Conclusion
In this study, the sliding isolation bearing was introduced to underground structures to enhance the anti-seismic capacity. Firstly, the collapse mechanism of underground structures was analyzed by taking the Daikai Station as an example. It was concluded that the collapse of underground structures originated from the poor ductility of columns at high normalized force state. Reducing the lateral deformation of columns was an effective approach to mitigating seismic damage of underground structures from earthquakes. Therefore, Pure-FrictionSystem bearings with low friction coefficient were installed in underground structures to assess the seismic performance of the retrofitted structures. Numerical results showed that the sliding bearing in the retrofitted underground structures worked well during earthquakes. The sliding of the bearing decreased remarkably the lateral deformation of the column when μ = 0.02. Consequently, the columns worked within their loading capacity, which makes the deformations of the lateral walls were also reduced. Therefore, sliding bearings is the effective device to improve the anti-seismic capacity of underground structures. In addition, the deformations of the whole structure and the components were all greatly influenced by the frictional coefficient, thus, to give an optimum range of the frictional coefficient is important for the design of bearings. In other words, the determination of the frictional coefficient is the key issue to keep the column stand straightly and to prevent the collapse of underground structures. Further, from this study, it can also be concluded that the technologies of seismic mitigation and isolation using in above ground structures can also be applied to underground structures for aseismic design.
