Experimental investigation of bond strength under high loading rates

Abstract

Abstract. The structural behaviour of reinforced concrete is governed significantly by the transmission of forces between steel and concrete. The bond is of special importance for the overlapping joint and anchoring of the reinforcement, where rigid bond is required. It also plays an important role in the rotational capacity of plastic hinges, where a ductile bond behaviour is preferable. Similar to the mechanical properties of concrete and steel also the characteristics of their interaction changes with the velocity of the applied loading. For smooth steel bars with its main bond mechanisms of adhesion and friction, nearly no influence of loading rate is reported in literature. In contrast, a high rate dependence can be found for the nowadays mainly used deformed bars. For mechanical interlock, where ribs of the reinforcing steel are bracing concrete material surrounding the bar, one reason can be assumed to be in direct connection with the increase of concrete compressive strength. For splitting failure of bond, characterized by the concrete tensile strength, an even higher dynamic increase is observed. For the design of Structures exposed to blast or impact loading the knowledge of a rate dependent bond stress-slip relationship is required to consider safety and economical aspects at the same time. The bond behaviour of reinforced concrete has been investigated with different experimental methods at the University of the Bundeswehr Munich (UniBw) and the Joint Research Centre (JRC) in Ispra. Both static and dynamic tests have been carried out, where innovative experimental apparatuses have been used. The bond stress-slip relationship and maximum pull-out-forces for varying diameter of the bar, concrete compressive strength and loading rates have been obtained. It is expected that these experimental results will contribute to a better understanding of the rate dependent bond behaviour and will serve for calibration of numerical models.

Influences on the structural response of beams in drop tower experiments

“…There are many contributions studying the bond between reinforcement bars and concrete on small-scale specimens. Some researchers, for example, Máca et al, 14,15 and Michal et al 16 conducted push-in tests, Wensauer 17 tested specimens in spallation configuration, and beam end tests were carried out by Michal et al 18 The areas that are critical for the bond between reinforcement and the surrounding concrete in drop tower beam tests with small and fast impactors are described in Leicht et al 19 There is firstly the center of the 1450 mm long beams between the two inclined cracks restricting the punching cone. Then, there is the area outside but directly next to the punching cone.…”