# Development and Application of Digital Twin-BIM Technology for Bridge Management
## 4 Building Information Management
### Digital Twin of Comoro Bridge for Structural Performance Evaluation
#### 4.4.2 Structural Performance Evaluation Based on FE Analysis
The uniform normal stress distribution along the flange of thin-walled flexural members, such as box girders, is recognized as shear-lag effects [23; 24]. According to elementary beam theory (Bernoulli-Euler theory), the normal stress in the longitudinal direction resulting from a bending deformation is assumed to be proportional to the distance from the neutral axis. As a result, it is expected to be uniform across the flange width, as formulated in Equation (3). \[\sigma_{\text{x}}=\frac{\text{M}_{\text{y}}}{\text{I}_{\text{z}}}\text{y}= \frac{\text{M}}{\text{z}} \tag{3}\]  
However, when the flange width increases, this assumption becomes invalid. The phenomenon of shear-lag effect can also be defined as the nonuniform distribution of normal stress in the wide flange. Nevertheless, the stress reaches its maximum value at the intersection of the flange and web, gradually decreasing towards the center of the flange [23; 24]. Figure 23: Coefficient \(Z\) value. (**a**) \(Z\) value along the bridge axis; (**b**) \(Z\) value results from the FEA and theory. Shear-Lag Effect Evaluation on PC Box-Girder Section  
Shear-lag effect Evaluation  
The normal stress distribution at the top and bottom flanges of the box girder at pier 3 was evaluated and is depicted in Figure 26a. Figure 26b,c illustrate the occurrence of a nonuniform stress distribution at the top and bottom surface flanges, deviating from the predictions of the Euler-Bernoulli theory. Consequently, a significant shear-lag effect phenomenon was observed on the box-girder section at both the top and bottom flanges at pier 3. The normal stress distribution at the top and bottom flanges of the box girder, positioned 1/4 L away from pier 3, is depicted in Figure 27a. Figure 27b,c demonstrate the occurrence of a nonuniform stress distribution at the top and bottom surface flanges, deviating from the predictions of the Euler-Bernoulli theory. Nevertheless, the shear-lag effect was notably diminished towards the midspan when considering the 1/4 L location. Figure 24: Nonuniform normal stress distribution on box-girder section. (**a**) the distribution of nonuniform normal stress along the bridge axis. (**b**) Nonuniform normal stress distribution in the PC box-girder section. Figure 25: Evaluation Point of Shear-Lag Effect. The contour map of the stress distribution (Figure 28a) clearly illustrates that the shear-lag effects at both the bottom and top flanges of the midspan box girders were negligible, closely aligning with the assumptions of the Euler-Bernoulli beam theory (refer to Figure 28b,c). Consequently, given the limited occurrence of shear forces, the shear-lag effect could be disregarded in the midspan section of the box girder. Figure 20:0 Normal stress distribution on the girder section at 1/4 L from pier 3. (**a**) Contour map of the normal stress distribution; (**b**) at the top flange; (**c**) at the bottom flange. Figure 20:1 Normal stress distribution on the girder section at pier 3. (**a**) Contour map of the normal stress distribution; (**b**) at the top flange; (**c**) at the bottom flange. Therefore, the assessment of the shear-lag effect for the PC box-girder section of the Comoro Bridge was as follows:  
1. The nonuniform normal stress distribution due to the shear-lag effect obviously occurred at the top and bottom flanges. 2. The shear-lag effect significantly occurred at the top of the piers, especially at the web and flanges interactions. 3. However, when it moved towards the midspan, the shear-lag effect was diminished linearly and could even be neglected. * Shear-Lag Effect at Double-Cell Box Vs. Single-Cell Box Girder  
In order to investigate the shear-lag effect phenomenon on the PC box-girder bridge in Comoro, a double-cell box girder was designed to replicate the original configuration of the Comoro Bridge compared to a single-cell box girder. The single-cell box girder possessed identical dimensions and cross-sectional area.