W. B. Krätzig

W. B. Krätzig
Ruhr-Universität Bochum | RUB · Institut für Konstruktiven Ingenieurbau

Prof. Dr.-Ing. habil. Dr.-Ing. E.h. mult.

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172
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Publications

Publications (172)
Chapter
Die in den ersten drei Kapiteln behandelten Fragestellungen der Strukturmechanik waren auf lineares Systemverhalten beschränkt. In diesem Kapitel wird eine Erweiterung der Theorien für geometrisch und physikalisch nichtlineare Phänomene dargelegt. Nachdem zu Beginn die grundlegenden Unterschiede zwischen der Behandlung linearer und nichtlinearer Pr...
Chapter
Die bisherige Vorgehensweise der strukturmechanischen Analyse von Tragwerken über die Definition der Kraftgrößen als primäre Variablen und die Formulierung von Gleichgewichtsbedingungen wird in diesem Kapitel durch eine alternative Vorgehensweise ergänzt, die auf den Weggrößen als primären Variablen basiert und kinematische Verträglichkeitsbedingun...
Chapter
In diesem Kapitel werden die Ansätze des Kraftgrößenverfahrens aus dem ersten Kapitel stärker abstrahiert und formalisiert, um das Verfahren in einer matriziellen Schreibweise zu formulieren. Dazu werden die Grundlagen der diskreten Tragwerksmodelle vorgestellt, die eine Übertragung der mechanischen Eigenschaften von einzelnen Stäben auf beliebig k...
Chapter
Das erste Kapitel gibt eine Einführung in das Kraftgrößenverfahren in klassischer Darstellung. Sein Ziel ist die anschauliche Vermittlung der Grundlagen des Kraftgrößenverfahrens für beliebig statisch unbestimmte Tragwerke, welche als Vorbereitung für die in Kap. 2 eingeführte matrizielle Formulierung des Kraftgrößenverfahrens dient. Zunächst wird...
Book
Dieses Buch behandelt statisch unbestimmte Stabtragwerke. Das Kraftgrößenverfahren wird in klassischer und matrizieller Form erläutert. Nach Einführung diskreter Tragwerksmodellierungen wird der Leser mit verschiedenen Varianten des Weggrößenverfahrens vertraut gemacht und an die computerbasierte Tragwerksanalysen herangeführt. Einführungen in die...
Article
Preiswerte Energie bildet die Grundlage des Wohlstands von Industrienationen. Erzeugt wird diese derzeit und in naher Zukunft in thermischen Großkraftwerken von bis zu 1,2 GW Leistung, auf der Basis von Kohle oder Kernkraft. Derartige Kraftwerke benötigen zur Rück-Kondensation ihres Arbeitsmediums Dampf große Naturzugkühltürme, um natürliche Gewäss...
Article
Full-text available
The Solar Updraft Power Plant technology addresses a very challenging idea of combining two kinds of renewable energy: wind and solar. The working principle is simple: a Solar Updraft Power Plant (SUPP) consists of a collector area to heat the air due to the wide-banded ultra-violet solar radiation, the high-rise solar tower to updraft the heated a...
Conference Paper
Full-text available
Natural Draft Cooling Towers (NDCTs) are extremely thin shell structures, sensitive to instability failure. After the Ferrybridge-disaster in 1965, worldwide research efforts started in this field. The paper will elucidate the different stability verification concepts for NDCTs over the last 40 years, starting with early experiments. This is follow...
Chapter
Moderne Naturzugkühltürme aus Stahlbeton dominieren heute bei Wärmekraftwerken das Landschaftsbild . Insbesondere die Kühlerschalen faszinieren viele Menschen: ihre harmonischen Formen, ihre Kühnheit durch große Höhen und äußerst geringe Wandstärken, ihre Funktion als überdimensionale Kraftwerkskomponenten. Einzelfundamente stellen die wirtschaftli...
Article
Full-text available
This paper applies recent research on structural damage description to earthquake-resistant design concepts. Based on the primary design aim of life safety, this work adopts the necessity of additional protection aims for property, installation, and equipment. This requires the definition of damage indicators, which are able to quantify the arising...
Article
Solar updraft power plants (SUPPs) form a very modern and rather efficient solar power technology. SUPPs consist of the glass-covered collector area (CA), in its centre the solar chimney (SC), and around the SC’s perimeter the power conversion unit (PCU). To evaluate the power/energy harvest of such plants, computer simulations comprise all physica...
