The character of cracking in the beams with loop joints

Abstract

In connection with rather wide distribution of prefabricated-monolithic reinforced concrete in Ukraine, there was a need to increase areas of using various joints, in particular joints of reinforcement without welding. The loop joint (Perederiya joint) represents the releases of the armature from the ends of the elements in the form of concentric loops forming rings. The concrete in the space between the rings works on a comprehensive compression. Laboratory studies in this direction made it possible to add a certain picture of the cracking of test specimens with loop joints. The majority of researchers noted the intensive formation and development of cracks along the contour of contact between old and new concretes in the zone of the loop joints under various loads. And most of the existing recommendations are aimed at reducing cracking in such zones. In view of poor knowledge of the issue, it was decided to test the crack resistance of the splined loop joint in comparison with the keyless. The nature of the formation and development of cracks were established. Cracks are concentrated in the middle of the span in the place of the loop joint. In general, normal cracks were observed, but horizontal cracks also occurred. Cracking in samples with loop joints began with the appearance of hair cracks in the stretched zone in the middle part of the span and at the border of beams and joints concrete. Due to the jagged form of the keyed joint, the development of a crack along the border of old and new concrete in such joints was delayed at the tops of the «teeth».