Post-installed connection in low-strength concrete beam with code minimum reinforcement: performance in tension

The connections of existing Reinforced Concrete (RC) or masonry buildings to external seismic retrofitting systems are called to resist a multiaxial stress state, including tension and shear. In this paper, the tensile behaviour of rebar post-installed into low-strength, narrow concrete element with code minimum reinforcement is investigated through 26 monotonic and 10 cyclic pullout tests, whereas the shear response will be analyzed in another study. Each specimen is intended to represent a portion of peripheral shallow beam in pre-seismic-code building, featuring poor material properties and small longitudinal reinforcement ratio. The effects due to concrete strength, rebar diameter and edge distance are taken into account by considering two concrete mixes (fcm = 16.0 MPa and 12.9 MPa), two fastener’s diameters (ϕ = 12 mm and 16 mm), and two specimen depths (H = 200 mm and 250 mm), respectively. The combined influence of rebar distance to embedded stirrups (cs′) and embedment length (lb) is considered through ratio ξ = cs′/(0.75lb). No significant cyclic degradation of connection performance is observed. For most specimens, combined pullout and concrete cone failure is obtained. Pure concrete cone failure is achieved only in five cases featuring the smallest concrete strength and, in four out of them, showing ξ > 1. Conversely, available design methods would always predict this failure mode as the most probable. This discrepancy is motivated by stress transfer to embedded reinforcement observed for ξ ≤ 1, highlighted by plastic deformation in the stirrups and increased mean load-carrying capacity compared to ξ > 1.