Experimental Research on Damage Identification of Square Steel Tubes Based on Laser Doppler Vibrometry Principle

As the scale of high-rise and super-high-rise building structures becomes increasingly large and their types become increasingly diverse， structural abnormalities frequently occur during their long-term service due to the continuous cumulative effect of structural damage. Efficiently conducting damage identification has become a technical bottleneck that needs to be overcome in the engineering field. This paper proposes a damage identification method for square steel tubes based on laser Doppler vibrometry. To investigate the application of this method in damage identification for simplified high-rise structure models， a square steel tube specimen with a slenderness ratio of 40∶1 was designed， and experimental studies were conducted to assess and localize damage. By establishing a physical model of the square steel tube， laser Doppler vibrometry was used to collect vibration response signals before and after structural damage. Frequency domain decomposition （FDD） was utilized to extract modal parameters including natural frequencies and mode shapes. Furthermore， modal curvature difference analysis was introduced to achieve precise damage localization based on mutation characteristics in modal curvature before and after damage. Experimental verification through predefined damages at different locations demonstrated the method's sensitivity to structural damage. The results indicated that the modal curvature difference index effectively identified structural damage. In addition， the damage in the square steel tube was analyzed by finite element analysis. The modal identification results were compared with the numerical simulation results， showing good consistency in vibration modes between the two.