Untersuchungen zur Verbundwirkung von Betondübeln - Anwendung von tiefliegenden Betondübeln bei Slim-Floor-Konstruktionen (CoSFB)

Analysis of the composite action of concrete dowels - Application of concrete dowels for slim-floor construction (CoSFB).

With the aim to design slim-floor beams more economically, acting as composite beams, concrete dowels have been investigated to transfer the longitudinal shear force. First pilot tests executed in 2009 have demonstrated a great potential of this new construction system. It has also shown that the existing models for concrete dowels cannot be directly applied. Consequently, further test campaign has been carried out in 2011 to extend the already examined application range of the concrete dowels with slim-floor beams and to obtain General Technical Approval from the Deutschen Institut für Bautechnik (DIBt - German Institute for Civil Engineering). Through out all the tests, a ductile behaviour of concrete dowels has been confirmed. The analysis of the test results leads further to the conclusion that the ultimate load bearing capacity is mainly composed of three bearing parts: a concrete compression strut running into the dowel, resistance of the reinforcement bar and friction. In this paper, an influence of the concrete compressive strength on the load bearing capacity of the shear connection is specifically explained, since the experiments showed that a higher concrete compressive strength has not necessarily led to a higher load bearing capacity of the dowels. From the experimental results recommendations for the characteristic longitudinal shear capacity of the concrete dowels in the examined application were derived and are presented in here. The paper also provides guideline to the design, promoting economic application of the developed composite slim-floor beam (CoSFB), whose potential is demonstrated by examples of realized projects.