Article
Solar updraft power technology will generate highly sustainable electricity in world-wide deserts in future. It will overcome certain deficits of present renewable energy technologies. In several countries, such power plants are in pre-design stage, forming an important contribution of structural engineering to future energy supply. The present man...
Article
Renewable energy technologies are generally complex, requiring nonlinear simulation concepts. This holds true especially for solar updraft power plants, the scope of this treatment, which starts with a short introduction into their functioning. Then the basic physical conditions of the thermo-fluiddynamic processes in such plants including the sola...
Article
Full-text available
Solar updraft chimneys (SUCs) form as engines of solar updraft power plants tower-like shell structures of extreme height with rather thin shell walls, similar to high chimneys comprising multiple flue gas ducts. The height of presently pre-designed SUCs reaches up to 1000 m. Thus they are exposed chiefly to extreme natural wind-loads, and to therm...
Conference Paper
Full-text available
As known to the audience, solar updraft power plants (SUPPs) represent a very modern and extremely efficient solar power technology. SUPPs consist of the collector area (CA), the solar chimney (SC) and the power conversion unit (PCU). Evaluation of the power/energy output of such a plant is by computer simulations, comprising all physical processes...
Chapter
Industrienationen benötigen große Mengen an elektrischer Energie. Deren Erzeugung sollte wirtschaftlich, zuverlässig sowie in hohem Maße ökologisch nachhaltig sein. Bei allen modernen Kraftwerkstechniken spielen Bauleistungen eine wichtige Rolle. Das energiearme Deutschland wird nach dem Ausstiegsbeschluss aus der Kernenergie noch lange bedeutende...
Article
Solare Aufwindkraftwerke stellen eine Technologie zur Erzeugung solar-basierter elektrischer Energie in den Wüsten unserer Erde dar, die verschiedene Defizite bisheriger Konzepte überwindet. Weltweit sind derartige Kraftwerksprojekte in der Vorplanung. Der vorliegende Beitrag beginnt mit der Skizzierung des Arbeitsprinzips solarer Aufwindkraftwerke...
Article
In the medium term, European energy policy is aiming at low-emission energy supply with solar-based energy playing a main part. Solar updraft power plants are one option, the concept of which is being outlined. A mathematical model of a solar updraft power plant is presented and the resulting simulation program is scaled with a pilot plant. Besides...
Article
Kap. 4 war den beiden grundsätzlichen Methoden der Auflager- und Schnittgrößenermittlung gewidmet. Der Schwerpunkt dieses Kapitels liegt dagegen im Tragverhalten und den darauf aufbauenden Verfahren zur Kraftgrößenermittlung wichtiger Tragwerkstypen. Schließlich zielt es auch auf eine Erweiterung der baustatischen Fertigkeiten des Lesers ab, wozu e...
Article
Neben der Ermittlung von Kraftgrößenzuständen stellt die Bestimmung korrespondierender Verformungszustände eine gleichermaßen wichtige Aufgabe der Statik der Tragwerke dar. Zur Beschreibung von Verformungszuständen hatten wir in den Tafeln 2.7 und 2.8 zwischen äuβeren Weggröβen, den Verschiebungen und Verdrehungen, sowie inneren Weggröβen, den Verz...
Article
Im zweiten Kapitel haben wir ausführlich die Statik gerader, ebener Stäbe behandelt. Derartige, gegebenenfalls auf räumliche Tragwirkungen erweiterte Stabkontinua bilden—gemeinsam mit Stützen und Anschlüssen—die Grundelemente jedes Stabtragwerks. In diesem Kapitel wollen wir uns mit Stabtragwerken und deren Tragstrukturen befassen.
Article
In diesem Buch wollen wir nur statisch bestimmte Stabtragwerke behandeln. Bei ihnen lassen sich definitionsgemäß (siehe Abschn. 3.3.2) sämtliche Schnitt- und Auflagergrößen ausschließlich aus den Gleichgewichtsbedingungen ermitteln.
Article
Jeder Tragwerkspunkt erleidet als Folge von Beanspruchungen eine—vorausset-zungs-gemäß—infinitesimal kleine Verformung, gelangt also an eine andere, seine verformte Position im Raum. Die Verbindungslinie aller verformten Positionen repräsentiert die Zustandslinie des Verformungsvektors u, meist als Biege- oder Verformungslinie des Tragwerks bezeich...
