PSI - Issue 64

Nima Kian et al. / Procedia Structural Integrity 64 (2024) 1049–1056 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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transverse reinforcements (i.e. stirrups) are modeled and defined to take into account the confinement effect. For concrete mesh, eight nodes hexahedral brick elements are used. However, for CFRP sheets quadrilateral surface mesh is defined. Since the failure mode in CFRP retrofitted specimen was rupture of the CFRP sheet rather than debonding, a fixed contact surface was defined between CFRP sheets and column interface in ATENA. Figure 4 shows the numerical (ATENA) and experimental load-displacement hysteretic curves for comparison purposes. As can be seen, slightly high prediction of lateral load strength by ATENA is due to neglection of longitudinal bar slip proportions on top displacement. This issue will be solved by consideration of strain penetration in OpenSees model described in the next section.

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Fig. 3. Constituent material model of a) concrete and b) steel (Cervenka et al. 2005).

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Fig. 4. Lateral load-displacement hysteretic curves of experiment and ATENA, a) Specimen S, b) Specimen C, c) Specimen RS.

Figure 5 shows principle strain distribution in the longitudinal rebars at ultimate state. As it can be seen, specimen S reinforcements had already been buckled at this stage. Note that reinforcements of RS specimens were significantly restricted from buckling due to provided proper confinement representing the efficiency of the retrofitting. Also, in specimen C, buckling of longitudinal rebars were restricted due to proper confinement originated from transverse reinforcements. Numerical models showed reasonable agreement with their experimental counterparts. It is clear that ATENA fails in mimicking pinching behavior in the hystereses due to the reasons explained above.

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Fig. 5. Strain distribution of reinforcements at ultimate state, a) Specimen S b) Specimen C, c) Specimen RS.

3.2. Modeling in OpenSees For the analytical models developed in OpenSees, a force-based nonlinear beam-column element is considered. The constituent material for concrete and reinforcement are shown in Figure 6. By means of concrete02 command,