## 4 Test Results and Analysis
### Confinement Effect by Spiral Rebar Design (A12H-1 and 3-7)  
#### 4.2.1 Fracture Mode  
In this section, the effect of spiral diameter or confined area on the anchorage zone behavior is investigated through a comparison with the group 1 specimens. The dimensions of the concrete blocks in A12H-1 and -4 were 350 \(\times\) 350 mm, while that in A12H-3, 5-7 were 800 \(\times\) 800 mm. For A12H-1 and -4, the effect of confining pressure was investigated. For A12H-3 and -5-7, the effect of spiral diameter was additionally investigated. As shown in Figure 8, both A12H-6 and -7 show breakage of the anchorage devices at the ultimate state regardless of the reinforcement details, and the fracture modes were very similar to those of A12H-3 and -5. However, in the comparison of A12H-5 and -7, which only differed in spiral diameter, the peak loads and plastic behavior after the proportional limit of the load-displacement curves were different, as shown in Figure 9a. A12H-5 (\(b800-D295-\varnothing 10\)) exhibited a smaller peak value and softening behavior after the peak point, so the test was terminated, but A12H-7 (\(b800-D745-\varnothing 10\)) exhibited a long flat curve after the proportional limit, and it was tested up to about 20 mm displacement. The bearing plate of A12H-7 broke at a displacement of around 15 mm, and the fracture load was smaller, and the displacement at fracture was much smaller than those of A12H-3 and -6. This implies that deformation of the specimen was concentrated at the local zone below the bearing plate; then, local damage to the concrete leads to uneven support by the concrete, resulting in an excessive concentration of stress on the bearing plate followed by fracture of the plate. Figure 8: Fracture modes of group 2 specimens: (**a**) A12H-6; (**b**) A12H-7. A sudden change but almost linear slope was observed after the proportional limit of A12H-7, as shown in Figure 9a, as also seen in the curve of A12H-5, and the proportional limits of the two were almost the same. This reveals that the sudden change in A12H-7 may have originated from yielding of the spiral rebar, as for A12H-5, and implies that the local concrete beneath the bearing plate reached peak stress right after yielding of the rebar because the curve after the proportional limit was almost linear. Considering that the only difference between A12H-5 and -7 was the diameter of the spiral, these findings suggest that the concrete within the spiral of A12H-7 played a greater role in the load-transfer behavior of the local anchorage zone than the concrete outside the spiral of A12H-5. In sum, the behaviors of the two specimens were governed by yielding of the rebar followed by localized concrete damage beneath the bearing plate, and the behavior may be due to the small amount of lateral reinforcement that was used. For A12H-5, the damage in the ultimate state seemed to be concentrated in the inner part of the spiral, and local stress was not properly transferred to the surrounding concrete because the confined area by the spiral was as small as 295 mm in diameter and the load-displacement curve exhibited softening behavior right after the proportional limit. For A12H-7, the long flat curve after the proportional limit implies that the local stress beneath the bearing plate was properly transferred to the surrounding concrete within the large spiral of \(D=745\) mm. However, the confining pressure was not sufficient to enhance the strength and hardening behavior after the proportional limit. For A12H-6, a proportional limit and fluctuations in the curves similar to those of A12H-3 were seen at around 4500 kN when a fracture or severe damage to the bearing plate occurred. However, in contrast to A12H-3, A12H-6 exhibited a steep hardening curve after the proportional limit, even after fracture of the bearing plate. This may have been because, as in A12H-7, the larger spiral diameter led to proper stress distribution in the inner part of the spiral and introduced confinement over the large area of the inner concrete.