# Model Updating of Bridges Using Measured Influence Lines
## 4 Conclusions  
The Tomacevo case study bridge serves as a B-WIM and SHM living laboratory, designed to develop and test new technologies, sensors, and methodologies. Data from this bridge demonstrated that measured strain ILs, a by-product of B-WIM measurements, offer new opportunities for leveraging B-WIM results in FEMU and SHM applications. Strain ILs have been shown to enhance acceleration and MAC-based FEMU results for multi-span concrete bridges, particularly when assessing bridge responses under traffic loads. This finding was validated through an independent comparison of measured vertical mid-span displacements during calibration vehicle crossings, showing strong agreement between the results of the measurements and the strain IL-based updated model. The EDMF methodology was applied to conduct four independent FEMU studies: frequency-based, MAC-based, frequency and MAC-based, and strain IL-based. Three key variables were updated: \(\alpha_{\text{MG1}}\), \(\alpha_{\text{MG2}}\), and \(\alpha_{\text{OTHER}}\), representing [PERSON]'s modulus adjustment factors for the two main girders (MG1 and MG2) and all other structural elements, respectively. Combining frequency and MAC-based methods proved more effective than using them separately, yielding a narrower range for \(\alpha_{\text{MG1}}\) and \(\alpha_{\text{MG2}}\), compared with the frequency-based EDMF. The frequency and MAC-based EDMF led to moderate stiffness increases of 25% (range 20-30%) and 20% (range 10-30%) for MG1 and MG2, respectively. In contrast, the strain IL-based approach resulted in more pronounced increases of 35% (range 30-40%) and 50%. For other structural elements, the two methods diverged: while the frequency and MAC-based approach suggested a 10% decrease (range from \(-\)20% to 0%), the strain IL-based method indicated a 35% (range from 20-50%) increase in stiffness. FEMU must be applied cautiously, particularly when relying solely on modal parameters, as their misinterpretation can lead to incorrect adjustments and inaccurate bridge response predictions. This study reinforces the value of incorporating strain ILs in FEMU to improve model accuracy and enhance agreement between simulated and measured bridge behaviour under traffic loads. These findings expand the potential applications of B-WIM in both FEMU and SHM. As FEMU methodologies evolve, advancements in sensor technology and computational techniques are driving progress in structural assessment and monitoring. Future research should focus on understanding discrepancies between different FEMU approaches, refining strain IL extraction under extreme traffic conditions, and integrating FEMU into long-term SHM frameworks. These developments will further improve FEMU's reliability and broaden its applications in bridge performance assessment. Conceptualisation, D.H., A.Z., P.C. and A.A.; formal analysis, D.H., J.K. and P.C. ; methodology, D.H., A.Z., P.C. and A.A.; software, D.H., J.K. and P.C. ; investigation, D.H., J.K., A.Z. and A.A.; resources, D.H., A.A., A.Z. and P.C. ; data curation, D.H.; writing--original draft preparation, D.H., A.Z., P.C. and A.A.; writing--review and editing, D.H., J.K., A.Z. and P.C. ;  
Figure 27: Comparison of D_MG2 displacements under V2_F crossings: measurements (30 km/h), frequency and MAC-based, and strain IL-based updated FE models. visualisation, D.H. and A.Z. ; supervision, A.Z., P.C. and A.A.; project administration, A.Z., P.C. and A.A.; funding acquisition, A.Z., P.C. and A.A. All authors have read and agreed to the published version of the manuscript. The authors acknowledge the financial support from the Slovenian Research and Innovation Agency: Young Researcher Funding Programme No. 53694, Research core funding No. P2-0260 and P2-0273 and Infrastructure funding I0-0032. The finite element models and the data from the case study are available upon request from the corresponding author.