# Seismic Performance of Corroded Reinforced Concrete Columns Strengthened with Basalt Fiber Sheets
## 3 Test Results and Analysis  
### Failure Mode  
When the load of intact specimen Z1 reached 40 kN, 50 kN and 60 kN, the first three bending transverse cracks would appear at the root, 25 cm and 50 cm from the root in turn. When the load was 80 kN, the bending shear oblique crack appeared at 35 cm away from the root and developed along the bending crack. With the increase of the shear force, the bending shear cracks in the parallel plane of the column root continued to develop, penetrate and finally staggered into a network. After the specimen reached the ultimate load, the concrete near the root would be crushed and peeled off in the vertical shear plane, resulting in the decrease of bearing capacity. The plastic hinge was formed at the bottom of the column and the specimen was damaged. With the increase of loading cycles, the horizontal cracks gradually appeared and continued to widen. The cracks were mainly distributed in the height range of about 350 mm to 500 mm from the column root. The horizontal cracks gradually developed obliquely until the forward and reverse cracks were connected. Two or three cracks at the root developed into main cracks. The core concrete was divided into several pieces, which were crushed and destroyed, as shown in Figure 7.  
For the intact specimen Z1, the original longitudinal cracks continued to develop under horizontal cyclic loads. The failure process was similar to that of the intact specimen, while the bending transverse crack and bending shear oblique crack appeared when the load reached 30 kN and 60 kN, respectively. Due to the corrosion of steel bars, the bonding  
Figure 6: Loading procedure. Figure 7: Z1 (\(\rho=0\)). performance between the steel bar and the concrete was degraded. When the damage occurred, a large area of protective layer fell off. The longitudinal bar was exposed with the yield of compressed steel bars, as shown in Figure 8. Short vertical cracks appeared only when the specimen was close to the failure load. For the specimens reinforced with basalt fibers, since the specimens were wrapped, the development of cracks could not be observed during the loading process. However, with the continuous application of horizontal repeated loads, the sound of crackling was constantly heard in the basalt fibers. It can be seen from the last few cycles before the end of the test that the basalt fiber sheet near the root of the column bulged, indicating that the concrete was crushed. However, the concrete was still well wrapped in basalt fiber sheet, as shown in Figures 9 and 10, which means that the basalt fiber can play a useful role in restraining concrete. The corrosion rate of specimen Z3 was 8% and the specimen Z3 was reinforced with one layer of fiber sheet. A slight sound of cracking could be heard when the lateral load was 50 kN, which could be attributed to the breaking of hardened resins. As the test proceeded, the sounds were loud and continuous. However, no evident cracks of the concrete at the surface were observed in the first stage. In the displacement control stage, BFRP sheets fractured at the corners and bulged at the core area when the displacement was 32 and 36 mm, respectively. Due to the crushing of concrete at the core area, the BFRP sheets were entirely bulged and delaminated from the surface when the displacement was 44 mm, as well as the load-bearing capacity decreasing. The test was terminated when the displacement was 66 mm, and the shearing failure mode can be found in Figure 9.  
The corrosion rate of specimen Z4 reinforced with two layers of fiber sheet was 8%. A slight sound of cracking could be heard when the lateral load was 60 kN, which could be attributed to the breaking of hardened resins. As the test proceeded, the sounds were loud and continuous. However, no evident cracks of the concrete at the surface were observed in the first stage. In the displacement control stage, BFRP sheets fractured at the corners and bulged at the core area when the displacement was 36 and 40 mm, respectively.