Bewertung von komplexen Windlastwirkungen auf die Gebäudehülle

Appraisement of complex wind load effects on the building envelope. The natural wind loading normally dominates the design of building silhouettes in its ultimate limit state. With respect to the static load bearing capacity, simplified load models are available which are accepted and approved. However, for certain situations a more thorough analysis, taking into account more complex loading effects, is meaningful. In the present contribution, it is shown exemplary to which extent the increased modelling effort is worthwhile.     

Verfahrensprüfung zur Bestimmung von Anziehparametern für vorgespannte geschraubte Verbindungen

Procedure qualification for the determination of tightening parameters for preloaded bolted connections. DIN EN 1090‐2 and DIN EN 1993‐1‐8/NA define tightening procedures for preloaded bolted assemblies tightened at the nut side by simple use thereof. However, in a multitude of applications, preloaded bolted connections are used, which for example are tightened on the head side, designed as tapped hole connections and/or are to be used several times. In these cases, a procedure test is necessary to determine the tightening parameters. The present paper describes the principal procedure for carrying out such a procedure test, in particular the target level of preloading, the length of thread engagement for components with internal threads, the single and multiple use of components, and the boundary criteria for determining the tightening parameters. Furthermore, the procedure is explained using practical examples.     

Das Druckgurtmodell für Stahlbetonbauteile

In den vergangenen Jahren wurden verschiedene auf die Bemessung von Stahl‐ und Spannbetonbauteilen ausgerichtete theoretische Modelle entwickelt. Heute stehen das Zuggurtmodell, das Modell der gerissenen (Steg‐)Scheibe und das Druckgurtmodell zur Verfügung, auf deren Grundlage Verformungsverhalten und Tragwiderstände umfassend beurteilt werden können. Auf das Druckgurtmodell wird im vorliegenden Beitrag detailliert eingegangen. Es berücksichtigt die Festigkeits‐ und Duktilitätssteigerung durch eine Umschnürungsbewehrung sowie die bruchmechanisch begründete Entfestigung des Betons und die damit einhergehende Verformungslokalisierung. Auf der Grundlage neuerer Versuchsergebnisse können für die komplexen Interdependenzen zwischen diesen Effekten plausible Beziehungen angegeben werden. Die mithilfe des Druckgurtmodells gewonnenen Erkenntnisse sind für die Baupraxis von Bedeutung: Das Verhalten von auf Druck beanspruchten Bauteilen (z. B. Druckplatten von Brückenquerschnitten, Stützen) lässt sich zuverlässig erfassen; darüber hinaus ergeben sich wichtige Hinweise für die konstruktive Durchbildung. Compression Chord Model for Structural Concrete In recent years, several theoretical models have been developed with the scope on the design of reinforced and prestressed concrete structures. Today, the tension chord model, the cracked membrane model and the compression chord model are available, with which the deformation behaviour as well as ultimate loads can be determined. In the present contribution the compression chord model is discussed in detail. The model takes the increase of strength and ductility due to a confining reinforcement into account and considers the softening as well as the localisation of deformations accompanying the fracture of concrete. On the basis of new test results plausible relations for the complex interdependencies between these effects are found. The results of the compression chord model are relevant for practical applications: The behaviour of compressed members (e.g. in bridge girders or columns) can be assessed reliably; moreover, hints for the detailing of reinforcement can be deduced.     

Querkrafttragfähigkeit von Fahrbahnplatten ohne Querkraftbewehrung

Es wird über Versuche zur Querkrafttragfähigkeit von Brückenfahrbahnplatten aus Stahlbeton berichtet. Diese zeigen, dass die bekannten Rechenansätze für Bauteile ohne Querkraftbewehrung nach DIN 1045‐1 bzw. DIN‐FB 102 für Fahrbahnplatten auf der sicheren Seite liegen, die tatsächliche Tragfähigkeit aber weit unterschätzt wird. Weitere Ansätze zur Berechnung der Querkrafttragfähigkeit von Stahlbetonbauteilen ohne Querkraftbewehrung werden erörtert. Während die Modelle bei der Auswertung einer Datenbank von Balkenversuchen eine gute Übereinstimmung aufweisen, zeigt der Vergleich mit den Modellversuchen, dass die meisten Rechenverfahren die Tragfähigkeit der Platten unterschätzen. Zur Berechnung der Querkrafttragfähigkeit von Platten ohne Querkraftbewehrung unter Punktlasten wird ein Modell vorgeschlagen, welches die Querkrafttragfähigkeit mit der Zugbeanspruchung der Biegezugzone im kritischen Bereich verknüpft. Shear Resistance of Bridge Decks without Transverse Reinforcement The design of concrete bridge deck slabs is of major concern since the introduction of the Eurocodes as the calculated shear capacity of slabs without stirrups and staggered reinforcement according to the new design standards is often considerably smaller compared to the former regulations i.e. DIN 1045:88. This raises the question whether the existing structures are still save. A series of 12 tests on 4 different specimens representing a bridge deck was performed to examine the real load bearing behaviour of a slab with and without shear reinforcement under a wheel (point) load. The evaluation of the test results revealed, that the current design formula with an assumed elastic shear force distribution leads to rather conservative values of shear capacity for bridge deck slabs. Various approaches for shear design are discussed and the accuracy is checked by means of a shear database and the test results. A new model to calculate the shear capacity is proposed which shows a better agreement with test data than the known approaches.     

Experimentelle Validierung von Bemessungsregeln für Stahltrapezprofile mit Öffnungen

Experimental validation of design rules for trapezoidal profiles with openings. Structural design and detailing of trapezoidal steel sheets in Germany currently follows the rules provided by the still valid National Standard DIN 18807‐3 (1987). This Standard is based on the old design concept using one global safety factor and contains references to outdated codes which had been long since withdrawn. Within the framework of transition of design rules from DIN 18807‐3 to the European Standard EN 1090‐4 available provisions for openings in trapezoidal profiles, which exist since 30 years, were brought into question. The investigations regarding background information on these rules revealed a number of open questions concerning their application in practice as well as the mechanical performance of the cover plates. The basic concept for consideration of openings consists of the application of increased loads and verification using the complete cross‐section of trapezoidal profiles. On the one head, several details regarding the application of this method are, however, not clearly specified leaving space for interpretations which may lead to non‐economic results in case of over‐conservative interpretation. On the other hand, non‐safe results may be obtained if neglecting the increased loads while relying on the (non‐existing) strengthening effect of the cover plates.