## 4 Test Results and Analysis  
### Effect of A/A\({}_{g}\) Ratio (A12h-1-5)  
#### 4.1.1 Fracture Mode  
Figure 5 shows the test results for all specimens. In Figure 6, which shows the fracture modes of group 1 specimens, A12H-1 and -4, with side lengths of 350 mm, show more cracks on the side surfaces of the concrete blocks than the other specimens; however, the cracks were more concentrated near the anchorage bearing plate in A12H-4. This implies that local concrete fracture right beneath the bearing plate was involved in A12H-4 due to a lack of lateral confinement. On the other hand, overall concrete failure was observed in A12H-1 along the height. This confirmed that the entire concrete section in the specimen was used effectively because the maximum test load (4093 kN) exceeded the net compressive strength of the concrete block (3834 kN) computed by multiplying the concrete compressive strength (\(f_{ci}^{\prime}\)) by the concrete net area excluding the duct area. That is, the sectional load-carrying efficiency, defined as \(P_{u}/\left(f_{ci}^{\prime}(A-A_{duct})\right)\), of A12H-1 was larger than 100%, as shown in Figure 5b. Figure 5: Cont. A12H-2, with a side length of 550 mm, also showed concentrated horizontal cracks on the side surfaces of the concrete block, as well as wide cracks on the top surface of the block. That is, the specimen seemed to be governed by spalling more than bursting, and the behavior was concentrated near the top surface. Given the fracture mode, it seems that the concrete within the spiral rebar was crushed and, as a consequence, the anchorage bearing plate sunk slightly, and the cast iron bearing plate was inelastically deformed. However, the behavior seemed to be localized within the spiral so that fewer cracks were observed than in A12H-1 and A12H-4. A12H-3 and -5, with 800 mm sides, showed very narrow cracks on the side surfaces of the concrete block; however, a few wider cracks were observed on the top surface of the block after the test. In A12H-3, the anchorage bearing plate was fractured along the anchor head perimeter, but A12H-5 showed slight inelastic deformation in the cast iron bearing plate. Simple computations could be used to check whether the fracture in A12H-3 was due to the bearing strength of cast iron. That is, the yield and tensile strength of the cast iron multiplied by the net contact area between the anchor head and bearing plate (3471 and 5423 kN, respectively) could be compared with the test results. As shown in Figure 6, the anchorage bearing plate of A12H-5 had yielded but not fractured because its maximum load (3947 kN) was only slightly higher than the yield strength. On the other hand, even though the maximum load of A12H-3 (5228 kN) is slightly lower than the tensile strength of the cast iron (5423 kN), the bearing plate was fractured. This is because the inelastic deformation of the concrete beneath the bearing plate increased the concentration of stress on the bearing plate under the anchor head. In contrast to A12H-2, fracture of A12H-3 began with fracture of the anchorage bearing plate. This means that the concrete beneath the bearing plate was still available before the cast iron bearing plate broke, indicating that more confinement was applied to the concrete within the spiral of A12H-3 than A12H-2 by the concrete surrounding the spiral. Therefore, if stronger cast iron had been used, the ultimate strength could have been increased in A12H-3. It is reasonable to conclude that a larger concrete block with a size of more than \(A/A_{g}=4.50\) is more effective for enhancement of the ultimate bearing strength if the cast iron strength is secured. Figure 6 also shows that the length of the area with cracks and crack pattern depends on the size of the specimen and particular details of the reinforcement. In A12H-4, the length of the area through which cracks had propagated was approximately 200 mm, and most cracks grew in the vertical direction.