Detection and Safety Assessment of Large Stadium Structures Based on Millimeter-Wave Radar

Large stadiums commonly employ long-span spatial steel roof systems and require efficient non-contact monitoring. This study presents a millimeter-wave-radar-based detection and safety assessment method for a large in-service stadium roof. Ambient vibration tests were conducted on a representative steel truss using millimeter-wave radar and co-located accelerometers, and the modal frequencies and mode shapes were identified using peak picking and stochastic subspace identification. An undamaged finite-element model was established to interpret the measured modal information and simulate local stiffness-reduction scenarios. The first four vertical frequencies identified by radar were 3.32, 7.03, 10.35, and 13.18 Hz, compared with 3.32, 7.03, 10.35, and 13.48 Hz obtained from the accelerometers. The first three frequencies were identical at the reported precision, and the fourth-frequency difference was approximately 2.2%. Numerical results showed that the modal-curvature-based Safety Indicator was sensitive to local stiffness degradation and could indicate approximate abnormal regions. No pronounced localized modal anomaly was observed in the field-tested truss, consistent with the on-site inspection. The study demonstrates an integrated workflow combining non-contact radar measurement, operational modal identification, finite-element-supported interpretation, and preliminary condition assessment for large stadium roofs.