The design of foot-bridge is often influenced by natural frequency. Consequently, vibration frequency becomes important. The empirical expressions used to quantify this parameter at the design phase have not been developed enough to give guideline to Korean foot-bridge. This paper is concerned with the vertical natural frequency of steel foot-bridges. It describes the vibration measurement methods employed for testing structures and presents reliable methods of assessing natural frequency from jumping vibration tests. Data from measurements on 16 structures in Seoul are given. Regression formulas of natural frequency for steel-framed foot-bridges are suggested. Finally, obtained formula are compared with empirical expressions of Seoul City's guideline.

Since the terrorist attacks 9.11 in 2001, the public places such as subway, department stores or office buildings have become a target of terror in major public facilities. In this paper, for the prevention of terrorist attack in domestic building, the assessments of terror risk were conducted and their relationship with building heights was discussed through FEMA 455-Rapid Visual Screening(RVS). Explosive terror risk tends to increase rapidly with building heights(H<230m), showing the correlation coefficient between total risk and building heights(H<230m) is 0.93. In addition, The average of consequences is 8.47 and that of' threat is 8.95. Vulnerability is found to be 6.62 in average.