The full plastic moment of a circular steel tube is generally calculated by multiplying the plastic section modulus by the yield stress of the steel. It has been prescribed as a performance criterion of seismic-resistant pile-supported wharves for level-2 ground motion in Japan’s design standard for port facilities, which went through a major revision in 2007. The pier-type structures used in ports are frequently constructed by using steel-pipe piles with a large diameter-to-thickness ratio (D/t) of about 100. However, previous research has revealed that the values obtained for the full plastic moment exceed the actual bending strength of steel-pipe piles with a large D/t. We propose a new model of a circular steel tube for seismic performance verification to take the place of the models using the full plastic moment. The proposed model can eliminate dangerous evaluations obtained with the full plastic moment and evaluate the strength of the steel pipe from D/t and the axial force. The ductility factor is adopted as a performance criterion in place of the full plastic moment. Thus, the proposed model can be used to evaluate the deformation capacity of a steel pipe with a large D/t and axial force. We modified numerical expressions of the bending strength and the ductility factor in the proposed model for application to various port facilities. These were modified according to individual load and constraint conditions of steel-pipe piles. Then, seismic response analyses were performed to evaluate the proposed model for seismic performance verification of each facility. The following types of facilities were examined: pile-supported wharves with and without a cranes weight, a quay wall with steel pipe-type sheet piles, a sheet-pile quay wall with vertical pile anchorage, and a sheet-pile quay wall with coupled pile anchorage. The specifications of the steel piles for these facilities were designed to satisfy the seismic performance requirements according to conventional modeling. The results showed that, according to the proposed model, the thickness of pile should be increased depending on the degree of the axial compression force with a large D/t. On the other hand, when D/t is approximately 67, the thickness of the pile can be decreased because of the high deformation performance.

Key Words: steel pipe pile, local buckling, seismic performance evaluation,
pile-supported wharf, quay wall of steel pipe sheet pile type, seismic response analysis