Concrete fatigue in composite dowels

Abstract

In modern bridge construction, steel‐concrete composite structures with composite dowels are being built more than ever, especially for small and medium spans. In contrast to headed studs, in which initial steel cracks occur after only a few load cycles [1], [2], the lifetime of composite dowels is characterized by the compression of the multi‐axially stressed concrete in front of the composite dowel. Here, plastic compression strains occur in the concrete and accumulate over load cycles, leading to a cyclic increase in relative displacements in the connection. Certain proportions of these relative displacements, called inelastic slip, remain in the connection, even after the loading is relieved. The inelastic slip changes the characteristics of the static dowel curve. The initially rigid connection degrades over its lifetime, leading to redistributions of internal forces, which may be critical for fatigue design. In order to consider the degradation of the composite connection, a cyclic dowel curve can be used, which may be developed from the static dowel curve by introducing the inelastic slip. This paper presents the results of cyclic shear tests on different composite dowel geometries. The effect of load‐dependent parameters (upper load level and load range) was investigated. Furthermore, an engineering model for determining the cyclic dowel curve is presented, which was developed based on the results of experimental and numerical investigations.

Integriertes Deckensystem für den Stahl‐ und Verbundbau

“…Hierbei bilden sich in den auf Zug beanspruchten Trägerbereichen Querrisse im Betongurt aus. Diese setzen die Schubtragfähigkeit von Verbunddübelleisten mit Ausstanzversagen herab ( [17], [18] [21], [22], [23]). Die Prüfkraft wird über Bild 4.…”

Modelle für das nichtlineare Verformungsverhalten von Verbunddübelleisten mit Ausstanzversagen

“…Der elastische Schlupf hängt neben der Schubkraft (0,7 P po ) von der elastischen Dübelsteifigkeit C el,VD ab. Zur Bestimmung von C el,VD wird ein Federmodell verwendet, das in [19]…”

“…Die auf die rechnerische Schubtragfähigkeit P po bezogenen Bruchlasten liegen im Mittel leicht oberhalb von 1,0 und damit auf der sicheren Seite. Für die Versuchsserien aus [5], [12], [14] und [15] wird die Anfangssteifigkeit C el,VD mit dem Federmodell nach [19] [19] zur Bestimmung der elastischen Dübelsteifigkeit: Schnittdarstellungen parallel zur VDL (links) und rechtwinklig zur VDL (rechts). Fig.…”

“…6. Spring model from [19] for determination of the dowel stiffness: sections parallel (left) and orthogonal to the composite dowels (right) Bild 7. Auf Tragfähigkeit und elastischen Schlupf normierte Dübelkennlinien (links) und mit skaliertem nichtlinearem Bereich (rechts) Fig.…”

Fatigue and crack propagation investigations on composite dowels using an inclined single push-out test

“…The current concept for cyclic design is to avoid any fatigue of steel and concrete [3]. A concept which considers fatigue damage of concrete [4] and the residual loadbearing capacity and stiffness of torn steel dowels has a great economic potential. Therefore a knowledge of crack development in the steel dowel as well as of the redistribution of forces in the individual dowels of a composite beam is necessary.…”