Article
Zur Einführung in das Gleichgewichtsproblem eines Stabes seien die wichtigsten Grundlagen über Kräfte und Kräftesysteme aus der Mechanik kurz wiederholt. Bekanntlich können wir Menschen Kräfte nur an ihren Wirkungen erkennen: Kräfte vermögen Körper zu bewegen oder sie zu verformen. Folglich bezeichnen wir jede Ursache einer Bewegungs- oder Formände...
Article
Ausgehend vom allgemeinen Begriff der mechanischen Arbeit hatten wir im Abschnitt. 2.2.1 die Formänderungsarbeit eingeführt. In den Kap. 2 und 4 war diese dann bereits mehrfach angewendet worden, so diente sie zur Definition korrespondierender mechanischer Variablen oder ermöglichte als virtuelle Arbeit die Kraftgrößenberechnung nach der kinematisc...
Chapter
Zustandslinien dienen zur Darstellung von Schnittgrößenverläufen infolge ortsfester Belastungen. Einflusslinien dagegen werden zur übersichtlichen Erfassung des Einflusses ortsveränderlicher Lasten auf einzelne Zustandsgrößen verwendet. Ortsveränderliche Lasten kommen auf Brücken, Kranbahnen sowie befahrenen Hochbaukonstruktionen vor; ihre dynamisc...
Conference Paper
Natural draft cooling towers and chimneys of solar updraft power plants have many structural properties in common: They are dominated by thin ring-stiffened shell structures made of reinforced concrete, they transport by their internal updraft warm air into the atmosphere, and because of their height, gale actions play the most important role in th...
Conference Paper
Presently in the West of Germany, several thermal power plants are renewed to improve their efficiency. These new power stations are fuelled either by hard coal or by lignite; the maximum net electric capacity per power block is up to 1.100 MW. Also since the re-unification 1990, Germany had to renew a series of thermal power stations in its East,...
Article
As consequences of heavy floods in Germany in August 2002, the Umweltbundesamt UBA—German Environmental Protection Agency—started a research project on the safety of industrial installations due to technical as well as natural risks. Although the main focus of this research was on floods, risks due to storms and earthquakes were studied too. The pr...
Article
Full-text available
In power generation industries large RC shell-like structures are well in use, as safety containments for LNG tanks, shafts for wind generators, smoke stacks, nuclear power plant containments, natural draft cooling towers, and in future solar upwind chimneys. Especially these last two types of shells form the largest shell structures in technology....
Conference Paper
Especially in power industries exist very large reinforced concrete (RC) shell structures, namely natural draft cooling towers (NDCT), with maximum heights of presently up to 200 m. In the planning state there are even higher ones, so-called "dry" cooling towers up to 300 m of height. Future solar chimney power plants (SCPP) using the updraft of su...
Article
Full-text available
In solar chimney power plants the air under the glass-covered collector is heated by solar radiation, and then released via a central chimney into great atmospheric heights. This mass-stream of warm air drives turbo-generators in the chimney foot producing electricity. The article describes recent progresses in research and development of this tech...
Chapter
Shell structures are extremly efficient, thin walled load-carrying components, in the elastic as well as in the inelastic regime. Realistic and efficient computational strategies lately are in rapid development. Such computational strategy for modelling of nonisothermal, highly nonlinear hardening responses in elastoplastic shell analysis has been...
Article
Vorhandene Spannungskategorisierungen [2], [11] unterteilen mechanische Lastspannungen hinreichend genau in primäre Spannungen, sekundäre Spannungen und Spannungsspitzen, mit jeweils unterschiedlichen zulässigen Grenzwerten. Hingegen werden thermischverursachte Spannungen nur als solche aus behinderter Wärmedehnung aufgeführt und als Sekundärspannu...
Article
Accumulation of structural damage leads to the termination of the life of a structure. For structural-life estimation, a new paradigm is introduced defining final structural failure as the passing of damage evolution over an ultimate damage bound. During the life of the structure, the original safety margin will be reduced by deterioration of struc...
Article
A basic concept of structural damage assessment including carrying capacity, recently proposed by the authors, is complemented in the present work by a new global damage measure and a systematic study of its sensitivity to relevant uncertainties. The damage measure is based on the maximum compliance recovered from the structural eigenfrequencies an...
Article
In many engineering fields, durability aspects with damage-oriented structural assessments recently have gained increasing interest. Thus new demands both for theoretical developments and analysis concepts are required. Because of their complexity, previous published researches hereby often have followed some aspects very accurately, while others w...
