PSI - Issue 78

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

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Fig. 4. Damage patterns observed at the end of testing for specimens investigated by Melo et al. (2001).

Specimen TPC, detailed with 180-degree hooks, exhibited two prominent diagonal shear cracks accompanied by the expulsion of a concrete wedge from the joint core. The control specimens (TPA-1 and TPA-2) showed more distributed damage within the joint region and spalling of concrete from the exterior face of the joint. Specimen TD, reinforced with deformed bars, also experienced severe diagonal cracking within the joint core and pronounced concrete expulsion at the exterior face. However, unlike the plain bar specimens, specimen TD developed a greater number of flexural cracks along the beam, indicating improved bond behavior and energy dissipation capacity. In terms of strength, the specimens reinforced with plain bars and subjected to cyclic loading exhibited similar peak load capacities, which were approximately 10% lower than that of the specimen reinforced with deformed bars. The force-displacement envelope curves of cycling tests on specimens TPA-2 and TPB-2 were similar to the monotonic curves of TPA-1 and TPB-1, respectively until the ultimate strength was reached. Pampanin et al. (2002) investigated the cyclic response of an exterior beam – column joint specimen representative of the typical structural deficiencies found in reinforced concrete buildings constructed in Italy from the 1950s to the 1970s. The specimen was detailed with beam longitudinal reinforcement anchored using end hooks, and no horizontal reinforcement was provided within the joint core. The column axial load was not kept constant but was varied during testing as a function of the applied lateral load. Specifically, fluctuations of up to ±40 – 50% relative to the axial load due to gravity alone were recorded. The gravity-induced axial load was 100 kN, corresponding to approximately 10% of the column ’ s axial load capacity. After the formation of initial diagonal cracks within the joint core, significant slippage of the beam longitudinal reinforcement was observed, localized within the joint region. This slippage generated localized compressive stresses at the hook anchorage, resulting in the formation and eventual spalling of a concrete wedge from the joint core. This localized damage led to a brittle failure mechanism characterized by the loss of bearing capacity. The progression of this hybrid failure mechanism compromised the effectiveness of the diagonal strut mechanism within the joint, ultimately leading to the expulsion of the concrete wedge and a rapid degradation of shear strength at relatively early stages of the test. 1.8. Pampanin et al. (2002)