PSI - Issue 64

S. Kolemenoglu et al. / Procedia Structural Integrity 64 (2024) 857–868 Author name / Structural Integrity Procedia 00 (2019) 000–000

866 10

4. Discussion and Recovery Ratios The recovery ratios of strength, stiffness and ductility after repair (ratios of repaired specimen parameters to that of reference specimen) can be observed by the comparison of the column base moment versus lateral drift ratio backbone curves of the tested specimens, which are given in Figure 9 (a). The calculated recovery ratios, that are useful for the determination of plastic hinge modification factors mentioned in FEMA 307 (1998) and ATC 145 (2021), are presented in this part. Stiffnesses of the reference and repaired members were determined with the slope of the line between the origin and the point corresponding to the 75% of the maximum moment on the base moment-drift ratio curves. The ductility was defined as the ratio of the displacement corresponding to 20% lateral strength loss and the displacement corresponding to 75% of the maximum load before the peak. The lateral strengths were taken as the recorded maximum base moments during the reversed cyclic tests. The schematic representation for calculation of recovery ratios is given in Figure 9 (b). The recovery ratios are given in Table 4. It has to be stated that the responses of repaired columns in the pushing and pulling directions exhibit variations due to second stage test procedure (beginning the post-repair test from a residual displacement in the pulling direction). Therefore, recovery ratios are given separately for push and pull directions, together with their averages. For the repaired specimen after initiation of crushing (damage level I), stiffness was averagely reduced by 10% with respect to the reference specimen. The ductility ratio was increased 115% and 166% at push and pull direction respectively. The peak moment value reached in the pushing direction was 8% less than that of the reference specimen, while the peak moments of the reference and repaired specimens in the pulling direction were close to each other. The decrease in stiffness can be attributed to the existence of unrepaired cracks. This condition can lead to more lateral drift and lower earthquake demand for repaired structures. For the repaired specimen after local crushing (damage level II), the value of recovery ratio for stiffnesses was 85% and 97% for pushing and pulling directions, respectively. The ductility recovery ratio was reduced by 8% in pushing direction, while it was %100 in pull direction. The lateral strength was reduced by 7% in average. Decrease in lateral strength can be attributed to detachment of the repair mortar layer from the concrete substrate after the 2.0% drift ratio. For the repaired specimen after cover spalling (damage level III), the stiffness, ductility and lateral strength were significantly reduced in the pulling direction

potentially due to the higher extent and severity of first stage damage. Table 4. Recovery ratios for repaired columns with respect to the reference column

Stiffness [push/pull-average]

Strength [push/pull-average]

Ductility [push/pull-average]

Condition

Repaired after Damage Level I Repaired after Damage Level II Repaired after Damage Level III

0.84/0.95 – 0.90 0.85/0.97– 0.91 0.84/0.68 – 0.76

0.92/1.00 – 0.96 0.94/0.92 – 0.93 0.89/0.68 – 0.77

1.15/1.66 – 1.40 0.92/1.00 – 0.96

*/0.83 * Test of repaired specimen after damage level III was ended before the lateral strength was reduced by 20% in push direction. Therefore, ductility cannot be calculated.

250

200

150

100

R3013 R3012 R3011 R3010

50

Base Moment (kNm)

0

-5

-3

-1

1

3

5

Drift Ratio (%)

(a) (b) Fig 9. (a) Backbone curves (b) Schematical representation for calculation of recovery ratios.