## 5 Conclusions  
The results of a set of cyclic shear tests of reinforced interfaces in the presence of an externally acting normal stress were presented and discussed in terms of the failure mode and the influence of the test parameters on the interface capacity, the shear slip corresponding to the interface capacity, and the width of the crack across the interface. Figure 15: Plotted vs. experimental interface resistance calculated using Equation (1): (a) 119 specimens are included; (b) 102 specimens are included. The data experimental interface resistance is included in the current paper and in the literature [4; 5; 10; 11; 12; 13; 14; 15; 16; 17]. Based on the experimental results presented in this paper, the following conclusions can be drawn:  
1. The shear resistance of rough interfaces simulating cold joints (the new concrete is cast against the old concrete) depends on the value of the applied shear slip, as well as on the embedment length of the reinforcement, the increase in which has a positive effect on the mobilized shear resistance. Additionally, the shear resistance is affected by the anchoring mechanism of the reinforcement. Thus, for embedment lengths smaller than the development length, the cast-in bars mobilize smaller resistance than post-installed bars of the same embedment length. Nonetheless, in the presence of an external compressive stress, the effect of the embedment length of the interface reinforcement is reduced. This is due to the reduced activation of the clamping effect of the interface reinforcement. Indeed, in the presence of external compressive stress, the crack width across the interface is limited, and thus, the strains measured on the reinforcing bars are much smaller than for identical specimens tested without any external compression on the interface. 2. The application of cyclic shear slips has confirmed the negative effect of this type of loading in terms of ultimate shear resistance and stiffness degradation. Nonetheless, in this case, the presence of external compressive stress reduces the effect of cycling. Furthermore, the maximum resistance of interfaces subjected to external compression is mobilized for smaller shear slip values than the capacity of their counterparts with zero external stress. This is a feature to be accounted for in cases of displacement-based design. 3. The equation proposed by the authors to calculate the maximum resistance of interfaces was applied to the experimental results presented in this paper, as well as to relevant results from the literature, obtained from testing interfaces subjected to external compression. It is noted that the equation is based on a global model following the step-by-step development of the shear resisting mechanisms, as well as their interaction. The application of this equation was quite satisfying, as it was able to predict the ultimate shear resistance of interfaces quite accurately. 4. Taking into account that the equation proposed by the authors is already checked against a large number of experimental results from the literature, compiled in a database and covering a wide range of values for all influencing parameters, one may consider this equation as a sound basis for the design of interfaces. Conceptualization, V.P., C.Z. and E.V. ; methodology, V.P., C.Z. and E.V. ; validation, E.V. ; investigation, V.P. and C.Z. ; data curation V.P. ; writing--original draft preparation, V.P. and E.V. ; writing--review and editing, V.P., C.Z. and E.V. ; supervision, V.P., C.Z. and E.V. ; project administration, V.P. and C.Z. ; funding acquisition, C.Z. All authors have read and agreed to the published version of the manuscript. This research program was partly funded under the Basic Research Funding Program of the Research Accounts Department at NTUA. Financial support provided by the Hellenic State Scholarships Foundation, for the development of the doctoral research of the first author at NTUA, is gratefully acknowledged. Not applicable.