US-Japan cooperative earthquake research program on CFT structures: achievements on the Japanese side

The US–Japan Cooperative Earthquake Research Program began in 1979, following the recommendations as outlined in the final report of the US–Japan Planning Group for the Program. The first four phases of the Program have been implemented on: (1) reinforced concrete; (2) structural steel; (3) masonry, and (4) precast/prestressed concrete. Phase 5, on composite and hybrid structures, was carried out from the fiscal year 1993 over 5‐years. In this phase, the following four research topics were executed: (1) new materials, elements and systems; (2) concrete‐filled structural steel tube column systems; (3) reinforced concrete column and structural steel beam systems; and (4) reinforced concrete and steel‐reinforced concrete wall systems. In this paper, the technical research conducted on the Japanese side related to the research topic of the concrete‐filled structural steel tube column system is overviewed and summarized. It includes experimental results (columns, beam–columns and beam–and‐column subassemblages), proposed design recommendations and a design implication study.