韓半島內 主要 人工構造物의 適正 耐震設計震度

Optimum intensity for seismic design of major man-made structures in Korea

Earthquake disaster is dependent upon both site intensity and strength of structures. The higher the strength, structures become more safe, which in turn increases the construction cost. Therefore, it is necessary to decide an optimum design intensity in which the safety is balanced with the cost. Such an optimum design intensity for major man-made structures in Korea is determined in the present study from a simulation model as follows. 1) Hypothetical earthquake time series are generated from the probability distribution to represent appropriately the seismicity of Korea. 2) The strength of structures constructed with a certain design intensity is assumed to exponentially decrease with the elapsed time. The construction cost is also expressed as a function of design intensity. 3) Comparing the seismic intensity generated from the earthquake time series with the strength of structures, the safety of structures is examined. Then the time until the structure is damaged by an earthquake is obtained within the designed life time. 4) The above simulation is iterated several hundred times and hence the mean life time of structures having a certain design intensity is obtained. 5) After all, the optimum design intensity to minimize the annual mean loss, the ratio of construction cost to mean life time, is estimated. The major conclusions obtained from the above simulation model are as follows. 1) Depending upon the designed life time (Tp), the optimum design intensities are appeared to be 0.05-0.10g for Tp=50yr and 0.08-0.13g for Tp=100yr. 2) According to the sensitivity analysis, the optimum design intensity increases with the rapid strength decrease of structure and decreases with the increase of initial construction cost.