The impact factor response spectrum of bridges are generated based on the number of vehicle axles (one and three axles) and their boundary conditions (simply supported and both ends-fixed). In order to investigate the impact factor variation, a RC slab bridge aged over 40 years is considered. The natural frequencies for the current and undamaged initial state are evaluated from field test and FE model, respectively. Considering the natural frequencies and the generated response spectrum, the impact factors for each state are determined. From the result, the impact factor ratio defined the current to initial impact factor are almost same except the one axle and both ends-fixed case.

Abstract
 1. 서 론
 2. 대상교량의 고유진동수 변화
 3. 이동하중 축수와 경계조건에 따른 충격계수변화
 4. 결 론
 참고문헌

• 김태현(전북대학교, 토목공학과) | Kim TaeHyeon
• 박경훈(한국건설기술연구원, 인프라안전연구본부) | Park Kyung-Hoon
• 노화성(전북대학교, 토목공학과) | Roh Hwasung 교신저자