PSI - Issue 77

Ercan Işik et al. / Procedia Structural Integrity 77 (2026) 465 – 474 Ercan Işik et al./ Structural Integrity Procedia 00 (2026) 000 – 000

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In RC systems, columns and beams can be considered the primary structural elements of the structure. The connections between columns and beams are crucial for transferring loads from horizontal to vertical elements. In this context, in RC frame structures, significant shear forces occur in the beam-column joint regions under seismic loads, which can greatly impact earthquake safety. Earthquake forces generate high shear forces at the connection points, leading to the deterioration of the concrete in these areas. This issue can be mitigated by using adequate transverse reinforcement in the column-beam regions. However, examples of concrete crushing and buckling in the longitudinal reinforcements due to insufficient transverse reinforcement at the column-beam connections are illustrated in Figure 2.

Fig. 2. Examples of concrete crushing, buckling damage in the reinforcement.

After the load transfer in the column-beam joint regions, moments, especially under seismic loads, increase at the upper ends of the columns, potentially causing damage in these areas known as plastic hinge regions. The plastic hinges formed due to insufficient transverse reinforcement at the column tops, and the resulting observed damages are shown in Figure 3. In this area, the lack of confinement for transverse reinforcement, as specified in the earthquake regulations, leads to buckling of the longitudinal reinforcements and results in brittle failure of the

concrete.

Fig. 3. Damage in the upper confinement region due to insufficient transverse reinforcement

While it is recommended that transverse reinforcements in columns be wrapped around longitudinal reinforcements at an angle of 135º, in practice, wrapping them at 90º can lead to insufficient anchoring of the transverse reinforcements. As a result, the transverse reinforcements can more easily slip out of the longitudinal reinforcements. Examples of such damage are shown in Figure 4.