## 4 Experiments on Full-Scale Modular Bridge Pier
### Full-Scale Test Specimen  
The specimen comprised a pier cap, four concrete-filled tube columns, and three layers with twelve bracings (six on the strong axis and the remaining on the weak axis). The height of the specimen was 7950 mm, as shown in Figure 10(a). The column module had a length of 5830 mm, including the column embedded in the foundation. The circular steel tube utilized was a commercial product with dimensions of \(\Phi\)508.2 \(\times\) 16 mm, and the D/t ratio of the steel column was 17, satisfying the design provisions for local stability constraints (Table 3). The longitudinal and transverse spacing of the columns were 2500 mm (strong axis) and 2000 mm (weak axis). The bracing members were hollow steel tubes with a diameter of 216.3 mm and a thickness of 7 mm. The embedded length of the CFT columns into the footing concrete was 770 mm, equivalent to 1.5 times the CFT column diameter. The end plate and anchoring details at the end of the embedded column had a sufficient embedment length for the connection to prevent shear failure of the footing concrete and pulling out. The pier cap had a width of 5500 mm, length of 3000 mm, and height of 1900 mm, and transferred the weight of the superstructure to the column. To prevent stress concentration owing to the superstructure weight, a composite cross-section was constructed by applying a steel frame and reinforcing the cross-sectional structure to the pier cap. The dimensions of the steel structure were 4400 \(\times\) 407 \(\times\) 428 mm (length \(\times\) flange width \(\times\) height). The flange and web thicknesses were 35 and 20 mm, respectively. The concrete compressive strengths of the design and cylinder tests (average) were 40 and 42 MPa, respectively. The structural steel tubes of the circular CFT columns and bracing exhibited yield and tensile strengths of 315 and 490 MPa, respectively. Each connection between the bracing and column members utilized 16 bolts with a tensile strength of 352.5 kN, as shown in Figure 10(c). The placement of strain gauges on the bracings and columns at various height levels is shown in Figure 11. S0 represents the lowest level of the CFT columns embedded in the footing, whereas S1 signifies the plastic hinge region of the CFT columns. S2, S3, and S4 denote the bracing levels. S5 represents the middle height of the top floor of the CFT column. Eight strain gauges were affixed to the CFT columns at levels S0, S1, and S5. \begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Design Codes**} & \multicolumn{2}{c}{**D/t Limits**} & \multicolumn{2}{c}{**Test Specimen**} \\ \cline{2-4}  & **Equations** & **Calculation** & **Calculation** \\ \hline LRFD (2010) [7,27] & \(0.11E_{s}/f_{y}\)* & 73.3 & \\ \hline ACI-318 (2011) [28] & \(\sqrt{8E_{s}/f_{y}}\) & 73.0 & 17.0 \\ \hline Eurocode 4 (2004) [8] & \(90\big{(}235/f_{y}\big{)}\) & 67.1 & \\ \hline \hline \end{tabular}  
* \(E_{s}\): Elastic modulus of steel (210,000 MPa). \(f_{y}\): Yield strength of steel (315 MPa).  
\end{table} 
Table 3: Loading program for the full-scale test. Additionally, ten strain gauges were attached to the connection parts of the bracings at levels S2, S3, and S4. Figure 11: Full-scale test specimen for modular CFT pier (unit: mm). The test setup and loading protocols are presented in Figure 13 and Table 4, respectively. A cyclic load, reaching up to 90% of the elastic limit, was applied using an actuator with a capacity of 3000 kN to the pier cap at a height of 5800 mm. The dead weight of the pier cap module exerted compression on the CFT columns, equivalent to 1.8% of the compressive strength of the section. The lateral cyclic load was applied to the center of the pier cap, with the drift ratio increasing at a speed of 1.8 mm/min within the range of 0.03-0.31% from 1 to 17. \begin{table}
\begin{tabular}{c c} \hline Displacement (mm) & \(\pm\)1.5–\(\pm\)18.0 \\ \hline Drift Ratio (\%) & \(\pm\)0.03–\(\pm\)0.31 \\ \hline Velocity Increment (mm/s) & \(\pm\)1.8 \\ \hline Cycle & 1–17 \\ \hline \end{tabular}
\end{table}