Article
When natural-draft cooling towers started to exceed tower heights of about 100m in the early 1960s, they turned out to be the most unsafe existing engineering structures: within less than 20 years, worldwide at least 10 towers were lost out of approximately 100. Nearly none of the deadly problems was known in detail at that time: internal stress di...
Article
After more than 30 years of service, many German cooling towers demonstrate severe aging effects. The paper explains and illustrates typical aging processes of towers shells, as there are: Corrosion with losses of concrete on inner shell faces; carbonisation of concrete with reinforcement corrosion, visible mainly on outer faces; damage of concrete...
Article
Based on a fully 3-D elasto-plastic damage theory, the material behavior of all reinforced concrete components––concrete, reinforcement and bond––is, for biaxial loading, realistically modelled, including cyclic action. Thereby emphasis is layed on concrete in tension and compression. The presented model contains a minimum number of material parame...
Article
In this contribution, the simulation of the long-term behaviour of concrete members under high sustained loads and constant humidity is presented. It is based on a three-dimensional material model for concrete under monotonic, time-invariant loading, which is formulated within the thermodynamic framework of the elasto-plastic continuum-damage theor...
Chapter
In this presentation, we offer a comparison of different shell models presently in use. Basis of this work is a multidirector shell model as derived by semi-discretization over the structural thickness, starting from 3D continuum mechanics. Therewith, physical restrictions for shell models can be derived which validate for inelastic processes as we...
Chapter
This chapter presents a paper that discusses structural damage assessment with uncertainties. The approach to assess structural damage is based on global changes of structural stiffness or associated potential energy. The global damage measures derived correlate well with the actual damage degree and exhibits a potential for successful application...
Article
Full-text available
Problems of solid mechanics are most generally formulated within 3D continuum mechanics. However, engineering models favor reduced dimensions, in order to portray mechanical properties by surface or curvilinear approximations. Such attempts for dimensional reduction constitute interactions between theoretical formulations and numerical techniques....
Article
Dieser Aufsatz behandelt Auswirkungen mechanischer Schädigungen auf Stahlbetontragwerke sowie deren numerische Simulation. Nach Skizzierung des Analysekonzeptes als multi‐lavel‐iteration‐strategy wurde im bisherigen Teil das erforderliche schädigungsorientierte Stahlbeton‐Materialmodell detailliert erläutert. Dieses ist auf dasjenige des MC 90 bezo...
Article
This article tells about the effect of the damage evaluation of reinforced concrete structures and its numerical simulation. Part 1 of the study [1] showed the analysis concept als a multi-level-iteration-strategy and the required material model of reinforced concrete structures. It is leaned on the model of the MC 90, but goes further on in its de...
Article
The new German code DIN 1045-1 for reinforced concrete structures sets an unambiguous impact on structural durability and sustainability. Since structural degradations develop from environmental expositions in combination with mechanical deteriorations, future designs for improved durability will require analysis concepts for structural damage evol...
Article
The present paper deals with FE-simulations of damage and failure processes in reinforced concrete structures, with emphasis on the description of suitable material models. For concrete, the generally accepted equivalent strain concept (pseudo-1D) is applied, which allows consideration of arbitrary concrete qualities. In the case of cyclic processe...
Article
The present paper will outline the main aspects of the design and construction of cooling towers in Germany in the last decade. As part of electricity generating power plants, cooling towers play a significant role for the availability of reliable energy supplies, in a manner compatible with environmental requirements. They definitely belong to the...
Article
In the years 1999 to 2001 a new natural draft cooling tower has been built at the RWE power station at Niederaussem, with 200 m elevation the highest cooling tower world-wide. For many reasons, such structures can not be designed merely as enlargement of smaller ones, on the contrary, it is full of innovative new design elements. The present paper...
Article
This paper focuses on time-variant reliability assessment of deteriorating reinforced concrete structures under fatigue conditions. A strategy combining two time scales, namely the micro-scale of instantaneous structural dynamics (or statics) and the macro-scale of structural lifetime, is proposed. Non-linear response of reinforced concrete structu...
Article
In this paper, we present the concept and the implementation issues for an adaptive coupling of the finite element- and the element-free Galerkin discretization. The present algorithm implemented within flexible data structure facilitates the automatic inclusion of meshfree zones and establishes the coupling between the zones with interface element...
Article
Solid mechanics problems use to be formulated in tensor notation in three-dimensional (3D) Euclidean space. But engineering practice favors reduced dimensional models, in order to describe deformation processes in its most natural way by surface- and line-like geometries, mainly for ease of error controling.Modern surface-like structures, e.g. shel...
