## 3 Finite-Element Analysis and Interpretation  
In order to analytically verify the change according to the long-term prestress loss of the beam specimen installed with the OSPC strand, a finite-element model was prepared, as shown in Figure 15. MIDAS CIVIL 2020 (Seongnam, South Korea), which is a general-purpose structural analysis program, was used for finite-element analysis, and beam elements were used for modeling. Modeling was conducted using the dimensions based on the shape of the finished specimen and the values from the compressive strength test results. Time-dependent materials required for long-term time history analysis, such as creep and shrinkage, were applied in accordance with CEB-FIP (2010), Korea Standard (2015), and ACI 318-02 (2002), the standards of each country embedded in the MIDAS program. With respect to the relaxation coefficient, the widely used equation developed by [PERSON] [21] was applied to MIDAS, and it was entered as the value for a low relaxation strand. The curvature friction coefficient was not considered, and the wobble friction coefficient was considered to be 0.0066 (1/m). Both composite and non-composite specimens were considered, and the slip amount of the fixing unit was defined as 6 mm. The initial prestress force was 180.6 kN,  
Figure 14: Change in prestress force without the influence of temperature (**a**) in bonded condition, (**b**) in unbonded condition. Figure 15: Modeling for finite-element analysis. and the change in the prestress force for about 1600 days was analyzed considering the construction sequences. The prestress force acting on the tendon was analyzed for each construction phase, and the analysis was carried out by dividing it based on regulations and the composite/non-composite status, as shown in Figure 16. The arrangement of the strands was modeled using straight lines at the same location as each OSPC strand installed in the specimen. Table 2 below summarizes the main input values for each criterion applied to the finite-element analysis. There was no significant difference in the long-term prestress loss between the composite and non-composite specimens regarding each criterion applied to the analysis. Because KS had little difference compared to CEB-FIP, the difference was even smaller regarding these two sets of standards. However, the analytical results showed a difference in terms of the change in the prestress loss in the initial stage after prestressing. This may have been due to the difference in the time of developing the compressive strength that affected the creep of concrete, which resulted as KS followed the compress strength expression of ACI instead of that of CEB-FIP. On the other hand, the analytical results based on the ACI standard were slightly lower than those based on KS or CEB-FIP, indicating a long-term prestress loss. On the other hand, in the MIDAS analysis program or in general numerical calculations, the wedge slip was assumed to be 3 to 6 mm for calculating the amount of immediate prestress loss generated at the anchorage. Because the total length of the specimen was very short (6350 mm) in this study, a large amount of immediate prestress loss was expected at the anchorage. Therefore, the wedge slip was set to 6 mm. According to the results of the finite-element analysis, the amount of immediate loss occurring at the anchorage was 14.62 kN. However, when a prestress force was applied to the actual specimens, it was reduced from 184.1 kN to 132.7 kN in the composite specimen, and from 179.5 kN to 128.3 kN in the non-composite specimen. This indicated that the immediate prestress