PSI - Issue 78

Giada Frappa et al. / Procedia Structural Integrity 78 (2026) 89–97

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EJ2, the column transverse reinforcement above and below the joint core served solely to restrain the buckling of the column longitudinal bars. In contrast, in specimen EJ1, the transverse reinforcement had a dual function: in addition to preventing column bar buckling, it contributed to an alternative shear-resisting mechanism via the formation of a diagonal concrete strut (identified as strut D in Fig. 2c), thereby altering the stress flow path within the joint. Regarding the effect of axial load, specimens EJ3 and EJ4 attained maximum shear strengths equal to 87% and 91% of their respective theoretical flexural strengths. The presence of the applied column axial load enhanced the joint shear capacity, with EJ3 and EJ4 achieving strengths approximately 1.5 and 1.2 times higher than those of EJ1 and EJ2, respectively. This improvement is primarily attributed to the increased bond effectiveness between the beam tension reinforcement and the joint core concrete, which facilitated more efficient force transfer across the joint.

Fig. 2. Possible failure mechanisms and alternative force transfer paths in exterior beam-column joints: (a) opening of beam bar hooks bent into the joint core; (b) opening of beam bar hooks bent outside the joint core; (c) development of an alternative joint shear force path in specimens with beam bar hooks bent outside the joint core and extensive column transverse reinforcement. Liu et al. (2001). 1.7. Melo et al. (2012) Melo et al. (2012) investigated the cyclic behavior of six exterior beam-column joints (Fig. 3), five reinforced with plain bars, specimens TPA-1, TPA-2, TPB-1, TPB-2, and TPC, and one with deformed bars, specimen TD.