To reduce the dynamic response of high-speed railway (HSR) resonant bridges under train passages, additional support(s) reinforcement of adding new support(s) on the spans is put into practice. In this study, the effect of additional support reinforcement with different positions between the both sides of a girder, which has not been clarified, and a simple evaluation method using span shortening amount were numerically investigated. As a result, for a HSP bridge to which the reinforcement is planned, the effects of asymmetry supports on the maximum displacement are small. Therefore, the effect of asymmetrical additional supports in this study can be evaluated by the result of symmetry one with the same span shortening amount, which is the total of the additional support positions.
