From lessons learned after the 2011 Tohoku earthquake, it is clear that the quick procurement of an emergency public shelter and restoration of the city function are very important in the event of a disaster. Structural engineers are required to estimate the seismic damage of structural components in buildings, and to judge whether these are able to be repaired or not. However, seismic repair method considering damage degree for steel structural members has not been established, although most of the damaged buildings have been repaired after the 1995 Kobe earthquake. In the previous papers, visible damage indices for exposed column base, a single brace with angle section, and column have been established from the experimental studies.
This paper focuses on effects of the seismic repair to the residual out-of-plane deformations in local buckling region of steel column. In order to establish the seismic repair method considering the damage degree, cyclic loading tests of a steel column under axial compression force were carried out. The main parameter of the specimen is the cross section of the column, which are cold-formed RHS-200x6 (depth x thickness), 200x9, 300x9. In addition, the constant axial force which is 0.15 and 0.30 defined as the ratio to its yield axial strength is also selected as one of the parameters of the test. The experiments are consisted of two phases. The first tests were conducted to cause a local buckling to the column. Here, damage degree, the strength deterioration, is one of the test parameter. And then, the damaged column being repaired, the second tests were conducted to investigate effects of the seismic repair on the maximum strength, plastic rotation capacity, and region of local buckling. In this research, two repair methods were applied as follows: one is to attach the additional plates to all surfaces of column (RA series); and the others are to attach the plates to two surfaces which are flange or web in the concave (RF, RW series). In the case of RA series, the convex surfaces had to be made as flat as possible.
The major findings obtained from the test are summarized as follows: (1) the RA repair method brought the strength recovery from the residual strength and the maximum strength is larger than the original one; (2) RF and RW repair method also brought the strength recovery from the residual strength, however, the maximum strength is roughly same as the plastic moment of the original column; (3) finally, a simple seismic repair procedure using the additional plate to the damaged column is proposed.
