It is very important to establish a visible damage index for quick damage estimation of steel structures. In the reconnaissance of the 2011 Tohoku earthquake, many residual out-of-plane deformations of single angle brace and leg openings of its cross section were observed. Cyclic loading tests focusing on the residual out-of-plane deformation and the leg opening of single angle brace were conducted to investigate the relationship between structural performances and damage indices. The major findings obtained from the test are summarized as follows: (1) the maximum story drift angle and the maximum elongation of the brace can be estimated by using the residual out-of-plane deformation; (2) cumulative damage due to cyclic loading can be estimated by the length of the leg opening of its cross section.
