# Cyclic Behavior of Long Concrete Interfaces Crossed by Steel Screws
###### Abstract  
This study focuses on long concrete interfaces tested under cyclic actions, fastened with post-installed industrial steel screws. The overall behavior and the effect of roughness were investigated in three long interfaces, representative of connections between, e.g., a slab and a wall, a beam and a wall, etc. The results were compared with those of short interfaces tested by the authors in previous campaigns. It was observed that rough long interfaces activate their maximum resistance at small values of imposed shear slip. When roughness was reduced, the maximum resistance was also reduced, the corresponding shear slip was increased, and the overall behavior was stable. For large values of the shear slip, imposed at one end of the interface, the shear slips along it tended to be uniform, both in short and long interfaces. The limited embedment length of the screws led to their pronounced pullout. Finally, the asymmetry of resistance between the two loading directions that was observed in short interfaces was alleviated in the long ones, where also the scatter of the results was limited among duplicate specimens.  
reinforced concrete interfaces; steel screws; post-installed connectors; cyclic behavior; interface dimensions +
Footnote †: journal: Applied Sciences  
0024 14 8246 10  
the entire length of a long interface or \"is there any chance of redistribution of forces among a large number of connectors\", cannot be answered on the basis of the published experimental results.  
Another aspect needing more attention is the investigation of behavior (monotonic and cyclic) and, thus, the proper use of types of connectors other than pieces of steel reinforcing bars. For the time being, the latter constitute the most used type of interface reinforcement, and definitely the most investigated one (see Section 2). Nonetheless, industrial anchors (such as powder-driven nails or steel screws, etc.) may constitute a viable alternative in cases where the intervention is to be urgently applied, either for safety or for economic/social reasons. For example, to avoid fast deterioration of the state of a building after a strong earthquake, the filling of some frame spans with reinforced or unreinforced concrete walls might be sought. In such an application, the installation of industrial anchors (not requiring the drilling of holes to concrete and time for hardening of the bonding material) as reinforcement of interfaces between the existing frame and the to-be-added wall may be a good choice. Moreover, to reinstate the decayed deck of a bridge, the construction of a thin RC overlay may be needed, connected to the existing concrete using a large number of connectors. In such applications, the use of industrial anchors, easy and fast to apply, is worth investigating as an alternative to steel reinforcing bars.  
Being focused on the seismic behavior of concrete-to-concrete interfaces, the authors of this paper have also investigated the case of using steel screws as interface reinforcement. The results of tests, published in [4], were obtained on interfaces 500 mm long and 200 mm wide, crossed by three 10 mm diameter screws and subjected to cyclic shear.  
To investigate possible differences between short and long interfaces crossed by screws and subjected to cyclic actions, and to thus contribute to the design of relevant applications, a testing campaign was planned and executed. In the current study, the results of testing long interfaces reinforced with steel screws of short length are reported. For the sake of comparison, selected experimental results obtained from testing short interfaces, presented elsewhere [4], are repeated here to allow for identification of similarities and differences with the long ones.