A Novel Video-Based Approach for Dynamic Structural Identification of Iron Tie-Rods Under Adverse Environmental Conditions

Iron tie-rods are essential components in historic masonry arches, contributing both to structural stability and long-term conservation. Accurate axial force assessment is vital for their performance evaluation, yet conventional contact-based techniques are often hindered by high costs, installation constraints, and reduced practicality in heritage contexts. This study presents a novel, step-by-step video-based measurement (VBM) procedure for contactless monitoring, dynamic response identification, and axial force estimation of tie-rods. The method integrates Hybrid Motion Magnification (HMM) for noise suppression in poor environmental conditions with Video Vibration Sensing (VVS) for pixel-level displacement tracking, enabling reliable measurements without specialized equipment. Applied to four tie-rods in the Ali Paşa Cami Mosque (Turkey), the procedure achieved modal frequency and damping ratio estimates within 1.6% and 4.9% of reference accelerometer data, and motion response peaks within 5%. The approach also provided calibrated axial force estimation, accounting for semi-rigid connections, and is suitable for long-term online monitoring. The results demonstrate that the VBM framework offers a low-cost, non-invasive, and high-accuracy alternative to conventional sensing, with potential applications to other slender structural members in heritage and modern engineering contexts.