Seismic Assessment and Retrofit of Reinforced Concrete Structures

Many constructions are built with reinforced or prestressed concrete, and most of them are designed or expected to resist earthquake actions in addition to gravity loads. To limit the effects of seismic events on reinforced or prestressed concrete structures, many attempts have been made by researchers in order to (i) improve the knowledge of the response of materials (steel bars and concrete) and members by means of laboratory tests, (ii) develop numerical and capacity models, (iii) enhance procedures for the dynamic analysis and assessment of the seismic performance of structures and (iv) suggest innovative interventions for the seismic retrofit of old and damaged reinforced or prestressed concrete structures. This Special Issue is a collection of 11 important research works that cover a wide range of problems related to the previously mentioned research fields. Both researchers and practical engineers are expected to greatly benefit from this Special Issue in view of their own work and for a better comprehension of the response of r.c. members and structures

複素減衰の因果的近似法とその巨大地震を受ける長周期構造物への適用

Tohoku University五十子幸樹課

Modal identification of linear non-proportionally damped systems by wavelet transform

International audienceA time-frequency identification technique based on wavelet transform is formulated and applied to free-decay responses of linear systems with non-proportional viscous damping. The Cauchy mother wavelet is used. Frequencies, modal damping ratios and complex mode shapes are identified from output-only free vibration signals. This identification technique has also shown to be effective when the (non-proportional) damping is significant

Thermophysical and Thermochemical Property Measurement and Prediction of Liquid Metal Titanium Alloys with Applications in Additive Manufacturing

Accurate high-temperature thermophysical property data for liquid metals and alloys are important for simulation of laser-based 3D printing processes. To understand and better control such additive manufacturing processes, knowledge of density, viscosity, and surface tension of liquid metals and alloys versus composition and temperature is needed. Likewise, thermochemical property data information regarding alloys, including chemical activities and free energies relative to composition and temperature, aid in the understanding and development of phase data important in the material design process. Vacuum electrostatic levitation (ESL) is an important technique through which both thermophysical and thermochemical property measurements can be accomplished without physical contact with the liquid. We performed ESL measurements on molten Ti-based alloys, including elemental Ti, Ti-xAl binaries (x = 0-10 percent weight), Ti-6Al-4V, and Ti-6Al-4V-10Mo, through a container-less oscillating drop technique at the NASA Marshall Space Flight Center. Ti-Al-V-Mo quaternary alloy was studied for laser-based 3D printing, and showed improved mechanical properties over traditional β Ti alloys. Results for elemental Ti, Ti-xAl, and Ti-6Al-4V are compared with previously published results, while those for Ti-6Al-4V-10Mo are reported here for the first time. Additional thermodynamic data are generated for binary Ti-Al, and compared to CALPHAD results while viscosity and density values of liquid titanium were calculated via molecular dynamics and compared to experimental values. The test and simulation procedure developed provides a framework for the development of new and higher-order alloys in the high temperature regime and in the liquid phase

An Experimental Characterization of the Mechanical Properties of Thermal Barrier Coatings at Elevated Temperatures

This research program developed the apparatus and associated techniques to mechanically characterize the complex modulus of hard coatings across a temperature range from about 70 deg F to 900 deg F. Major effort in designing, analyzing, and experimentally validating the chamber were performed to establish that it isothermally heated a beam specimen, accomplished modal detuning, and achieved a near free-free boundary condition, and that the chamber was characterized for its forcing excitation. Novel aspects of the chamber include non-contact for the excitation, nearly non-contacted boundary conditions, and measurement of the field variables within the specimen using a hybrid experimental-numerical approach. This allowed for very low damping values to be measured. A common thermal barrier coating material, 8YSZ, was characterized in the chamber to determine its loss-factor (damping) and storage modulus (stiffness), at both a system-level, and well as, extracted bulk material properties-sense at temperatures from 70 to 900 deg F. The use of the free-decay technique using logarithmic decrement was the primary means used to characterize the coating, although some forced response was also performed and showed agreement. Some specimens that were bare titanium and bond-coat-only were studied as well. The former resulted in the discovery that the chamber is a very sensitive to slight modulus changes in classical engineering materials and the latter was shown to have fairly minimal influence on the coated beam system dynamics

Experiments and Fragility Analyses of Piping Systems Connected by Grooved Fit Joints With Large Deformability

