Entwicklung von weichen Türmen für Windenergieanlagen – Softtower

Development of soft towers for wind energy plants – Softtower. The tower plays an increasingly important role in the wind energy due to the fact that tower and foundation are responsible for the overall costs up to 45 %. For further yield increase the tower height will go up to 160 m in the future. Soft towers, designed purposefully with their natural frequency in the area of resonance of the rotor, will be developed to work against the growing cost pressures. This gives the tower a key role in the development of turbine control and load simulation. This article describes how the soft tower along with the turbine as a unit will determine the future wind energy plants. The aero‐elastical relations and the related positive aero‐dynamical damping will be implicated and analysed.     

Bauzeit und Baukosten für Stahlbetonarbeiten – Berechnungsmethoden und Anwendung

Construction Time and Cost of Reinforced Concrete Works – Calculation Methods and Application Construction time is of crucial importance when it comes to utilizing the production factors in an effective and efficient way. Construction periods that are too short usually result in higher cost, poorer quality and a larger number of disputes. This paper sets out to demonstrate the calculation of construction time whilst considering key construction management parameters. Beyond a simple, deterministic method, other options for calculation are shown that rely on probability calculus. The approaches described to determine construction time and cost are illustrated by a building project example. The deterministic method results in one value per each calculation process (calculation mode 1). In calculation mode 2, probability calculus is applied in a simple fashion. Both range and probability of occurrence can be considered for the relevant input variables. For the third calculation mode, the Monte‐Carlo method is applied using the @RISK software. For each of the parameters to be determined, this method shows a probability distribution.     

Rissbildung und Zugtragverhalten von mit Fasern verstärktem Stahlbeton am Beispiel ultrahochfesten Betons

Crack Formation and Tensile Behaviour of Concrete Members Reinforced with Rebars and Fibres exemplified by Ultra‐High‐Performance Concrete Part 1: Crack Mechanical Relationships When combining conventional non‐pre‐stressed or pre‐stressed reinforcement with fibres, differences in the load‐carrying and deformation behaviour arise in comparison to the well‐known reinforced and pre‐stressed concrete. This fact holds true comparably for all concrete classes. However, it is of special interest for ultra‐high‐performance concretes (UHPC), because fibres are added to these concretes generally to improve ductility. With regard to durability, the positive influence of the fibres on the crack formation process and the crack widths in the serviceability range is significant. Especially for enhanced requirements concerning the crack width (order of magnitude: 0.1 mm) with combined reinforcement of rebars and fibres an essential improve compared to reinforced concrete can be achieved. The analysis of the crack formation process presumes the understanding of the different behaviours of the two reinforcing elements ”rebars” and ”fibres”. In part 1 of this contribution, the therefore required mechanical relationships are presented and linked with each other considering equilibrium and compatibility. In part 2 the derived relationships are validated on the basis of experimental investigations on tensile members with combined reinforcement made of UHPC. The application is furthermore illustrated by means of two examples. Because of its universal formulation, the presented proposal is generally applicable to all types of concrete reinforced with rebars and fibres, i.e. it is not limited to ultra‐high‐performance concrete.     

Rissbildung und Zugtragverhalten von mit Fasern verstärktem Stahlbeton am Beispiel ultrahochfesten Betons

Wegen des Problems möglicher Inhomogenitäten der Faserverteilung/‐ orientierung ist der Einsatz von Fasern als alleinige Bewehrung im konstruktiven Ingenieurbau auf wenige Anwendungsgebiete beschränkt (z. B. Aufnahme von Zwangbeanspruchungen). Unter Zugbeanspruchung lässt sich zudem mit den in der Praxis für normalfeste Betone gebräuchlichen Fasergehalten nach der Erstrissbildung kaum ein verfestigendes Verhalten erzielen. Kombiniert man jedoch Stabstahlbewehrung und Faserbewehrung zu einem stahlfaserverstärkten Stahlbeton, so addieren sich die Vorteile beider Verbundwerkstoffe gleichermaßen. Besonders bei erhöhten Anforderungen an die Rissbreite (Größenordnung: unter 0, 1 mm) kann durch gemischte Bewehrung aus Stabstahl und Fasern eine wesentliche Verbesserung gegenüber Stahlbeton erzielt werden. Im Teil 1 dieses Beitrags wurden die für das Verständnis der unterschiedlichen Wirkungsweisen der beiden Bewehrungselemente “Stabstahl” und “Fasern” erforderlichen mechanischen Zusammenhänge dargestellt. Im Teil 2 erfolgt eine Überprüfung der abgeleiteten Beziehungen anhand experimenteller Untersuchungen an gemischt bewehrten Zugelementen aus ultrahochfestem Beton (UHPC). Für UHPC erreicht die Thematik besondere Aktualität, da aus Gründen der Duktilität der Einsatz von Fasen bei diesen Betonen die Regel ist. Der Nachweis der Begrenzung der Rissbreite bei kombinierter Bewehrung wird zudem an zwei Rechenbeispielen veranschaulicht. Crack Formation and Tensile Behaviour of Concrete Members Reinforced with Rebars and Fibres exemplified by Ultra‐High‐Performance Concrete. Part 2: Experimental Investigations and Examples of Application Due to the problem of possible inhomogeneities of fibre distribution/orientation the use of fibres as sole reinforcement is limited in engineering practice to few applications (e. g. coverage of stresses due to constraints). In addition, it is hardly possible to obtain strain hardening after first crack formation with fibre contents commonly used for normal strength concretes. However, if steel fibre reinforcement is used in combination with bar reinforcement, the advantages of both components are additive in the composite material. Especially for enhanced requirements concerning the crack width (order of magnitude: 0.1 mm), with combined reinforcement of rebars and fibres an essential improvement compared to reinforced concrete can be achieved. In part 1 of this contribution the mechanical relationships required for the understanding of the different behaviours of the two reinforcing elements “rebars” and “fibres” have been presented. In part 2 the derived relationships are validated on the basis of experimental investigations on tensile members with combined reinforcement made of ultra‐high‐performance concrete (UHPC). For UHPC the topic is of special interest, because fibres are added to these concretes generally to improve ductility. The crack width control with combined reinforcement is furthermore illustrated by means of two examples.     

