This paper addresses the problem of condition assessment of bridge expansion joints using long-term measurement data under changing environmental conditions.The effects of temperature,traffic loading and wind on the expansion joint displacements are analyzed and interpreted,which reveal that measured displacements are observed to increase with an increase in temperature and to decrease with increased traffic loading,while the correlation between displacement and wind speed is very weak.Two regression models are developed to simulate the varying displacements under the changes in temperature and traffic loadings.Based on these models,the effects of the environmental conditions are removed to obtain the normalized displacement.Statistical process control using mean value control charts is further used to detect damage to the bridge expansion joints.The results reveal that the proposed method had a good capability for detecting the damage-induced 1.0％ variances of the annual changes in the expansion joint displacements.