained in accordance to the requirements of the optimisation method.

Updating of an instrumented building model considering amplitude dependence of dynamic resonant properties extracted from seismic response records

The authors would like to express their gratitude to their supporters. Drs Jim Cousins, S.R. Uma and Ken Gledhill facilitated this research by providing access to GeoNet seismic data and structural building information. Piotr Omenzetter’s work within the Lloyd’s Register Foundation Centre for Safety and Reliability Engineering at the University of Aberdeen is supported by Lloyd’s Register Foundation. The Foundation helps to protect life and property by supporting engineering-related education, public engagement and the application of research.

Updating of an instrumented building model considering amplitude dependence of dynamic resonant properties extracted from seismic response records

The authors would like to express their gratitude to their supporters. Drs Jim Cousins, S.R. Uma and Ken Gledhill facilitated this research by providing access to GeoNet seismic data and structural building information. Piotr Omenzetter’s work within the Lloyd’s Register Foundation Centre for Safety and Reliability Engineering at the University of Aberdeen is supported by Lloyd’s Register Foundation. The Foundation helps to protect life and property by supporting engineering-related education, public engagement and the application of research.

Performance and Assessment of Rehabilitated Steel Culverts

This thesis explores the effects of rehabilitation on the structural performance of corrugated steel culverts. A full-scale laboratory experiment investigated the effects of grouted slip-liners on the performance of two buried circular corrugated steel culverts. One culvert was slip-lined and grouted using low strength grout, while the other was slip-lined and grouted using high strength grout. The performances of the culverts were measured before and after rehabilitation under service loads using single wheel pair loading at 0.45m of cover. Then, the rehabilitated culverts were loaded to their ultimate limit states. Results showed that the low and high strength grouted slip-liners provided strength well beyond requirements, with the low strength specimen failing at a load 2.4 times the fully factored service load, while the high strength specimen did not reach an ultimate limit state before bearing failure of the soil stopped testing. Results also showed that the low strength specimen behaved rigidly under service loads and flexibly under higher loads, while the high strength specimen behaved rigidly under all loads. A second full-scale experiment investigated the effect of a paved invert rehabilitation procedure on the performance of a deteriorated horizontal ellipse culvert. The performance of the culvert before and after rehabilitation was examined under service loads using tandem axle loading at 0.45m of cover. The rehabilitated culvert was then loaded up to its ultimate limit state. The culvert failed due to the formation of a plastic hinge at the West shoulder, while the paved invert cracked at the invert. Results showed that the rehabilitation increased the structural performance of the culvert, increasing the system stiffness and reducing average strains and local bending at critical locations in the culvert under service loads. A sustainability rating tool specifically for the evaluation of deteriorated culvert replacement or rehabilitation projects was also developed. A module for an existing tool, called GoldSET, was created and tested using two case studies, each comparing the replacement of a culvert using a traditional open-cut method with two trenchless rehabilitation techniques. In each case, the analyses showed that the trenchless techniques were the better alternatives in terms of sustainability.

Creep deflection of low-strength reinforced concrete flexural members strengthened with carbon fiber composite sheets

The low-strength concrete is defined as a concrete where the compressive cubic strength is less than 15 MPa. Since the beginning of the last century, many low-strength concrete buildings and bridges have been built all over the world. Being short of deeper study, composite sheets are prohibited in strengthening of low-strength reinforced concrete members (CECS 146; ACI 440). Moreover, there are few relevant information about the long-term behavior and durability of strengthened RC members. This fact undoubtedly limits the use of the composite materials in the strengthening applications, therefore, it is necessary to study the behaviours of low-strength concrete elements strengthened with composite materials (FRP) for the preservation of historic constructions and innovation in the strengthening technology. Deformability is one of criteria in the design of concrete structures, and this for functionality, durability and aesthetics reasons. Civil engineer possibly encounters more deflection problems in the structural design than any other type of problem. Many materials common in structural engineering such as wood, concrete and composite materials, suffer creep; if the creep phenomenon is taken into account, checks for serviceability limit state criteria can become onerous, because the creep deformation in these materials is in the same order of magnitude as the elastic deformation. The thesis presents the results of an experimental study on the long-term behavior of low-strength reinforced concrete beams strengthened with carbon fiber composite sheets (CFRP). The work has investigated the accuracy of the long-term deflection predictions made by some analytical procedures existing in literature, as well as by the most widely used design codes (Eurocode 2, ACI-318, ACI-435).

Ecology, physiology and performance in high-rate anaerobic digestion

The design demands on water and sanitation engineers are rapidly changing. The global population is set to rise from 7 billion to 10 billion by 2083. Urbanisation in developing regions is increasing at such a rate that a predicted 56% of the global population will live in an urban setting by 2025. Compounding these problems, the global water and energy crises are impacting the Global North and South alike. High-rate anaerobic digestion offers a low-cost, low-energy treatment alternative to the energy intensive aerobic technologies used today. Widespread implementation however is hindered by the lack of capacity to engineer high-rate anaerobic digestion for the treatment of complex wastes such as sewage. This thesis utilises the Expanded Granular Sludge Bed bioreactor (EGSB) as a model system in which to study the ecology, physiology and performance of high-rate anaerobic digestion of complex wastes. The impacts of a range of engineered parameters including reactor geometry, wastewater type, operating temperature and organic loading rate are systematically investigated using lab-scale EGSB bioreactors. Next generation sequencing of 16S amplicons is utilised as a means of monitoring microbial ecology. Microbial community physiology is monitored by means of specific methanogenic activity testing and a range of physical and chemical methods are applied to assess reactor performance. Finally, the limit state approach is trialled as a method for testing the EGSB and is proposed as a standard method for biotechnology testing enabling improved process control at full-scale. The arising data is assessed both qualitatively and quantitatively. Lab-scale reactor design is demonstrated to significantly influence the spatial distribution of the underlying ecology and community physiology in lab-scale reactors, a vital finding for both researchers and full-scale plant operators responsible for monitoring EGSB reactors. Recurrent trends in the data indicate that hydrogenotrophic methanogenesis dominates in high-rate anaerobic digestion at both full- and lab-scale when subject to engineered or operational stresses including low-temperature and variable feeding regimes. This is of relevance for those seeking to define new directions in fundamental understanding of syntrophic and competitive relations in methanogenic communities and also to design engineers in determining operating parameters for full-scale digesters. The adoption of the limit state approach enabled identification of biological indicators providing early warning of failure under high-solids loading, a vital insight for those currently working empirically towards the development of new biotechnologies at lab-scale.

Critical lattice size limit for synchronized chaotic state in one- and two-dimensional diffusively coupled map lattices

We consider diffusively coupled map lattices with P neighbors (where P is arbitrary) and study the stability of the synchronized state. We show that there exists a critical lattice size beyond which the synchronized state is unstable. This generalizes earlier results for nearest neighbor coupling. We confirm the analytical results by performing numerical simulations on coupled map lattices with logistic map at each node. The above analysis is also extended to two-dimensional P-neighbor diffusively coupled map lattices.