Shear behaviour of composite dowels in transversely cracked concrete

Abstract

In steel-concrete composite girders, innovative composite dowels can be used to transfer the shear forces between the concrete slab and the steel section. Today, composite IntroductionComposite dowels are efficient, innovative shear connectors consisting of interlocking steel and concrete dowels for use in filigree composite beams (Fig. 1). The steel dowels are produced by oxygen cutting in which the cutting torch burns regular recesses into a steel plate or the web of a steel section in a continuous pass. In the composite connection, the steel dowels embedded vertically and the interstitial concrete dowels ensure an interlocking structural connection. The use of composite dowels yields very economical solutions, especially in composite sections with single-flange steel beams, since the relatively ineffective cross-sectional area of the structural steel near the plastic neutral axis is reduced [1]. Today, composite dowels are predominately used in engineering structures such as prefabricated composite bridges [2]. However, due to their ease of manufacture, excellent loadbearing and deformation properties and suitability for slender concrete slabs, these dowels are being applied more than ever in building construction as well, e.g. in integrated composite floor sys-The design of conventional shear connectors is addressed in EN 1994-1-1 [5], where approaches for determining the shear capacity of headed studs are given. EN 1994-1-1 allows for the use of alternative shear connectors other than headed studs if distinctive qualities in terms of shear and deformation behaviour are met. In conjunction with EN 1994-1-1, the design of composite dowels with puzzle-or clothoid-shaped geometry under predominantly static and cyclic loading can be carried out according to a general technical approval [6], which was certified by the DIBt in May 2013.If the concrete slab of a composite beam is exposed to tensile stresses in the longitudinal direction, transverse cracking occurs; for example, cracking can arise in the region of the interior supports of a continuous composite beam. In EN 1994-1-1, as well as in the general technical approval [6], the impact of transverse cracking on the static shear capacity of the shear connectors (headed studs as well as composite dowels) is neglected. Indeed, the effect of transverse cracks and longitudinal tension in the concrete slab on the structural behaviour of composite dowels has not yet been systematically studied. In the few known shear tests under longitudinal tension in concrete slabs [7], [8], no significant deterioration of the dowel's loadbearing capacity due to transverse cracking has been observed. In [7] it is assumed that a local pressure field in the concrete dowel resulting from the transferred dowel force leads to closure of the transverse cracks. According to [7], this crack closure yields a reduced stiffness in the shear connector, but without a significant decrease in shear capacity. However, the small database of usable experiments does not allow for a definitive asse...

Ausstanzen von Verbunddübelleisten im gerissenen Beton

“…Die Defizite bisher bekannter Versuchsaufbauten zur Untersuchung des Querrisseinflusses auf das Schubtragverhalten werden in Bild 3 (links) beispielhaft anhand des Versuchsstands aus [16] veranschaulicht.…”

“…Hinzu kommt die bekannte Problematik, dass im Standard-Abscherversuch nach [19] bzw. dem hieran angelehnten Versuchsaufbau aus [16] nicht alle Verbundmittel gleich stark beansprucht werden, sondern lastnahe Ver-suchsergebnissen herausgerechnet, verbleibt eine Tragfähigkeitsreduktion von über 18 %, die folglich dem Querrisseinfluss zuzuschreiben ist. Die Schubkraft-Schlupf-Beziehungen und die Geometrie der Versuchskörper sind in Bild 2 dargestellt.…”

“…B. integraler Deckenaufbau [14], [15] in der Biegezugzone angeordnet, bilden sich in den auf Zug beanspruchten Trägerbereichen Querrisse im Betongurt aus. Diese setzen die Schubtragfähigkeit von Verbunddübelleisten mit Ausstanzversagen herab [16], [17].…”

Concrete fatigue in composite dowels

“…In order to investigate how geometrical and material parameters affect static dowel stiffness, finite element calculations have been performed using ABAQUS . The simulation of composite dowel shear connectors has been described extensively in . An identical modelling approach has been implemented in the present paper, with the normal‐strength concrete being modelled by the material model ”Concrete Damaged Plasticity“ (CDP) .…”

Anchorage of composite dowels in UHPC under fatigue loading

“…After encasing the strip in concrete, the vertically embedded steel dowels and the interstitial concrete dowels ensure a structural, interlocked connection. Innovative shear connectors combine excellent shear performance with sufficient deformation capacity in both normal‐strength concrete (NSC) and ultra‐high‐performance concrete (UHPC) .…”