Pipes with a diameter of 150 mm, also called DN150, are often connected by grooved fit joints and employed as stem pipelines, which are used to transport water vertically to different building stories and distribute it horizontally to different rooms. A large deformability is often required for the grooved fit joints to accommodate the deformation concentrated between adjacent stories during an earthquake. To this end, the grooved fit joint is often improved with a wider groove to achieve such a large deformability. However, its seismic performance has not been thoroughly studied yet. This study conducted quasi-static tests on twelve DN150 grooved fit joints, including four elbow joints and eight DN150-DN80 Tee joints. The mechanical behavior, rotational capacity and failure mode were examined and discussed. The test results indicate that the fracture of the grooved fitting and the pull-out of pipes from the grooved fitting are the major damage patterns at deformations larger than 0.1 rad. At small deformations of <0.06 rad, although slight abrasions and wear were observed on the contact surface between the galvanized steel pipe and the grooved fitting, they would not result in significant leakage. Three damage states are defined accordingly, and the fragility models are developed for different grooved fit joints based on test results. Finally, seismic fragility analysis of DN150 stem pipeline system in a 10-story building was conducted. It is demonstrated that the improved joints survive under the maximum credible earthquake and the leakage is highly unlikely to occur

Quasinormal modes of black holes and black branes

Quasinormal modes are eigenmodes of dissipative systems. Perturbations of classical gravitational backgrounds involving black holes or branes naturally lead to quasinormal modes. The analysis and classification of the quasinormal spectra require solving non-Hermitian eigenvalue problems for the associated linear differential equations. Within the recently developed gauge-gravity duality, these modes serve as an important tool for determining the near-equilibrium properties of strongly coupled quantum field theories, in particular their transport coefficients, such as viscosity, conductivity and diffusion constants. In astrophysics, the detection of quasinormal modes in gravitational wave experiments would allow precise measurements of the mass and spin of black holes as well as new tests of general relativity. This review is meant as an introduction to the subject, with a focus on the recent developments in the field

Theory and application of optimization strategies for the design of seismically excited structures

The study introduces into the theory and application of optimization strategies in earthquake engineering. The optimization algorithm substitutes the intuitive solution of practical problems done by the engineer in daily practice, providing automatic design tools and numerical means for further exploration of the design space for various extremum states. This requires a mathematical formulation of the design task, that is provided for typical seismic evaluations within this document. Utilizing the natural relation between design and optimization tasks, appropriate mechanical concepts are developed and discussed. The explanations start with an overview on the mechanical background for continua. Hereby the focus is placed on elasto-plastic structures. The given extremum formulations are treated with help of discretization methods in order to obtain optimization problems. These basics are utilized for derivation of programs for eigenvalue and stability analysis, that are applied in simplified linear analysis for the design of seismically excited structures. Another focus is set on the application in simplified nonlinear design, that uses limit state analyses on the basis of nonlinear problem formulations. Well known concepts as the response and pushover analysis are covered as well as alternative strategies on the basis of shakedown theory or cycle and deformation based evaluations. Furthermore, the study gives insight into the application of optimization problems in conjunction with nonlinear time history analyses. The solution of step-by-step procedures within optimization algorithms is shown and aspects of dynamic limit state analyses are discussed. For illustration of the great variety of optimization-based concepts in earthquake engineering, several specialized applications are presented, e.g. the generation of artificial ground motions and the determination of reduction coefficients for design spectrum reduction due to viscous and hysteretic damping. As well alternative strategies for the design of base isolated structures with controlled impact are presented. All presented applications are illustrated with help of various examples.Die vorliegende Arbeit führt in die Theorie und Anwendung von Optimiierungsverfahren im Erdbebeningenieurwesen ein. Die vorgestellten Optimierungsalgorithmen ersetzen die typische intuitive Lösung von praktischen Bemessungsaufgaben, mit Bereitstellung von automatischen Methoden und numerischen Mitteln für die Bewertung des Designraumes bezüglich extremer Zustände. Dies erfordert eine geeignete mathematische Formulierung der Bemessungsaufgaben, die für typische Anwendungsfälle bereitgestellt werden. Ausgehend von der engen Beziehung von Bemessungs- und Optimierungsaufgaben werden wesentliche theoretische Grundlagen für die Ableitung praxistauglicher Analysekonzepte entwickelt und diskutiert. Die Darstellung beginnt mit einem Überblick zum mechanischen Hintergrund. Der Schwerpunkt wird dabei auf die Analyse von elastisch-plastischen Tragwerken gelegt. Die vorgestellten Extremalformulierungen werden mit Methoden der Diskretisierung in Optimierungsprobleme umgeformt. Diese bilden die Grundlage für die Analyse von Eigenwert- und Stabilitätsproblemen im Erdbebeningenierwesen. Weiterhin werden vereinfachte lineare Bemessungsmethoden besprochen. Eine Erweiterung wird duch die Einbeziehung von nichlinearen Aspekten erzielt, die einen wesentlichen Teil der Arbeit ausmachen. Einerseits werden bekannte Konzepte auf der Basis von Antwortspektren und Pushoveranalysen einbezogen, andererseits werden auch alternative Strategien auf der Basis der Einspieltheorie oder zyklen- oder deformationsbasierten Analyse vorgestellt. Desweiteren werden Anwendungen von Optimierungsverfahren im Zusammenhang mit nichtlinearen Zeitverlaufsmethoden diskutiert. Die Lösung von Zeitverlaufsproblemen in Form von Optimierungsaufgaben wird vorgestellt und Aspekte der Grenzzustandsanalyse für dynamische Probleme behandelt. Die Vielfältigkeit von Optimierungsanwendungen im Erdbebeningenieurwesen wird anhand verschiedener Spezialanwendungen demonstriert wie z.B. die Generierung von künstlichen Erdbebenzeitverläufen und die Modifikation von Bemessungsspektren für die Analyse von nichtlinear beanspruchten Tragwerken mit viskoser und hysteretischer Dämpfung. Darüberhinaus wird eine alternative Methode für die Bemessung von basisisolierten Tragwerken unter Verwendung von kontrollierten Kollisionen vorgestellt. Alle Anwendungen werden in zahlreichen Beispielen näher erläutert

