The Parchi Viaduct, a vital 3-km multi-span structure on Milan’s A51 Eastern Ring Road, faced a critical challenge due to degradation in its Gerber saddles, necessitating a temporary closure for safety assessments. Milano Serravalle Milano Tangenziali S.p.A. and CAEmate S.R.L. addressed this issue by deploying an advanced SHM system integrating distributed fiber optic sensing (DOFS) and a physics-informed digital twin for real-time load-bearing capacity evaluation. This paper presents the application of the WeStatiX SHM platform, utilizing DOFS to capture strain, temperature, and vibration responses. The digital twin, calibrated iteratively through inverse analysis, dynamically updates via multi-objective optimization, providing accurate modal frequencies, mode shapes, and damping ratios to detect structural degradation. The platform verified the viaduct’s residual load-bearing capacity despite saddle deterioration, enabling its safe reopening under real-time monitoring per Italian NTC standards. Field data revealed taller piers exhibited ~20% greater deflection under load, highlighting pier height's impact on load distribution and deflection. These insights improve stress predictions, inform maintenance strategies, and prolong structural lifespan.