PSI - Issue 78

Teklewoin Haile Fitwi et al. / Procedia Structural Integrity 78 (2026) 1775–1782

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4. Result and discussion 4.1 Control specimen

The unstrengthened control specimen (Specimen 1) exhibited peak lateral forces of +29.55 kN and -25.34 kN at corresponding lateral displacements of +75 mm and -61 mm, respectively as shown in Fig. 5. The specimen showed rapid stiffness deterioration prior to reaching ultimate capacity, reflecting progressive damage accumulation under cyclic loading conditions. Further, the stiffness, calculated as = ( , ∆ ⁄ ) where , represent the maximum force at the ℎ loading cycle and ∆ is the corresponding displacements. In addition, cyclic behavior was characterized by pronounced pinching behavior, where the hysteretic loops exhibited narrow, pinched configurations that limited energy dissipation during the loading history. The structural response was dominated by brittle joint shear mechanisms, evidenced by extensive diagonal cracking patterns within the joint panel region and concrete spalling around the beam-column interface. 4.2 Pre-damaged specimens Specimen 2, designated for carbon FRCM strengthening, demonstrated maximum lateral forces of +22.05 kN and -22.27 kN at displacement amplitudes of ±35 mm during the pre-damage loading phase. The specimen exhibited a rapid degradation of the initial stiffness. The pattern (Fig. 4c) was characterized by steep initial loss of elastic behavior followed by continuous deterioration throughout the loading history, consistent with progressive joint panel damage mechanisms. The force-displacement response, as shown in Fig. 4a, highlights a pinching behavior with limited hysteretic area, resulting in poor energy dissipation characteristics throughout the damaging phase.

Fig. 4. (a) hysteretic response; (b) envelop; (c) stiffness degradation; (d) cumulative energy dissipation.