## 3 Performance of IWP with Steel Anchor Box
### FE Analysis Results and Performance Comparison
#### 3.1.4 Stress State at the Steel-Concrete Interface  
Figure 22 illustrates the force distribution of the studs in Segment 3 of the anchoring zone for the internal steel anchor box. The studs are numbered sequentially as N-1 to N-8 along the transverse direction from the center of the end plate to both sides and as 1-15 along the vertical direction from the bottom to the top of the segment. The overall shear force distribution of the connectors is smaller in the middle and larger on both sides along the transverse direction of the bridge, due to the shear lag effect. In the vertical direction, the shear forces are slightly larger at the bottom and the top and smaller at the mid-height. This is in accordance with the typical distribution for a column of studs under shear, which is due to the axial deformation of the end plate. In the horizontal direction, the studs are subjected to compressive forces from the cable. Therefore, the compressive forces are larger for rows 3-6. For the N-7 column, the ratio between average transverse compressive force to vertical shear force reaches 0.50, with the maximum ratio for an individual stud being 0.63. The ratio of the maximum vertical shear force to the average force for each column ranges from 1.04 to 1.11. The ratio of the maximum horizontal compressive force to the average force ranges from 1.35 to 1.65. Figure 23 shows the force distribution of the studs in Segment 3 of the anchoring zone for the exposed-type steel anchor box. The studs are sequentially numbered as W-1 to W-8 from the inner side of the pylon wall outward and as 1-15 from the bottom to the top of the segment. Along the longitudinal direction of the bridge, the forces are larger on the inner side of the pylon wall and smaller on the outer side. This is because the cable force is applied on the inner side of the pylon; therefore, the slips at inner studs are larger. In the vertical direction, the forces are larger in the middle and smaller at both ends, and the location of the peak force moves downwards from column W-1 to W-8. The reason for this phenomenon is that the cable force is gradually transferred sloping downwards to the concrete, from the inner to the outer side. Both the vertical and longitudinal directions are the primary shear directions for the connectors. For Row 7, the ratio of average transverse shear force to average vertical shear force reaches 0.94, with the maximum ratio for an individual stud being 1.3. The ratio of the maximum vertical shear force to the average vertical shear force for each column ranges from 1.27 to 1.36, and the ratio of the maximum longitudinal shear force to the average longitudinal shear force ranges from 1.75 to 2.47. Figure 22: Distribution of stud load on the end plate of internal type anchorage. Figure 24 shows the force distribution of the perfobond connectors in Segment 3 of the anchoring zone for the IWP detail with a steel anchor box. The perforations on the side plate are sequentially numbered as C-1 to C-5 from the inner side to the outer side of the pylon wall, whereas the perforations on the end plate are labeled as Column D-1, and those on the surface plate are numbered as Columns M-1 and M-2, from both sides inward. The rows are sequentially numbered 1-10 from the bottom to the top of the segment. In the vertical direction, the forces are almost uniform in the vertical direction, and gradually decrease from the inner to the outer side, due to the bending of pylon wall. Along the longitudinal direction of the bridge, the forces are larger on the inner side of the pylon wall and smaller on the outer side, due to the differences in the slip of perfobond connectors. The primary shear direction for the connectors is vertical. The maximum ratio of longitudinal shear force to vertical shear force for an individual perforation is 0.21, indicating minimal longitudinal shear forces. The ratio of the maximum vertical shear force to the average vertical shear force for each column ranges from 1.04 to 1.14.