Parallel simulation of volume-coupled multi-field problems with special application to soil dynamics

Zur Lösung vieler ingenieur- und naturwissenschaftlichen Problemstellungen sind numerische Simulationen ein wichtiges Hilfsmittel. Sie dienen beispielsweise der Wettervorhersage in der Meteorologie oder der Strukturanalyse und Strukturoptimierung im Maschinenbau. In vielen Aufgabenstellungen kann das untersuchte Problem, aufgrund seiner starken Wechselwirkung mit den angrenzenden Systemen, nicht losgelöst betrachtet werden, so dass eine gesamtheitliche Betrachtungsweise notwendig wird. Diese Systeme werden in der Literatur als gekoppelte Probleme bezeichnet. Aufgrund der Komplexität der betrachteten Probleme sind zur effizienten Lösung der zugrunde liegenden Gleichungen parallele Lösungsstrategien von Vorteil. Hierbei wird das Gesamtproblem in kleinere Teilprobleme zerlegt, die gleichzeitig auf verschiedenen Rechnern oder Prozessoren gelöst werden. Um die Vorteile dieses Lösungsverfahrens bestmöglich nutzen zu können, sind erhebliche Anstrengungen zunächst für die initiale Entwicklung und Umsetzung eines effizienten Lösungsverfahrens sowie anschließend für dessen kontinuierliche Weiterentwicklung notwendig. Die vorliegende Monographie beschreibt einen Ansatz zur Kosimulation numerischer Probleme zwischen dem kommerziellen auf der Finite-Elemente-Methode (FEM) basierenden Programmpaket Abaqus und dem für die Forschung entwickelten Löser PANDAS. Durch die Entwicklung einer allgemeinen Schnittstelle können die Materialmodelle von PANDAS direkt, ohne eine langwierige und fehleranfällige Reimplementierung, in eine für die industrielle Anwendung wichtige Simulationsumgebung überführt werden. Hierbei kann direkt auf die umfangreiche Materialmodellbibliothek von PANDAS zurückgegriffen werden. Zur Illustration der Anwendungsmöglichkeiten der Abaqus-PANDAS-Kopplung wird diese exemplarisch zur Simulation verschiedener volumengekoppelter Mehrfeldprobleme herangezogen. Als bodenmechanisches Anwendungsbeispiel wird die Tragfähigkeit eines flüssigkeitgesättigten granularen Materials unter quasi-statischen und dynamischen zyklischen Belastungen untersucht. Weiterhin werden mehrphasige Strömungsprozesse, wie sie z. B. im Produktionsprozess von faserverstärkten Kunststoffen auftreten, numerisch simuliert. Im sogenannten Vaccum-Assisted-Resin-Transfer-Moulding (VARTM), wird ein zunächst trockenes (gasgesättigtes) Fasergewebe kontinuierlich mit Harz getränkt, wobei für die praktische Anwendung insbesondere die Zeit bis zur vollständigen Sättigung und der sich einstellende Faservolumenanteil im fertigen Bauteil von großem Interesse sind. Weiterhin werden die Effizienz und die parallele Skalierbarkeit des vorgeschlagenen Kosimulationsansatzes untersucht