Abstract: Based on the vehicle scanning method,this study proposes an indirect approach for identifying bridge damage using a test vehicle subjected to a passing social vehicle.First,analytical solutions are derived for the vertical responses of the bridge,the test vehicle,and the contact point.Subsequently,according to the Fourier transform and the Hilbert transform,the instantaneous amplitude squared (IAS) of the driving-frequency component extracted from the contact response is used as the damage-sensitive indicator,and an IAS-based theoretical framework for damage identification is established.Then,numerical simulations are conducted to validate the derived analytical solutions,followed by a parametric sensitivity analysis to investigate the effect of social vehicles.Finally,laboratory experiments are performed to further verify the effectiveness and accuracy of the proposed method.The results indicate that when the two vehicles travel at similar speeds,the presence of a social vehicle markedly amplifies the IAS magnitude,thereby improving the sensitivity of damage identification.In contrast,when the vehicle speeds differ substantially,abrupt changes in the bridge dynamic response induced by the social vehicle entering/leaving the bridge and passing the damaged location can significantly perturb the IAS,potentially leading to biased damage assessment or even false identification.This study provides a theoretical basis for applying Vehicle Scanning Method to bridge damage detection under mixed-traffic conditions.