Experimental Testing on Reinforced Concrete Beam–Column Connections with Strand Slippage for Seismic Design Bioinspired by the Norway Spruce Tree
Abstract
Seismic assessment of reinforced concrete structures requires characterization of member and connection behavior under large cyclic deformations. Moment-resisting frames are widely adopted in seismic regions, but meeting code requirements is problematic when beams are reinforced with prestressing steel strands because their ultimate elongation differs substantially from that of conventional high-ductility reinforcement (e.g., εu,k ≈ 3.5% for Y1770S7 strands versus εu,k ≈ 7.5% for B500C rebars). This study reports the findings of an experimental program conducted on reinforced concrete beam–column joints (NGS), representative of moment-resisting frame systems typically employed in seismic regions. To explore innovative structural solutions, a biomimetic design strategy was adopted, drawing inspiration from the micromechanics of Picea abies (Norway spruce). Five half-scale (1:2) specimens were subjected to quasi-static, displacement-controlled cyclic loading following the ACI 374.2R-13 (ACI T.1.1R-01) protocol, and their performance was evaluated against prescribed acceptance criteria. Adding one longitudinal steel strand and partially anchoring it in normal concrete (NGS2) and in biomaterial-adapted grout (NGS4) did not increase the amount of dissipated energy when compared to the reinforced concrete conventional solution (NGS1). Moreover, the effects of replacing the rebars with partially anchored steel strands (NGS3 and NGS5) proved to be negative.