Universitätsbibliothek
Weimar Open Access

Recent years have seen a gradual shift in focus of international policies from a national and regional perspective to that of cities, a shift which is closely related to the rapid urbanization of developing countries. As revealed in the 2011 Revision of the World Urbanization Prospects published by the United Nations, 51% of the global population (approximately 3.6 billion people) lives in cities. The report predicts that by 2050, the world’s urban population will increase by 2.3 billion, making up 68% of the population. The growth of urbanization in the next few decades is expected to primarily come from developing countries, one third of which will be in China and India. With rapid urbanization and the ongoing growth of mega cities, cities must become increasingly resilient and intelligent to cope with numerous challenges and crises like droughts and floods arising from extreme climate, destruction brought by severe natural disasters, and aggregated social contradictions resulting from economic crises. All cities face the urban development dynamics and uncertainties arising from these problems. Under such circumstances, cities are considered the critical path from crisis to prosperity, so scholars and organizations have proposed the construction of “resilient cities.” On the one hand, this theory emphasizes cities’ defenses and buffering capacity against disasters, crises and uncertainties, as well as recovery after destruction; on the other hand, it highlights the learning capacity of urban systems, identification of opportunities amid challenges, and maintenance of development vitality. Some scholars even believe that urban resilience is a powerful supplement to sustainable development. Hence, resilience assessment has become the latest and most important perspective for evaluating the development and crisis defense capacity of cities. Rather than a general abstract concept, urban resilience is a comprehensive measurement of a city’s level of development. The dynamic development of problems is reflected through quantitative indicators and appraisal systems not only from the perspective of academic research, but also governmental policy, so as to scientifically guide development, and measure and compare cities’ development levels. Although international scholars have proposed quantitative methods for urban resilience assessment, they are however insufficiently systematic and regionally adaptive for China’s current urban development needs. On the basis of comparative study on European and North American resilient city theories, therefore, this paper puts forwards a theoretical framework for resilient city systems consistent with China’s national conditions in light of economic development pressure, natural resource depletion, pollution, and other salient development crises in China. The key factors influencing urban resilience are taken into full consideration; expert appraisal is conducted based on the Delphi Method and the analytic hierarchy process (AHP) to design an extensible and updatable resilient city evaluation system which is sufficiently systematic, geographically adaptable, and sustainable for China’s current urban development needs. Finally, Changsha is taken as the main case for empirical study on comprehensive evaluation of similar cities in Central China to improve the indicator system.

Gashochdruckleitungen aus Stahl werden mit Hilfe eines deterministischen Sicherheitskonzeptes bemessen. Im unveränderten Bemessungszustand und im bestimmungsgemäßem Betrieb ist die statische Tragfähigkeit der Gashochdruckleitungen gegeben. Mit den Jahren unterliegen Gashochdruckleitungen aus Stahl geometrischen Veränderungen, die häufig durch Korrosion hervorgerufen werden. Die Beurteilung der statischen Tragfähigkeit erfolgt dann unter Berücksichtigung dieser geometrischen Änderung. Deterministische Sicherheitsbeiwerte der Bemessung neuer Gashochdruckleitungen können für die Bemessung bestehender korrosionsgeschädigter Gashochdruckleitungen nicht herangezogen werden, da diese einen definierten Beanspruchungs- und Geometriezustand unterstellen, welcher durch den geometrischen Einfluss der Korrosion so nicht mehr besteht. Die Arbeit befasst sich mit der Ermittlung deterministischer Sicherheitsbeiwerte für die Bemessung korrosionsgeschädigter Gashochdruckleitungen auf Basis von Versagenswahrscheinlichkeiten und stellt ein Anwendungskonzept zu deren Nutzung vor.

Frei nach dem Motto "Money for nothing and content for free" werden tagesaktuelle Informationen ebenso wie aufwändig recherchierte Reportagen im Digitalen vornehmlich kostenfrei genutzt. Wie können journalistische Angebote sich also nachhaltig refinanzieren? Die vorliegende Studie stellt Nutzerinnen und Nutzer in den Mittelpunkt. Sie fragt nach den Gründen für fehlende Zahlungsbereitschaft sowie danach, warum und wofür gezahlt wird. Außerdem gibt sie Medienschaffenden konkrete Handlungsempfehlungen, um ihre journalistischen Produkte ansprechend zu gestalten und so die Zahlungsbereitschaft von Leserinnen und Lesern zu steigern.

