10% drop of natural frequency from the initial healthy condition is reviewed to include the possibility of danger of foundation scour. To improve bridge safety management, legislations of measuring initial natural frequency, informing initial embedded depth, and systematic management of bridges under the control of the local governments are suggested.

• 박병철(국립재난안전연구원 시설연구관, 공학박사) | Park Byung-cheol
• 장성희(국립재난안전연구원 시설연구사, 토목구조기술사) | Chang Sunghee