PSI - Issue 64

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

859

3

2.1. Column Details and Specimen Production The code confirming column specimens were designed and detailed according to the current rules stated in the Turkish Building Earthquake Code 2018 (TBEC 2018). Generally, the residential buildings are designed for Life-Safety “LS” performance level, which are expected to be damaged during design level earthquakes. The specimens had cross section dimensions of 250x400 mm (bxh), a shear span ratio of a/d=3.84, longitudinal reinforcement ratio of r l =0.0123 and volumetric transverse reinforcement ratio of r h =0.01. The clear distance between longitudinal rebars were 157 mm, which is in compliance with TBEC (2018) (25* f transverse =200 mm). In American Concrete Institution 318 (2019), if clear spacing between longitudinal bars exceed 6 inch (152 mm), they should be supported with a cross-tie or closed tie. Also, clear spacing of longitudinal bar cannot exceed the values of “16* f longitudinal = 224mm; 48* f transverse = 384 mm; minimum dimension of member = 250 mm”. Since all longitudinal rebars were tied with stirrups or cross-tie in reinforcement details, and their maximum clear distance was 157 mm, they were also in compliance with ACI 318 (2019). The geometry and reinforcement details of the specimens represent the base story columns of modern residential buildings. The dimensions and reinforcement details of the column specimens are shown in Figure 1 (a). All column specimens were cast at the same time using the same mixer. 2.2. Loading Protocol and Test Setup The loading protocol determined according to ACI 374.2R-13 (2013) is presented in Figure 2a. It should be stated that all first stage and second stage test of repaired specimens were used same load history. However, loading history of second stage tests were started upon residual displacements of first stage tests. Therefore, absolute top displacements of repaired specimens were shifted to pull side (Figure 2 (b)). The loading system was capable of applying the axial load in the gravitational direction during the entire test. Therefore, the second order effects which increase in the maximum bending moments at the column base and residual deformations were represented more realistically. Prior to the tests, the specimens were fixed to the laboratory strong floor to prevent sliding and rocking. The lateral displacement history was applied to top of the column by using a double acting servo-controlled horizontal hydraulic actuator, after the axial load was applied by a vertical hydraulic actuator. Lateral movement was allowed at the interface between vertical actuator and base plate of steel frame. In addition, rotation is allowed at the connection between vertical actuator and test specimen to keep the direction of axial load parallel to the gravitational direction during the entire test (Figure 3). Therefore, second order effect has significant influence on test results. . Linear variable displacement transducers “LVDTs” and strain gauges were used to measure response of the specimens. Strain gauges were placed on two corner longitudinal reinforcing bars, and they were distributed in between foundation and expected plastic hinge zone. LVDT’s were placed in between base level of the column and the level corresponding to the 1.5 times of specimen’s section height. The representation of measurement devices installation is presented in Figure 1 (b). 2.3. Repair Procedure Specimens were repaired after they were tested at three different damage levels as presented mentioned in Tables 1 and 2. It was planned to use sustainable structural mortar for repairing of crushed or spalled cover concrete without removing the axial load on the columns. The fib 102 (2022) document was followed for the repair procedure. Firstly, the crushed or spalled concrete was removed with a jackhammer at all sides of the column plastic hinge region. The repair zone height began from the top surface of the column foundation and extended to the top of the damaged region. The damaged concrete was removed until the undamaged layer of concrete was reached. Depending on the damage levels, the depth and the height of the repair applications were adjusted accordingly. Height and depth values of repair applications for the specimens with damage level I, II and III were 80mmx10mm, 350mmx20mm and 500mmx40mm, respectively. The depth values represent the average depths around the perimeter. It should be stated that the repair depth slightly exceeded the cover thicknesses for damage level III. After the dust was cleaned from the surface via vacuum cleaner and air compressor, the surfaces were saturated with water. Then, the cement-based bonding primer was applied to the surface. Before the primer dried, the mortar was applied to the surface without formwork. The axial load was not removed after the first