Contemporary planning practice is often criticized as too design-driven with a lack of both quantitative evaluation criteria and employment of models that anticipate the self-organizational forces shaping cities, resulting in significant gaps between plan and reality. This study aims to introduce a modular toolbox prototype for spatial-analysis in data-poor environments. It is proposed to integrate designing, evaluation, and monitoring of urban development into one framework, thus supporting data-driven, on-demand urban design, and planning processes. The proposed framework’s value will exemplarily be tested, focussing on the analysis and simulation of spatiotemporal growth trajectories taking the Lanzhou New Area as a case-study - a large scale new town project that struggles to attract residents and businesses. Conducted analysis suggests that more attention should be given to spatiotemporal development paths to ensure that cities work more efficiently throughout any stage of development. Finally, early hints on general design strategies to achieve this goal are discussed with the assistance of the proposed toolbox.

In recent years the demand on dynamic analyses of existing structures in civil engineering has remarkably increased. These analyses are mainly based on numerical models. Accordingly, the generated results depend on the quality of the used models. Therefore it is very important that the models describe the considered systems such that the behaviour of the physical structure is realistically represented. As any model is based on assumptions, there is always a certain degree of uncertainty present in the results of a simulation based on the respective numerical model. To minimise these uncertainties in the prediction of the response of a structure to a certain loading, it has become common practice to update or calibrate the parameters of a numerical model based on observations of the structural behaviour of the respective existing system. The determination of the behaviour of an existing structure requires experimental investigations. If the numerical analyses concern the dynamic response of a structure it is sensible to direct the experimental investigations towards the identification of the dynamic structural behaviour which is determined by the modal parameters of the system. In consequence, several methods for the experimental identification of modal parameters have been developed since the 1980ies. Due to various technical restraints in civil engineering which limit the possibilities to excitate a structure with economically reasonable effort, several methods have been developed that allow a modal identification form tests with an ambient excitation. The approach of identifying modal parameters only from measurements of the structural response without precise knowledge of the excitation is known as output-only or operational modal analysis. Since operational modal analysis (OMA) can be considered as a link between numerical modelling and simulation on the one hand and the dynamic behaviour of an existing structure on the other hand, the respective algorithms connect both the concepts of structural dynamics and mathematical tools applied within the processing of experimental data. Accordingly, the related theoretical topics are revised after an introduction into the topic. Several OMA methods have been developed over the last decades. The most established algorithms are presented here and their application is illustrated by means of both a small numerical and an experimental example. Since experimentally obtained results always underly manifold influences, an appropriate postprocessing of the results is necessary for a respective quality assessment. This quality assessment does not only require respective indicators but should also include the quantification of uncertainties. One special feature in modal testing is that it is common to instrument the structure in different sensor setups to improve the spacial resolution of identified mode shapes. The modal information identified from tests in several setups needs to be merged a posteriori. Algorithms to cope with this problem are also presented. Due to the fact that the amount of data generated in modal tests can become very large, manual processing can become extremely expensive or even impossible, for example in the case of a long-term continuous structural monitoring. In these situations an automated analysis and postprocessing are essential. Descriptions of respective methodologies are therefore also included in this work. Every structural system in civil engineering is unique and so also every identification of modal parameters has its specific challenges. Some aspects that can be faced in practical applications of operational modal analysis are presented and discussed in a chapter that is dedicated specific problems that an analyst may have to overcome. Case studies of systems with very close modes, with limited accessibility as well as the application of different OMA methods are described and discussed. In this context the focus is put on several types of uncertainty that may occur in the multiple stages of an operational modal analysis. In literature only very specific uncertainties at certain stages of the analysis are addressed. Here, the topic of uncertainties has been considered in a broader sense and approaches for treating respective problems are suggested. Eventually, it is concluded that the methodologies of operatinal modal analysis and related technical solutions have been well-engineered already. However, as in any discipline that includes experiments, a certain degree of uncertainty always remains in the results. From these conclusions has been derived a demand for further research and development that should be directed towards the minimisation of these uncertainties and to a respective optimisation of the steps and corresponding parameters included in an operational modal analysis.