J. Hegger, M. Feldmann, S. Rauscher, O. Hechler, Germany
Scope of the investigations was the fatigue behavior of different shear connectors like headed studs and the puzzle-strip, which is a continuous shear connector in high strength concrete. For both types of shear connectors cyclic push-out tests as well as large-scale beam tests under cyclic loading were carried out. The cyclic beam tests with headed studs show that the prediction of the fatigue failure according to the current standards is not satisfactorily. A good prediction of the crack propagation (thus fatigue) can rather be accomplished by using an approach based on the crack-slip relationship. For the continuous puzzle strip the fatigue behavior depends on the manufactoring process, the state of the cutting-induced heat treatment of the surface material and on the surface roughness. For the tested connector geometry a threshold value for the crack propagation was determined. The cyclic beam tests with headed studs show, that their fatigue behavior in high strength concrete is in good accordance with the model according to [6], which predicts the slip-and-crack-development for displacement controlled loading of the studs. However, the tests also indicate that there is crack development underneath the proposed minimum level of slip amplitude. Further investigations are required to examine the region of low slip amplitudes and compare the differences between normal and high strength materials.
