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In this study, the authors propose a new exposed-type column base which is a non base-plate square CFT column base with built-in high strength reinforcements (square CFTR column base). The base plate and anchor bolts are omitted in this CFTR column base, but the high strength reinforcements are inserted from the CFT column to the RC foundation. A total of three specimens was fabricated. The parameter for the study is the axial force ratio (0, 0.25, 0.50). The specimens were tested under the horizontal cyclic lateral load while subjected to a constant axial load. The mechanical behaviors of the column bases are investigated. The test results indicate that the non base-plate CFTR column bases have excellent seismic performances and are applicable in the practical structural design.

The purpose of this research is to investigate the mechanical behavior of bare type column base connection in SRC structures damaged due to Hyogoken-Nanbu earthquake in Japan, and two series of tests were carried out. The first series is the flexural failure tests of column base. The second series is the shear failure, tests of column base. From the test results, it was shown that ultimate flexural strength can be estimated by the design code in AIJ Standard. On the other hand, ultimate shear strength can be estimated to proposed new evaluation method. In addition, it proposed an evaluation method for limit rotation angle of column bases. From the structural, tests and performance evaluation method, seismic performance of SRC columns using bare type column base were became very clear.

A simplified design equation was proposed in this paper to evaluate ultimate flexural strength of reinforced concrete columns retrofitted by circular steel tube. Ultimate axial load versus moment interactive curve of a circularly retrofitted column section, which is defined by the proposed design equation, consists of two parabolas. The proposed design equation has a very simple mathematical expression and enables structural engineer to easily take into account confinement effect of circular steel tube on ultimate flexural strength of the retrofitted column.