In 1980s, a seismic design concept was introduced for the first time in Korea. Since 1995's Kobe Earthquake in Japan, Korean government Ministry of Construction and Transportation presented 'Earthquake Resistance Design Criteria(1997)', 'Seismic Design Code for Highway Bridges(1996)', etc.
There are two seismic analysis methods for Bridge Foundations. One is pseudo static analysis, and the other is dynamic analysis. The most reliable analysis is dynamic analysis which analyses whole foundation-pier-super structure model using time-acceleration histories. But this method is too complicate for working level. Current seismic design code for bridge foundation in 'Seismic Design Code for Highway Bridges(1996)' uses pseudo static analysis method. In this method, the equivalent static load for the real earthquake load is calculated using design earthquake coefficient and the mass of structures. Current pseudo static analysis, however, assumes that foundation node is completely fixed instead of considering soil-pile interactions.
For the purpose of developing the seismic analysis method which is reliable and simplified, a new seismic analysis method considering soil-pile interactions was proposed. The soil-pile system was modeled by equivalent linear elastic spring element which has six degree of freedom. The seismic analysis procedures proposed in this study are as follows. First, The soil-pile spring stiffnesses are determined using linear soil-pile stiffness charts or soil resistance(p)-deflection(y) curves. Second, the seismic analysis is conducted for the whole structure attached the soil-pile spring. Finally, pile behavior analysis is performed for the load at the foundation node which is determined by whole structure analysis.
In addition, the applicability of the proposed method was validated through the case study for a real bridge. From the case study, it can be concluded that the proposed analysis method is more reliable than the current pseudo static analysis. It is also revealed that the proposed method considering soil-pile interactions is adoptable for the structures which is more important for an earthquake.