Article
In the present paper, we derive an efficient data structure for the organization of the nodes in the coupled finite element/element-free Galerkin method. With respect to its implementation, we compare various approaches of recursive spatial discretizations that facilitate most flexible handling of the nodes. The goal of the paper is to refine the i...
Chapter
Using continuum damage theories the effects of discrete material defects are homogenized to the macro-level. This results in an easy way of incorporating damage into existing continuum models. Nevertheless it remains necessary to recognize that the validity range of continuum damage mechanics terminates, if neighbouring voids start to coalesce, for...
Article
This lecture deals with two actual issues of computational structures technology: simulation and assessment of structural damage. Material damage modeling is considered by example of reinforced concrete. Time-independent as well as time-dependent damage processes are considered. Structural damage simulation is implemented in the framework of the no...
Chapter
This chapter discusses the main aspects of the design and construction of cooling towers in Germany in the past decade. These towers definitely belong to the largest and thinnest concrete buildings worldwide at present. Because of the combined action of wind, thermal, and hygric effects, special care has to be taken on fatigue, cracking, and corros...
Article
In the present paper, efficient numerical algorithms for elastoplastic analysis of shell-like structural components will be proposed employing nonisothermal, realistic, highly nonlinear hardening responses. The closest point projection integration algorithm is presented using a Reissner–Mindlin type kinematic shell model, completely formulated in t...
Conference Paper
The present manuscript proposes a rational concept of description and evaluation of the damage states of structures. All mechanical, chemical or bio-chemical deterioration processes will reduce the originally virgin stiffnesses of a particular structure over its life-time. In the following it shall be outlined, how the consequences of structural da...
Conference Paper
The present article will give a brief introduction into the shape optimization, design and construction of the 200 m high natural draught cooling tower shell at Niederauβem, which has been completed in the last year. This tower belongs world-wide to the largest and thinnest concrete buildings at present. Because of these dimensions, special care ha...
Article
Full-text available
RWE Energie AG, the second largest German electricity producer, operates since 1961 a lignite power plant at the small village of Niederaussem, 20 km west of Cologne. Construction began on a new Niederaussem power station in 1998 with an intended electricity capacity of 965 MW, which, after completion in 2002, will become the largest lignite power...
Article
 In the present-day solid mechanics research damage is treated predominantly on material point level, in constitutive laws, wherein it is formulated for further treatment in boundary value problems of continuum damage mechanics. Damage of a particular structure, on the other hand, is primarily observed on a structural level. Damage effects on struc...
Article
In building codes, the design of structures is generally based on their virgin state omitting most damage processes and disregarding future physical as well as chemical deterioration. Such concepts of disregard of structural stiffness degradation are in principle incapable of quantifying structural failure and thus of describing important aspects i...
Article
An efficient computational strategy for modelling of cyclic elastoplastic deformation of shell structures employing the Reissner–Mindlin type kinematic model has been proposed. A realistic highly nonlinear hardening model in multi-component form has been applied. The closest point projection algorithm, completely formulated in tensor notation, is p...
Article
 For more than 50 years, the technology of linear damage processes has been known and mastered. Strong, progressive damage processes have recently been discovered on various types of structures, for which a uniform theory has been unavailable. A common feature of these processes is the wide-band excitation of the dominant forces (ocean waves, storm...
Article
Efficient numerical algorithms for elastoplastic analysis of thin-walled shell-like structural components employing nonisothermal, realistic hardening responses have been proposed. A computational strategy for integration of the elastoplastic constitutive model using the Reissner-Mindlin shell kinematics, completely formulated in tensor notation, i...
Article
For an efficient analysis of shell structures, effective error-controlled and adaptive refinement procedures have become an indispensable tool to provide a reliable solution with a discretization error less than a specified tolerance. In this present paper we apply an error estimator based on the smoothing technique to the incremental adaptive comp...
Article
The present article introduces a highly efficient numerical simulation strategy for the analysis of elasto-plastic shell structures. An isoparametric Finite Element, based on a Finite Rotation Reissner–Mindlin shell theory in isoparametric formulation, is enhanced by a Layered Approach for a realistic simulation of nonlinear material behaviour. A g...
Chapter
Cracking processes damage a structure in local areas, but their effects can be — apart from very small cracks — not at all local. Cracks can influence the overall load-bearing capacity considerably and thus modify safety and reliability of the structure. The simulation of cracking phenomena consequently requires a computational treatment in a 3D en...