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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2.2. Experimental results

Summarized results of previous experiments are highlighted in this section. In specimen C concrete crushing was witnessed at 2% drift ratio representing a prolonged displacement capacity after yielding point of the longitudinal reinforcements. This specimen was fully confined based on requirements of the 1975 code. In specimen S longitudinal reinforcements did not contribute as much as the other specimens due to premature concrete crushing at early drift ratios. Buckling of longitudinal rebars were seen at 0.5% drift ratio before the peak lateral load capacity. The ultimate drift ratio of retrofitted specimen with CFRP (RS) was enhanced to 3% for RS specimen (doubled when compared with S). External confinement provided by CFRP wraps hindered the buckling of reinforcements at ultimate load state. At drift ratio of 3% in pushing, CFRP ruptured and then, lateral load capacity decreased significantly in pulling. Results showed that specimen C dissipated 91% and 745% more energy in comparison to RS and S specimens, respectively. Summary of the test results for the specimens is shown in Table 4. Tests continued until significant loss in the lateral or axial strength.

(mm) (mm) Drift Ratio at Collapse (%)

Table 4. Test results. Specimen ID

Peak force (kN)

Load capacity increase (%)

Drift Ratio Increase

S C

81.4 173.6 157.2

N.A. 115

5.4 10.1 10.2

13.5 38.7 30.2

1.3 3.8 3.0

N.A. 1.86

RS 1.23 The contribution of flexural, slip, and shear deformations in top displacement is significant and shown in Figure 2. As seen, the shear deformations are negligible in specimen C as it is confined thoroughly, though shear deformations are much pronounced for specimen S. For RS specimen, shear deformations were reduced by the proper confinement of external CFRP jacket. For all specimens, slip deformations increased and then remained almost constant until failure. 94

Push

ected dis lacement umo each com onent le ure li hear

Push

Push

ected dis lacement umo each com onent le ure li hear

ected dis lacement umo each com onent le ure li hear

o dis lacement mm

o dis lacement mm

o dis lacement mm

Pull

Pull

Pull

is lacement mm

is lacement mm

is lacement mm

Fig. 2. Contribution of flexure, slip, and shear deformation in top displacement for a) C, b) S, and c) RS specimens.

3. Numerical program 3.1. Modeling in ATENA

Numerical models of the tested specimens were modeled in GiD pre-processor, then analyzed by means of a commercial software ATENA (Cervenka et al. 2005). There are several constitutive material models that could be defined in ATENA for RC members. Thus, for concrete, steel bars, and CFRP, the material models used are CC3DNonLinCementitious2 (Kupfer et al. 1969, Hsieh et al. 1982), CCCyclingReinforcement (Menegotto and Pinto 1973) and CCCombinedMaterial, respectively. Concrete and steel bar constituent material models are shown in Figure 3. In the concrete model, W d is critical compressive displacement adjusting the concrete stress-strain descending branch. Models for concrete include the possibility of modeling crack direction. This model takes into account the nonlinear behavior of concrete in compression, the fracture mechanics for the tension softening, reduction of compressive strength due to cracking, and biaxial failure criteria. Loading and reloading consider plastic strains for compression ( ) , while in tension, a modification is performed such that system comes back to the origin linearly or parallel to the initial elastic stiffness. Steel bars are considered as truss or link elements embedded in concrete. Also,