# Flexural Behavior of Corroded High-Speed Railway Simply Supported Prestressed Concrete Box Grider
## 2 Experiment Details  
### Design and Fabrication of Scaled Beams  
The present experimental study is mainly concerned with the flexural behavior of PC box girders. As the prototype box girder was not suitable for carrying out series tests, we first designed the scaled beam according to the similarity theory [22; 23; 24]. The standard 32 m double-line PC simply supported box girder of Chinese high-speed railway bridges (referred to as 2322A-II in Tong Bridge (2008)) was taken as the prototype structure. This prototype structure is a typical single-box, single-room PC box girder with equal height, whose length and width are 32.6 m and 12.0 m, respectively. To arrange the prestressing strands at 120-140 kN/m prestress, a total of 246 strands were required. Detailed dimensions of the PC box girder are shown in Figure 1.  
Similarity theory in structural testing needs to follow both geometric similarity and physical similarity requirements. Geometric similarity means that the linear dimensions, cross-section area, section moment of inertia corresponding to the prototype structure, and scaled beam are in a certain proportion. The beam should be designed as a scaled box beam, but the web and bottom plates in this condition were too thin to be fabricated. Therefore, the test beam was designed as a T-section by matching the flexural stiffness of the scaled box beam. To arrange only one strand in the test beam for subsequent analysis of the effect of strand mass loss on the flexural properties of the test beam, the scale ratio was set as 1:15.68 according to the principle of prestressing similarity. The dimensions of the scaled beam were calculated and are shown in Figure 2. Table 1 compares some geometric parameters of the scaled beam and the prototype structure. The theoretical similarity ratio and actual similarity ratio are, respectively, the design scale ratio and measured scale ratio of the model beams. Small differences can be found between these two similar ratios due to the construction, fabrication, and concrete protective layer requirements of the specimens. However, the differences are relatively small, which indicates that the dimensions of the model beam were chosen reasonably. Figure 1: Tong Bridge (2008) 2322A-II standard box girder dimensions (units: mm); the left cross-section is near the midspan, and the right cross-section is near the support. Figure 2: Dimensions and section reinforcement diagram of scale beam (units: mm): (**a**) cross-section near the support; (**b**) cross-section near the midspan; (**c**) section reinforcement diagram near the support; (**d**) section reinforcement diagram near the midspan; (**e**) side view; (**f**) top view. Physical similarity requires the stress, strain, stiffness, and deformation to be similar between the scaled beam and the prototype structure. All materials used for the scaled beam were therefore strictly consistent with the prototype structure. The standard value of concrete strength was designed to be 50 MPa, a grade of C50 in the Chinese code [25]. To match the concrete mix ratio of the prototype structure exactly (as shown in Table 2), the laboratory self-mixing method was used to fabricate the test beam. The gelling materials included 425# low-alkali silicate cement, first-grade fly ash, and S95-grade finely ground mineral powder. Three standard cubic concrete specimens were cast simultaneously as the test beam. Due to the uneven mixture in the laboratory, the measured 28-day compressive strength was 45.24 MPa [25], which was slightly lower than the design value. The prototype girder has a total of 246 seven-wire strands. According to the similarity requirement of effective prestress, the scaled beams had only one seven-wire strand with an outer diameter of 15.2 mm and a standard ultimate strength of 1860 MPa. A metal bellow with a diameter of 50 mm was used to fix the strand position.