A computational method for analyzing response of large floating structures which are supported on multiple columns was proposed by a part of the authors. In this method, hydrodynamic interaction is taken into account as well as flexibility of the structures. We extend this method to similar structures with braces and/or lower hulls. The applicability is confirmed through tank test results, using a model whose upper structure is supported on 45 columns with braces at the bottoms, and also by previous experimental results of a simpler model. First, we show that present method can fairly predict the responses of large floating structures in waves. Second, we show that the characteristics of responses can be explained by those of wave exciting forces or pressures to some extent. Hydrodynamic interaction effects in designing large floating structures are also discussed. It is concluded that hydrodynamic interaction effects are negligible from the viewpoint of designing when the ratio of the length between columns to the diameter of the column is over 4.