## 2 Testing the Cho'ponota L1 Bridge
### Digital Twin Construction: Experimental Setup, Field Instrumentation, and Modeling Interface  
The test-assisted digital twin framework developed for the Cho'ponota L1 Bridge is structured around a hybrid methodology that combines a physics-based numerical model with targeted experimental data. The process begins with the development of an initial finite-element model constructed using as-built drawings and project specifications. This preliminary model establishes the geometric and mechanical foundation of the virtual structure. To optimize the experimental design, a modal analysis is performed, identifying the critical mode shapes and response zones. These findings inform the sensor placement strategy, ensuring that field measurements capture the most structurally informative locations. Prior to field testing, a preliminary modal analysis was conducted using the initial finite-element model developed from as-built drawings and project specifications. This analysis provided estimates of the structure's natural frequencies and mode shapes, which were used to optimize the sensor layout by identifying antinodal positions for critical bending modes. The resulting sensor configuration ensured effective capture of modal responses during OMA. Additionally, the preliminary model outputs guided the planning of static and dynamic load test scenarios, allowing for the safe excitation of the bridge while maximizing the structural response data required for subsequent model calibration. Subsequently, field testing is conducted using static and dynamic vehicular load tests, in \begin{table}
\begin{tabular}{c c c} \hline \hline
**No.** & **Element** & **Material Class** \\ \hline
1 & Pile & C25/30 \\
2 & Foundation & C25/30 \\
3 & Column & C30/35 \\
4 & Slab & C50/60 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Material properties of Cho’ponota L1 Bridge (Structural Analysis Report, 2020). Figure 1: Views of Cho’ponota L1 Bridge. addition to ambient vibration measurements through OMA. The collected raw data are processed to extract structural response characteristics such as natural frequencies, mode shapes, and displacement time histories. These experimental results serve as the benchmark for the calibration of the finite-element model. Through an iterative validation process, model parameters--particularly concrete stiffness and boundary conditions--are adjusted to minimize discrepancies between simulated and measured responses. This calibration step transforms the numerical model into a digital twin that reflects the actual behavior of the bridge. Although the digital twin constructed in this study does not operate with continuous data flow, its validation through high-fidelity test data allows it to be used for realistic simulations under both current and design-level loading conditions. The final digital twin provides a reliable platform for condition assessment, structural diagnostics, and predictive simulations, even in the absence of long-term monitoring infrastructure. This approach shows a practical and scalable pathway for integrating digital twin technologies into civil infrastructure projects, particularly where logistical or financial constraints preclude real-time data integration. An overview of this test-assisted digital twin workflow is illustrated in Figure 2.  
The finite element model of the Cho'ponota L1 Bridge was developed using RM Bridge software based on as-built drawings and design documentation. The bridge deck, piers, and pile foundations were modeled using 3D frame (beam) elements capable of capturing flexural, torsional, axial, and shear behavior. Post-tension effects were incorporated through equivalent section properties reflecting the increased stiffness of the post-tension concrete components. Rigid link elements were used to represent the connections between the superstructure and substructure.