This paper presents a new strengthening method for underground RC box structures against seismic loads. Numerical results confirmed that the proposed pre-flexed member system can enhance the seismic capacity of the underground RC box structures.

For the corner joint strengthening of the underground box structures, the strengthening method using pressure members was developed. By the applied pressure on the reinforcing members and the increase of nominal strength due to reinforcing member, the size of the reinforcing members are reduced and the performance of corner joint strengthening is improved.