## 3 Experimental Results and Discussions  
### Failure Mode and Analysis  
Figure 9a-d show the failure modes of the four columns. No debonding was observed at the interface between the concrete and SMRC. For each column, the crack pattern of the SMRC surface is plotted. Multiple distributed cracks were observed in the four columns. When the column failed, crushed concrete was observed in the compression zone. In S-0, the first crack appeared when the load was increased to 73 kN. The distance between the crack and the actuator was 110 cm, as shown in Figure 9a. With the increase of the load, the crack  
Figure 8: Test setup for eccentric compressive testing: (**a**) Overall view and dimensions (unit: mm), (**b**) details at the two ends of the loading device. was widened and propagated; more cracks appeared in the column at the tensile side. After the column failed, 13 major cracks were observed. The average spacing of the major cracks was 115 mm. The maximum crack width was 4.2 mm. In S-1, the first crack in the SMRC appeared, when the load was increased to 143 kN. The distance between the crack and the actuator was 110 cm, as shown in Figure 9b. The second crack in the SMRC appeared near the mid-span, when the load was increased to 162 kN, and the strain gauges that were attached on the SMRC failed because of the cracks. No crack was observed in the normal concrete until the load was increased to 220 kN. The crack was at the cross section that was about 45 cm away from the actuator. At the same time, five cracks were observed in the SMRC. The five cracks were, respectively, 110 cm, 72 cm, 45 cm, 33 cm, and 85 cm away from the actuator. After the column failed, 12 major cracks were observed in the SMRC; the average spacing between the major cracks was 125 mm; the maximum crack width was 7.1 mm. A limited number of microcracks were observed in the vicinity of the major cracks. The steel mesh in the SMRC was ruptured. In S-2, the first crack in the SMRC appeared, when the load was increased to 155 kN. The distance between the crack and the actuator was 105 cm, as shown in Figure 9c. The first crack in the normal concrete was observed when the load was increased to 250 kN. The crack was at the cross section that was about 27 cm away from the actuator. At the same time, six cracks were observed in the SMRC. The six cracks were respectively 105 cm, 120 cm, 98 cm, 86 cm, 65 cm, and 27 cm away from the actuator. As the load was further increased, a number of densely distributed microcracks appeared. After the column failed, the maximum crack width was 2.4 mm. A limited number of wires of the steel meshes were ruptured. In S-3, the first crack in the SMRC appeared, when the load was increased to 158 kN. The distance between the crack and the actuator was 115 cm, as shown in Figure 9d. The first crack in the normal concrete was observed when the load was increased to 285 kN. The crack was at the cross section that was about 48 cm away from the actuator. At the same time, five cracks were observed in the SMRC. The five cracks were, respectively, 115 cm, 66 cm, 95 cm, 51 cm, and 105 cm away from the actuator. Similar to S-2, as the load was further increased, a number of densely distributed microcracks appeared. After the column failed, the maximum crack width was 1.8 mm. No wire of the steel meshes was ruptured. Further analysis is conducted to understand the crack patterns. Figure 10a illustrates a segment of a column for analyzing stresses in the steel bar, steel mesh and concrete. The stress in the steel bar is denoted by \(\sigma_{\mathrm{s}}\), which reaches the maximum value at the crack section. Between two adjacent cracks, \(\sigma_{\mathrm{s}}\) decreases because a part of tensile force is resisted by the concrete due to force transfer between steel bar and concrete. The stress reduction is denoted by \(\Delta\sigma_{\mathrm{s}}\). Similarly, the stress in steel wire is denoted by \(\sigma_{\mathrm{w}}\); and, the stress reduction is denoted by \(\Delta\sigma_{\mathrm{w}}\).