Experimental and analytical study for retrofitting with thin concrete overlay

The retrofitting of existing reinforced concrete structures is of paramount importance due to aging structures, changes in design codes, and the need to enhance resilience against seismic events. This paper addresses this critical issue by presenting the results of an experimental campaign focused on evaluating the shear performance of old-to-new concrete interface, considering the application of a thin (5 cm) concrete overlay. Both monotonic and cyclic shear tests were conducted to assess the behavior under static and seismic loading conditions. Mechanical anchors were installed into the existing concrete as connectors. The study investigates the influence of different concrete types, i.e. normal-weight and lightweight concrete, used for the overlay. The experimentally obtained shear strength values were compared with predictions derived from established design codes and guidelines: Eurocode 2 (old and new versions) and EOTA TR066. The aim of the comparison was to understand if the available codes are able to predict the experimental behavior when using an overlay with limited thickness and a lightweight concrete. TR066 results conservative but able to predict the failure mode, while the new Eurocode 2 gives the best prediction of resistance, although it does not cover very short embedment depth and seismic action. Lastly, the evaluation of the reduction coefficient αseis is made to account the behavior of the connectors under seismic action.