Methods for evaluating the ultimate capacity of existing RC half-joints

Reinforced Concrete (RC) discontinuity regions (D-regions), such as half-joints, can represent vulnerable zones in existing RC structures since they can be affected by a quasi-brittle failure mechanism. In common design practice, the ultimate strength of D-regions is assessed through Strut and Tie (S&T) models. It is well recognized that the resistant lattice trusses suggested by the Eurocode 2 (EC2) and usually adopted in determining the resistance of new D-regions during the design phase, provide results on the safe side. Nevertheless, in existing half-joints, primary reinforcing bars are frequently distributed across multiple layers, which makes it not easy to identify the appropriate S&T model. For instance, the ultimate capacity of these half-joints could be misestimated if distributed bars are replaced by an equivalent tie passing for their centroid, as is typically done in common practice. The present paper provides two analytical methods for identifying the reinforcement bars involved in the resistant mechanism of D-regions and determining the axial forces in all of them. The proposed methods estimate the ultimate shear resistance of existing half-joints. The accuracy of the proposed procedures is checked through a comparison with numerical results. The methods, capable of identifying the weakest component in the resistant mechanisms of RC D-regions, can be adopted for the assessment of the load-carrying capacity of existing half-joints and identify the proper structural strengthening works to increase the ultimate strength and ductility.