Recently, novel types of shear connectors have been investigated enthusiastically in Europe. Among the new connector geometries, clothoid-shaped shear connectors are used practically for bridge engineering. Although various schemes for evaluating mechanical performance can be used, they were established based on the pushout test database. During their time of use, the concrete slab is expected to be subjected to fully reversed cyclic stress during an earthquake. The stress history thereby differs from those of standard pushout tests, resulting in the discrepancy from the evaluation equations. To address this concern through this study, cyclic loading tests were conducted, imposing compressive and tensile stresses cyclically. A comprehensive experiment using 14 specimens with various influential parameters revealed the cyclic behavior and stress transfer mechanism. The results confirmed that the mechanical capacity of a composite dowel with a clothoid-shaped shear connector is dependent on the stress orientation. Furthermore, the applicability of earlier evaluation formulae was clarified based on established knowledge of experimentally obtained data. Because the necessity for reflecting the stress history was demonstrated, this research newly presents a formula for evaluation of the ultimate shear strength and load-displacement relation.

In seismically retrofitted reinforced concrete (RC) structures, new members are connected to existing members using interfaces with roughened surfaces and post-installed dowel bars. During an earthquake, the interfaces are subjected to cyclic shear and normal stresses. Therefore, the structural design of interfaces is essential. In a previous study, normal and shear loads were applied to interface specimens. Moreover, a shear strength estimation method was proposed; however, the cyclic behavior was not discussed. This paper presents a cyclic model of the roughened surface in retrofitted RC structures. First, an envelope model was constructed using the previous shear strength estimation method and Saenz model, a constitutive law of concrete. Subsequently, the cyclic rules were modeled. Moreover, a previous dowel model was incorporated into the proposed cyclic model to estimate the test results. Finally, the proposed model provided reasonably estimated test results; the average ratio of the test results to the model results was 1.04. In addition, as δ increased, the effect of the dowel bar intensified in terms of shear.