Aktualisierte Diagramme zur Bemessung von Stahlkonstruktionen für den Brandfall nach Eurocode 3

Updated diagrams for fire design of steel structures based on Eurocode 3. The forthcoming design methods for steel structures subjected to fire in Eurocode 3 [1] differ considerably from the methods in the current German standard DIN 4102. The required fire protection material cannot be specified by simplified tables any longer. The structure will now be designed for the case of fire like it is done for ambient temperature. With this method the cost‐intensive structural fire protection can be optimized or even be avoided. However, the more realistic design comes along with a higher effort of calculation. To minimize this effort, in [3] a design tool was developed and published in [4]. In this tool the design methods of the Eurocode have been diagrammed for simple use. However, it is based on the prestandard and cannot be used any longer due to some changes in the current Eurocode. Therefore updated diagrams are presented and further diagrams are added to reduce the calculation effort for the design of steel structures in fire as much as possible.     

Schubfeldwerte für Wellbleche – Zusätzliche Untersuchungen für Trapezbleche

Thrust field values for corrugated iron sheets – Including additional considerations for trapezoidal profiles. According to the Generalized Bending Theory (VTB) the thrust field values for 15 typical corrugated iron profiles are determined. The computational model has been presented already 1976 [5]. In the model the curvatures of the corrugated profiles are approximated by polygonal chains. The number of segments determines the number of eigenvalues and the number of eigenvectors which have to be solved. The algorithm for determination of the eigenvalues is described and the required accuracy of the solution is discussed. Considering trapezoidal profiles the influence of web offset and ripped chords is studied, too. By knowledge of the author these influences have been not yet investigated so far. The evaluation of results for various profiles shows that the simplified computational model can be used furthermore.     

Teilsicherheitsfaktoren für die Berechnung von Großkraftwerken

Die Baustrukturen von Großkraftwerken werden in Deutschland u. a. auf Basis der VGB‐Richtlinie R 602 U berechnet und bemessen. In dieser Richtlinie sind unter Berücksichtigung der Besonderheiten des Großkraftwerksbaus Einwirkungen und Teilsicherheitsfaktoren definiert. Während die Lasten auf diese Randbedingungen abgestimmt wurden, hat man die Teilsicherheitsfaktoren auf der Lastseite aus der DIN 1055‐100 entnommen und lediglich die Kombinationsbeiwerte angepasst. Diese Sicherheitsbeiwerte tragen jedoch den speziellen Randbedingungen eines Kraftwerks oder Schwerindustriebaus nur bedingt Rechnung. Im Rahmen des Beitrags werden die Teilsicherheitsbeiwerte auf der Einwirkungsseite – insbesondere für das Konstruktionseigengewicht – für die Bemessung von Stahlbetonteilen vor diesem Hintergrund kritisch diskutiert und ein optimierter, wissenschaftlich abgesicherter Vorschlag unterbreitet. Partial Safety Factors for the Design of Power Plants In Germany power plants are designed in accordance to VGB regulation R 602 U. In this code load actions and partial safety factors are applied taking the special characteristics of power plants into consideration. The actions are defined regarding these circumstances, however the safety coefficients are assumed according to DIN 1055‐100 and only the combination coefficients are adjusted. However it has to be recognized that the partial safety factors in DIN 1055‐100 are calibrated for building constructions and thus do not consider the specialities of power plants in an adequate manner. In this paper the partial safety factors for the design of power plants and other heavy industry buildings are discussed for structural concrete elements and a scientific based optimized approach for the safety factor for dead load is presented.